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Human Behavior

Human sexual activity – Wikipedia

This article is about sexual practices and related social aspects. For broader aspects of sexual behaviour, see Human sexuality. "Sexual activity" and "sexual behavior" redirect here. For sexual activity among other animals, see Animal sexual behaviour.

Human sexual activity, human sexual practice or human sexual behavior is the manner in which humans experience and express their sexuality. People engage in a variety of sexual acts, ranging from activities done alone (e.g., masturbation) to acts with another person (e.g., sexual intercourse, non-penetrative sex, oral sex, etc.) in varying patterns of frequency, for a wide variety of reasons. Sexual activity normally results in sexual arousal and physiological changes in the aroused person, some of which are pronounced while others are more subtle. Sexual activity may also include conduct and activities which are intended to arouse the sexual interest of another or enhance the sex life of another, such as strategies to find or attract partners (courtship and display behavior), or personal interactions between individuals (for instance, foreplay or BDSM). Sexual activity may follow sexual arousal.

Human sexual activity has sociological, cognitive, emotional, behavioral and biological aspects; these include personal bonding, sharing emotions and the physiology of the reproductive system, sex drive, sexual intercourse and sexual behavior in all its forms.

In some cultures, sexual activity is considered acceptable only within marriage, while premarital and extramarital sex are taboo. Some sexual activities are illegal either universally or in some countries or subnational jurisdictions, while some are considered contrary to the norms of certain societies or cultures. Two examples that are criminal offenses in most jurisdictions are sexual assault and sexual activity with a person below the local age of consent.

Sexual activity can be classified in a number of ways. It can be divided into acts which involve one person, also called autoeroticism, such as masturbation, or two or more people such as vaginal sex, anal sex, oral sex or mutual masturbation. If there are more than two participants in the sex act, it may be referred to as group sex. Autoerotic sexual activity can involve use of dildos, vibrators, anal beads, and other sex toys, though these devices can also be used with a partner.

Sexual activity can be classified into the gender and sexual orientation of the participants, as well as by the relationship of the participants. For example, the relationships can be ones of marriage, intimate partners, casual sex partners or anonymous. Sexual activity can be regarded as conventional or as alternative, involving, for example, fetishism, paraphilia, or BDSM activities.[1][2] Fetishism can take many forms ranging from the desire for certain body parts, for example large breasts, armpits or foot worship. The object of desire can often be shoes, boots, lingerie, clothing, leather or rubber items. Some non-conventional autoerotic practices can be dangerous. These include erotic asphyxiation and self-bondage. The potential for injury or even death that exists while engaging in the partnered versions of these fetishes (choking and bondage, respectively) becomes drastically increased in the autoerotic case due to the isolation and lack of assistance in the event of a problem.

Sexual activity can be consensual, which means that both or all participants agree to take part and are of the age that they can consent, or it may take place under force or duress, which is often called sexual assault or rape. In different cultures and countries, various sexual activities may be lawful or illegal in regards to the age, gender, marital status or other factors of the participants, or otherwise contrary to social norms or generally accepted sexual morals.

The physiological responses during sexual stimulation are fairly similar for both men and women and there are four phases.[3]

Sexual dysfunction is the inability to react emotionally or physically to sexual stimulation in a way projected of the average healthy person; it can affect different stages in the sexual response cycles, which are desire, excitement and orgasm.[7] In the media, sexual dysfunction is often associated with men, but in actuality, it is more commonly observed in females (43 percent) than males (31 percent).[8]

Sexual activity can lower blood pressure and overall stress levels, regardless of age.[citation needed] It releases tension, elevates mood, and may create a profound sense of relaxation, especially in the postcoital period. From a biochemical perspective, sex causes the release of endorphins and increases levels of white blood cells that actually boost the immune system. A study published in the journal Biological Psychology described how men who had had sex the previous night responded better to stressful situations, it suggested that if a person is regularly sexual, theyre regularly relaxed, and when the person is relaxed, they cope better with stressful situations.[citation needed] A 2007 study published in the Archives of Sexual Behavior 36, (no. 3 (June 2007): 35768) reported that sexual behavior with a partner on one day significantly predicted lower negative mood and stress, and higher positive mood, on the following day.

People engage in sexual activity for any of a multitude of possible reasons. Although the primary evolutionary purpose of sexual activity is reproduction, research on college students suggested that people have sex for four general reasons: physical attraction, as a means to an end, to increase emotional connection, and to alleviate insecurity.[9]

Most people engage in sexual activity because of pleasure they derive from the arousal of their sexuality, especially if they can achieve orgasm. Sexual arousal can also be experienced from foreplay and flirting, and from fetish or BDSM activities,[1][10] or other erotic activities. Most commonly, people engage in sexual activity because of the sexual desire generated by a person to whom they feel sexual attraction; but they may engage in sexual activity for the physical satisfaction they achieve in the absence of attraction for another, as in the case of casual or social sex.[11] At times, a person may engage in a sexual activity solely for the sexual pleasure of their partner, such as because of an obligation they may have to the partner or because of love, sympathy or pity they may feel for the partner.

A person may engage in sexual activity for purely monetary considerations, or to obtain some advantage from either the partner or the activity. A man and woman may engage in sexual intercourse with the objective of conception. Some people engage in hate sex, which occurs between two people who strongly dislike or annoy each other. It is related to the idea that opposition between two people can heighten sexual tension, attraction and interest.[12]

It has been shown that sexual activity plays a large part in the interaction of social species. Joan Roughgarden, in her book Diversity, Gender, and Sexuality in Nature and People, postulates that this applies equally to humans as it does to other social species. She explores the purpose of sexual activity and demonstrates that there are many functions facilitated by such activity including pair bonding, group bonding, dispute resolution and reproduction.[13]

Research has found that people also engage in sexual activity for reasons associated with self-determination theory. The self-determination theory can be applied to a sexual relationship when the participants have positive feelings associated with the relationship. These participants do not feel guilty or coerced into the partnership.[14] Researchers have proposed the model of self-determined sexual motivation. The purpose of this model is to connect self-determination and sexual motivation.[15] This model has helped to explain how people are sexually motivated when involved in self-determined dating relationships. This model also links the positive outcomes, (satisfying the need for autonomy, competence, and relatedness) gained from sexual motivations.[15]

According to the completed research associated with this model, it was found that people of both sexes who engaged in sexual activity for self-determined motivation had more positive psychological well-being.[15] While engaging in sexual activity for self-determined reasons, the participants also had a higher need for fulfillment. When this need was satisfied, they felt better about themselves. This was correlated with greater closeness to their partner and higher overall satisfaction in their relationship.[15] Though both sexes engaged in sexual activity for self-determined reasons, there were some differences found between males and females. It was concluded that females had more motivation than males to engage in sexual activity for self-determined reasons.[15] Females also had higher satisfaction and relationship quality than males did from the sexual activity.[15] Overall, research concluded that psychological well-being, sexual motivation, and sexual satisfaction were all positively correlated when dating couples partook in sexual activity for self-determined reasons.[15]

The frequency of sexual activity might range from zero (sexual abstinence) to 15 or 20 times a week.[16] In the United States, the average frequency of sexual intercourse for married couples is 2 to 3 times a week.[17] It is generally recognized that postmenopausal women experience declines in frequency of sexual intercourse[18] and that average frequency of intercourse declines with age. According to the Kinsey Institute, the average frequency of sexual intercourse in the US is 112 times per year (age 1829), 86 times per year (age 3039), and 69 times per year (age 4049).[19]

The age at which adolescents tend to become sexually active varies considerably between different cultures and from time to time. (See Prevalence of virginity.) The first sexual act of a child or adolescent is sometimes referred to as the sexualization of the child, and may be considered as a milestone or a change of status, as the loss of virginity or innocence. Youth are legally free to have intercourse after they reach the age of consent.

A 1999 survey of students indicated that approximately 40% of ninth graders across the United States report having had sexual intercourse. This figure rises with each grade. Males are more sexually active than females at each of the grade levels surveyed. Sexual activity of young adolescents differs in ethnicity as well. A higher percent of African American and Hispanic adolescents are sexually active than White adolescents.[20]

Research on sexual frequency has also been conducted solely on female adolescents who engage in sexual activity. Female adolescents tended to engage in more sexual activity due to positive mood. In female teenagers, engaging in sexual activity was directly positively correlated with being older, greater sexual activity in the previous week or prior day, and more positive mood the previous day or the same day as the sexual activity occurred.[21] Decreased sexual activity was associated with prior or current day negative mood or vaginal bleeding.[21]

Although opinions differ, others[who?] suggest that sexual activity is an essential part of humans, and that teenagers need to experience sex. Sexual experiences help teenagers understand pleasure and satisfaction.[22] In relation to hedonic and eudaimonic well-being, teenagers can positively benefit from sexual activity according to one particular research study. In the United States[which?] of America, a cross-sectional study of teenagers was completed.[when?] Teenagers who had their first sexual experience at age 16 revealed a higher well-being than those who were sexually inexperienced or who were first sexually active at a later age of 17.[22] Furthermore, teenagers who had their first sexual experience at age 15 or younger, or who had many sexual partners were not negatively affected and did not have associated lower well-being.[22]

Sexual activity is a normal physiological function,[23] but like other physical activity, it comes with risks. There are four main types of risks that may arise from sexual activity: unwanted pregnancy, contracting a sexually transmitted infection (STI/STD), physical injury, and psychological injury.

Any sexual activity that involves the introduction of semen into a woman's vagina, such as during sexual intercourse, or even contact of semen with her vulva, may result in a pregnancy.[24] To reduce the risk of unintended pregnancies, some people who engage in penile-vaginal sex may use contraception, such as birth control pills, a condom, diaphragms, spermicides, hormonal contraception or sterilization.[25] The effectiveness of the various contraceptive methods in avoiding pregnancy varies considerably.

Sexual activity that involves skin-to-skin contact, exposure to an infected person's bodily fluids or mucosal membranes[26] carries the risk of contracting a sexually transmitted infection. People may not be able to detect that their sexual partner has one or more STIs, for example if they are asymptomatic (show no symptoms).[27][28] The risk of STIs can be reduced by safe sex practices, such as using condoms. Both partners may opt be tested for STIs before engaging in sex.[29] There may also be an increased risk of contracting a STI when having sex with multiple partners.

Some STIs can also be contracted by using IV drug needles after their use by an infected person, as well as through childbirth or breastfeeding.

Typically, older men and women maintaining interest in sexual interest and activity could be therapeutic; it is a way of expressing their love and care for one another. Factors such as biological and psychological factors, diseases, mental conditions, boredom with the relationship, and widowhood have been found to contribute with the common decrease in sexual interest and activity in old age. National sex surveys given in Finland in the 1990s revealed aging men had a higher incidence of sexual intercourse compared to aging women and that women were more likely to report a lack of sexual desire compared to men. Regression analysis, factors considered important to female sexual activity included: sexual desire, valuing sexuality, and a healthy partner, while high sexual self-esteem, good health, and active sexual history were important to male sexual activity. Both aging genders agreed they needed good health, good sexual functioning, positive sexual self-esteem, and a sexually skilful partner to maintain sexual desire.[30]

Heterosexuality is the romantic or sexual attraction to the opposite sex. Heterosexual sexual practices are subject to laws in many places. In some countries, mostly those where religion has a strong influence on social policy, marriage laws serve the purpose of encouraging people to have sex only within marriage. Sodomy laws were seen as discouraging same-sex sexual practices, but may affect opposite-sex sexual practices. Laws also ban adults from committing sexual abuse, committing sexual acts with anyone under an age of consent, performing sexual activities in public, and engaging in sexual activities for money (prostitution). Though these laws cover both same-sex and opposite-sex sexual activities, they may differ in regard to punishment, and may be more frequently (or exclusively) enforced on those who engage in same-sex sexual activities.[31]

Different-sex sexual practices may be monogamous, serially monogamous, or polyamorous, and, depending on the definition of sexual practice, abstinent or autoerotic (including masturbation). Additionally, different religious and political movements have tried to influence or control changes in sexual practices including courting and marriage, though in most countries changes occur at a slow rate.

Homosexuality is the romantic or sexual attraction to the same sex. People with a homosexual orientation can express their sexuality in a variety of ways, and may or may not express it in their behaviors.[32] Research indicates that many gay men and lesbians want, and succeed in having, committed and durable relationships. For example, survey data indicate that between 40% and 60% of gay men and between 45% and 80% of lesbians are currently involved in a romantic relationship.[33]

It is possible for a person whose sexual identity is mainly heterosexual to engage in sexual acts with people of the same sex. For example, mutual masturbation in the context of what may be considered normal heterosexual teen development. Gay and lesbian people who pretend to be heterosexual are often referred to as being closeted (hiding their sexuality in "the closet"). "Closet case" is a derogatory term used to refer to people who hide their sexuality. Making that orientation public can be called "coming out of the closet" in the case of voluntary disclosure or "outing" in the case of disclosure by others against the subject's wishes (or without their knowledge). Among some communities (called "men on the DL" or "down-low"), same-sex sexual behavior is sometimes viewed as solely for physical pleasure. Men who have sex with men, as well as women who have sex with women, or men on the "down-low" may engage in sex acts with members of the same sex while continuing sexual and romantic relationships with the opposite sex.

People who engage exclusively in same-sex sexual practices may not identify themselves as gay or lesbian. In sex-segregated environments, individuals may seek relationships with others of their own gender (known as situational homosexuality). In other cases, some people may experiment or explore their sexuality with same (and/or different) sex sexual activity before defining their sexual identity. Despite stereotypes and common misconceptions, there are no forms of sexual acts exclusive to same-sex sexual behavior that cannot also be found in opposite-sex sexual behavior, except those involving the meeting of the genitalia between same-sex partners tribadism (generally vulva-to-vulva rubbing, commonly known by its "scissoring" position) and frot (generally penis-to-penis rubbing).

People who have a romantic or sexual attraction to both sexes are referred to as bisexual.[34][35] People who have a distinct but not exclusive preference for one sex/gender over the other may also identify themselves as bisexual.[36] Like gay and lesbian individuals, bisexual people who pretend to be heterosexual are often referred to as being closeted.

Pansexuality (also referred to as omnisexuality)[37] may or may not be subsumed under bisexuality, with some sources stating that bisexuality encompasses sexual or romantic attraction to all gender identities.[38][39] Pansexuality is characterized by the potential for aesthetic attraction, romantic love, or sexual desire towards people without regard for their gender identity or biological sex.[40] Some pansexuals suggest that they are gender-blind; that gender and sex are insignificant or irrelevant in determining whether they will be sexually attracted to others.[41] As defined in the Oxford English Dictionary, pansexuality "encompasses all kinds of sexuality; not limited or inhibited in sexual choice with regards to gender or practice".[42]

Most people experiment with a range of sexual activities during their lives, although they tend to engage in only a few of these regularly. Some people enjoy many different sexual activities, while others avoid sexual activities altogether for religious or other reasons (see chastity, sexual abstinence, asexuality). Some prefer monogamous relationships for sex, while others may prefer many different partners throughout their lives.

Alex Comfort and others propose three potential social aspects of intercourse in humans, which are not mutually exclusive: reproductive, relational, and recreational.[43] The development of the contraceptive pill and other highly effective forms of contraception in the mid- and late 20th century has increased people's ability to segregate these three functions, which still overlap a great deal and in complex patterns. For example: A fertile couple may have intercourse while using contraception to experience sexual pleasure (recreational) and also as a means of emotional intimacy (relational), thus deepening their bonding, making their relationship more stable and more capable of sustaining children in the future (deferred reproductive). This same couple may emphasize different aspects of intercourse on different occasions, being playful during one episode of intercourse (recreational), experiencing deep emotional connection on another occasion (relational), and later, after discontinuing contraception, seeking to achieve pregnancy (reproductive, or more likely reproductive and relational).

Most world religions have sought to address the moral issues that arise from people's sexuality in society and in human interactions. Each major religion has developed moral codes covering issues of sexuality, morality, ethics etc. Though these moral codes do not address issues of sexuality directly, they seek to regulate the situations which can give rise to sexual interest and to influence people's sexual activities and practices. However, the effect of religious teaching has at times been limited. For example, though most religions disapprove of extramarital sexual relations, it has always been widely practiced. Nevertheless, these religious codes have always had a strong influence on peoples' attitudes to issues of modesty in dress, behavior, speech etc.

On the other hand, some people adopt the view that pleasure is its own justification for sexual activity. Hedonism is a school of thought which argues that pleasure is the only intrinsic good.[44]

Human sexual activity, like many other kinds of activity engaged in by humans, is generally influenced by social rules that are culturally specific and vary widely. These social rules are referred to as sexual morality (what can and can not be done by society's rules) and sexual norms (what is and is not expected).

Sexual ethics, morals, and norms relate to issues including deception/honesty, legality, fidelity and consent. Some activities, known as sex crimes in some locations, are illegal in some jurisdictions, including those conducted between (or among) consenting and competent adults (examples include sodomy law and adult-adult incest).

Some people who are in a relationship but want to hide polygamous activity (possibly of opposite sexual orientation) from their partner, may solicit consensual sexual activity with others through personal contacts, online chat rooms, or, advertising in select media.

Swinging, on the other hand, involves singles or partners in a committed relationship engaging in sexual activities with others as a recreational or social activity.[45] The increasing popularity of swinging is regarded by some as arising from the upsurge in sexual activity during the sexual revolution of the 1960s. Swinging sexual activity can take place in a sex club, also known as a swinger club (not to be confused with a strip club).[46]

Some people engage in various sexual activities as a business transaction. When this involves having sex with, or performing certain actual sexual acts for another person in exchange for money or something of value, it is called prostitution. Other aspects of the adult industry include phone sex operators, strip clubs, and pornography.

Social gender roles can influence sexual behavior as well as the reaction of individuals and communities to certain incidents; the World Health Organization states that, "Sexual violence is also more likely to occur where beliefs in male sexual entitlement are strong, where gender roles are more rigid, and in countries experiencing high rates of other types of violence."[47] Some societies, such as those where the concepts of family honor and female chastity are very strong, may practice violent control of female sexuality, through practices such as honor killings and female genital mutilation.[48][49]

The relation between gender equality and sexual expression is recognized, and promotion of equity between men and women is crucial for attaining sexual and reproductive health, as stated by the UN International Conference on Population and Development Program of Action:[50]

BDSM is a variety of erotic practices or roleplaying involving bondage, dominance and submission, sadomasochism, and other interpersonal dynamics. Given the wide range of practices, some of which may be engaged in by people who do not consider themselves as practicing BDSM, inclusion in the BDSM community or subculture is usually dependent on self-identification and shared experience. BDSM communities generally welcome anyone with a non-normative streak who identifies with the community; this may include cross-dressers, extreme body modification enthusiasts, animal players, latex or rubber aficionados, and others.

B/D, a form of BDSM, is bondage and discipline. Bondage includes the restraint of the body or mind.[51] D/S means "dominant and submissive." A dominant is someone who takes control of someone who wishes to give up control. A submissive is someone who gives up the control to a person who wishes to take control.[51] S/M (sadism and masochism) means an individual who takes pleasure in the humiliation or pain of others. Masochism means an individual who takes pleasure from their own pain and/or humiliation.[51]

Unlike the usual "power neutral" relationships and play styles commonly followed by couples, activities and relationships within a BDSM context are often characterized by the participants' taking on complementary, but unequal roles; thus, the idea of informed consent of both the partners becomes essential. Participants who exert sexual dominance over their partners are known as dominants or tops, while participants who take the passive, receiving, or obedient role are known as submissives or bottoms.

Individuals are also sometimes abbreviated when referred to in writing, so a dominant person may be referred to as a "dom" for a man or a woman. Sometimes a woman may choose to use the female specific term "Domme". Both terms are pronounced the same when spoken. Individuals who can change between top/dominant and bottom/submissive roleswhether from relationship to relationship or within a given relationshipare known as switches. The precise definition of roles and self-identification is a common subject of debate within the community.[52]

In a 2013 study, the researchers suggest that BDSM is a sexual act where they play role games, use restraint, use power exchange, use suppression and pain is sometimes involved depending on individual(s).[53] The study indicates that, in the past, BDSM has been seen as maladaptive to one's psychological health, but that this may be incorrect. According to the study, one who participates in BDSM can have greater strength socially, mentally and have greater independence than those who do not practice BDSM.[53] It states that people who participate in BDSM play actually have higher subjective well-being, and that this might be due to the fact that BDSM play requires extensive communication. Before any sexual act occurs, the partners must discuss their agreement of their relationship. They discuss how long the play will last, the intensity, their actions, what each participant needs and/or desires. The sexual acts are all consensual and pleasurable to both parties.[53]

In a 2015 study, BDSM relationships were suggested to have a higher level of connection, intimacy, trust and communication compared to individuals who do not practice BDSM.[51] The study suggests that dominants and submissives exchange control for each other's pleasure and to satisfy a need. They mention that both parties enjoys pleasing their partner in any way they can. Submissive and Dominants who participated in their research, felt that this is one of the best things about BDSM. It gives a submissive pleasure to do things in general for their dominant. Where Dominant enjoys making their encounters all about the submissive. They enjoy doing things that makes their submissive happy. Their findings suggest that submissives and dominants found BDSM play more pleasurable and fun. BDSM was also suggested to improve personal growth, romantic relationships, their sense of community, their sense of self, the dominants confidence, and help an individual cope with everyday things by giving them a psychological release.[51]

There are many laws and social customs which prohibit, or in some way affect sexual activities. These laws and customs vary from country to country, and have varied over time. They cover, for example, a prohibition to non-consensual sex, to sex outside of marriage, to sexual activity in public, besides many others. Many of these restrictions are non-controversial, but some have been the subject of public debate.

Most societies consider it a serious crime to force someone to engage in sexual acts or to engage in sexual activity with someone who does not consent. This is called sexual assault, and if sexual penetration occurs it is called rape, the most serious kind of sexual assault. The details of this distinction may vary among different legal jurisdictions. Also, what constitutes effective consent in sexual matters varies from culture to culture and is frequently debated. Laws regulating the minimum age at which a person can consent to have sex (age of consent) are frequently the subject of debate, as is adolescent sexual behavior in general. Some societies have forced marriage, where consent may not be required.

Many locales have laws that limit or prohibit same-sex sexual activity.

In the West, sex before marriage is not illegal. There are social taboos and many religions condemn pre-marital sex. In many Muslim countries, such as Saudi Arabia, Pakistan,[54] Afghanistan,[55][56][57] Iran,[57] Kuwait,[58] Maldives,[59] Morocco,[60] Oman,[61] Mauritania,[62] United Arab Emirates,[63][64] Sudan,[65] Yemen,[66] any form of sexual activity outside marriage is illegal. Those found guilty, especially women, may be forced to wed the sexual partner, publicly beaten, or stoned to death.[67] In many African and native tribes, sexual activity is not viewed as a privilege or right of a married couple, but rather as the unification of bodies and is thus not frowned upon.[68]

Other studies have analyzed the changing attitudes about sex that American adolescents have outside of marriage. Adolescents were asked how they felt about oral and vaginal sex in relation to their health, social, and emotional well-being. Overall, teenagers felt that oral sex was viewed as more socially positive amongst their demographic.[69] Results stated that teenagers believed that oral sex for dating and non-dating adolescents was less threatening to their overall values and beliefs than vaginal sex was.[69] When asked, teenagers who participated in the research viewed oral sex as more acceptable to their peers, and their personal values than vaginal sex.[69]

The laws of each jurisdiction set the minimum age at which a young person is allowed to engage in sexual activity.[70] This age of consent is typically between 14 and 18 years, but laws vary. In many jurisdictions, age of consent is a person's mental or functional age.[71][71][72][73] As a result, those above the set age of consent may still be considered unable to legally consent due to mental immaturity.[71][72][73][74][75] Many jurisdictions regard any sexual activity by an adult involving a child as child sexual abuse.

Age of consent may vary by the type of sexual act, the sex of the actors, or other restrictions such as abuse of a position of trust. Some jurisdictions also make allowances for young people engaged in sexual acts with each other.[76]

Most jurisdictions prohibit sexual activity between certain close relatives. These laws vary to some extent; such acts are called incestuous.

Non-consensual sexual activity or subjecting an unwilling person to witnessing a sexual activity are forms of sexual abuse, as well as (in many countries) certain non-consensual paraphilias such as frotteurism, telephone scatophilia (indecent phonecalls), and non-consensual exhibitionism and voyeurism (known as "indecent exposure" and "peeping tom" respectively).[77]

People sometimes exchange sex for money or access to other resources. This practice, called prostitution, takes place under many varied circumstances. The person who receives payment for sexual services is called a prostitute and the person who receives such services is known by a multitude of terms, including (and most commonly) "john." Prostitution is one of the branches of the sex industry. The legal status of prostitution varies from country to country, from being a punishable crime to a regulated profession. Estimates place the annual revenue generated from the global prostitution industry to be over $100 billion.[78] Prostitution is sometimes referred to as "the world's oldest profession".[79] Prostitution may be a voluntary individual activity or facilitated or forced by pimps.

Survival sex is a form of prostitution engaged in by people in need, usually when homeless or otherwise disadvantaged people trade sex for food, a place to sleep, or other basic needs, or for drugs.[80] The term is used by sex trade and poverty researchers and aid workers.[81][82]

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Human sexual activity - Wikipedia

Immunology

Cancer immunology – Wikipedia

Cancer immunology is a branch of immunology that studies interactions between the immune system and cancer cells (also called tumors or malignancies). It is a field of research that aims to discover cancer immunotherapies to treat and retard progression of the disease. The immune response, including the recognition of cancer-specific antigens, forms the basis of targeted therapy (such as vaccines and antibody therapies) and tumor marker-based diagnostic tests.[1][2] For instance tumour infiltrating lymphocytes are significant in human colorectal cancer.[3] The host was given a better chance at survival if the cancer tissue showed infiltration of inflammatory cells, in particular those prompting lymphocytic reactions. The results yielded suggest some extent of anti-tumour immunity is present in colorectal cancers in humans.

Cancer immunosurveillance and immunoediting is based on (i) protection against development of spontaneous and chemically induced tumors in animal systems and (ii) identification of targets for immune recognition of human cancer.[4]

Cancer immunosurveillance is a theory formulated in 1957 by Burnet and Thomas, who proposed that lymphocytes act as sentinels in recognizing and eliminating continuously arising, nascent transformed cells.[4][5] Cancer immunosurveillance appears to be an important host protection process that decreases cancer rates through inhibition of carcinogenesis and maintaining of regular cellular homeostasis.[6] It has also been suggested that immunosurveillance primarily functions as a component of a more general process of cancer immunoediting.[4]

Immunoediting is a process by which a person is protected from cancer growth and the development of tumour immunogenicity by their immune system. It has three main phases: elimination, equilibrium and escape.[7] The elimination phase consists of the following four phases:

The first phase of elimination involves the initiation of an antitumor immune response. Cells of the innate immune system recognize the presence of a growing tumor which has undergone stromal remodeling, causing local tissue damage. This is followed by the induction of inflammatory signals which is essential for recruiting cells of the innate immune system (e.g. natural killer cells, natural killer T cells, macrophages and dendritic cells) to the tumor site. During this phase, the infiltrating lymphocytes such as the natural killer cells and natural killer T cells are stimulated to produce IFN-gamma.

In the second phase of elimination, newly synthesized IFN-gamma induces tumor death (to a limited amount) as well as promoting the production of chemokines CXCL10, CXCL9 and CXCL11. These chemokines play an important role in promoting tumor death by blocking the formation of new blood vessels. Tumor cell debris produced as a result of tumor death is then ingested by dendritic cells, followed by the migration of these dendritic cells to the draining lymph nodes. The recruitment of more immune cells also occurs and is mediated by the chemokines produced during the inflammatory process.

In the third phase, natural killer cells and macrophages transactivate one another via the reciprocal production of IFN-gamma and IL-12. This again promotes more tumor killing by these cells via apoptosis and the production of reactive oxygen and nitrogen intermediates. In the draining lymph nodes, tumor-specific dendritic cells trigger the differentiation of Th1 cells which in turn facilitates the development of cytotoxic CD8+ T cells also known as killer T-cells.

In the final phase of elimination, tumor-specific CD4+ and CD8+ T cells home to the tumor site and the cytotoxic T lymphocytes then destroy the antigen-bearing tumor cells which remain at the site.

Tumor cell variants which have survived the elimination phase enter the equilibrium phase. In this phase, lymphocytes and IFN-gamma exert a selection pressure on tumor cells which are genetically unstable and rapidly mutating. Tumor cell variants which have acquired resistance to elimination then enter the escape phase. In this phase, tumor cells continue to grow and expand in an uncontrolled manner and may eventually lead to malignancies. In the study of cancer immunoediting, knockout mice have been used for experimentation since human testing is not possible.[4]Tumor infiltration by lymphocytes is seen as a reflection of a tumor-related immune response.[8]

Obeid et al.[9] investigated how inducing immunogenic cancer cell death ought to become a priority of cancer chemotherapy. He reasoned, the immune system would be able to play a factor via a bystander effect in eradicating chemotherapy-resistant cancer cells.[10][11][12] However, extensive research is still needed on how the immune response is triggered against dying tumour cells.[13]

Professionals in the field have hypothesized that apoptotic cell death is poorly immunogenic whereas necrotic cell death is truly immunogenic.[14][15][16] This is perhaps because cancer cells being eradicated via a necrotic cell death pathway induce an immune response by triggering dendritic cells to mature, due to inflammatory response stimulation.[17][18] On the other hand, apoptosis is connected to slight alterations within the plasma membrane causing the dying cells to be attractive to phagocytic cells.[19] However, numerous animal studies have shown the superiority of vaccination with apoptotic cells, compared to necrotic cells, in eliciting anti-tumor immune responses.[20][21][22][23][24]

Thus Obeid et al.[9] propose that the way in which cancer cells die during chemotherapy is vital. Anthracyclins produce a beneficial immunogenic environment. The researchers report that when killing cancer cells with this agent uptake and presentation by antigen presenting dendritic cells is encouraged, thus allowing a T-cell response which can shrink tumours. Therefore activating tumour-killing T-cells is crucial for immunotherapy success.[25]

However, advanced cancer patients with immunosuppression have left researchers in a dilemma as to how to activate their T-cells. The way the host dendritic cells react and uptake tumour antigens to present to CD4+ and CD8+ T-cells is the key to success of the treatment.[26]

Various strains of human papillomavirus (HPV) have been found to play an important role in the development of cervical cancer. The HPV oncogenes E6 and E7 that these viruses possess have been shown to immortalise some human cells and thus promote cancer development.[27] Although these strains of HPV have not been found in all cervical cancers, they have been found to be the cause in roughly 70% of cases. The study of these viruses and their role in the development of various cancers is still continuing, however a vaccine has been developed that can prevent infection of certain HPV strains, and thus prevent those HPV strains from causing cervical cancer, and possibly other cancers as well.

A virus that has been shown to cause breast cancer in mice is mouse mammary tumor virus.[28][29] It is from discoveries such as this and the role of HPV in cervical cancer development that research is currently being undertaken to discover whether or not human mammary tumour virus is a cause of breast cancer in humans.[30][clarification needed]

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Cancer immunology - Wikipedia

Embryology

Oogenesis – Embryology

The most interesting in connection with oogenesis is the development of the different follicle stages. The complex processes that are connected with it are treated in the fertilization module.

Following the immigration of the primordial germ cells into the gonadal ridge, they proliferate, are enveloped by coelomic epithelial cells, and form germinal cords that , though, keeptheir connection with the coelom epithelium. Now a cortical zone(cortex ovarii) and a medulla can be distinguished, whereby itshould be mentioned that in females the germinal cords neverpenetrate into the medullary zone. In the genital primordium thefollowing processes then take place:

More info

Stages of the first meiotic prophase of the oocyte.

From birth there are thus two different structures to be distinguished that, at least conceptually, do not develop further synchronously:

Birth The continuation of the development / maturation of the oocyte begins again only a few days before ovulation (see fertilization module).

Since a follicle can die at any moment in its development (= atresia), not all reach the tertiary follicle stage.

The sex hormones influence the primordial follicles to grow and a restructuring to take place. From the primordial follicles the primary follicles, secondary follicles, and tertiary follicles develop in turn. Only a small percentage of the primordial follicles reach the tertiary follicle stage - the great majority meet their end beforehand in the various maturation stages. Large follicles leave scars behind in the cortical compartment and the small ones disappear without a trace. The tertiary follicles get to be the largest and, shortly before ovulation, can attain a diameter up to 2.5 mm through a special spurt of growth. They are then termed graafian follicles.

Fig. 18 The follicles in various stages are shown in the ovarian cortical compartment. This very schematic drawing shows the relationships shortly before ovulation. In reality the primordial follicles are the most prevalent numerically.

More information to this diagram

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Oogenesis - Embryology

Biochemistry

Laboratory Assistant – Biochemistry (Bowen Hills Laboratory)

Sullivan Nicolaides Pathology is one of the largest pathology practices in Australia, providing comprehensive services to patients and doctors over a geographic area throughout Queensland and New South Wales and employing more than 2000 people.

Sullivan Nicolaides Pathology services the Brisbane metropolitan area and regional areas extending as far north as Cairns and south to Coffs Harbour.

Sullivan Nicolaides Pathology has an exciting opportunity for a permanent full-time Laboratory Assistant - Biochemistry to work from their new Bowen Hills laboratory in Brisbane.

The work will involve sample sorting and processing in the pre-analytical area of the laboratory.

Some of the more specific responsibilities of the position will include:

To be successful in this role, you'll have excellent communication and organisational skills as well as a high attention to detail to enable maximum accuracy of processing. Previous relevant laboratory experience highly regarded, but not essential.

This is a perfect role for an enthusiastic individual who has a flexible approach to their work as you will be required to work rostered shifts. The rotating roster involves shifts over a 24 hour period, along with weekend shifts and public holidays when fully trained.

You will also require good keyboard skills and the ability to work as a team member in this busy department.

The high level of service provided by Sullivan Nicolaides Pathology is delivered by a dedicated staff comprising of pathologists, scientists, technicians, laboratory assistants, collection personnel, couriers, computer personnel, pathology services assistants and other support staff.

The Bowen Hills laboratory is well-situated for access to nearby public transport.

The successful candidate will enjoy a competitive remuneration packageranging from $19.40 - $24.74 per hour.

In addition, permanent employees enjoy the following benefits:

Please note: Applications close Friday, 18th November.

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Laboratory Assistant - Biochemistry (Bowen Hills Laboratory)

Biochemistry

Biology – Biochemistry

Photosynthesis - an important biochemical reaction

Photosynthesis and the Web: 2008 - photosynthesis-related web sites grouped into several categories, e.g Subject Sites, Educational etc.- from Arizona State University

Milestones in Photosynthesis Research - Govindjee - a 32 page .pdf document (611 KB)

The Photosynthetic Process - from the Photosynthesis Research Unit, University of Illinois at Urbana-Champaign, includes history of photosynthesis

A Primer on Photosynthesis and the Functioning of Cells - from the University of Michigan, Global Change I

The Nutrient requirements of Cells - from Kimball's Biology Pages

Photosynthesis- from the On-line Biology Book, Estrella Mountain Community College

Photosynthesis Study Guide - from Modern Biology textbook site

Photosynthesis in providing a source of energy

Vehicle Technologies Program from Office of Fuels Development US Dept of Energy -

Biodiesel, from US Dept of Energy Efficiency and Renewable Energy

Just the basics: Biodiesel -.pdf (283 KB), U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy

Carbon currency the credits and debits of carbon emissions trading - from Australian Academy of Sciences

Solar to Fuel: Catalyzing the Science - a paper from the Berkeley National Laboratory

Making Packaging Greener - Biodegradable Plastics, Reading list - from Australian Academy of Sciences

ABCs of Biopower - from the US Dept of Energy Efficiency and Renewable Energy

The development of the theory of photosynthesis

Photosynthesis - including the contributions of key botanists, from Botany Online (The Internet Hypertextbook), University of Hamburg

Highlights in photosynthesis research - from the Nobel e-Museum

Research into Photosynthesis - from University of California, Berkeley

Chlorophyll - from Bristol University, UK

The people who contributed to the theory of photosynthesis

Analyzing van Helmont's Experiment - a student exercise

Hales, Stephen 1671-1761 - from History of Horticulture, the Ohio-State University

Nicolas-Theodore de SAUSSURE - from CYBERLIPID CENTER

Photosynthesis - from Botany Online, Hamburg University, details Blackman and Mathei's findings

Sachs, Julius Von 1832-1897 - from History pf Horticulture, the Ohio-State University

Julius v. SACHS (1832-1897) - from Botany Online, University of Hamburg

Mikhail Tswett (1872-1919) - from Le Moyne College

History of Development of Chromatography - from Wiley Publishing (pdf 1.28 MB)

Mikhail Tsvet - from Chemistry Daily

The Light Reactions of Photosynthesis - from Botany On-line, University of Hamburg

Robert HILL FRS (1899-1991) - brief memoir by a student (pdf, 550 KB)

Martin Kamen, Who Discovered Carbon-14 Here, Wins Fermi Award

Nobel Prize Awarded to Nine Berkeley Lab Scientists - from Science Beat at The Berkeley Labs

MELVIN CALVIN - from Nobel e-Museum

Melvin Calvin, 1961 Nobelist and UC Berkeley professor, dies at age 85 - from University of California, Berkeley

Photosynthesis - a light dependent reaction

Why study photosynthesis? - from Arizona State University

An Introduction to Photosynthesis and Its Applications - from Arizona State University

Johnsons's Photosynthesis Simulation - requires Shockwave - investigate the effects of light intensity and wavelength on Photosynthesis

Photosynthesis Simulation - laboratory activity based on the above simulation

Photosynthetic Pictures Are Worth More Than a Thousand Words - from Access Excellence

Photosynthesis: The Role of Light - Biology Pages are produced by John Kimball formerly a professor at Harvard University

Photosynthesis - Light Reactions. from Old Dominion University

Photosynthesis Problem Set 1 - from The Biology Project, University of Arizona, set of multiple choice questions with detailed feedback

Photosynthesis Problem Set 2 - from The Biology Project, University of Arizona, set of multiple choice questions with detailed feedback

Without pigments we're nothing - from University of Arizona

Chloroplasts and chlorophyll

Chloroplasts - from Kimball's Biology Pages

What the Heck is a Chloroplast? from Bugs in the News, Kansas University

Photosynthesis and Chromatography of its Pigments - from Science Projects

An Introduction to Chromatography - from Access Excellence

Chromatography - from Rensselaer Polytchnic Institute

Paper Chromatography - from Kimball's Biology pages

Chromatography - from Chemistry Daily

Lab 5 Green Plant I - Kean University, scroll down to SEPARATION AND IDENTIFICATION OF LEAF PIGMENTS

Use of radioisotopes in tracing biochemical reactions

Photosynthesis: Pathway of Carbon Fixation - Biology Pages are produced by John Kimball formerly a professor at Harvard University

Biosynthesis of Carbohydrates - from The Biology Project, The University of Arizona

The Dark Reactions of Photosynthesis, Assimilation of Carbon Dioxide and The CALVIN Cycle - from Botany Online, University of Hamburg

Photosynthesis Study Guide - for Modern Biology, Holt, Reinhart and Winston

ATP - energy currency

The Energy Relationships in Cellular Respiration and Photosynthesis: the Balance Sheet - Biology Pages are produced by John Kimball formerly a professor at Harvard University

Energy: Making ATP - a detailed overview from University of Connecticut

Adenosine Triphosphate - ATP - from Molecule of the Month, Bristol University

Peter Mitchell (1920 - 1992) - and the chemiosmotic hypothesis from University of Illinois at Urbana-Champaign

The Nobel Prize in Chemistry 1997 - Walker, Boyer and Skou, from the Nobel e-Museum

Electron microscope and visualising plant organelles

Chloroplast - from Cells Alive

Chloroplasts - from Kimball's Biology Pages

Cell Structure and Function - Studyguide -see Question 27 (pdf, 300 KB)

Transmission Electron Microscope (TEM) - from The University of Nebraska

An Introduction to Microscopy - including The History of the Microscope

Virtual Microscopy - Interactive Java Tutorials, from Molecular Expressions

Page Maintained By: uniserve@usyd.edu.au Last Update: Monday, 30-Apr-2012 14:29:02 AEST URL: http://science.uniserve.edu.au/school/curric/stage6/biol/biolchem.html

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Biology - Biochemistry

Neuroscience

Home | Institute of Neuroscience

Institute of Neuroscience

The Institute of Neuroscience (ION) is a group of biologists, psychologists, and human physiologists at theUniversity of Oregon that has pooled its expertise to tackle fundamental questions in neuroscience questions such as, "How do neural stem cells choose between self-renewal and differentiation?" "What mechanisms generate the large diversity of neurons within the brain?" "How do these neurons 'wire up' into functional circuits?" "How do neural circuits produce behavior?"

These questions are being explored at all levels of organization from the relatively simple nervous systems of Drosophila, C. elegans, and zebrafish to the more complex networks in mice, owls, and humans.

ION boasts a highly collaborativefacultywith expertise in genetics, development, electrophysiology, optogenetics, and functional MRI. As a result, students enrolled in ourPhD programcome away with the broad conceptual and technical skills necessary to run an independent neuroscience research lab or pursue many other related career paths. Our state-of-the-artfacilitiesand excellent support staff allow ION members to progress rapidly by making exploratory or pilot experiments accessible.

MEET OUR CO-DIRECTORS

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Home | Institute of Neuroscience

Neuroscience

Neuroscience :: Biology :: Swarthmore College

Video: [1 min 23 sec]

Swarthmore students have direct access to faculty research opportunities. Stephen, a Neuroscience major, explains what it was like for him to collaborate with a Biology professor on her neuron research.

The Departments of Psychology and Biology offer a course major and an honors major in Neuroscience. Applications for this special major must be submitted to both departments. Each Neuroscience major will be assigned a primary advisor from whichever of the two departments best reflects the focus of that student's plan of study.

A. Entry Requirements for the Neuroscience Course Major and Honors Major

The study of Neuroscience involves advanced coursework with the following prerequisites. For admission to the Neuroscience special major, students must

a. complete (or otherwise satisfy) the following required courses (up to two credits of these taken at Swarthmore may be counted as Group B electives for the major), and

b. obtain a minimum GPA of 3.0 (B) for these courses overall, as well as within all Biology courses and within all Psychology courses.

Biology BIOL 001: Cellular and Molecular Biology

BIOL 002: Organismal and Population Biology

Chemistry CHEM 010: General Chemistry

CHEM 022: Organic Chemistry I

Math/Stat MATH 015: Elementary Single-Variable Calculus

STAT 011: Statistical Methods

Psychology PSYC 001: Introduction to Psychology

PSYC 025: Research Design and Analysis

The requirement for BIOL 001 and/or BIOL 002 may be satisfied by credit from the Biology AP exam (score of 5) if at least one credit in Biology has been completed at Swarthmore.

The requirement for CHEM 010 will be satisfied if the student has placed out of it and completed CHEM 022.

The requirements for MATH 015 and STAT 011 may be satisfied by placement out of these courses, as determined by the Department of Mathematics and Statistics

The requirement for PSYC 001 may be satisfied with a Psychology AP exam score of 5.

Provisional admission to the special major will normally be granted based on substantial progress in satisfying these entry requirements at the time of application.

B. Neuroscience Course Major Requirements

A special major at Swarthmore must include at least 10 credits and no more than 12 credits. A Neuroscience major will normally include two (2) Entry Requirement Courses (i.e., any two that have been taken at Swarthmore) and eight (8) Elective credits as specified below, including fulfilling the comprehensive requirement. Up to twelve credits may be included in the major, but only ten are required.

1. Electives

Majors will complete at least eight (8) elective credits from the following lists, to include at least one seminar. At least five (5) elective credits must be from Group A including at least one Foundation course and at least one course from each of Psychology and Biology. The remaining three (3) credits can be from either Group A, Group B, or Group C (see restrictions below). It is possible to substitute or add electives from other universities (e.g., Systems Neuroscience at UPenn), including abroadbut students should seek Swarthmore faculty approval for such courses in advance.

Group A: Neuroscience Electives

PSYC 030 Behavioral Neuroscience[Foundation Course*]

BIOL 022 Neurobiology [Foundation Course*]

BIOL 011 Epigenetics (spring 2015 ONLY)

BIOL 020 Animal Physiology

BIOL 029 Developmental Neurobiology

BIOL 030 Animal Behavior

BIOL 120 Sleep and Circadian Rhythms seminar (2 credits)

BIOL 123 Learning and Memory seminar (2 credits)

BIOL 124 Hormones and Behavior seminar (2 credits)

BIOL 131 Animal Communication seminar (2 credits)

BIOL 134 Evolution of Social Behavior (2 credits)

PSYC 031 Cognitive Neuroscience

PSYC 031A Social, Cognitive, and Affective Neuroscience

PSYC 032 Perception

PSYC 091 Advanced Topics in Behavioral Neuroscience

PSYC 130 Behavioral Neuroscience seminar (1 credit)

PSYC 131 Seminar in Cognitive Neuroscience (1 credit seminar)

PSYC 131A Psychology and Neuroscience: The Social Brain (1 credit seminar)

PSYC 132 Perception, Cognition, and Embodiment seminar (1 credit)

*At least one Foundation Course must be included. Both are recommended.

Group B: Course Electives in Related/Overlapping Scientific Areas

BIOL 010 Genetics

BIOL 014 Cell Biology

BIOL 019 Omics

BIOL 021 Comparative Vertebrate Anatomy

BIOL 024 Developmental Biology

BIOL 026 Invertebrate Biology

BIOL 034 Evolution

BIOL/CPSC 068 Bioinformatics

BIOL 110 Human Genetics seminar (2 credits)

BIOL 112 From Cells to Organs (2 credits)

BIOL 125 Frontiers in Developmental Biology seminar (2 credits)

BIOL 119 Genomics and Systems Biology seminar (2 credits)

BIOL 126 Biomechanics seminar (2 credits)

BIOL 136 Molecular Ecology and Evolution seminar (2 credits)

CHEM 038 Biological Chemistry

COGS 001 Introduction to Cognitive Science

CPSC 021 Introduction to Computer Science

MATH 056 Modeling

PSYC 033 Cognitive Psychology

PSYC 034 Psychology of Language

PSYC 035 Social Psychology

PSYC 036 Thinking, Judgment & Decision Making

PSYC 038 Clinical Psychology

PSYC 039 Developmental Psychology

PSYC 133 Metaphor and Mind seminar (1 credit)

PSYC 134 Psycholinguistics seminar (1 credit)

PSYC 138 Clinical Psychology seminar (1 credit)

PSYC 139 Developmental Psychology seminar (1 credit)

Group C: Research Electives

One unit of research (of up to 2 credits) in neuroscience from the following may be counted toward the minimum required 10 credits of the major. Additional research units may be counted for optional credits up to 12. Research electives are one way of fulfilling the comprehensive requirement (see below) for the Neuroscience major.

BIOL 098 Neuroscience Thesis Research

PSYC 096/097 Senior Thesis (2 credits)

PSYC099 Senior Neuroscience Thesis

PSYC 102 Research Practicum in Perception and Cognition

PSYC 103 Research Practicum in Behavioral Neuropharmacology

PSYC 104 Research Practicum in Mind and Language

PSYC 105 Research Practicum in Psychology and Neuroscience

PSYC 110 Research Practicum in Cognitive Neuroscience

2. Comprehensive Requirement

The comprehensive requirement is a Neuroscience Research Thesis, a complete scientific paper based on a research project conducted in Biology or Psychology or some other area related to neuroscience. The Research Thesis may either (1) be a research paper from a Group C elective, or (2) be based on a separate research project, such as might occur during a summer (whether at Swarthmore or at another institution) or as part of a laboratory project in a Neuroscience Elective (e.g., a 2-credit Biology seminar *).

In either case, a proposal will be submitted no later than the beginning of the senior year that explains the student's plan for conducting or completing the comprehensive requirement. If option 2 is selected, the proposal must be detailed. Upon approval of an option 2 proposal, students will register for a 0.5 credit unit of Neuroscience Thesis during either (but not both) semester of the senior year.; a 2-credit thesis will be evaluated by two faculty members, typically from two different departments.

*Students in Biology seminars often work on group projects and sometimes produce multi-authored research papers. Such a project may serve as the basis of a Neuroscience Research Thesis, but the paper must be a unique product of the student who submits it as his/her Thesis.

Neuroscience Research Thesis: Guidelines for content and organization.

The thesis should be organized in the format of a formal scientific paper, including the following sections: abstract, introduction, materials and methods, results, discussion, acknowledgments, and literature cited.

The thesis should report new empirical data on a research project that was conducted by the student.

As the comprehensive exercise for an interdisciplinary special major, students should endeavor to explain their scientific question(s) and how their work is related to larger questions or themes in neuroscience in the thesis introduction and/or discussion.

The length of the thesis is to be no more than 20 pages, double-spaced (exclusive of figures, tables, and references).

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Neuroscience :: Biology :: Swarthmore College

Embryology

Human embryogenesis – Wikipedia

This article is about Human embryogenesis. For Embryogenesis in general, see Embryogenesis.

Human embryogenesis is the process of cell division and cellular differentiation of the embryo that occurs during the early stages of development. In biological terms, human development entails growth from a one celled zygote to an adult human being. Fertilisation occurs when the sperm cell successfully enters and fuses with an egg cell (ovum). The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of prenatal development commences.[1] Embryogenesis covers the first eight weeks of development and at the beginning of the ninth week the embryo is termed a fetus. Human embryology is the study of this development during the first eight weeks after fertilisation. The normal period of gestation (pregnancy) is nine months or 38 weeks.

The germinal stage, refers to the time from fertilization, through the development of the early embryo until implantation is completed in the uterus. The germinal stage takes around 10 days.[2]

During this stage, the zygote, which is defined as an embryo because it contains a full complement of genetic material, begins to divide, in a process called cleavage. A blastocyst is then formed and implanted in the uterus. Embryogenesis continues with the next stage of gastrulation when the three germ layers of the embryo form in a process called histogenesis, and the processes of neurulation and organogenesis follow. The embryo is referred to as a fetus in the later stages of prenatal development, usually taken to be at the beginning of the ninth week. In comparison to the embryo, the fetus has more recognizable external features, and a more complete set of developing organs. The entire process of embryogenesis involves coordinated spatial and temporal changes in gene expression, cell growth and cellular differentiation. A nearly identical process occurs in other species, especially among chordates.

Fertilization takes place when the spermatozoon has successfully entered the ovum and the two sets of genetic material carried by the gametes fuse together, resulting in the zygote (a single diploid cell). This usually takes place in the ampulla of one of the fallopian tubes. The zygote contains the combined genetic material carried by both the male and female gametes which consists of the 23 chromosomes from the nucleus of the ovum and the 23 chromosomes from the nucleus of the sperm. The 46 chromosomes undergo changes prior to the mitotic division which leads to the formation of the embryo having two cells.

Successful fertilization is enabled by three processes, which also act as controls to ensure species-specificity. The first is that of chemotaxis which directs the movement of the sperm towards the ovum. Secondly there is an adhesive compatibility between the sperm and the egg. With the sperm adhered to the ovum, the third process of acrosomal reaction takes place; the front part of the spermatozoon head is capped by an acrosome which contains digestive enzymes to break down the zona pellucida and allow its entry.[3] The entry of the sperm causes calcium to be released which blocks entry to other sperm cells. A parallel reaction takes place in the ovum called the zona reaction. This sees the release of cortical granules that release enzymes which digest sperm receptor proteins, thus preventing polyspermy. The granules also fuse with the plasma membrane and modify the zona pellucida in such a way as to prevent further sperm entry.

The beginning of the cleavage process is marked when the zygote divides through mitosis into two cells. This mitosis continues and the first two cells divide into four cells, then into eight cells and so on. Each division takes from 12 to 24 hours. The zygote is large compared to any other cell and undergoes cleavage without any overall increase in size. This means that with each successive subdivision, the ratio of nuclear to cytoplasmic material increases.[4] Initially the dividing cells, called blastomeres (blastos Greek for sprout), are undifferentiated and aggregated into a sphere enclosed within the membrane of glycoproteins (termed the zona pellucida) of the ovum. When eight blastomeres have formed they begin to develop gap junctions, enabling them to develop in an integrated way and co-ordinate their response to physiological signals and environmental cues.[5]

When the cells number around sixteen the solid sphere of cells within the zona pellucida is referred to as a morula [6] At this stage the cells start to bind firmly together in a process called compaction, and cleavage continues as cellular differentiation.

Cleavage itself is the first stage in blastulation, the process of forming the blastocyst. Cells differentiate into an outer layer of cells (collectively called the trophoblast) and an inner cell mass. With further compaction the individual outer blastomeres, the trophoblasts, become indistinguishable, and are still enclosed within the zona pellucida. This compaction serves to make the structure watertight since the cells will later secrete fluid. The inner mass of cells differentiate to become embryoblasts and polarise at one end. They close together and form gap junctions in order to facilitate cellular communication. This polarisation leaves a cavity, the blastocoel in which is now termed the blastocyst. (In animals other than mammals, this is called the blastula). The trophoblasts secrete fluid into the blastocoel. By this time the size of the blastocyst has increased which makes it 'hatch' through the zone pellucida which then disintegrates.[7][8]

The inner cell mass will give rise to the embryo proper, the amnion, yolk sac and allantois, while the fetal part of the placenta will form from the outer trophoblast layer. The embryo plus its membranes is called the conceptus and by this stage the conceptus is in the uterus. The zona pellucida ultimately disappears completely, and the now exposed cells of the trophoblast allow the blastocyst to attach itself to the endometrium, where it will implant. The formation of the hypoblast and epiblast occurs at the beginning of the second week, which are the two main layers of the bilaminar germ disc.[9] Either the inner cells embryoblast or the outer cells trophoblast will turn into two sub layers each other.[10] The inner cells will turn into the hypoblast layer that will surround the other layer called epiblast layer, and these layers will form the embryonic disc in which the embryo will develop.[9][10] The place where the embryo develops is called the amniotic cavity, which is the inside the disc.[9] Also the trophoblast will develop two sub-layers; the cytotrophoblast that is front of the syncytiotrophoblast that is inside of the endometrium.[9] Next, another layer called the exocoelomic membrane or Heusers membrane will appear and surround the cytotrophoblast, as well as the primitive yolk sac.[10] The syncytiotrophoblast will grow and will enter a phase called lacunar stage, in which some vacuoles will appear and be filled by blood in the following days.[9][10] The development of the yolk sac starts with the hypoblastic flat cells that form the exocoelomic membrane, which will coat the inner part of the cytotrophoblast to form the primitive yolk sac. An erosion of the endothelial lining of the maternal capillaries by the syncytiotrophoblastic cells of the sinusoids will form where the blood will begin to penetrate and flow through the trophoblast to give rise to the uteroplacental circulation.[11][12] Subsequently new cells derived from yolk sac will be established between trophoblast and exocelomic membrane and will give rise to extra-embryonic mesoderm, which will form cavities known as chorionic cavity.[10]

At the end of the second week of development, some cells of the trophoblast penetrate and form rounded columns into the syncytiotrophoblast. These columns are known as primary villi. At the same time, other migrating cells form into the exocelomic cavity, a new cavity named as secondary or definitive yolk, smaller in size than the primitive yolk sac.[10][11]

After ovulation, the endometrial lining becomes transformed into a secretory lining in preparation of accepting the embryo. It becomes thickened with its secretory glands becoming elongated, and is increasingly vascular. This lining of the uterine cavity (or womb), is now known as the decidua and it produces a great number of large decidual cells in its increased interglandular tissue. The trophoblast then differentiates into an inner layer, the cytotrophoblast and an outer layer, the syncytiotrophoblast. The cytotrophoblast contains cuboidal epithelial cells having cell boundaries and are the source of dividing cells and the syncytiotrophoblast is a layer without cell boundaries.

The syncytiotrophoblast implants the blastocyst in the decidual epithelium, by projections of chorionic villi forming the embryonic part of the placenta. The placenta develops once the blastocyst is implanted, and forms to connect the embryo to the uterine wall. The decidua here is termed the decidua basalis and lies between the blastocyst and the myometrium and forms the maternal part of the placenta. The implantation is assisted by hydrolytic enzymes that erode the epithelium. The syncytiotrophoblast also produces human chorionic gonadotropin (hCG), a hormone that stimulates the release of progesterone from the corpus luteum. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can oxygenate and sustain the developing embryo. The uterus liberates sugar from stored glycogen from its cells to nourish the embryo.[13] The villi begin to branch and contain blood vessels of the embryo. Other villi, called terminal or free villi, have the role of nutrient exchange. The embryo is joined to the trophoblastic shell by a narrow connecting stalk that develops into the umbilical cord to attach the placenta to the embryo.[10][14] Arteries in the decidua are remodelled to increase the maternal blood flow into the intervillous spaces of the placenta, allowing gas exchange to take place as well as the transfer of nutrients to the embryo. Waste products from the embryo will diffuse across the placenta.

As the syncytiotrophoblast starts to penetrate the uterine wall, the inner cell mass (embryoblast) also develops. The inner cell mass is the source of embryonic stem cells, which are pluripotent and can develop into any one of the three germ layer cells.

The embryoblast forms an embryonic disc which is a bilaminar disc of two layers, an upper layer the epiblast (primitive ectoderm), and a lower layer the hypoblast (primitive endoderm). The disc is stretched between what will become the amniotic cavity and the yolk sac. The epiblast is adjacent to the trophoblast and made of columnar cells; the hypoblast is closest to the blastocyst cavity, and made of cuboidal cells. The epiblast migrates away from the trophoblast downwards, forming the amniotic cavity, the lining of which is formed from amnioblasts developed from the epiblast. The hypoblast is pushed down and forms the yolk sac (exocoelomic cavity) lining. Some hypoblast cells migrate along the inner cytotrophoblast lining of the blastocoel, secreting an extracellular matrix along the way. These hypoblast cells and extracellular matrix are called Heuser's membrane (or exocoelomic membrane), and they cover the blastocoel to form the yolk sac (or exocoelomic cavity). Cells of the epiblast migrate along the outer edges of this reticulum and form the extraembryonic mesoderm, which makes it difficult to maintain the extraembryonic reticulum. Soon pockets form in the reticulum, which ultimately coalesce to form the chorionic cavity or extraembryonic coelom.

The primitive streak, a linear band of cells formed by the migrating epiblast, appears, and this marks the beginning of gastrulation, which takes place around the sixteenth day (week 3) after fertilisation. The process of gastrulation reorganises the two-layer embryo into a three-layer embryo, and also gives the embryo its specific head-to-tail, and front-to-back orientation, by way of the primitive streak which establishes bilateral symmetry. A primitive node (or primitive knot) forms in front of the primitive streak which is the organiser of neurulation. A primitive pit forms as a depression in the centre of the primitive node which connects to the notochord which lies directly underneath. The node has arisen from epiblasts of the amniotic cavity floor, and it is this node that induces the formation of the neural plate which serves as the basis for the nervous system. The neural plate will form opposite the primitive streak from ectodermal tissue which thickens and flattens into the neural plate. The epiblast in that region moves down into the streak at the location of the primitive pit where the process called ingression, which leads to the formation of the mesoderm takes place. This ingression sees the cells from the epiblast move into the primitive streak in an epithelial-mesenchymal transition; epithelial cells become mesenchymal stem cells, multipotent stromal cells that can differentiate into various cell types. The hypoblast is pushed out of the way and goes on to form the amnion.The epiblast keeps moving and forms a second layer, the mesoderm. The epiblast has now differentiated into the three germ layers of the embryo, so that the bilaminar disc is now a trilaminar disc, the gastrula.

The three germ layers are the ectoderm, mesoderm and endoderm, and are formed as three overlapping flat discs. It is from these three layers that all the structures and organs of the body will be derived through the processes of somitogenesis, histogenesis and organogenesis.[15] The embryonic endoderm is formed by invagination of epiblastic cells that migrate to the hypoblast, while the mesoderm is formed by the cells that develop between the epiblast and endoderm. In general, all germ layers will derive from the epiblast.[10][14] The upper layer of ectoderm will give rise to the outermost layer of skin, central and peripheral nervous systems, eyes, inner ear, and many connective tissues.[16] The middle layer of mesoderm will give rise to the heart and the beginning of the circulatory system as well as the bones, muscles and kidneys. The inner layer of endoderm will serve as the starting point for the development of the lungs, intestine, thyroid, pancreas and bladder.

Following ingression, a blastopore develops where the cells have ingressed, in one side of the embryo and it deepens to become the archenteron, the first formative stage of the gut. As in all deuterostomes, the blastopore becomes the anus whilst the gut tunnels through the embryo to the other side where the opening becomes the mouth. With a functioning digestive tube, gastrulation is now completed and the next stage of neurulation can begin.

Following gastrulation, the ectoderm gives rise to epithelial and neural tissue, and the gastrula is now referred to as the neurula. The neural plate that has formed as a thickened plate from the ectoderm, continues to broaden and its ends start to fold upwards as neural folds. Neurulation refers to this folding process whereby the neural plate is transformed into the neural tube, and this takes place during the fourth week. They fold, along a shallow neural groove which has formed as a dividing median line in the neural plate. This deepens as the folds continue to gain height, when they will meet and close together. The cells that migrate through the most cranial part of the primitive line form the paraxial mesoderm, which will give rise to the somitomeres that in the process of somitogenesis will differentiate into somites that will form the sclerotome, the syndetome,[17] the myotome and the dermatome to form cartilage and bone, tendons, dermis (skin), and muscle. The intermediate mesoderm gives rise to the urogenital tract and consists of cells that migrate from the middle region of the primitive line. Other cells migrate through the caudal part of the primitive line and form the lateral mesoderm, and those cells migrating by the most caudal part contribute to the extraembryonic mesoderm.[10][14]

The embryonic disc begins flat and round, but eventually elongates to have a wider cephalic part and narrow-shaped caudal end.[9] At the beginning, the primitive line extends in cephalic direction and 18 days after fertilization returns caudally until it disappears. In the cephalic portion, the germ layer shows specific differentiation at the beginning of the 4th week, while in the caudal portion it occurs at the end of the 4th week.[10] Cranial and caudal neuropores become progressively smaller until they close completely (by day 26) forming the neural tube.[18]

Late in the fourth week, the superior part of the neural tube flexes at the level of the future midbrainthe mesencephalon. Above the mesencephalon is the prosencephalon (future forebrain) and beneath it is the rhombencephalon (future hindbrain).

The optical vesicle (which eventually becomes the optic nerve, retina and iris) forms at the basal plate of the prosencephalon. The alar plate of the prosencephalon expands to form the cerebral hemispheres (the telencephalon) whilst its basal plate becomes the diencephalon. Finally, the optic vesicle grows to form an optic outgrowth.

Cranial neural crest cells migrate to the pharyngeal arches as neural stem cells, where they develop in the process of neurogenesis into neurons.

Haematopoietic stem cells that give rise to all the blood cells develop from the mesoderm.

The development of the organs starts during the third to eighth weeks of embryogenesis.

The heart is the first functional organ to develop and starts to beat and pump blood at around 21 or 22 days.[19] Cardiac myoblasts and blood islands in the splanchnopleuric mesenchyme on each side of the neural plate, give rise to the cardiogenic region.[10]:165This is a horseshoe-shaped area near to the head of the embryo. By day 19, following cell signalling, two strands begin to form as tubes in this region, as a lumen develops within them. These two endocardial tubes grow and by day 21 have migrated towards each other and fused to form a single primitive heart tube, the tubular heart. This is enabled by the folding of the embryo which pushes the tubes into the thoracic cavity.[20]

Also at the same time that the tubes are forming, vasculogenesis (the development of the circulatory system) has begun. This starts on day 18 with cells in the splanchnopleuric mesoderm differentiating into angioblasts that develop into flattened endothelial cells. These join to form small vesicles called angiocysts which join up to form long vessels called angioblastic cords. These cords develop into a pervasive network of plexuses in the formation of the vascular network. This network grows by the additional budding and sprouting of new vessels in the process of angiogenesis.[20]

The tubular heart quickly forms five distinct regions. From head to tail, these are the infundibulum, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus. Initially, all venous blood flows into the sinus venosus, and is propelled from tail to head to the truncus arteriosus. This will divide to form the aorta and pulmonary artery; the bulbus cordis will develop into the right (primitive) ventricle; the primitive ventricle will form the left ventricle; the primitive atrium will become the front parts of the left and right atria and their appendages, and the sinus venosus will develop into the posterior part of the right atrium, the sinoatrial node and the coronary sinus.[19]

Cardiac looping begins to shape the heart as one of the processes of morphogenesis, and this completes by the end of the fourth week. Programmed cell death (apoptosis) is involved in this process, at the joining surfaces enabling fusion to take place.[20] In the middle of the fourth week, the sinus venosus receives blood from the three major veins: the vitelline, the umbilical and the common cardinal veins.

During the first two months of development, the interatrial septum begins to form. This septum divides the primitive atrium into a right and a left atrium. Firstly it starts as a crescent-shaped piece of tissue which grows downwards as the septum primum. The crescent shape prevents the complete closure of the atria allowing blood to be shunted from the right to the left atrium through the opening known as the ostium primum. This closes with further development of the system but before it does, a second opening (the ostium secundum) begins to form in the upper atrium enabling the continued shunting of blood.[20]

A second septum (the septum secundum) begins to form to the right of the septum primum. This also leaves a small opening, the foramen ovale which is continuous with the previous opening of the ostium secundum. The septum primum is reduced to a small flap that acts as the valve of the foramen ovale and this remains until its closure at birth. Between the ventricles the septum inferius also forms which develops into the muscular interventricular septum.[20]

From the third to the eighth week the face and neck develop.

In the fourth week limb development begins.

Toxic exposures during the germinal stage may cause prenatal death resulting in a miscarriage, but do not cause developmental defects. However, toxic exposures in the embryonic period can be the cause of major congenital malformations, since the precursors of the major organ systems are now developing.

Each cell of the preimplantation embryo has the potential to form all of the different cell types in the developing embryo. This cell potency means that some cells can be removed from the preimplantation embryo and the remaining cells will compensate for their absence. This has allowed the development of a technique known as preimplantation genetic diagnosis, whereby a small number of cells from the preimplantation embryo created by IVF, can be removed by biopsy and subjected to genetic diagnosis. This allows embryos that are not affected by defined genetic diseases to be selected and then transferred to the mother's uterus.

Sacrococcygeal teratomas, tumours formed from different types of tissue, that can form, are thought to be related to primitive streak remnants, which ordinarily disappear.[9][10][12]

Spina bifida a congenital disorder is the result of the incomplete closure of the neural tube.

Vertically transmitted infections can be passed from the mother to the unborn child at any stage of its development.

Hypoxia a condition of inadequate oxygen supply can be a serious consequence of a preterm or premature birth.

Representing different stages of embryogenesis

Early stage of the gastrulation process

Phase of the gastrulation process

Top of the form of the embryo

Establishment of embryo medium

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Biochemistry

History of biochemistry – Wikipedia

The history of biochemistry can be said to have started with the ancient Greeks who were interested in the composition and processes of life, although biochemistry as a specific scientific discipline has its beginning around the early 19th century.[1] Some argued that the beginning of biochemistry may have been the discovery of the first enzyme, diastase (today called amylase), in 1833 by Anselme Payen,[2] while others considered Eduard Buchner's first demonstration of a complex biochemical process alcoholic fermentation in cell-free extracts to be the birth of biochemistry.[3][4] Some might also point to the influential work of Justus von Liebig from 1842, Animal chemistry, or, Organic chemistry in its applications to physiology and pathology, which presented a chemical theory of metabolism,[1] or even earlier to the 18th century studies on fermentation and respiration by Antoine Lavoisier.[5][6]

The term biochemistry itself is derived from the combining form bio-, meaning "life", and chemistry. The word is first recorded in English in 1848,[7] while in 1877, Felix Hoppe-Seyler used the term (Biochemie in German) in the foreword to the first issue of Zeitschrift fr Physiologische Chemie (Journal of Physiological Chemistry) as a synonym for physiological chemistry and argued for the setting up of institutes dedicate to its studies.[8][9] Nevertheless, several sources cite German chemist Carl Neuberg as having coined the term for the new discipline in 1903,[10][11] and some credit it to Franz Hofmeister.[12]

The subject of study in biochemistry is the chemical processes in living organisms, and its history involves the discovery and understanding of the complex components of life and the elucidation of pathways of biochemical processes. Much of biochemistry deals with the structures and functions of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules; their metabolic pathways and flow of chemical energy through metabolism; how biological molecules give rise to the processes that occur within living cells; it also focuses on the biochemical processes involved in the control of information flow through biochemical signalling, and how they relate to the functioning of whole organisms. Over the last 40 years the field has had success in explaining living processes such that now almost all areas of the life sciences from botany to medicine are engaged in biochemical research.

Among the vast number of different biomolecules, many are complex and large molecules (called polymers), which are composed of similar repeating subunits (called monomers). Each class of polymeric biomolecule has a different set of subunit types. For example, a protein is a polymer whose subunits are selected from a set of twenty or more amino acids, carbohydrates are formed from sugars known as monosaccharides, oligosaccharides, and polysaccharides, lipids are formed from fatty acids and glycerols, and nucleic acids are formed from nucleotides. Biochemistry studies the chemical properties of important biological molecules, like proteins, and in particular the chemistry of enzyme-catalyzed reactions. The biochemistry of cell metabolism and the endocrine system has been extensively described. Other areas of biochemistry include the genetic code (DNA, RNA), protein synthesis, cell membrane transport, and signal transduction.

In these regards, the study of biochemistry began when biology first began to interest societyas the ancient Chinese developed a system of medicine based on yin and yang, and also the five phases,[13] which both resulted from alchemical and biological interests. It began in the ancient Indian culture also with an interest in medicine, as they developed the concept of three humors that were similar to the Greek's four humours (see humorism). They also delved into the interest of bodies being composed of tissues. As in the majority of early sciences, the Islamic world greatly contributed to early biological advancements as well as alchemical advancements; especially with the introduction of clinical trials and clinical pharmacology presented in Avicenna's The Canon of Medicine.[14] On the side of chemistry, early advancements were heavily attributed to exploration of alchemical interests but also included: metallurgy, the scientific method, and early theories of atomism. In more recent times, the study of chemistry was marked by milestones such as the development of Mendeleev's periodic table, Dalton's atomic model, and the conservation of mass theory. This last mention has the most importance of the three due to the fact that this law intertwines chemistry with thermodynamics in an intercalated manner.

As early as the late 18th century and early 19th century, the digestion of meat by stomach secretions[15] and the conversion of starch to sugars by plant extracts and saliva were known. However, the mechanism by which this occurred had not been identified.[16]

In the 19th century, when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that this fermentation was catalyzed by a vital force contained within the yeast cells called ferments, which he thought functioned only within living organisms. He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells."[17]

Anselme Payen discovered in 1833 the first enzyme who called diastase[18] and in 1878 German physiologist Wilhelm Khne (18371900) coined the term enzyme, which comes from Greek "in leaven", to describe this process. The word enzyme was used later to refer to nonliving substances such as pepsin, and the word ferment used to refer to chemical activity produced by living organisms.

In 1897 Eduard Buchner began to study the ability of yeast extracts to ferment sugar despite the absence of living yeast cells. In a series of experiments at the University of Berlin, he found that the sugar was fermented even when there were no living yeast cells in the mixture.[19] He named the enzyme that brought about the fermentation of sucrose "zymase".[20] In 1907 he received the Nobel Prize in Chemistry "for his biochemical research and his discovery of cell-free fermentation". Following Buchner's example; enzymes are usually named according to the reaction they carry out. Typically the suffix -ase is added to the name of the substrate (e.g., lactase is the enzyme that cleaves lactose) or the type of reaction (e.g., DNA polymerase forms DNA polymers).

Having shown that enzymes could function outside a living cell, the next step was to determine their biochemical nature. Many early workers noted that enzymatic activity was associated with proteins, but several scientists (such as Nobel laureate Richard Willsttter) argued that proteins were merely carriers for the true enzymes and that proteins per se were incapable of catalysis. However, in 1926, James B. Sumner showed that the enzyme urease was a pure protein and crystallized it; Sumner did likewise for the enzyme catalase in 1937. The conclusion that pure proteins can be enzymes was definitively proved by Northrop and Stanley, who worked on the digestive enzymes pepsin (1930), trypsin and chymotrypsin. These three scientists were awarded the 1946 Nobel Prize in Chemistry.[21]

This discovery, that enzymes could be crystallized, meant that scientists eventually could solve their structures by x-ray crystallography. This was first done for lysozyme, an enzyme found in tears, saliva and egg whites that digests the coating of some bacteria; the structure was solved by a group led by David Chilton Phillips and published in 1965.[22] This high-resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail.

The term metabolism is derived from the Greek Metabolismos for "change", or "overthrow".[23] The history of the scientific study of metabolism spans 800 years. The earliest of all metabolic studies began during the early thirteenth century (1213-1288) by a Muslim scholar from Damascus named Ibn al-Nafis. al-Nafis stated in his most well-known work Theologus Autodidactus that "that body and all its parts are in a continuous state of dissolution and nourishment, so they are inevitably undergoing permanent change."[24] Although al-Nafis was the first documented physician to have an interest in biochemical concepts, the first controlled experiments in human metabolism were published by Santorio Santorio in 1614 in his book Ars de statica medecina.[25] This book describes how he weighed himself before and after eating, sleeping, working, sex, fasting, drinking, and excreting. He found that most of the food he took in was lost through what he called "insensible perspiration".

One of the most prolific of these modern biochemists was Hans Krebs who made huge contributions to the study of metabolism.[26] He discovered the urea cycle and later, working with Hans Kornberg, the citric acid cycle and the glyoxylate cycle.[27][28][29] These discoveries led to Krebs being awarded the Nobel Prize in physiology in 1953,[30] which was shared with the German biochemist Fritz Albert Lipmann who also codiscovered the essential cofactor coenzyme A.

In 1960, the biochemist Robert K. Crane revealed his discovery of the sodium-glucose cotransport as the mechanism for intestinal glucose absorption.[31] This was the very first proposal of a coupling between the fluxes of an ion and a substrate that has been seen as sparking a revolution in biology. This discovery, however, would not have been possible if it were not for the discovery of the molecule glucose's structure and chemical makeup. These discoveries are largely attributed to the German chemist Emil Fischer who received the Nobel Prize in chemistry nearly 60 years earlier.[32]

Since metabolism focuses on the breaking down (catabolic processes) of molecules and the building of larger molecules from these particles (anabolic processes), the use of glucose and its involvement in the formation of adenosine triphosphate (ATP) is fundamental to this understanding. The most frequent type of glycolysis found in the body is the type that follows the Embden-Meyerhof-Parnas (EMP) Pathway, which was discovered by Gustav Embden, Otto Meyerhof, and Jakob Karol Parnas. These three men discovered that glycolysis is a strongly determinant process for the efficiency and production of the human body. The significance of the pathway shown in the adjacent image is that by identifying the individual steps in this process doctors and researchers are able to pinpoint sites of metabolic malfunctions such as pyruvate kinase deficiency that can lead to severe anemia. This is most important because cells, and therefore organisms, are not capable of surviving without proper functioning metabolic pathways.

Since then, biochemistry has advanced, especially since the mid-20th century, with the development of new techniques such as chromatography, X-ray diffraction, NMR spectroscopy, radioisotopic labelling, electron microscopy and molecular dynamics simulations. These techniques allowed for the discovery and detailed analysis of many molecules and metabolic pathways of the cell, such as glycolysis and the Krebs cycle (citric acid cycle). The example of an NMR instrument shows that some of these instruments, such as the HWB-NMR, can be very large in size and can cost anywhere from a few hundred dollars to millions of dollars ($16 million for the one shown here).

Polymerase chain reaction (PCR) is the primary gene amplification technique that has revolutionized modern biochemistry. Polymerase chain reaction was developed by Kary Mullis in 1983.[33] There are four steps to a proper polymerase chain reaction: 1) denaturation 2) extension 3) insertion (of gene to be expressed) and finally 4) amplification of the inserted gene. These steps with simple illustrative examples of this process can be seen in the image below and to the right of this section. This technique allows for the copy of a single gene to be amplified into hundreds or even millions of copies and has become a cornerstone in the protocol for any biochemist that wishes to work with bacteria and gene expression. PCR is not only used for gene expression research but is also capable of aiding laboratories in diagnosing certain diseases such a lymphomas, some types of leukemia, and other malignant diseases that can sometimes puzzle doctors. Without polymerase chain reaction development, there are many advancements in the field of bacterial study and protein expression study that would not have come to fruition.[34] The development of the theory and process of polymerase chain reaction is essential but the invention of the thermal cycler is equally as important because the process would not be possible without this instrument. This is yet another testament to the fact that the advancement of technology is just as crucial to sciences such as biochemistry as is the painstaking research that leads to the development of theoretical concepts.

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History of biochemistry - Wikipedia

Neuroscience

Neuroscience – William Beaumont Health System

A concussion is a brain injury caused by a bump or blow to the head, and is the most common type of traumatic brain injury in both adults and children. Concussions range from minor to major and are usually diagnosed based on symptoms and severity of head trauma.

The Beaumont Concussion Clinic offers comprehensive, specialized acute care for children and adults who experience a concussion.

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Neuroscience - William Beaumont Health System