San Antonio, TX University of Texas Health Science Center At San Antonio Cell Biology, Genetics, and Molecular Medicine
Cell Biology, Genetics & Molecular Medicine (CGM) includes courses can be individually tailored to a specific student's interests including aging, cancer, genetics, immunology, neuroscience, metabolism and physiology.
Program: Hybrid
Degree: Master, Doctorate
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Neuroscience Graduate Programs - gradschools.com
UCLA's Graduation Program in Neuroscience offers the following degree(s):
Doctor of Philosophy (Ph.D.)
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Neuroscience Graduate Program at UCLA 1506D Gonda Center Box 951761 Los Angeles, CA 90095-1761
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Neuroscience | UCLA Graduate Programs
The Interdepartmental Program in Neuroscience (IPN) at George Mason brings together experimental and theoretical scientists.
It draws from research in many departments -- Psychology, Molecular Neuroscience, Molecular and Microbiology, Electrical Engineering, Physics and Astronomy, and Computational Biology and Bioinformatics.
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Neuroscience Program
Psychoneuroimmunology (PNI), also referred to as psychoendoneuroimmunology (PENI) or psychoneuroendocrinoimmunology (PNEI), is the study of the interaction between psychological processes and the nervous and immune systems of the human body.[1] PNI takes an interdisciplinary approach, incorporating psychology, neuroscience, immunology, physiology, genetics, pharmacology, molecular biology, psychiatry, behavioral medicine, infectious diseases, endocrinology, and rheumatology.
The main interests of PNI are the interactions between the nervous and immune systems and the relationships between mental processes and health. PNI studies, among other things, the physiological functioning of the neuroimmune system in health and disease; disorders of the neuroimmune system (autoimmune diseases; hypersensitivities; immune deficiency); and the physical, chemical and physiological characteristics of the components of the neuroimmune system in vitro, in situ, and in vivo.
Interest in the relationship between psychiatric syndromes or symptoms and immune function has been a consistent theme since the beginning of modern medicine.
Claude Bernard, a French physiologist of the Musum national d'Histoire naturelle, formulated the concept of the milieu interieur in the mid-1800s. In 1865, Bernard described the perturbation of this internal state: "... there are protective functions of organic elements holding living materials in reserve and maintaining without interruption humidity, heat and other conditions indispensable to vital activity. Sickness and death are only a dislocation or perturbation of that mechanism" (Bernard, 1865). Walter Cannon, a professor of physiology at Harvard University coined the commonly used term, homeostasis, in his book The Wisdom of the Body, 1932, from the Greek word homoios, meaning similar, and stasis, meaning position. In his work with animals, Cannon observed that any change of emotional state in the beast, such as anxiety, distress, or rage, was accompanied by total cessation of movements of the stomach (Bodily Changes in Pain, Hunger, Fear and Rage, 1915). These studies looked into the relationship between the effects of emotions and perceptions on the autonomic nervous system, namely the sympathetic and parasympathetic responses that initiated the recognition of the freeze, fight or flight response. His findings were published from time to time in professional journals, then summed up in book form in The Mechanical Factors of Digestion, published in 1911.
Hans Selye, a student of Johns Hopkins University and McGill University, and a researcher at Universit de Montral, experimented with animals by putting them under different physical and mental adverse conditions and noted that under these difficult conditions the body consistently adapted to heal and recover. Several years of experimentation that formed the empiric foundation of Selye's concept of the General Adaptation Syndrome. This syndrome consists of an enlargement of the adrenal gland, atrophy of the thymus, spleen, and other lymphoid tissue, and gastric ulcerations.
Selye describes three stages of adaptation, including an initial brief alarm reaction, followed by a prolonged period of resistance, and a terminal stage of exhaustion and death. This foundational work led to a rich line of research on the biological functioning of glucocorticoids.[2]
Mid-20th century studies of psychiatric patients reported immune alterations in psychotic individuals, including lower numbers of lymphocytes[3][4] and poorer antibody response to pertussis vaccination, compared with nonpsychiatric control subjects.[5] In 1964, George F. Solomon, from the University of California in Los Angeles, and his research team coined the term "psychoimmunology" and published a landmark paper: "Emotions, immunity, and disease: a speculative theoretical integration."[6]
In 1975, Robert Ader and Nicholas Cohen, at the University of Rochester, advanced PNI with their demonstration of classic conditioning of immune function, and they subsequently coined the term "psychoneuroimmunology".[7][8] Ader was investigating how long conditioned responses (in the sense of Pavlov's conditioning of dogs to drool when they heard a bell ring) might last in laboratory rats. To condition the rats, he used a combination[clarification needed] of saccharin-laced water (the conditioned stimulus) and the drug Cytoxan, which unconditionally induces nausea and taste aversion and suppression of immune function. Ader was surprised to discover that after conditioning, just feeding the rats saccharin-laced water was associated with the death of some animals and he proposed that they had been immunosuppressed after receiving the conditioned stimulus. Ader (a psychologist) and Cohen (an immunologist) directly tested this hypothesis by deliberately immunizing conditioned and unconditioned animals, exposing these and other control groups to the conditioned taste stimulus, and then measuring the amount of antibody produced. The highly reproducible results revealed that conditioned rats exposed to the conditioned stimulus were indeed immuno suppressed. In other words, a signal via the nervous system (taste) was affecting immune function. This was one of the first scientific experiments that demonstrated that the nervous system can affect the immune system.
In 1981, David L. Felten, then working at the Indiana University School of Medicine, discovered a network of nerves leading to blood vessels as well as cells of the immune system. The researcher, along with his team, also found nerves in the thymus and spleen terminating near clusters of lymphocytes, macrophages, and mast cells, all of which help control immune function. This discovery provided one of the first indications of how neuro-immune interaction occurs.
Ader, Cohen, and Felten went on to edit the groundbreaking book Psychoneuroimmunology in 1981, which laid out the underlying premise that the brain and immune system represent a single, integrated system of defense.
In 1985, research by neuropharmacologist Candace Pert, of the National Institutes of Health at Georgetown University, revealed that neuropeptide-specific receptors are present on the cell walls of both the brain and the immune system.[9][10] The discovery that neuropeptides and neurotransmitters act directly upon the immune system shows their close association with emotions and suggests mechanisms through which emotions, from the limbic system, and immunology are deeply interdependent. Showing that the immune and endocrine systems are modulated not only by the brain but also by the central nervous system itself affected the understanding of emotions, as well as disease.
Contemporary advances in psychiatry, immunology, neurology, and other integrated disciplines of medicine has fostered enormous growth for PNI. The mechanisms underlying behaviorally induced alterations of immune function, and immune alterations inducing behavioral changes, are likely to have clinical and therapeutic implications that will not be fully appreciated until more is known about the extent of these interrelationships in normal and pathophysiological states.
PNI research is looking for the exact mechanisms by which specific brainimmunity effects are achieved. Evidence for nervous systemimmune system interactions exists at several biological levels.
The immune system and the brain talk to each other through signaling pathways. The brain and the immune system are the two major adaptive systems of the body. Two major pathways are involved in this cross-talk: the Hypothalamic-pituitary-adrenal axis (HPA axis) and the sympathetic nervous system (SNS). The activation of SNS during an immune response might be aimed to localize the inflammatory response.
The body's primary stress management system is the HPA axis. The HPA axis responds to physical and mental challenge to maintain homeostasis in part by controlling the body's cortisol level. Dysregulation of the HPA axis is implicated in numerous stress-related diseases, with evidence from meta-analyses indicating that different types/duration of stressors and unique personal variables can shape the HPA response.[11] HPA axis activity and cytokines are intrinsically intertwined: inflammatory cytokines stimulate adrenocorticotropic hormone (ACTH) and cortisol secretion, while, in turn, glucocorticoids suppress the synthesis of proinflammatory cytokines.
Molecules called pro-inflammatory cytokines, which include interleukin-1 (IL-1), Interleukin-2 (IL-2), interleukin-6 (IL-6), Interleukin-12 (IL-12), Interferon-gamma (IFN-Gamma) and tumor necrosis factor alpha (TNF-alpha) can affect brain growth as well as neuronal function. Circulating immune cells such as macrophages, as well as glial cells (microglia and astrocytes) secrete these molecules. Cytokine regulation of hypothalamic function is an active area of research for the treatment of anxiety-related disorders.[12]
Cytokines mediate and control immune and inflammatory responses. Complex interactions exist between cytokines, inflammation and the adaptive responses in maintaining homeostasis. Like the stress response, the inflammatory reaction is crucial for survival. Systemic inflammatory reaction results in stimulation of four major programs:[13]
These are mediated by the HPA axis and the SNS. Common human diseases such as allergy, autoimmunity, chronic infections and sepsis are characterized by a dysregulation of the pro-inflammatory versus anti-inflammatory and T helper (Th1) versus (Th2) cytokine balance.
Recent studies show pro-inflammatory cytokine processes take place during depression, mania and bipolar disease, in addition to autoimmune hypersensitivity and chronic infections.
Chronic secretion of stress hormones, glucocorticoids (GCs) and catecholamines (CAs), as a result of disease, may reduce the effect of neurotransmitters, including serotonin[medical citation needed], norepinephrine and dopamine, or other receptors in the brain, thereby leading to the dysregulation of neurohormones. Under stimulation, norepinephrine is released from the sympathetic nerve terminals in organs, and the target immune cells express adrenoreceptors. Through stimulation of these receptors, locally released norepinephrine, or circulating catecholamines such as epinephrine, affect lymphocyte traffic, circulation, and proliferation, and modulate cytokine production and the functional activity of different lymphoid cells.
Glucocorticoids also inhibit the further secretion of corticotropin-releasing hormone from the hypothalamus and ACTH from the pituitary (negative feedback). Under certain conditions stress hormones may facilitate inflammation through induction of signaling pathways and through activation of the Corticotropin-releasing hormone.
These abnormalities and the failure of the adaptive systems to resolve inflammation affect the well-being of the individual, including behavioral parameters, quality of life and sleep, as well as indices of metabolic and cardiovascular health, developing into a "systemic anti-inflammatory feedback" and/or "hyperactivity" of the local pro-inflammatory factors which may contribute to the pathogenesis of disease.
This systemic or neuro-inflammation and neuroimmune activation have been shown to play a role in the etiology of a variety of neurodegenerative disorders such as Parkinson's and Alzheimer's disease, multiple sclerosis, pain, and AIDS-associated dementia. However, cytokines and chemokines also modulate central nervous system (CNS) function in the absence of overt immunological, physiological, or psychological challenges.[14]
There is now sufficient data to conclude that immune modulation by psychosocial stressors and/or interventions can lead to actual health changes. Although changes related to infectious disease and wound healing have provided the strongest evidence to date, the clinical importance of immunological dysregulation is highlighted by increased risks across diverse conditions and diseases. For example, stressors can produce profound health consequences. In one epidemiological study, all-cause mortality increased in the month following a severe stressor the death of a spouse.[15] Theorists propose that stressful events trigger cognitive and affective responses which, in turn, induce sympathetic nervous system and endocrine changes, and these ultimately impair immune function.[16][17] Potential health consequences are broad, but include rates of infection[18][19] HIV progression[20][21] cancer incidence and progression,[15][22][23] and high rates of infant mortality.[24][25]
Stress is thought to affect immune function through emotional and/or behavioral manifestations such as anxiety, fear, tension, anger and sadness and physiological changes such as heart rate, blood pressure, and sweating. Researchers have suggested that these changes are beneficial if they are of limited duration,[16] but when stress is chronic, the system is unable to maintain equilibrium or homeostasis.
In one of the earlier PNI studies, which was published in 1960, subjects were led to believe that they had accidentally caused serious injury to a companion through misuse of explosives.[26] Since then decades of research resulted in two large meta-analyses, which showed consistent immune dysregulation in healthy people who are experiencing stress.
In the first meta-analysis by Herbert and Cohen in 1993,[27] they examined 38 studies of stressful events and immune function in healthy adults. They included studies of acute laboratory stressors (e.g. a speech task), short-term naturalistic stressors (e.g. medical examinations), and long-term naturalistic stressors (e.g. divorce, bereavement, caregiving, unemployment). They found consistent stress-related increases in numbers of total white blood cells, as well as decreases in the numbers of helper T cells, suppressor T cells, and cytotoxic T cells, B cells, and Natural killer cells (NK). They also reported stress-related decreases in NK and T cell function, and T cell proliferative responses to phytohaemagglutinin [PHA] and concanavalin A [Con A]. These effects were consistent for short-term and long-term naturalistic stressors, but not laboratory stressors.
In the second meta-analysis by Zorrilla et al. in 2001,[28] they replicated Herbert and Cohen's meta-analysis. Using the same study selection procedures, they analyzed 75 studies of stressors and human immunity. Naturalistic stressors were associated with increases in number of circulating neutrophils, decreases in number and percentages of total T cells and helper T cells, and decreases in percentages of Natural killer cell (NK) cells and cytotoxic T cell lymphocytes. They also replicated Herbert and Cohen's finding of stress-related decreases in NKCC and T cell mitogen proliferation to Phytohaemagglutinin (PHA) and Concanavalin A (Con A).
More recently, there has been increasing interest in the links between interpersonal stressors and immune function. For example, marital conflict, loneliness, caring for a person with a chronic medical condition, and other forms on interpersonal stress dysregulate immune function.[29]
Release of corticotropin-releasing hormone (CRH) from the hypothalamus is influenced by stress.
Furthermore, stressors that enhance the release of CRH suppress the function of the immune system; conversely, stressors that depress CRH release potentiate immunity.
Glutamate agonists, cytokine inhibitors, vanilloid-receptor agonists, catecholamine modulators, ion-channel blockers, anticonvulsants, GABA agonists (including opioids and cannabinoids), COX inhibitors, acetylcholine modulators, melatonin analogs (such as Ramelton), adenosine receptor antagonists and several miscellaneous drugs (including biologics like Passiflora edulis) are being studied for their psychoneuroimmunological effects.
For example, SSRIs, SNRIs and tricyclic antidepressants acting on serotonin, norepinephrine and dopamine receptors have been shown to be immunomodulatory and anti-inflammatory against pro-inflammatory cytokine processes, specifically on the regulation of IFN-gamma and IL-10, as well as TNF-alpha and IL-6 through a psychoneuroimmunological process.[32][33][34] Antidepressants have also been shown to suppress TH1 upregulation.[32][33][34][35][36]
Tricyclic and dual serotonergic-noradrenergic reuptake inhibition by SNRIs (or SSRI-NRI combinations), have also shown analgesic properties additionally.[37][38] According to recent evidences antidepressants also seem to exert beneficial effects in experimental autoimmune neuritis in rats by decreasing Interferon-beta (IFN-beta) release or augmenting NK activity in depressed patients.[12]
These studies warrant investigation for antidepressants for use in both psychiatric and non-psychiatric illness and that a psychoneuroimmunological approach may be required for optimal pharmacotherapy in many diseases.[39] Future antidepressants may be made to specifically target the immune system by either blocking the actions of pro-inflammatory cytokines or increasing the production of anti-inflammatory cytokines.[40]
Extrapolating from the observations that positive emotional experiences boost the immune system, Roberts speculates that intensely positive emotional experiences sometimes brought about during mystical experiences occasioned by psychedelic medicinesmay boost the immune system powerfully. Research on salivary IgA supports this hypothesis, but experimental testing has not been done.[41]
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Psychoneuroimmunology - Wikipedia
San Antonio, TX University of Texas Health Science Center At San Antonio Cell Biology, Genetics, and Molecular Medicine
Cell Biology, Genetics & Molecular Medicine (CGM) includes courses can be individually tailored to a specific student's interests including aging, cancer, genetics, immunology, neuroscience, metabolism and physiology.
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Degree: Master, Doctorate
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Neuroscience Graduate Programs - Graduate School | Masters ...
Genetics is a discipline of the Biological sciences that studies personal traits the human or living organism inherit from its ancestors through genes and Embryology studies the development of the fertilized embryo from the ovum to the fetus stage.
Journal of Human Genetics and Embryology is a peer reviewed scientific journal known for rapid dissemination of high-quality research. This Human Genetics Journal with high impact factor offers an open access platform to the authors in academia and industry to publish their novel research in the mode of original articles, review articles, case reports, short communications, etc. It serves the International Scientific Community with its standard research publications.
This scholarly publishing is using Editorial Manager System for quality in the review process. Editorial Manager is an online manuscript submission, review and tracking system. Review process is performed by the editorial board members of Human Genetics & Embryology journal or outside experts; at least two independent reviewers approval followed by the editor is required for the acceptance of any citable manuscript. Authors may submit manuscripts and track their progress through the system, hopefully to publication. Reviewers can download manuscripts and submit their opinions to the editor. Editors can manage the whole submission/review/revise/publish process.
Human genetics is the study of inheritance in human beings. Human characteristics are inherited from parents to offspring in discrete unites called genes. Genes consist of specific information coded in the chromosome that consists of segments of chromosomes. Human genetics includes a variety of overlapping fields like classical, molecular, biochemical, population, developmental, clinical and cytogenetics.
Related Journals of Human Genetics
Human Genetics and Embryology,Journal of Cytology & Histology,Hereditary Genetics: Current Research,General Medicine: Open Access,Journal of Molecular and Genetic Medicine,Immunogenetics: Open Access, American Journal of Human Genetics, Annals of Human Genetics, Annual Review of Genomics and Human Genetics, Current Protocols in Human Genetics, European Journal of Human Genetics, Human Genetics, Twin Research and Human Genetics, International Journal of Human Genetics, Journal of Human Genetics
Genome biology deals with genomes. Genomes are the genetic material of an organism. They consists of DNA or RNA. Genome includes both the genes and as well as non-coding sequences of DNA or RNA.
Related Journals of Genome Biology
Human Genetics and Embryology,Cellular and Molecular Biology,Transcriptomics: Open Access,Journal of Probiotics & Health,Advancements in Genetic Engineering,Journal of Next Generation Sequencing & Applications,Genome Biology, Genome Biology and Evolution, Advances in Genome Biology, Egyptian Journal of Medical Human Genetics, Annals of Human Genetics
Mendelian genetics are the set of theories proposed by Gregor Johann Mendel. Mendelian genetics tends to explain inheritance and biological diversity regarding the transmission of genetic characters from parents to offsprings. These are based on statistical analysis and scientific breeding experiments on pea plants. Mendelian genetics is used to study the pattern of segregation of phenotypes under the control of genes taken one at a time.
Related Journals of Mendelian Genetics Human Genetics and Embryology,Journal of medical Microbiology and Medicine, Journal of phylogenetics and Evolutionary Biology, Journal of Molecular and Genetic Medicine,Trends in Genetics, Tree Genetics and Genomes, Topics in Current Genetics-TAG, Theoretical and applied genetics,Theoretische and angewandte Genetik, Statistical Applications in Genetics and Molecular Biology, Russian Journal of Genetics
Genetic linkagesis the tendency of alleles that are located close together on a chromosome to be inherited together during meiosis. Genes whose loci are nearer to each other are less likely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be genetically linked. In other words, the nearer two genes are on a chromosome, the lower is the chance of a swap occurring between them, and the more likely they are to be inherited together.
Related Journals of Genetic Linkage Human Genetics and Embryology,Cellular and Molecular Biology, Herediatry Genetics: Current Research,Journal of Molecular and Genetic Medicine,Biochimica et Biophysica Acta - Gene Regulatory Mechanisms, Molecular Medicine, Genetics Selection Evolution, Chromosoma, Journal of Medical Genetics, Evolution-international journal of organic evolution, PLoS Genetics
Genetic code helps in carrying the information of living cells by DNA and RNA molecules. The genetic code is the set of rules by which information encoded within genetic material (DNA or mRNA sequences) is translated into proteins by living cells. This help in determining the amino acid sequence used in the synthesis of an organism proteins. It is the basis of heredity. It is universal in all organisms.
Related Journals of Genetic CodeHuman Genetics and Embryology,Journal of Medical Microbiology and Diagnosis,Journal of Phylogenetics and Evolutionary Biology, Biology and Medicine, Genetics Selection Evolution, Genes Chromosomes and Cancer, Journal of Medical Genetics, Advances in Genetics, Nucleic Acids Research, Cell Stem Cell, Systematic Biology
Gene mapping is any method used for determining the location of gene and relative distances between genes on a chromosome. gene maps are used for linkage analysis. Relative positions of genes can be determined by inheritance patterns. locating and identifying genes in a genetic map is known as gene mapping or genetic mapping.
Related Journals of Genome Mapping Human Genetics and Embryology,Journal of Molecular and Genetic Medicine,Biology and Medicine,Cellular and Molecular Biology,Genome Mapping and Genomics in Animals, Human Brain Mapping, Mapping and Image Science, Genome Mapping and Genomics in Animals, American Journal of Human Genetics
Huntington disease is an inherited disease.Huntington disease causes the degeneration of nerve cells in brain. This leads to functional inabilities and psychiatric disorders. Huntington disease also affects muscle coordination. It is caused by an inherited defect in a single gene. Gene that causes Huntington disease is HIT gene. Symptoms of the disease can vary between individuals and affected members of the same family, but usually progress predictably.
Related Journals of Huntington Disease Human Genetics and Embryology,Journal of Medical Microbiology and Diagnosis,Journal of Phylogenetics and Evolutionary Biology, Biology and Medicine, American Journal of Medical Genetics - Seminars in Medical Genetics, American Journal of Medical Genetics, Part A, American Journal of Medical Genetics-Part B, Neuropsychiatric Genetics, American Journal of Medical Genetics, Neuropsychiatric Genetics, Annual Review of Genetics, BAG - Journal of Basic and Applied Genetics
Embryology is a branch of biology. Embryology is the state of embryo development from the fertilization of the ovum to the fetus stage. Embryology deals with the origin, growth and development of an embryo. cells which result after fertilisation is termed as an embryo. After eight weeks the developed embryo can be termed as fetus. there are different stages of embryonic development. the study of embryo is also known as embryology.
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Human fertilization is a union of egg and sperm resulting in a fertilized egg, also called as zygote. Fertilization takes place inside the fallopian tube. Embryogenesis starts with fertilization of egg cell. Embryogenesis forms and develop the embryo.
Related Journals of Human Fertilization and Embryogenesis Human Genetics and Embryology,Molecular Biology, Journal of Medicine Microbiology and Diagnosis, Cellular and Molecular Biology, Herediatry Genetics: Current Research, Journal of embryo transfer, Journal of In Vitro Fertilization and Embryo Transfer, Iraqi Journal of Embryos and Infertility Research, Zygote, Advances in Anatomy Embryology and Cell Biology
Correlative embryology is a branch of embryology. It is used to compare and contrasts embryos of different species. Correlative embryology is used to show how all animals are related. Many things are compared, whether or not the organism has a notochord or whether or not it has gill arches. All embryos pass from single cells to multi celled zygotes, clumps of cells called morulas and hallow balls of cells called blastula before they differentiate into organs and systems of body. Many components go into Comparative Embryology and about the developmental similarities between species can be taken from its study, which many conclusions can be drawn.
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Embryonic development takes 8weeks to the embryo to develop. human embryo development depends on stem cells. During embryonic development cells divide, migrate and specialize. Early development stages forms a group of cells called inner cell mass which are able to produce all tissues of the body. Later during gastrulation period, the three germ layers are formed and most cells become restricted in type of cells that they produce.
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Morphogenesis is an embryological process of differentiation of cells, tissues and organs and the development of organ systems according to genetic blueprint of the organism and environmental conditions. Morphogenesis is the development of biology along with the control of growth and cellular differentiation.
Related Journals of Morphohenesis Human Genetics and Embryology,Journal of Phylogenetics and Evolutiomnary Biology, Herediatry Genetics: Current Research, Journal of Molecular and Genetic Medicine, Biology and Medicine,Journal of Medical MIcrobiology and Diagnosis, Biology and Medicine, General Medine: Open Access, Journal of Molecular and Genetic Medicine, Journal of Morphology, Journal of Anatomy, Italian Journal of Anatomy and Embryology, Human Reproduction, Reproduction, Fertility and Development, Molecular Reproduction and Development,
Sex chromosomes are either a pair of chromosomes that determines whether an individual is male or female. Sex chromosomes are designated as X and Y. There are 23 pairs of sex chromosomes. The other 22 chromosome are called as autosomes. chromosome which differs from shape or function of other chromosome that determines the sex of child. If the sex chromosome is Xy then it is male child and if sex chromosome is XY then it is female child. sex chromosomes carry those genes that control development of reproductive organs and secondary sex characteristics.
Related Journals of Sex chromosomes Human Genetics and Embryology,Journal of Medical Microbiology and Diagnosis, Journal of Phylogenetics and Evolutionary Biology, Genes Chromosomes and Cancer, Genes, Chromosomes and Cancer - Index Copernicus, European Journal of Human Genetics, Journal of Genomics
Journal of Human Genetics and Embryology is associated with our international conference " 5th International Conference and Exhibition on Cell & Gene Therapy during May 19-21, 2016 at San Antonio, USA. We are particularly interested in research area Human genetics, Genome Sequencing, Embryology, Human fertilization, Genetic Disorders, Embryonic Development, Genetic code, Fertilization, Comparative Embryology, genome biology.
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British Society for Immunology | Celebrating the first 60 years
The Department of Obstetrics and Gynecology at the Medical College of Georgia at Augusta University is a comprehensive clinical service and educational department, specializing in the healthcare of women both on a primary and referral basis. We provide quality clinical services in following areas: General Obstetrics and Gynecology, Gynecologic Oncology, Maternal-Fetal Medicine, Reproductive Endocrinology, Infertility, and Genetics, and Urogynecology and Pelvic Surgery.
General Obstetrics and Gynecology provides a full range of general obstetrical and gynecological services ranging from outpatient care to surgery, and from routine visits to complicated consultations. In addition to normal obstetrical and gynecological services, our specialized research and interest areas include urodynamics, dysmenorrhea, menorrhagia, pelvic pain, menopause, and others.
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Obstetrics & Gynecology
Glossary Click here to go to Prefixes and Suffixes.
Most of the words in this glossary are followed by a phonetic spelling that serves as a guide to pronunciation. The phonetic spellings reflect standard scientific usage and can be easily interpreted following a few basic rules.
abduction (ab-dukshun) The movement of a body part away from the axis or midline of the body; movement of a digit away from the axis of the limb.
ABO system The most common system of classification for red blood cell antigens. On the basis of antigens on the red blood cell surface, individuals can be type A, type B, type AB, or type O.
absorption (ab-sorpshun) The transport of molecules across epithelial membranes into the body fluids.
accessory organs (ak-sesuo-re) Organs that assist with the functioning of other organs within a system.
accommodation (ua-komuo-dashun) A process whereby the focal length of the eye is changed by automatic adjustment of the curvature of the lens to bring images of objects from various distances into focus on the retina.
acetabulum (asue-tabyuu-lum) A socket in the lateral surface of the hipbone (os coxa) with which the head of the femur articulates.
acetone (asue-t=on) A ketone body produced as a result of the oxidation of fats.
acetyl coenzyme A (acetyl CoA) (asue-tl, ua-setl) A coenzyme derivative in the metabolism of glucose and fatty acids that contributes substrates to the Krebs cycle.
acetylcholine (ACh) (ua-setl-kol=en) An acetic acid ester of choline-a substance that functions as a neurotransmitter in somatic motor nerve and parasympathetic nerve fibers.
acetylcholinesterase (ua-setl-kolu1-nestue-r=as) An enzyme in the membrane of postsynaptic cells that catalyzes the conversion of ACh into choline and acetic acid. This enzymatic reaction inactivates the neurotransmitter.
Achilles tendon (ua-kil=ez) See tendo calcaneous.
acid (asid) A substance that releases hydrogen ions when ionized in water.
acidosis (asu1-dosis) An abnormal increase in the H+ concentration of the blood that lowers the arterial pH to below 7.35.
acromegaly (akro-megua-le) A condition caused by the hypersecretion of growth hormone from the pituitary gland after maturity and characterized by enlargement of the extremities, such as the nose, jaws, fingers, and toes.
actin (aktin) A protein in muscle fibers that together with myosin is responsible for contraction.
action potential An all-or-none electrical event in an axon or muscle fiber in which the polarity of the membrane potential is rapidly reversed and reestablished.
active immunity (u1-myoonu1-te) Immunity involving sensitization, in which antibody production is stimulated by prior exposure to an antigen.
active transport The movement of molecules or ions across the cell membranes of epithelial cells by membrane carriers. An expenditure of cellular energy (ATP) is required.
adduction (au-dukshun) The movement of a body part toward the axis or midline of the body; movement of a digit toward the axis of the limb.
adenohypophysis (adn-o-hi-pofu1-sis) The anterior, glandular lobe of the pituitary gland that secretes FSH (follicle-stimulating hormone), LH (luteinizing hormone), ACTH (adrenocorticotropic hormone), TSH (thyroid-stimulating hormone), GH (growth hormone), and prolactin. Secretions of the adenohypophysis are controlled by hormones produced by the hypothalamus.
adenoids (adue-noidz) The tonsils located in the nasopharynx; pharyngeal tonsils.
adenylate cyclase (ua-denl-it sikl=as) An enzyme found in cell membranes that catalyzes the conversion of ATP to cyclic AMP and pyrophosphate (PP1). This enzyme is activated by an interaction between a specific hormone and its membrane receptor protein.
ADH Antidiuretic hormone; a hormone produced by the hypothalamus and released by the posterior pituitary that acts on the kidneys to promote water reabsorption; also known as vasopressin.
ADP Adenosine diphosphate; a molecule that together with inorganic phosphate is used to make ATP (adenosine triphosphate).
adrenal cortex (ua-drenal korteks) The outer part of the adrenal gland. Derived from embryonic mesoderm, the adrenal cortex secretes corticosteroid hormones (such as aldosterone and hydrocortisone).
adrenal medulla (mue-dulua) The inner part of the adrenal gland. Derived from embryonic postganglionic sympathetic neurons, the adrenal medulla secretes catecholamine hormones-epinephrine and (to a lesser degree) norepinephrine.
adrenergic (adreu-nerjik) A term used to describe the actions of epinephrine, norepinephrine, or other molecules with similar activity (as in adrenergic receptor and adrenergic stimulation).
adventitia (adven-tishua) The outermost epithelial layer of a visceral organ; also called serosa.
afferent (afer-ent) Conveying or transmitting to.
afferent arteriole (ar-tire-=ol) A blood vessel within the kidney that supplies blood to the glomerulus.
afferent neuron (nooron) See sensory neuron.
agglutinate (ua-glootn-=at) A clump of cells (usually erythrocytes) formed as a result of specific chemical interaction between surface antigens and antibodies.
agranular leukocytes (ua-granyuu-lar loo kuo-s1=tz) White blood cells (leukocytes) that do not contain cytoplasmic granules; specifically, lymphocytes and monocytes.
albumin (al-byoomin) A water-soluble protein produced in the liver; the major component of the plasma proteins.
aldosterone (al-doster-=on) The principal corticosteroid hormone involved in the regulation of electrolyte balance (mineralocorticoid).
alimentary canal The tubular portion of the digestive tract. See also gastrointestinal tract (GI tract).
allantois (ua-lanto-is) An extraembryonic membranous sac involved in the formation of blood cells. It gives rise to the fetal umbilical arteries and vein and also contributes to the formation of the urinary bladder.
allergens (aler-jenz) Antigens that evoke an allergic response rather than a normal immune response.
allergy (aler-je) A state of hypersensitivity caused by exposure to allergens. It results in the liberation of histamine and other molecules with histaminelike effects.
all-or-none principle The statement of the fact that muscle fibers of a motor unit contract to their maximum extent when exposed to a stimulus of threshold strength.
allosteric (aluo-sterik) A term used with reference to the alteration of an enzyme's activity as a result of its combination with a regulator molecule. Allosteric inhibition by an end product represents negative feedback control of an enzyme's activity.
alveolar sacs (al-veuo-lar) A cluster of alveoli that share a common chamber or central atrium.
alveolus (al-veuo-lus) 1.An individual air capsule within the lung. The alveoli are the basic functional units of respiration. 2.The socket that secures a tooth(tooth socket).
amniocentesis (amne-o-sen-tesis) A procedure in which a sample of amniotic fluid is aspirated to examine suspended cells for various genetic diseases.
amnion (amne-on) A developmental membrane surrounding the fetus that contains amniotic fluid.
amphiarthrosis (amfe-ar-throsis) A slightly movable articulation in a functional classification of joints.
amphoteric (am-fo-terik) Having both acidic and basic characteristics; used to denote a molecule that can be positively or negatively charged, depending on the pH of its environment.
ampulla (am-poolua) A saclike enlargement of a duct or tube.
ampulla of Vater (Fuater) See hepatopancreatic ampulla.
anabolic steroids (anua-bolik steroidz) Steroids with androgenlike stimulatory effects on protein synthesis.
anabolism (ua-nabuo-lizem) A phase of metabolism involving chemical reactions within cells that result in the production of larger molecules from smaller ones; specifically, the synthesis of protein, glycogen, and fat.
anaerobic respiration (an-ua-robik respu1-rashun) A form of cell respiration involving the conversion of glucose to lactic acid in which energy is obtained without the use of molecular oxygen.
anal canal (anal) The terminal tubular portion of the large intestine that opens through the anus of the GI tract.
anaphylaxis (anua-fu1-laksis) An unusually severe allergic reaction that can result in cardiovascular shock and death.
anastomosis (ua-nastuo-mosis) An interconnecting aggregation of blood vessels or nerves that form a network plexus.
anatomical position (anua-tomu1-kal) An erect body stance with the eyes directed interior, the arms at the sides, the palms of the hands facing interior, and the fingers pointing straight down.
anatomy (ua-natuo-me) The branch of science concerned with the structure of the body and the relationship of its organs.
androgens (andruo-jenz) Steroids containing 18 carbons that have masculinizing effects; primarily those hormones(such as testosterone) secreted by the testes, although weaker androgens are also secreted by the adrenal cortex.
anemia (ua-neme-ua) An abnormal reduction in the red blood cell count, hemoglobin concentration, or hematocrit, or any combination of these measurements. This condition is associated with a decreased ability of the blood to carry oxygen.
angina pectoris (an-jinua pektuo-ris) A thoracic pain, often referred to the left pectoral and arm area, caused by myocardial ischemia.
angiotensin II (anje-o-tensin) An 8-amino-acid polypeptide formed from angiotensin I(a 10-amino-acid precursor), which in turn is formed from cleavage of a protein(angiotensinogen) by the action of renin(an enzyme secreted by the kidneys). Angiotensin II is a powerful vasoconstrictor and a stimulator of aldosterone secretion from the adrenal cortex.
anions (ani-onz) Ions that are negatively charged, such as chloride, bicarbonate, and phosphate.
antagonist (an-taguo-nist) A muscle that acts in opposition to another muscle.
antebrachium (ante-brake-em) The forearm.
anterior (ventral) Toward the front; the opposite of posterior, or dorsal.
anterior pituitary (pu1-toou1-ter-e) See adenohypophysis.
anterior root The anterior projection of the spinal cord, composed of axons of motor neurons.
antibodies (antu1-bod=ez) Immunoglobin proteins secreted by B lymphocytes that have transformed into plasma cells. Antibodies are responsible for humoral immunity. Their synthesis is induced by specific antigens, and they combine with these specific antigens but not with unrelated antigens.
anticodon (antu1-kodon) A base triplet provided by three nucleotides within a loop of transfer RNA that is complementary in its base-pairing properties to a triplet(the codon) in mRNA. The matching of codon to anticodon provides the mechanism for translating the genetic code into a specific sequence of amino acids.
antigen (antu1-jen) A molecule that can induce the production of antibodies and react in a specific manner with antibodies.
antigenic determinant site (an-tu1-jenik) The region of an antigen molecule that specifically reacts with particular antibodies. A large antigen molecule may have a number of such sites.
antiserum (antu1-sirum) A serum that contains specific antibodies.
anus (anus) The terminal opening of the GI tract.
aorta (a-ortua) The major systemic vessel of the arterial system of the body, emerging from the left ventricle.
aortic arch The superior left bend of the aorta between the ascending and descending portions.
apex (apeks) The tip or pointed end of a conical structure.
aphasia (ua-fazhua) Defects in speech, writing, or in the comprehension of spoken or written language caused by brain damage or disease.
apneustic center (ap-noostik) A collection of nuclei(nerve cell bodies) in the brain stem that participates in the rhythmic control of breathing.
apocrine gland (apuo-krin) A type of sweat gland that functions in evaporative cooling. It may respond during periods of emotional stress.
aponeurosis (apuo-noo-rosis) A fibrous or membranous sheetlike tendon.
appendix A short pouch that attaches to the cecum.
aqueous humor (akwe-us) The watery fluid that fills the anterior and posterior chambers of the eye.
arachnoid mater (ua-raknoid) The weblike middle covering(meninx) of the central nervous system.
arbor vitae (arbor vite) The branching arrangement of white matter within the cerebellum.
arm (brachium) The portion of the upper extremity from the shoulder to the elbow.
arrector pili muscle (ah-rektor pihle) The smooth muscle attached to a hair follicle that, upon contraction, pulls the hair into a more vertical position, resulting in "goose bumps."
arteriole (ar-tire-=ol) A minute arterial branch.
arteriosclerosis (ar-tire-o-sklue-rosis) Any one of a group of diseases characterized by thickening and hardening of the artery wall and in the narrowing of its lumen.
arteriovenous anastomoses (ar-tire-o-venus ua-nastuo-mos=ez) Direct connections between arteries and veins that bypass capillary beds.
artery (artue-re) A blood vessel that carries blood away from the heart.
arthrology (ar-throluo-je) The scientific study of the structure and function of joints.
articular cartilage (ar-tikyuu-lar kartu1-lij) A hyaline cartilaginous covering over the articulating surface of the bones of synovial joints.
articulation (ar-tikyuu-lashun) A joint.
arytenoid cartilages (arue-tenoid) A pair of small cartilages located on the superior aspect of the larynx.
ascending colon (kolon) The portion of the large intestine between the cecum and the hepatic flexure.
association neuron (nooron) A nerve cell located completely within the central nervous system. It conveys impulses in an arc from sensory to motor neurons; also called interneuron or internuncial neuron.
astigmatism (ua-stigmua-tizem) Unequal curvature of the refractive surfaces of the eye (cornea and/or lens), so that light entering the eye along certain meridians does not focus on the retina.
atherosclerosis (athue-ro-sklue-rosis) A common type of arteriosclerosis found in medium and larger arteries in which raised areas within the tunica intima are formed from smooth muscle cells, cholesterol, and other lipids. These plaques occlude arteries and serve as sites for the formation of thrombi.
This Chapter is written following discussions with my colleague, Leif Vanggaard, MD, Arctic Institute, Copenhagen.
Study Objectives
To define body core and body shell, heat balance, heat exchange (conduction, conversion, evaporation and radiation), hyperthermia, hypothermia, mean body temperature, heat capacity, and thermal steady state.
To describe fever (pyrogens), benignant and malignant hyperthermia, heat exhaustion, heat syncope, heat stroke, sun stroke, and hypothermia.
To describe radiation sickness.
To calculate one thermal variable, when relevant variables are given.
To explain the concepts heat exchange, thermogenesis by food and shivering, the human temperature control system and its function at different environmental temperatures.
To use the above concepts in problem solving and case histories.
Principles
Newtons law of cooling: The dry heat loss is proportional to the temperature difference between the human body (shell) and the surroundings.
The total energy of a system is conserved in an interaction, not the kinetic energy or the mass (Einstein). If the mass changes during an interaction, there is a resultant change in kinetic energy, so that the total energy remains constant. Heat energy is proportional to molecular movement rates heat energy equals movement.
Stefan-Boltzmanns rule: The higher the temperature of an object, the more it radiates. The energy radiated from an object is proportional to the fourth power of its Kelvin temperature. The energy radiating from an object and received by the human body is proportional to the temperature difference between the object and the skin (see Eq. 21-4). This is because human life implies relatively small temperature gradients.
Definitions
Body core consists of the thermoregulated deeper parts of the body and the proximal extremity portions of warm-blooded animals including man.
Body shell refers to those outer parts of the body (skin and subcutaneous tissue) that change temperature at cold exposure.
Conductance changes of the shell are used as a measure of skin bloodflow.
Conductive heat loss describes a direct transfer of heat energy by contact between two bodies of different temperature (eg, skin and objects).
Convective heat loss is defined as the heat loss by contact between the surface (skin) and a moving medium (air or water).
Evaporative heat loss is defined as the heat loss by evaporation from the body surface or lungs.
Fever occurs when the core temperature of the body is raised above normal steady state levels. The body reacts as if it is too cold. Fever implies a disorder resulting in shivering combined with vasoconstriction, headache, dedolation, and general discomfort (eg, malaria).
Heat flow is defined as energy exchanged due to a temperature difference. Heat flow is transmitted along a temperature gradient.
Heat capacity is the amount of heat required to produce a temperature increase for a given amount of substance.
Heat energy balance in a resting person is a condition, where the heat production is equal to the heat loss. Thus the body temperature is constant and the heat storage is zero (thermal steady state). Usually, there is no internal heat energy flux between body core and shell.
Hyperthermia is an increase in core temperature above normal.
Hypothermia refers to a clinical condition with a lowered core temperature (below 35 oC).
Mean body temperature is defined according to Eq. 21-1 (see end of Chapter).
Non-shivering thermogenesis is a rise in metabolism, which is not related to muscular activity (shivering or exercise).
Insensible perspiration (leakage of the skin) is the small cutaneous evaporation loss, which is unrelated to sweat gland function.
Insulation refers to resistance to heat transfer.
Radiative heat loss is a transfer of heat energy between 2 separate objects at different temperature. Heat energy is transferred via electromagnetic waves (photons). This heat transfer does not require a medium, and the temperature of any intervening medium is immaterial.
Shell temperature is the temperature of the outer parts of the body (measured on the skin surface) and related to cold environments.
Shivering is a reflex myogenic response to cold with asynchronous or balanced muscle contractions performing no external work.
Specific heat capacity is the relationship between heat energy exchanged per weight unit of a substance and the corresponding temperature change. The specific heat capacity of water is 4.18 and of the human body (blood and tissues) 3.49 kJ kg-1 oC-1, respectively. The specific heat capacity of atmospheric air is 1.3 kJ (m3)-1 oC-1.
Temperature is the measurement of heat energy content.
Essentials
This paragraph deals with
1. The temperatures of the body, 2. Body responses to cold, 3. Body responses to heat, 4. Emotional sweating, 5. Metabolic Rate and environmental temperature, 6. Temperature control, 7. The human thermo-control system, and 8. Thermoregulatory effectors.
1. The temperatures of the body
The human body consists of a peripheral shell and a central core (Fig. 21-1). The heat content (H or enthalpy) of the human body is reflected by its temperature. By definition a thermometer only measures the temperature of the thermometer, so its location is essential. The mean core temperature is 37 oC in healthy adults at rest, but small children have larger diurnal variations.
The skin is the main heat exchanger of the body. The skin temperature is determined by the core temperature and by the environment (temperature, humidity, air velocity). Thus the shell temperature is governed by the needs of the body to exchange heat energy.
Fig. 21-1: Heat transfers, body cores and shells temperatures of a naked person standing in cold and warm air, respectively.
The shell temperature is measured on the skin surface and at the hands and feet to approach the room temperature of 19oC in a person standing in a cold room for hours (Fig. 21-1, left). The shell temperature is several degrees lower than the temperature in the central core. The limbs have both a longitudinal and a radial temperature gradient. The shell temperature and the size of the shell vary with the environmental temperature and the termal state of the person. A naked person, standing on a cold floor in 19oC air has a small core and a thick shell compared to the same person in a warm environment (Fig. 21-1). The shell temperature of the skin and distal extremities is difficult to evaluate. The best estimate is measurement of the infrared heat radiation flux with a radiometer.
The core temperature is the rather constant temperature in the deeper parts of the body and in the proximal extremity portions (see the red stippled lines of Fig. 21-1). However, the core temperature may vary several Centigrades between different regions depending on the cellular activity. The brain has a radial temperature gradient between its deep and superficial parts. In a sense, the temperature of the mixed venous blood represents an essential core temperature.
The rectal temperature
A high core temperature is found to be constant in the rectum about 10-15 cm from the anus. When measuring the rectal temperature a standard depth of 5-10 cm is used clinically. The venous plexus around the rectum communicate with the cutaneous blood in the anal region. The rectal temperature falls when the feet are cold, because cold blood passes the rectum in the veins from the legs for the same reason. The rectal temperature rises during heavy work involving the legs.
Parents should be advised to measure the rectal temperature in disease suspect children. The rectal temperature is a reliable estimate of the core temperature in resting persons.
Sublingual (oral) or axillary temperatures are unreliable measures of the core temperature - often more than half a degree lower than the rectal temperature.
The cranial temperature (tympanic and nasal)
The main control of temperature is performed by the anterior hypothalamus, which has a high bloodflow. Within the cranium the hypothalamus lies over the Circle of Willis, which supplies it with blood, and close to the cavernous sinus which drains it. Hypothalamus elicits heat loss responses when stimulated by heat. The tympanic membrane and areas in the nasal cavity (the anterior ethmoidal region, part of the sphenoid sinus) are supplied with blood from the internal carotid artery just like the hypothalamus. These cranial locations then serve as a substitute for the measurement of the inaccessible hypothalamic temperature.
Intake of 250 g of ice releases an abrupt fall in the nasal temperature in a warm person, whereas the change in rectal temperature is smaller and delayed (Fig. 21-2). The cranial core temperature is more dynamic than the rectal.
Fig. 21-2: Intake of ice reduces the temperature in a warm person resting at 45oC.
In sports and in surgical hypothermia dynamic measurements of core temperature are essential. The cranial temperature is often preferred. During forceful movements the thermistor may be displaced. In such situations an oesophageal location is applied at heart level. This is an approximative measure of the temperature of the mixed venous blood of the right heart located close to the thermistor.
The mean body temperature is defined according to Eq. 21-1. The storage of heat energy in the body can be calculated according to its heat capacity (3.49 kJ* kg-1*oC-1), the body weight (kg) and the change in mean body temperature in the period (Eq. 21-2).
According to the first law of thermodynamics, the storage of heat energy equals the metabolic energy change minus the heat loss (Eq. 21-3). Quantification of thermodynamics in humans is possible using equations 21-1 to 21-7 (later in this chapter).
The body is in heat energy balance, when the storage is zero. However, the core temperature may change with internal fluxes of heat energy between core and shell without storage or loss of heat energy at a constant activity.
Venous blood draining active muscles and the liver is likely to be warmer than pulmonary venous blood, since this has undergone evaporative cooling in the alveoli. A patient with high fever can be in thermal steady state, with a high constant heat production, if both core- and shell-temperatures are constant, and no internal energy flux occurs.
Warm-blooded animals, homeotherms such as humans, can change their metabolism in order to keep their heat production equal to the heat loss. Such animals have a temperature control system and thereby maintain a rather constant core temperature. Warm-blooded animals live with the advantage of an unchanged cell activity and temperature in their core. However, the human core temperature falls during the oestrogen phase of the menstrual cycle and during sleep (circadian rhythm). The lowest temperature is between 18 at night and 6 oclock in the morning (Fig. 21-3). The temperature cycle is part of the circadian periodicity. Our biological clock seems to be synchronised with the rotation of the globe. Also meals, light and temperature plays a role.
Ovulation releases a sharp rise in morning temperature. Progesterone effects seem to explain the higher temperature in the last phase of the menstrual cycle (Fig. 21-3).
Fig. 21-3: Variations of the core temperature during 24 hour (above), and variations related to phases of the menstrual cycle (below).
Cold-blooded animals (poikilotherms) live with a behavioural temperature rhythm, but have no autonomic temperature control. The core- and shell-temperatures vary with the environment and the cellular activity. Reptiles, premature and low weight-premature newborn babies are cold-blooded. These babies have no thermoregulation (see later). However, their capacity for heat production is 5-10 times as great per unit weight as that of adults.
Humans have a warm-blooded (homeothermic) coreand a cold-blooded (poikilothermic) shell in a cold environment.
Persons exposed to general anaesthesia, alcohol, and certain drugs lose the autonomic thermoregulation. Cold-blooded animals must live with varying core and shell temperature, whereby the rate of their cellular activities varies with the surrounding temperature (Fig. 21-4).
Fig. 21-4: The body core temperature and the environmental body temperature for a warm-blooded animal (cat) and a cold-blooded animal (lizard).
a) Convection. The convective heat loss is calculated by Eq. 21-7. A healthy person in sports clothes experiences thermal comfort at three times the resting metabolic rate (3 MET), when the surrounding temperature is 20oC, the humidity is 50% and the wind velocity is 0.5 m*s-1.
Diving (water has a high thermal conductivity) illustrates the importance of conduction andconvection in heat energy transfer.
The dry diving suit excludes water from contact with the skin and traps low-conductance air in insulating clothing worn inside the watertight sealing.
The wet suit traps water next to the skin but prevents its circulation. The water is warmed through contact with the skin, and the high insulation of the foam rubber wet diving suit, with its many pockets of trapped air, minimises the rate of heat energy loss to the surrounding water. Air is a poor heat conductor and thus a good insulator. During deep diving high pressures compress these air pockets and thus reduce the insulation properties of wet diving suits.
b) Radiation describes a transfer of energy between objects in the form of electromagnetic waves (photons). This includes ultraviolet and visible (sun light) radiation from the outside and from the body infrared or warm heat radiation.
Radiative heat transfer can be calculated for a naked person according to Eq. 21-4.
When the skin temperature (Tskin) is less than the temperature of the surrounding objects, heat is gained by radiation.
At wintertime, heat can be lost through a window glass by radiation from the body to the cold environment irrespective of the room temperature. This is because the skin temperature is higher than the outside temperature.
c) Conduction. Sitting on a cold stone is a typical example of conduction loss, just as standing on a cold floor (Fig. 21-1). Conduction heat can also be gained, although it is really possible to walk on glowing coals with speed and a thick epidermal horn layer.
d) Evaporative heat loss- see sweat secretion below.
2. Body-responses to cold
Cutaneous vasoconstriction lowers skin temperature, and thereby reduces the conductive-convective heat loss that is determined by the temperature gradient from the skin surface to the environment. Cutaneous vasoconstriction directs the peripheral venous blood back to the body core through the deep veins and the commitant veins. These veins are located around the arteries with warm blood, so that the venous blood receives part of the heat energy from the arterial blood - so-called counter current heat exchange (Fig. 21-5). The vasoconstriction is so effective, that the bloodflow through the arterio-venous anastomoses in the fingers and toes can fall to below one percent of the flow at normal temperature. The cooling of the shell is immediate, and the size of the shell increases (Fig. 21-1). Obviously, the shell is large for a naked person in cold air. The resistance vessels of the hands may open periodically to nourish the tissues, but the high viscosity of the cold blood can endanger the tissue nutrition and result in trench foot.
The arterio-venous shunts of the hands and feet are closed, so the bloodflow to the limbs is a nutritive minimum.
The deep arteries and veins of the limbs lie in parallel, so the arterial bloodflow loses heat to the incoming venous blood partially surrounding the arteries (Fig. 21-5). This is a typical counter-current heat exchange. In a cold environment, where vasoconstriction and heat exchange produces cold extremities, the total insulation is increased at the expense of reduced neuromuscular efficiency.
Fig. 21-5: Counter-current exchange in a human arm conserving heat energy in a cold climate (left). Superficial venous cooling ribs eliminate heat energy in a warm climate (right).
In a warm climate the high bloodflow of the extremities ensures an optimal temperature of the deeper structures (eg, the neuromuscular system). The temperature of the arterial blood is maintained (Fig. 21-5, right) and the arterio-venous anastomoses are wide open conveying warm blood to the superficial veins. The superficial veins also act as cooling ribs and transfer large amounts of heat to the skin surface, where it is eliminated from the body by convection, conduction and evaporation (Fig. 21-5, right).
Shivering is a reflex myogenic response to cold with asynchronous or balanced muscle contractions elicited from the hypothalamus via cutaneous receptors. The activity in agonist and antagonist muscles balance, so there is no external work. Without outside work, all energy is liberated as metabolic heat energy. Heat production is also increased by thyroid gland activity and by release of catecholamines from the adrenal medulla.
External work, such as running, is helpful in maintaining body temperature when feeling cold. Cold increases the motivation for warm-up exercises and illustrates the voluntary, cortical (feedforward influence) on temperature homeostasis. The core temperature increases proportionally to the work intensity during prolonged steady state work (Fig. 21-6). The mean skin temperature falls with increasing work intensity at 20oC, because the sweat evaporation cools the skin.
Fig. 21-6: Muscular and oesophageal temperature during steady state exercise. The levels of exercise range from zero to 100% of the maximum oxygen uptake.
The temperature in the active muscles determines the level of the rectal temperature. Following marathon rectal temperatures of more than 41oC have been measured and heat strokes have occurred. A marathon is even more difficult to accomplish in warm, humid environments and strong sun may cause sunstroke (see later).
People may adapt to prolonged exposure to cold by increasing their basal metabolic rate up to 50% higher than normal. This metabolic adaptation is found in Inuits (Eskimos) and other people continuously subject to cold.
The environmental temperature, where we maintain our autonomic temperature control, is in the range of zero to 45oC. Below and above this range we adapt to the environment by behaviour (adding or removing clothing, warm or cold bath, sun or shadow). A core temperature above 44oC starts protein denaturation in all cells and is incompatible with life. Below 32oC humans lose consciousness and below 28oC the frequency of malignant cardiac arrhythmias is increasing, ending with ventricular fibrillation and death at a core temperature below 23 oC (Fig. 21-7).
Fig. 21-7: Environmental temperature variations and temperature control. Lack of vital signs in the clinic (respiration, heart rate, EEG) must not be taken as death. Treatment must be instituted until death signs are developed.
3. Body-responses to heat
Sweat secretion. Three million sweat glands produce sweat at a rate of up to 2 litres per hour or more during exercise in extreme warm conditions. If not compensated by drinking, such high sweat rates lead to circulatory failure and shock. Sweat resembles a dilute ultrafiltrate of plasma. Healthy humans cannot maintain their body temperature, if the environmental air reaches body temperature and the air is saturated with water vapour. Primary sweat is secreted as an isosmotic fluid into the sweat duct, and subsequent NaCl reabsorption results in the final hypo-osmotic sweat. Thermal sweating is abolished by atropine, proving that the postganglionic fibres are cholinergic. Cholinergic drugs provoke sweating just as adrenergic agonists do. Evaporation of water on the body surface eliminates 2428-2436 J g-1 at mean shell temperatures of 30-32oC. Evaporation of a large volume of sweat per time unit (Vsweat) implies a substantial loss of heat according to Eq. 21-5.
Normally, the skin temperature falls with increasing work intensity, because the sweat evaporation cools the skin (Fig. 21-6). Danger occurs when the average skin temperature and the body core temperature converge towards the same value.
Condensation of water on the skin gains heat energy, which is stored in the body. This is what happens in a Sauna.
Vasodilatation of skin vessels in warm environments results in increased cardiac output. The arterio-venous anastomoses in the hands and feet are open, and the bloodflow can rise up to at least 10 folds. The shell is minimal, when a naked person is in warm air (Fig. 21-1, right). The skin bloodflow, mainly in the extremities, determines the amount of heat energy, which is carried from the body core to be lost on the surface. The heat energy is transported from the large body core to the skin by convection in the blood. A substantial part of the heat energy is lost through the superficial veins of the extremities acting as cooling ribs (Fig. 21-5). The blood of the superficial veins is thus arterialized, when the person is warm.
A piece of steak has the same composition as human skin but of course no blood flow and no sweat evaporation. Thus the steak will be cooked at an air temperature that humans can survive. A person can stay in a room with dry air at 128oC for up to 10 min during which time the steak is partially cooked.
Read more from the original source:
New Human Physiology Ch 21 - zuniv.net