Estradiol is a female sex hormone necessary for many processes in the body. It is also present in males, but at lower levels. Estradiol is a form of estrogen, which has not only a critical impact on reproductive and sexual functioning, but also affects other organs including the bones. Like other steroids, estradiol is derived from cholesterol. After side chain cleavage and utilizing the delta-5 pathway or the delta-4 pathway, androstenedione is the key intermediary. A fraction of the androstenedione is converted to testosterone, which in turn undergoes conversion to estradiol by an enzyme called aromatase. In an alternative pathway, androstenedione is "aromatized" to estrone, which is subsequently converted to estradiol.
Estradiol increases the risk of developing endometrial hyperplasia, which is a condition that may lead to cancer of the uterus. To lower this risk of developing endometrial hyperplasia, it is adviced to take progestins. Estradiol has a profound effect on bone. If severe side-effects of low levels of estradiol in a woman's blood are experienced at the beginning of menopause, hormone replacement therapy may be prescribed. Often such therapy is combined with a progestin. Estrogen therapy may also be used in treatment of infertility in women when there is a need to develop sperm-friendly cervical mucus or an appropriate uterine lining.
Individuals without estradiol will become tall and eunuchoid as epiphysieal closure is delayed or may not take place. Bone structure is affected resulting in early osteopenia and osteoporosis. Also, women past menopause experience an accelerated loss of bone mass due to a relative estrogen deficiency.
Wednesday, March 31, 2010
Tuesday, March 30, 2010
Progesterone
Progesterone is a female hormone important for the regulation of ovulation and menstruation, C-21 steroid hormone, which takes part in the female menstrual cycle, pregnancy and embryogenesis of humans and other species. Progesterone belongs to a class of hormones called progestogens, and is the major naturally occurring human progestogen.
Progesterone is produced in the ovaries, the adrenal glands, and, during pregnancy, in the placenta. Progesterone is also stored in adipose tissue. It is used to treat secondary amenorrhea. This is when a woman stops getting menstrual periods due to low levels of progesterone.
Progesterone is commonly manufactured from the yam family, Dioscorea. Dioscorea produces large amounts of a steroid called diosgenin, which can be converted into progesterone in the laboratory.
Progesterone is produced in the ovaries, the adrenal glands, and, during pregnancy, in the placenta. Progesterone is also stored in adipose tissue. It is used to treat secondary amenorrhea. This is when a woman stops getting menstrual periods due to low levels of progesterone.
Progesterone is commonly manufactured from the yam family, Dioscorea. Dioscorea produces large amounts of a steroid called diosgenin, which can be converted into progesterone in the laboratory.
Monday, March 29, 2010
Inhibin
Inhibin is an endocrine hormone produced in the ovaries and the testes. This hormone has several functions in the body, with inhibin levels in women being linked to the menstrual cycle and playing a role in fetal development. Inhibin and Activin are two closely related protein complexes that have opposing biological effects.
Inhibin is released into the bloodstream to control and inhibit the secretion of follicle stimulating hormone by the pituitary gland. It is an important part of an endocrine feedback loop. There are two functional forms of inhibin, A and B. Inhibin A has two protein subunits, an a subunit and a ßA subunit, whereas inhibin B has an a subunit and a ßB subunit. In both forms, the two subunits, of almost the same size, are held together by covalent linkages. On the other hand, Activin enhances FSH biosynthesis and secretion, and participates in the regulation of the menstrual cycle. Many other functions have been found to be exerted by activin, including roles in cell proliferation, differentiation, apoptosis, metabolism, homeostasis, immune response, wound repair, and endocrine function.
Inhibin is released into the bloodstream to control and inhibit the secretion of follicle stimulating hormone by the pituitary gland. It is an important part of an endocrine feedback loop. There are two functional forms of inhibin, A and B. Inhibin A has two protein subunits, an a subunit and a ßA subunit, whereas inhibin B has an a subunit and a ßB subunit. In both forms, the two subunits, of almost the same size, are held together by covalent linkages. On the other hand, Activin enhances FSH biosynthesis and secretion, and participates in the regulation of the menstrual cycle. Many other functions have been found to be exerted by activin, including roles in cell proliferation, differentiation, apoptosis, metabolism, homeostasis, immune response, wound repair, and endocrine function.
Friday, March 26, 2010
Androgen
Androgen is a steroid hormone, such as testosterone or androsterone, that controls the development and maintenance of masculine characteristics. Androgen is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This includes the activity of the accessory male sex organs and development of male secondary sex characteristics.
Androgens were first discovered in 1936. Androgens are also the original anabolic steroids and the precursor of all estrogens, the female sex hormones. The primary and most well-known androgen is testosterone. Androgen ablation can be used as an effective therapy in prostate cancer.
Androgens were first discovered in 1936. Androgens are also the original anabolic steroids and the precursor of all estrogens, the female sex hormones. The primary and most well-known androgen is testosterone. Androgen ablation can be used as an effective therapy in prostate cancer.
Thursday, March 25, 2010
Thyroid Gland
The thyroid gland is a small, butterfly-shaped endocrine organ which synthesize important hormones which participate in the human growth and metabolism. The thyroid gland is consists of two cone-like lobes or wings, lobus dexter (right lobe) and lobus sinister (left lobe), which are connected by a band of tissue called the isthmus. This endocrine gland is situated on the anterior side of the neck, lying against and around the larynx and trachea, reaching posteriorly the oesophagus and carotid sheath. The lobes of the thyroid are each approximately 2 inches (5 cm) in length, and the isthmus is approximately 2 inches (5 cm) in width and length and the thyroid gland weighs approximately 1 ounce (28 g).
Thyroid Gland Video
The thyroid gland is one of the largest endocrine glands in the body. This gland is found in the neck, inferior to (below) the thyroid cartilage (also known as the Adam's apple) and at approximately the same level as the cricoid cartilage. The thyroid controls how quickly the body uses energy, makes proteins, and controls how sensitive the body should be to other hormones.
The thyroid takes part in these processes by producing thyroid hormones, principally thyroxine (T4) and triiodothyronine (T3). Thyroid tissues trap iodine circulating in the blood and use it to produce thyroxine and triiodothyronine. These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. Iodine and tyrosine are used to form both T3 and T4. The thyroid also produces the hormone calcitonin, which plays a role in calcium homeostasis.
The thyroid gland is regulated by the hypothalamus and pituitary. The gland gets its name from the Greek word for "shield", after the shape of the related thyroid cartilage. Hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) are the most common problems of the thyroid gland.
Thyroid Gland Video
Wednesday, March 24, 2010
Enkephalins
Enkephalins are molecules which are synthesized naturally by the central nervous system to numb pain. Enkephalins lock into receptors on the surface of a nerve cell and open ion channels. An enkephalin is a pentapeptide involved in regulating nociception in the body. The enkephalins are termed endogenous ligands, or specifically endorphins, as they are internally derived and bind to the body's opioid receptors. Discovered in 1975, two forms of enkephalin were revealed, one containing leucine ("leu"), and the other containing methionine ("met"). Both are products of the proenkephalin gene.
Tuesday, March 23, 2010
Endocytosis
Endocytosis is the process by which the plasma membrane folds inward to bring substances into the cell. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma membrane or cell membrane. The process opposite to endocytosis is exocytosis.
Through endocytosis animal cells engulf particulate material, such as cellular debris and microorganisms; macromolecules, such as proteins and complex sugars; and low-molecular-weight molecules, such as vitamins and simple sugars. Cells engage in at least three different types of endocytosis: 1) Phagocytosis (literally, cell-eating) is the process by which cells ingest solids, such as bacteria, viruses, or the remnants of cells which have undergone apoptosis; in phagocytosis the membrane invaginates enclosing the wanted particles in a pocket, then engulfs the object by pinching it off, and the object is sealed off into a large vacuole known as a phagosome. 2) Pinocytosis (literally, cell-drinking), which is how cells take in liquids. 3) Receptor-mediated endocytosis is a more specific active event where the cytoplasm membrane folds inward to form coated pits; in this case, proteins or other trigger particles lock into receptors/ ligands in the cell’s plasma membrane; it is then, and only then that the particles are engulfed.
Endocytosis (Video)
Through endocytosis animal cells engulf particulate material, such as cellular debris and microorganisms; macromolecules, such as proteins and complex sugars; and low-molecular-weight molecules, such as vitamins and simple sugars. Cells engage in at least three different types of endocytosis: 1) Phagocytosis (literally, cell-eating) is the process by which cells ingest solids, such as bacteria, viruses, or the remnants of cells which have undergone apoptosis; in phagocytosis the membrane invaginates enclosing the wanted particles in a pocket, then engulfs the object by pinching it off, and the object is sealed off into a large vacuole known as a phagosome. 2) Pinocytosis (literally, cell-drinking), which is how cells take in liquids. 3) Receptor-mediated endocytosis is a more specific active event where the cytoplasm membrane folds inward to form coated pits; in this case, proteins or other trigger particles lock into receptors/ ligands in the cell’s plasma membrane; it is then, and only then that the particles are engulfed.
Endocytosis (Video)
Monday, March 22, 2010
Exocytosis
Exocytosis is a process of cellular excretion in which substances contained in vesicles are discharged from the cell by fusion of the vesicular membrane with the outer cell membrane. Or, put it in other words, exocytosis is a cellular process in which cells eject waste products or chemical transmitters (such as hormones) from the interior of the cell. Exocytosis is similar in function to endocytosis but working in the opposite direction.
In multicellular organisms there are two types of exocytosis: 1) Ca2+ triggered non-constitutive and 2) non Ca2+ triggered constitutive. Exocytosis in neuronal chemical synapses is Ca2+ triggered and serves interneuronal signalling. Constitutive exocytosis is performed by all cells and serves the release of components of the extracellular matrix, or just delivery of newly-synthesized membrane proteins that are incorporated in the plasma membrane after the fusion of the transport vesicle. Exocytosis is the opposite of endocytosis.
There are five steps to exocytosis: 1) in this first step, the vesicle containing the waste product is transported through the cytoplasm towards the part of the cell from which it will be eliminated; 2) as the vesicle approaches the cell membrane, it is secured and pulled towards the part of the cell from which it will be eliminated; 3) in third step, the vesicle comes in contact with the cell membrane, where it begins to chemical and physically merge with the proteins in the cell membrane; 4) the fourth step involves the chemical preparations for the last step of exocytosis; 5) in the last step, the proteins forming the walls of the vesicle merge with the cell membrane and breach, pushing the vesicle contents (waste products or chemical transmitters) out of the cell. This step is the primary mechanism for the increase in size of the cell's plasma membrane.
Exocytosis (video)
In multicellular organisms there are two types of exocytosis: 1) Ca2+ triggered non-constitutive and 2) non Ca2+ triggered constitutive. Exocytosis in neuronal chemical synapses is Ca2+ triggered and serves interneuronal signalling. Constitutive exocytosis is performed by all cells and serves the release of components of the extracellular matrix, or just delivery of newly-synthesized membrane proteins that are incorporated in the plasma membrane after the fusion of the transport vesicle. Exocytosis is the opposite of endocytosis.
There are five steps to exocytosis: 1) in this first step, the vesicle containing the waste product is transported through the cytoplasm towards the part of the cell from which it will be eliminated; 2) as the vesicle approaches the cell membrane, it is secured and pulled towards the part of the cell from which it will be eliminated; 3) in third step, the vesicle comes in contact with the cell membrane, where it begins to chemical and physically merge with the proteins in the cell membrane; 4) the fourth step involves the chemical preparations for the last step of exocytosis; 5) in the last step, the proteins forming the walls of the vesicle merge with the cell membrane and breach, pushing the vesicle contents (waste products or chemical transmitters) out of the cell. This step is the primary mechanism for the increase in size of the cell's plasma membrane.
Exocytosis (video)
Thyrotrope Cells
Thyrotrope cells are cells found in the anterior pituitary which produce thyroid stimulating hormone (or thyrotropin). Thyrotropin-releasing hormone induces the thyrotrope cells to secrete thyrotropin into the systemic circulation. Thyrotropin binds its receptor on thyroid follicular cells, stimulating the production and secretion of thyroid hormones which provide feedback inhibition of thyrotropin secretion.
Pituitary tumors may arise in thyrotrope cells, resulting in excessive thyroid gland function, and in gonadotrope cells, that often do not secrete any functional hormone. Headaches, visual disturbances and abnormal pituitary function may result from local growth of the tumor.
Pituitary tumors may arise in thyrotrope cells, resulting in excessive thyroid gland function, and in gonadotrope cells, that often do not secrete any functional hormone. Headaches, visual disturbances and abnormal pituitary function may result from local growth of the tumor.
Friday, March 19, 2010
G Protein-Coupled Receptors
G protein-coupled receptors (GPCRs) constitute a large protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal transduction pathways and, ultimately, cellular responses. G protein-coupled receptors are found only in eukaryotes, including yeast, choanoflagellates, and animals. The ligands that bind and activate the G protein-coupled receptors include light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters, and vary in size from small molecules to peptides to large proteins. G protein-coupled receptors are involved in many diseases, and are also the target of approximately 30% of all modern medicinal drugs.
The main function of the G protein-coupled receptors is to transduce extracellular stimuli into intracellular signals. They are among the largest and most diverse protein families in mammalian genomes. On the basis of homology with rhodopsin, they are predicted to contain seven membrane-spanning helices, an extracellular N-terminus and an intracellular C-terminus. This gives rise to their other names, the 7-TM receptors or the heptahelical receptors. GPCRs transduce extracellular stimuli to give intracellular signals through interaction of their intracellular domains with heterotrimeric G proteins, and the crystal structure of one member of this group, bovine rhodopsin, has recently been solved.
The main function of the G protein-coupled receptors is to transduce extracellular stimuli into intracellular signals. They are among the largest and most diverse protein families in mammalian genomes. On the basis of homology with rhodopsin, they are predicted to contain seven membrane-spanning helices, an extracellular N-terminus and an intracellular C-terminus. This gives rise to their other names, the 7-TM receptors or the heptahelical receptors. GPCRs transduce extracellular stimuli to give intracellular signals through interaction of their intracellular domains with heterotrimeric G proteins, and the crystal structure of one member of this group, bovine rhodopsin, has recently been solved.
There are two principal signal transduction pathways involving the G protein-coupled receptors: the cAMP signal pathway and the Phosphatidylinositol signal pathway. When a ligand binds to the GPCR it causes a conformational change in the GPCR, which allows it to act as a guanine nucleotide exchange factor (GEF). The GPCR can then activate an associated G-protein by exchanging its bound GDP for a GTP. The G-protein's a subunit, together with the bound GTP, can then dissociate from the ß and ? subunits to further affect intracellular signaling proteins or target functional proteins directly depending on the a subunit type.
Thursday, March 18, 2010
Calcitonin
Calcitonin is a linear polypeptide hormone which consists of 32-amino acids. In humans calcitonin is synthesized and secreted by the parafollicular cells (C-cells) of the thyroid. It acts to reduce blood calcium (Ca2+), opposing the effects of parathyroid hormone (PTH). High blood levels of Ca++ act as a humeral stimulus for releasing calcitonin, and lower levels reduce release. Calcitonin is important during youth, when the bones are growing rapidly. Calcitonin has a bone-sparing effect, by reducing bone resorption, and stimulating Ca++ uptake from dietary sources, and the circulation.
As a dietary supplement, calcitonin (Calcimar, Miacalcin) is a hormone that has been approved by the FDA in the United States for treating osteoporosis. Calcitonins come from several animal species, but salmon calcitonin is the most widely used. Calcitonin can be administered subcutaneously as a shot under the skin, or into the muscle (intramuscularly), or inhaled nasally. Intranasal calcitonin is the most convenient of the three methods.
Calcitonin has been shown to prevent bone loss in postmenopausal women. In women with established osteoporosis, calcitonin has been shown to increase bone density and strength in the spine only, though it is not as effective in increasing bone density and strengthening bone as estrogen.
Calcitonin is formed by the proteolytic cleavage of a larger prepropeptide, which is the product of the CALC1 gene (CALCA). The CALC1 gene belongs to a superfamily of related protein hormone precursors including islet amyloid precursor protein, calcitonin gene-related peptide, and the precursor of adrenomedullin.
Calcitonin protects against Ca2+ loss from skeleton during periods of Ca2+ stress such as pregnancy and lactation It also regulates serum calcium level, prevents postprandial hypercalcemia resulting from absorption of Ca2+ from foods during a meal, and also regulates vitamin D levels.
As a dietary supplement, calcitonin (Calcimar, Miacalcin) is a hormone that has been approved by the FDA in the United States for treating osteoporosis. Calcitonins come from several animal species, but salmon calcitonin is the most widely used. Calcitonin can be administered subcutaneously as a shot under the skin, or into the muscle (intramuscularly), or inhaled nasally. Intranasal calcitonin is the most convenient of the three methods.
Calcitonin has been shown to prevent bone loss in postmenopausal women. In women with established osteoporosis, calcitonin has been shown to increase bone density and strength in the spine only, though it is not as effective in increasing bone density and strengthening bone as estrogen.
Calcitonin is formed by the proteolytic cleavage of a larger prepropeptide, which is the product of the CALC1 gene (CALCA). The CALC1 gene belongs to a superfamily of related protein hormone precursors including islet amyloid precursor protein, calcitonin gene-related peptide, and the precursor of adrenomedullin.
Calcitonin protects against Ca2+ loss from skeleton during periods of Ca2+ stress such as pregnancy and lactation It also regulates serum calcium level, prevents postprandial hypercalcemia resulting from absorption of Ca2+ from foods during a meal, and also regulates vitamin D levels.
Wednesday, March 17, 2010
Parafollicular Cells
Parafollicular cells, also known as C cells, are cells situated around the follicles of the thyroid gland. They are rich in mitochondria and synthesize and secrete calcitonin. Parafollicular cells are large and have a pale stain compared with the follicular cells. Embryologically, they associate with the ultimobranchial body, which itself is a ventral derivative of the fourth pharyngeal pouch. Parafollicular cells themselves are derived from Neural Crest cells. C cells are not numerous in the thyroid and are typically situated basally in the epithelium, without direct contact with the follicular lumen. They are always situated within the basement membrane, which surrounds the entire follicle.
Thyroid parafollicular cells are neural crest-derived endocrine cells which produce calcitonin and serotonin. The secretory vesicles of parafollicular cells acidify when secretion is induced by increased extracellular Ca2+ or TSH. Scientists have tested the hypothesis that acidification is regulated by secretogogue-gated Cl- channels in vesicular membranes. Cl- channel (p64) immunoreactivity was enriched in purified PF vesicles. X-Ray microanalysis showed a change in chlorine level in C cells vesicles in response to secretogogue-stimulation of isolated cells. Secretogogue stimulation also altered the degree of p64 channel phosphorylation. Protein kinase and phosphatase inhibitors antagonized secretogogue- induced vesicle acidification and secretion; however, secretion could occur even when acidification was blocked. So, it has been concluded that acidification of C cells vesicles is regulated by a gatable Cl- channel in vesicle membranes and that protein phosphorylation and dephosphorylation are involved in channel activation. Acidification of vesicles is not required for exocytosis.
Tuesday, March 16, 2010
Somatostatin
Somatostatin is a peptide hormone which inhibits the secretion of growth hormone from the anterior pituitary gland. It regulates the endocrine system, affecting neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones. Somatostatin consists of 14 amino acids, with two cysteine residues joining by a disulfide bond so that the peptide forms a ring structure. A larger variant of this peptide, called somatostatin-28, is secreted in some cells.
Somatostatin is synthesized and released by neuroendocrine neurons of the periventricular nucleus of the hypothalamus. These neurons project to the median eminence, where somatostatin is released from neurosecretory nerve endings into the hypothalamo-hypophysial portal circulation. Somatostatin is carried in the blood stream through these blood vessels to the anterior pituitary gland, where somatostatin inhibits the secretion of growth hormone from somatotrope cells. The somatostatin neurons in the periventricular nucleus mediate negative feedback effects of growth hormone on its own release; the somatostatin neurons respond to high circulating concentrations of growth hormone and somatomedins by increasing the release of somatostatin, so reducing the rate of secretion of growth hormone.
Somatostatin is synthesized and released by neuroendocrine neurons of the periventricular nucleus of the hypothalamus. These neurons project to the median eminence, where somatostatin is released from neurosecretory nerve endings into the hypothalamo-hypophysial portal circulation. Somatostatin is carried in the blood stream through these blood vessels to the anterior pituitary gland, where somatostatin inhibits the secretion of growth hormone from somatotrope cells. The somatostatin neurons in the periventricular nucleus mediate negative feedback effects of growth hormone on its own release; the somatostatin neurons respond to high circulating concentrations of growth hormone and somatomedins by increasing the release of somatostatin, so reducing the rate of secretion of growth hormone.
Monday, March 15, 2010
Somatotropes
Somatotropes, also called somatotrophs, are cells located in the anterior pituitary. They synthesize and secrete somatotropin, or growth hormone. Somatotropes make up 40 to 50% of anterior pituitary cells. Somatoropes produce somatotropin (growth hormone) in response to somatocrinin (growth hormone releasing hormone); and the release of somatotropin is inhibited by somatostatin, both received from the hypothalamus via the hypophyseal portal system vein and the secondary plexus.
If there is an excess of growth hormone it is usually because of over-secretion of somatotrope cells in the anterior pituitary gland. This malfunction characterizes the disease gigantism. On the other hand, deficiency in somatotrope secretion before puberty, or before the end of new bone tissue growth, can lead to pituitary dwarfism.
Somatotropes are classified as acidophilic cells. These cells take years to grow and mature very slowly. If these cells grow large enough they can impair vision, cause headaches or damage other pituitary functions.
If there is an excess of growth hormone it is usually because of over-secretion of somatotrope cells in the anterior pituitary gland. This malfunction characterizes the disease gigantism. On the other hand, deficiency in somatotrope secretion before puberty, or before the end of new bone tissue growth, can lead to pituitary dwarfism.
Somatotropes are classified as acidophilic cells. These cells take years to grow and mature very slowly. If these cells grow large enough they can impair vision, cause headaches or damage other pituitary functions.
Sunday, March 14, 2010
Somatotropin
Somatotropin, also called Growth hormone, is a protein-based polypeptide which contained 191 amino acids. It is produced and secreted by the somatotroph cells of the anterior pituitary gland. Somatotropin acts by stimulating the release of another hormone called somatomedin by the liver, thereby causing growth. Somatotropin is also known as somatropin.
Somatotropin stimulates body growth generally, specially the lengthening of long bones in particular. Whereas anabolic steroids act primarily on muscles, somatotropin, or human growth hormone, strengthens bones and tendons as well. It is used clinically to treat children's growth disorders and adult growth hormone deficiency. In recent years, replacement therapies with human growth hormones (hGH) have become popular in the battle against aging and weight management. Reported effects on GH deficient patients (but not on healthy people) include decreased body fat, increased muscle mass, increased bone density, increased energy levels, improved skin tone and texture, increased sexual function and improved immune system function. At this time hGH is still considered a very complex hormone and many of its functions are still unknown.
In its role as an anabolic agent, somatotropin has been used by competitors in sports since the 1970s, and it has been banned by the IOC and NCAA. Traditional urine analysis could not detect doping with hGH, so the ban was unenforceable until the early 2000s, when blood tests that could distinguish between natural and artificial hGH were starting to be developed. Blood tests conducted by WADA at the 2004 Olympic Games in Athens, Greece primarily targeted hGH.
Somatotropin stimulates body growth generally, specially the lengthening of long bones in particular. Whereas anabolic steroids act primarily on muscles, somatotropin, or human growth hormone, strengthens bones and tendons as well. It is used clinically to treat children's growth disorders and adult growth hormone deficiency. In recent years, replacement therapies with human growth hormones (hGH) have become popular in the battle against aging and weight management. Reported effects on GH deficient patients (but not on healthy people) include decreased body fat, increased muscle mass, increased bone density, increased energy levels, improved skin tone and texture, increased sexual function and improved immune system function. At this time hGH is still considered a very complex hormone and many of its functions are still unknown.
In its role as an anabolic agent, somatotropin has been used by competitors in sports since the 1970s, and it has been banned by the IOC and NCAA. Traditional urine analysis could not detect doping with hGH, so the ban was unenforceable until the early 2000s, when blood tests that could distinguish between natural and artificial hGH were starting to be developed. Blood tests conducted by WADA at the 2004 Olympic Games in Athens, Greece primarily targeted hGH.
Saturday, March 13, 2010
Tyrosine
Tyrosine is a white crystalline amino acid, CHNO, which is used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. Tyrosine is obtained from the hydrolysis of proteins such as casein and is a precursor of epinephrine, thyroxine, and melanin. It was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese.
Tyrosine supports and assists neurotransmitters in the brain. L-Tyrosine supplementation helps reduce stress, improves mental alertness and mood, acts as an appetite suppressant and has a positive affect on sex drive. Tyrosine, which can be synthesized in the body from phenylalanine, is found in many high protein food products such as soy products, chicken, turkey, fish, peanuts, almonds, avocados, bananas, milk, cheese, and yogurt.
Tyrosine supports and assists neurotransmitters in the brain. L-Tyrosine supplementation helps reduce stress, improves mental alertness and mood, acts as an appetite suppressant and has a positive affect on sex drive. Tyrosine, which can be synthesized in the body from phenylalanine, is found in many high protein food products such as soy products, chicken, turkey, fish, peanuts, almonds, avocados, bananas, milk, cheese, and yogurt.
Friday, March 12, 2010
Thyrotropin
Thyrotropin, also known as thyroid-stimulating hormone (TSH), is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland at the base of the brain in response to signals from the hypothalamus. It regulates the endocrine function of the thyroid gland.
Thyrotropin stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3). Thyrotropin production is controlled by thyrotropin-releasing hormone (TRH), which is produced in the hypothalamus and transported to the anterior pituitary gland via the superior hypophyseal artery, where it increases thyrotropin production and release. Somatostatin is also produced by the hypothalamus, and has an opposite effect on the pituitary production of TSH, decreasing or inhibiting its release.
The thyrotropin receptor is found mainly on thyroid follicular cells. Stimulation of the receptor increases T3 and T4 production and secretion. Stimulating antibodies to this receptor mimic TSH and cause Graves' disease.
Thyrotropin stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3). Thyrotropin production is controlled by thyrotropin-releasing hormone (TRH), which is produced in the hypothalamus and transported to the anterior pituitary gland via the superior hypophyseal artery, where it increases thyrotropin production and release. Somatostatin is also produced by the hypothalamus, and has an opposite effect on the pituitary production of TSH, decreasing or inhibiting its release.
The thyrotropin receptor is found mainly on thyroid follicular cells. Stimulation of the receptor increases T3 and T4 production and secretion. Stimulating antibodies to this receptor mimic TSH and cause Graves' disease.
Thursday, March 11, 2010
Thyroglobulin
Thyroglobulin, or Tg, is a glycoprotein of high molecular weight produced by the thyroid epithelial cells in the thyroid gland. It is used by the thyroid gland to produce the thyroid hormones thyroxine (T4) and triiodothyronine (T3). The iodinated tyrosine moieties contained in thyroglobulin form the active hormones thyroxine and tri-iodothyronine.
Via a reaction with the enzyme thyroperoxidase, iodine is covalently bound to tyrosine residues in thyroglobulin molecules, forming monoiodotyrosine (MIT) and diiodotyrosine (DIT). Thyroxine is produced by combining two moieties of DIT. Triiodothyronine is produced by combining one molecule of MIT and one molecule of DIT.
Thyroglobulin is the protein precursor of thyroid hormone should not be confused with Thyroxine-binding globulin, which is a carrier protein responsible for carrying the thyroid hormones in the blood. Tg is secreted and stored in the follicular lumen.
Via a reaction with the enzyme thyroperoxidase, iodine is covalently bound to tyrosine residues in thyroglobulin molecules, forming monoiodotyrosine (MIT) and diiodotyrosine (DIT). Thyroxine is produced by combining two moieties of DIT. Triiodothyronine is produced by combining one molecule of MIT and one molecule of DIT.
Thyroglobulin is the protein precursor of thyroid hormone should not be confused with Thyroxine-binding globulin, which is a carrier protein responsible for carrying the thyroid hormones in the blood. Tg is secreted and stored in the follicular lumen.
Wednesday, March 10, 2010
Triiodothyronine
Triiodothyronine is a hormone secreted by the thyroid gland, taking part in the body's control of metabolism. It is the most powerful thyroid hormone, and affects almost every process in the body, including body temperature, growth, and heart rate. It is also known as T3.
Triiodothyronine helps regulate growth and development, helps control metabolism and body temperature, and, by a negative-feedback system, acts to inhibit the secretion of thyrotropin by the pituitary gland. Triiodothyronine is produced mainly from the deiodination of thyroxine in the peripheral tissues but is also synthesized by and stored in the thyroid gland as an amino acid residue of the protein thyroglobulin.
Thyroid-stimulating hormone (TSH) activates the production of thyroxine (T4) and triiodothyronine (T3). This process is under regulation. In the thyroid, T4 is converted to T3. TSH is inhibited mainly by T3. The thyroid gland releases greater amounts of T4 than T3, so plasma concentrations of T4 are 40-fold higher than those of T3. Most of the circulating T3 is formed peripherally by deiodination of T4 (85%), a process that involves the removal of iodine from carbon 5 on the outer ring of T4. Thus, T4 acts as prohormone for T3.
Triiodothyronine is similar to thyroxine but with one fewer iodine atoms per molecule. In addition, T3 exhibits greater activity and is produced in smaller quantity.
Triiodothyronine helps regulate growth and development, helps control metabolism and body temperature, and, by a negative-feedback system, acts to inhibit the secretion of thyrotropin by the pituitary gland. Triiodothyronine is produced mainly from the deiodination of thyroxine in the peripheral tissues but is also synthesized by and stored in the thyroid gland as an amino acid residue of the protein thyroglobulin.
Thyroid-stimulating hormone (TSH) activates the production of thyroxine (T4) and triiodothyronine (T3). This process is under regulation. In the thyroid, T4 is converted to T3. TSH is inhibited mainly by T3. The thyroid gland releases greater amounts of T4 than T3, so plasma concentrations of T4 are 40-fold higher than those of T3. Most of the circulating T3 is formed peripherally by deiodination of T4 (85%), a process that involves the removal of iodine from carbon 5 on the outer ring of T4. Thus, T4 acts as prohormone for T3.
Triiodothyronine is similar to thyroxine but with one fewer iodine atoms per molecule. In addition, T3 exhibits greater activity and is produced in smaller quantity.
Tuesday, March 9, 2010
Thyroid Epithelial Cells (Follicular Cells)
Thyroid epithelial cells, also known as follicular cells, are cells in the thyroid gland which produce thyroxine (T4) and triiodothyronine (T3). The follicular cells use iodine from the blood to make thyroid hormone, which helps regulate a person's metabolism. The main function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones: thyroxine (T4) and triiodothyronine (T3).
Thyroid epithelial cells are the only cells in the body which can absorb iodine. These cells combine iodine and the amino acid tyrosine to make T3 and T4. T3 and T4 are then released into the blood stream and are transported throughout the body where they control metabolism (which is the conversion of oxygen and calories to energy). Every cell in the body depends upon thyroid hormones for regulation of their metabolism. The normal thyroid gland produces about 80% T4 and about 20% T3, however, T3 is about four times as potent as T4. They are simple cuboidal epithelium and are arranged in spherical follicles surrounding colloid.
They have thyrotropin receptors on their surface, which respond to thyroid-stimulating hormone. Embryologic origin is from a median endodermal mass in the region of the tongue (foramen cecum) in contrast to the parafollicular (C) cells that arise from the 4th branchial pouch.
Thyroid epithelial cells are the only cells in the body which can absorb iodine. These cells combine iodine and the amino acid tyrosine to make T3 and T4. T3 and T4 are then released into the blood stream and are transported throughout the body where they control metabolism (which is the conversion of oxygen and calories to energy). Every cell in the body depends upon thyroid hormones for regulation of their metabolism. The normal thyroid gland produces about 80% T4 and about 20% T3, however, T3 is about four times as potent as T4. They are simple cuboidal epithelium and are arranged in spherical follicles surrounding colloid.
They have thyrotropin receptors on their surface, which respond to thyroid-stimulating hormone. Embryologic origin is from a median endodermal mass in the region of the tongue (foramen cecum) in contrast to the parafollicular (C) cells that arise from the 4th branchial pouch.
Monday, March 8, 2010
Thyroxine
Thyroxine, abbreviated as T4, is the major hormone produced by the follicular cells of the thyroid gland. Since it has four iodine molecules attached to its molecular structure, thyroxine is synthesized via the iodination and covalent bonding of the phenyl portions of tyrosine residues found in an initial peptide, thyroglobulin, which is secreted into thyroid granules. These iodinated diphenyl compounds are cleaved from their peptide backbone upon being stimulated by thyroid stimulating hormone. More in the T3 and T4 section of thyroid.
Thyroxine is carried in the blood stream, with 99.95% of the secreted thyroxine being protein-bound, principally to thyroxine-binding globulin (TBG), and, to a lesser extent, to transthyretin and serum albumin. Thyroxine is a prohormone and a reservoir for the active thyroid hormone triiodothyronine (T3), which is about four times more potent. T4 is converted in the tissues by deiodinases, including thyroid hormone iodine peroxidase (TPO), to T3.
Function: thyroxine is involved in controlling the rate of metabolic processes in the body and influencing physical development. Administration of thyroxine has been shown to significantly increase the concentration of nerve growth factor in the brains of adult mice. Thyroxine increases the number and activity of mitochondria in cells by binding to the cells' DNA, raising the basal metabolic rate. Administration of thyroxine causes an increase in the rate of carbohydrate metabolism and a rise in the rate of protein synthesis and breakdown. This hormone excites the nervous system, leading to increased activity of the endocrine system. T4 remains active in the body for more than a month.
Thyroxine is carried in the blood stream, with 99.95% of the secreted thyroxine being protein-bound, principally to thyroxine-binding globulin (TBG), and, to a lesser extent, to transthyretin and serum albumin. Thyroxine is a prohormone and a reservoir for the active thyroid hormone triiodothyronine (T3), which is about four times more potent. T4 is converted in the tissues by deiodinases, including thyroid hormone iodine peroxidase (TPO), to T3.
Function: thyroxine is involved in controlling the rate of metabolic processes in the body and influencing physical development. Administration of thyroxine has been shown to significantly increase the concentration of nerve growth factor in the brains of adult mice. Thyroxine increases the number and activity of mitochondria in cells by binding to the cells' DNA, raising the basal metabolic rate. Administration of thyroxine causes an increase in the rate of carbohydrate metabolism and a rise in the rate of protein synthesis and breakdown. This hormone excites the nervous system, leading to increased activity of the endocrine system. T4 remains active in the body for more than a month.
Sunday, March 7, 2010
Chromaffin Cells
Chromaffin cells are neuroendocrine cells which secrete adrenaline. They are found in the medulla of the adrenal gland (suprarenal gland, located above the kidneys) and in other ganglia of the sympathetic nervous system. These adrenaline-producing cells are called "chromaffin cells" since they only show up under the microscope when stained with chromium salts.
Chromaffin cells are stimulated by the splanchnic nerve to secrete adrenaline (epinephrine), noradrenaline, and enkephalin endogenous ligands, which are small opiate-like peptides, which are responsible for the euphoria that runners sometimes feel.
Chromaffin cells originate in the embryonic neural crest. In the fifth week of (human) fetal development, neuroblast cells migrate from the neural crest to form the sympathetic chain and preaortic ganglia. The cells migrate a second time to the adrenal medulla. Chromaffin cells also settle near the sympathetic ganglia, vagus nerve, paraganglia, and carotid arteries. In lower concentrations, extra-adrenal chromaffin cells also reside in the bladder wall, prostate, and behind the liver.
Saturday, March 6, 2010
Parathyroid Hormone
Parathyroid hormone, or parathormone, is a hormone secreted by the parathyroid glands as a polypeptide which contains 84 amino acids. It acts to increase the concentration of calcium (Ca2+) in the blood, whereas calcitonin, which is a hormone secreted by the parafollicular cells of the thyroid gland, acts to decrease calcium concentration. The parathyroid hormone causes the increase of the concentration of calcium in the blood by acting upon parathyroid hormone receptor in three parts of the body: bone, kidney, and intestine. The parathyroid hormone half-life is approximately 4 minutes and has a molecular mass of 9.4 kDa.
If calcium ion concentrations in extracellular fluid fall below normal, parathyroid hormone brings them back within the normal range. In conjunction with increasing calcium concentration, the concentration of phosphate ion in blood is reduced. Parathyroid hormone accomplishes its job by stimulating at least three processes:
1) Mobilization of calcium from bone: although the mechanisms remain obscure, a well-documented effect of parathyroid hormone is to stimulate osteoclasts to reabsorb bone mineral, liberating calcium into blood.
2) Enhancing absorption of calcium from the small intestine: Facilitating calcium absorption from the small intestine would clearly serve to elevate blood levels of calcium. Parathyroid hormone stimulates this process, but indirectly by stimulating production of the active form of vitamin D in the kidney. Vitamin D induces synthesis of a calcium-binding protein in intestinal epithelial cells that facilitates efficient absorption of calcium into blood.
3) Suppression of calcium loss in urine: In addition to stimulating fluxes of calcium into blood from bone and intestine, parathyroid hormone puts a brake on excretion of calcium in urine, thus conserving calcium in blood. This effect is mediated by stimulating tubular reabsorption of calcium. Another effect of parathyroid hormone on the kidney is to stimulate loss of phosphate ions in urine.
If calcium ion concentrations in extracellular fluid fall below normal, parathyroid hormone brings them back within the normal range. In conjunction with increasing calcium concentration, the concentration of phosphate ion in blood is reduced. Parathyroid hormone accomplishes its job by stimulating at least three processes:
1) Mobilization of calcium from bone: although the mechanisms remain obscure, a well-documented effect of parathyroid hormone is to stimulate osteoclasts to reabsorb bone mineral, liberating calcium into blood.
2) Enhancing absorption of calcium from the small intestine: Facilitating calcium absorption from the small intestine would clearly serve to elevate blood levels of calcium. Parathyroid hormone stimulates this process, but indirectly by stimulating production of the active form of vitamin D in the kidney. Vitamin D induces synthesis of a calcium-binding protein in intestinal epithelial cells that facilitates efficient absorption of calcium into blood.
3) Suppression of calcium loss in urine: In addition to stimulating fluxes of calcium into blood from bone and intestine, parathyroid hormone puts a brake on excretion of calcium in urine, thus conserving calcium in blood. This effect is mediated by stimulating tubular reabsorption of calcium. Another effect of parathyroid hormone on the kidney is to stimulate loss of phosphate ions in urine.
Friday, March 5, 2010
Parathyroid Glands
The parathyroid glands are four endocrine glands which are situated in the neck, protruding from the back surface of the thyroid gland. The parathyroid glands secrete parathyroid hormone, which is the most important regulator of calcium and phosphorus amounts in the body. Parathyroid glands also control the amount of calcium in the blood and within the bones.
Although the parathyroid glands are named for their proximity to the thyroid, they play a completely different role than the thyroid gland. They are quite easily recognizable from the thyroid because they are composed of densely packed cells, called parathyroid chief cells, in contrast with the follicle structure of the thyroid.
The main function of the parathyroid glands is to keep the body's calcium level within a very narrow range, so that the nervous and muscular systems can function properly. When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release hormone into the blood.
The Four Parathyroid Glands (Video)
Although the parathyroid glands are named for their proximity to the thyroid, they play a completely different role than the thyroid gland. They are quite easily recognizable from the thyroid because they are composed of densely packed cells, called parathyroid chief cells, in contrast with the follicle structure of the thyroid.
The main function of the parathyroid glands is to keep the body's calcium level within a very narrow range, so that the nervous and muscular systems can function properly. When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release hormone into the blood.
The Four Parathyroid Glands (Video)
Parathyroid Chief Cells
Also known as parathyroid principal cells, the parathyroid chief cells are cells in the parathyroid glands which secretes parathyroid hormone. They are often divided into dark chief cells and light chief cells. A parathyroid cell is a round and clear cell with a centrally located nucleus.
Parathyroid chief cells are one of the few cell types which regulate intracellular calcium levels as a consequence of extracellular changes in calcium concentration. The end result of increased secretion by the chief cells of a parathyroid gland is an increase in the serum level of Calcium. The calcium-sensing receptor is sensitive to an increase in serum calcium, and stimulates the uptake of calcium by the parathyroid chief cell. This mechanism is critically important, as it describes a physiological feed-back loop by which parathyroid hormone secretion is down-regulated in response to a restoration of serum calcium.
Parathyroid chief cells are one of the few cell types which regulate intracellular calcium levels as a consequence of extracellular changes in calcium concentration. The end result of increased secretion by the chief cells of a parathyroid gland is an increase in the serum level of Calcium. The calcium-sensing receptor is sensitive to an increase in serum calcium, and stimulates the uptake of calcium by the parathyroid chief cell. This mechanism is critically important, as it describes a physiological feed-back loop by which parathyroid hormone secretion is down-regulated in response to a restoration of serum calcium.
Thursday, March 4, 2010
Transcytosis
Also called vesicular transport, transcytosis is a form of intracellular vesicular traffic in which endocytosed macromolecules are transferred across the cell and released via exocytosis at the opposite plasma membrane domain. In other words, transcytosis is a mechanism for transcellular transport in which a cell encloses extracellular material in an invagination of the cell membrane to form a vesicle, then moves the vesicle across the cell to eject the material through the opposite cell membrane by the reverse process.
Vesicles are employed to intake the macromolecules on one side of the cell, draw them across the cell, and eject them on the other side. While transcytosis is most commonly observed in cells of an epithelium, the process is also present elsewhere. Blood capillaries are a well-known site for transcytosis, though it occurs in other cells, including neurons and intestinal cells.
Vesicles are employed to intake the macromolecules on one side of the cell, draw them across the cell, and eject them on the other side. While transcytosis is most commonly observed in cells of an epithelium, the process is also present elsewhere. Blood capillaries are a well-known site for transcytosis, though it occurs in other cells, including neurons and intestinal cells.
Wednesday, March 3, 2010
Pericytes
Pericytes, or mural cells, are connective tissue cells which are found wrapped about small blood vessels. They are elongated, contractile, pericapillary cells located about precapillary arterioles outside the basement membrane.
Pericytes are adjacent to endothelial cells of blood vessels. They are the mural cells of microvessels such as arterioles, capillaries and venules, stabilizing the walls of blood vessel and participate in the regulation of blood flow. These cells also influence the proliferation, survival, migration, and maturation of endothelial cells (Shepro and Morel, 1993) and also take an active part in developmental angiogenic processes (Betsholtz et al, 2005). Pericytes form pericyte tubes free of endothelial cells, which may reflect the early participation of these cells in the process of angiogenic sprouting.
Cerebral pericytes constitute an essential component of the blood-brain barrier, which they form together with endothelial cells and astrocytes (Dohgu et al, 2005). Newly formed blood vessels appear to become independent of VEGF when covered by pericytes (Alon et al, 1995; Benjamin et al, 1998). A lack of pericytes leads to endothelial hyperplasia and abnormal vascular morphogenesis (Hellstrom et al, 2001). Genetically engineered mice that lack pericytes have been shown to develop microaneurysms at late gestation and die before birth (Lindahl et al, 1997).
Tuesday, March 2, 2010
Hematocrit
Hematocrit, also known as erythrocyte volume fraction, is the blood volume which is occupied by red blood cells. In other words, hematocrit measures how much space in the blood is occupied by red blood cells. It is useful when evaluating a person for anemia. It gives a percentage of red blood cells found in whole blood. It is normally about 48% for men and 38% for women. Hematocrit is an integral part of a person's complete blood count results, along with hemoglobin concentration, white blood cell count, and platelet count.
Blood drawn from someone is put in a small capillary tube, which is then spun in a small centrifuge at 10,000 RPM for five minutes. As the tube spins, the red blood cells go to the bottom of the tube, the white blood cells cover the red in a thin layer called the buffy coat, and the liquid plasma rises to the top. The spun tube is examined for the line that divides the red cells from the buffy coat and plasma. The height of the red cell column is measured as a percent of the total blood column. The higher the column of red cells, the higher the hematocrit.
Monday, March 1, 2010
Angiotensin II
Angiotensin II is an octapeptide that is a potent vasopressor and a powerful stimulus for production and release of aldosterone from the adrenal cortex. Angiotensin II is formed from angiotensin I, which is converted into angiotensin II through the removal of two C-terminal residues by the enzyme angiotensin-converting enzyme (ACE, or kinase), which is found predominantly in the capillaries of the lung. ACE is actually found all over the body, but has its highest density in the lung due to the high density of capillary beds there. Angiotensin II acts as an endocrine, autocrine/paracrine, and intracrine hormone.
ACE is a target for inactivation by ACE inhibitor drugs, which decrease the rate of angiotensin II production. Angiotensin II increases blood pressure by stimulating the Gq protein in vascular smooth muscle cells (which in turn activates contraction by an IP3-dependent mechanism). ACE inhibitor drugs are major drugs against hypertension.
Other cleavage products of ACE, 7 or 9 amino acids long, are also known; they have differential affinity for angiotensin receptors, although their exact role is still unclear. The action of angiotensin II itself is targeted by angiotensin II receptor antagonists, which directly block angiotensin II AT1 receptors.
Angiotensin II is degraded to angiotensin III by angiotensinases that are located in red blood cells and the vascular beds of most tissues. It has a half-life in circulation of around 30 seconds, whereas, in tissue, it may be as long as 15–30 minutes.
ACE is a target for inactivation by ACE inhibitor drugs, which decrease the rate of angiotensin II production. Angiotensin II increases blood pressure by stimulating the Gq protein in vascular smooth muscle cells (which in turn activates contraction by an IP3-dependent mechanism). ACE inhibitor drugs are major drugs against hypertension.
Other cleavage products of ACE, 7 or 9 amino acids long, are also known; they have differential affinity for angiotensin receptors, although their exact role is still unclear. The action of angiotensin II itself is targeted by angiotensin II receptor antagonists, which directly block angiotensin II AT1 receptors.
Angiotensin II is degraded to angiotensin III by angiotensinases that are located in red blood cells and the vascular beds of most tissues. It has a half-life in circulation of around 30 seconds, whereas, in tissue, it may be as long as 15–30 minutes.
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