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2011PCAT_ENDOCRINE
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Endocrine Glands


Synthesize and secrete hormones directly into the circulatory system.


Exocrine Glands


Synthesize and secrete hormones into ducts and are then secreted into the external environment.


Adrenal Glands (location, composition, role)


1) Located on top of the kidneys. 2) Composed of the adrenal cortex and adrenal medulla. 3) In response to stress, the anterior pituitary is stimulated by the hypothalamus to secrete adrenocorticotropic hormone (ACTH), which causes the adrenal cortex to secrete glucocrticoids and other steroids in the class of adrenocortical steroids or corticosteroids. The adrenal medulla secretes catecholamines, which trigger "fight-or-flight" responses.


Adrenal Cortex (location, composition, role)


1&2) A component of the adrenal gland located on the kidneys. 3) In response to adrenocorticotropic hormone (ACTH) secreted by the pituitary gland, this organ secretes a multitude of steroid hormones collectively called adrenocortical steroids or corticosteroids. These hormones include glucocorticoids (triggered for release by ACTH and include cortisone and cortisol), mineralocorticoids (aldesterone), and cortical sex hormones (androgens). In the blood stream, these steroids bind to transport proteins called transcortins. Finally, these steroids determine which genes are transcribed and at what rate.


Adrenocorical Steroids


Or corticosteroids. Secreted by the adrenal cortex into the blood stream. In the blood stream they are transported by transcortin proteins. Once the steroids reach their target cell(s), they determine which genes are transcribed and at what rate. The steroids include glucocorticoids (cortisone, cortisol), mineralocorticoids (aldesterone) and cortical sex hormones (androgens).


Glucocorticoids


Steroids secreted by the adrenal cortex including cortisol and cortisone. These are involved in glucose regulation and protein metabolism. Glucocorticoids promote gluconeogenesis, leading to an increase in glucose levels in the blood. They also promote protein breakdown and decrease protein synthesis, reduce the effects of insulin, release amino acids from muscle and lipids from adipose (fatty) tissue. Their release is stimulated by the anterior pituitary's secretion of ACTH.


Cortisol


A glucocorticoid steroid that increases glucose in the blood and produces many other effects. It is released from the adrenal cortex.


Cortisone


A glucocorticoid steroid that increases glucose in the blood and produces other effects. It is released from the adrenal cortex.


Mineralocorticoids


Steroids secreted by the adrenal cortex, particularly aldosterone. They regulate levels of sodium and potassium in the blood, and therefore the extracellular volume of water.


Aldosterone


A mineralocorticoid steroid secreted by the adrenal cortex. It causes the kidneys' nephron to reabsorb sodium and potassium ions, as well as water. Overall, the steroid increases blood pressure.


Cortical Sex Hormones


Steroids (androgens) secreted by the adrenal cortex.


Androgens


Male sex hormones, cortical sex hormone, secreted by the adrenal cortex. Excessive production of this hormone in women results in masculinizing effects. Men also produce this hormone in the testes.


Adrenal Medulla (location, composition, role)


1&2) Located above the kidneys and is a component of the adrenal gland. 3) Secretes amino acid-derived catecholamines (epinephrine (adrenaline) and norepinephrine (noradrenaline)), leading to "fight or flight response".


Catecholamines


Amino acid-derived chemical compounds secreted by the adrenal medulla. Including epinephrine and norepinephrine.


Epinephrine


Amino acid-derived chemical compound - adrenaline. Secreted by the adrenal medulla, it leads to an increase in glycogen conversion to glucose, increasing glucose levels in the blood. It also increases the rate and strength of the heart beat and other "fight or flight responses". It inhibits vegetative functions that are not immediately required for survival, like digestion.


Norepinephrine


Amino-acid derived chemical compound - noradrenaline. Secreted by the adrenal medulla, it produces "fight or flight responses".


Pituitary Gland (location, composition, role)


1) Located at the base of the brain, below the hypothalamus connected by a small cord called the infundibulum. 2) The pituitary gland has two components - the anterior and posterior lobes. 3) It secretes a multitude of hormones when signaled by the hypothalamus. These hormones regulate homeostasis.


Anterior Pituitary (location, composition, role)


1&2) A component of the pituitary gland located at the base of the brain by the hypothalamus. 3) Its hormonal secretions are regulated by secretions of the hypothalamus. It hormones target specific organs (direct hormones) and other endocrine glands (tropic hormones). Direct Hormones


Infundibulum


The cord that connects the pituitary gland to the base of the brain near the hypothalamus.


Somatotropin


Or growth hormone. A direct hormone secreted by the anterior pituitary gland. Promotes bone and muscle growth as well as protein synthesis and lipid mobilization and catabolism. In children, incorrect secretion of the hormone can cause gigantism and dwarfism. In adults, over production of the hormone can cause acromegaly, which is localized disproportionate overgrowth of the bone.


Acromegaly


Occurs in adults when there is an over production of growth hormone from the anterior pituitary gland. This is characterized by localized, disproportionate overgrowth of the bone.


Prolactin


A direct hormone secreted by the anterior pituitary gland that stimulates milk production and lactation in females.


Adrenocorticotropic Hormone


Tropic hormone secreted by the anterior pituitary gland, which stimulates the adrenal cortex to synthesize and secret glucocorticoids. It is released when the hypothalamus responses to stress.


Thyroid-Stimulating Hormone


Tropic hormone secreted by the anterior pituitary gland to stimulate the thyroid to begin synthesizing and secreting thyroid hormones.


Luteinizing Hormone


A tropic hormone secreted by the anterior pituitary gland. In women the hormone stimulates ovulation and the development of the corpus luteum, as well as regulates progesterone secretion. In men, the hormone stimulates cells of the testes to synthesize testosterone.


Follicle-Stimulating Hormone


A tropic hormone secreted by the anterior pituitary gland. In women, it causes the maturation of the follicle, which will produce estrogen. In men, it causes maturation of the seminiferous tubules and sperm production.


Melanocyte-Stimulating Hormone


A tropic hormone secreted by the anterior pituitary gland. It is unclear what the hormone does in mammals. In frogs it causes darkening of the skin.


Endorphins


Tropic hormones secreted by the anterior pituitary gland and has pain-relieving effects.


Posterior Pituitary (location, composition, role)


1&2) A component of the pituitary gland. 3) This organ does not synthesize hormones, rather it stores and releases oxytocin and ADH produced by the hypothalamus.


Oxytocin


A hormone produced by the hypothalamus, but stored and released by the posterior pituitary gland. It is released during childbirth to increase the strength and frequency of uterine contractions. Its secretion also stimulates milk production in mammals.


Antidiuretic Hormone


ADH or vasopressin. Produced by the hypothalamus, but stored and secreted by the posterior pituitary. The hormone increases the permeability of the nephron to water, increasing blood volume.


Hypothalamus (location, composition, role)


1) Located below the the thalamus, but above the brain stem. 2) A single organ. 3) The Hypothalamus is the link between the nervous system and the endocrine system. This organ secretes hormones to trigger the anterior pituitary to secrete both direct and tropic hormones. The hypothalamus synthesizes oxytocin and ADH for the posterior pituitary to store and secrete with the signaling of the hypothalamus. All hormone secretions of the pituitary are controled by the hypothalamus.


Thyroid (location, composition, role)


1) Located in the neck below the Adam's Apple. 2) A single organ. 3) This endocrine gland is controlled by the hypothalamus and the anterior pituitary gland. When stimulated, it secretes thyroxine (T4) and triiodothyronine (T3), which regulate growth and metabolism. These hormones are synthesized on a glycoprotein in the thyroid cells called thyroglobulin.


Thyroxine


(T4) Is a hormone produced in the thyroid gland of a protein called thyroglobulin. Formed by the iodination of the amino acid tyrosine. It is responsible for metabolism and development in the body.


Triiodothyronine


(T3) Is a hormone produced and secreted by the thyroid gland, but is more often derived from thyroxine. If not formed from thyroxine, it is derived from the iodination of the amino acid tyrosine. It is more powerful than thyroxine and is responsible in metabolism, development and homeostasis.


Hypothyroidism


When thyroid hormones are undersecreted or not secreted at all. Symptoms include a slow down of heart and respiratory rate, weight gain, and other adverse homeostasis effects. hypothyroidism in infints is called cretinism, and is characterized by mental retardation and short stature.


Cretinism


Hypothyroidism in infants. Characterized by retardation and short stature.


Hyperthyroidism


The thyroid is over stimulated and produces too much of its hormones. Characterized by increased metabolic and perspiration rate as well as other changes in homeostasis, including weight lose.


Pancreas (location, composition, role)


1) Below the stomach, but connected at the beginning if the small intestine. 2) Single organ. 3) The organ has an exocrine and endocrine role. Its exocrine role is its secretion of digestive enzymes into the small intestine. Its endocrine role is to secrete hormones including insulin (beta cells) and glucagon (alpha cells) from the islet of Langerhans.


Glucagon


A hormone secreted by pancreas alpha cells in the islet of Langerhans. The hormone increases glucose in the blood. It degrades fats and proteins, breaks glycogen down to glucose and promotes gluconeogenesis.


Insulin


A hormone secreted by pancreas beta cells in the islet of Langerhans. The hormone is excreted in response to high glucose levels in the blood. It stimulates fat and amino acid synthesis from glucose, and the storage of glucose as glycogen in muscle and adipose cells.


Diabetes (Type I vs II)


Type I


Parathyroid Glands (location, composition, role)


1) Located on the posterior side of the thyroid gland. 2) Four or more peas sized glands. 3) These glands synthesize and secrete parathyroid hormone (PTH), which removes calcium from the bone to increase Ca2+ in the blood.


Parathyroid Hormone


(PTH) Synthesized and secreted by the parathyroid glands, this hormone releases calcium from the bone to increase Ca2+ levels in the blood. The hormone also decreases the amount of Ca2+ excreted by the kidneys. Since calcium is bonded to phosphate in the bone, the hormone also stimulates the excretion of phosphate by the kidneys.


Kidney (location, composition, role)


1) Located in the middle toward the back of the abdominal cavity. 2) There are two of these organs in each person. 3) The kidney's main role is to filter the blood and maintain homeostasis in the blood, including its volume and solute/electrolyte concentrations. The kidneys produce renin and erythropoietin (EPO).


Renin


Enzyme produced by the kidneys and released when blood volume falls. The enzyme converts the plasma protein angiotensinogen to angiotensin I. Angiotensin I is converted to angiotensin II, which stimulated the adrenal cortex to secrete aldosterone. Aldosterone helps restore blood volume by increasing sodium reabsorption at the kidney, ultimately leading to increase in water.


Erythropoietin


(EPO) A glycoprotein produced by the kidneys that stimulates red blood cell production.


Gastrin


A hormone released by the stomach in response in injested food.This hormone stimulates the gastric glands to release HCl when food is in the stomach.


Secretin


A hormone released by the small intestine when acidic food material, chyme, enters. The hormone triggers the pancreas to release pancreatic juices including alkaline bicarbonate solutions to neutralize the acidic chyme.


Cholecystokinin


A hormone released by the small intestine in response to the presence of fats. This hormone triggers the gallbladder to release bile to assist in fat digestion.


Pineal Gland (location, composition, role)


1) Located at the base of the brain. 2) A single, small gland. 3) Responsible for the secretion of the hormone melatonin. It's secretion is triggered by light and dark cycles in the environment.


Melatonin


Hormone secreted by the pineal gland in response to light and dark cycles in the environment. This hormone plays a role in the regulation of the circadian rhythms - physiological cycles lasting 24 hours.


Chyme


Acidic, partially digested food coming from the stomach.


Circadian Rhythms


Physiological cycles lasting 24 hours. These are regulated partially by melatonin release of the pineal gland.


What are the basic mechanisms of hormones?


They come in either a steroid or peptide form, and trigger target cells via extracellular or intracellular receptors. 1) Peptide hormones act by binding to specific receptors on the surface of the target cell and trigger an enzymatic reaction within the cell. The peptide hormone is the first messenger and cyclic adenosine monophosphate (ATP conversion carried out within the cell when the peptide binds) or cAMP is often the second messenger which relays further messages, resulting in a cascade effect. 2) Steroid hormones are lipid based, so they enter the target cell directly and bind to a receptor within the cytoplasm. The receptor-hormone complex then enters the nucleus and directly activates the expression of genes via receptors on the chromatin.


Auxins


An important class of plant hormones that are responsible for growth patterns such as phototropism by indole-acetic acid and geotropism. The stimulate the production of new xylem cells.


Phototropism


A plant's response to grow towards the light source. This response is stimulated by the auxin hormone, indole-acetic acid. The side of the plant struck by light has a reduced supply of auxin and grows more slowly than the shaded side. The result is that the shaded side grows more quickly, and the asymmetrical growth causes the plant to bend.


Geotropism


A plant's response to grow away from, or toward gravity. Negative geotropism


Gibberellins


Plant hormones that stimulate the growth of phloem cells. They inhibit the formation of new root cells and stimulate the rapid elongation of stem cells. They also play a role in the termination of seed dormancy and plant flowering.


Kinins


Or cytokinin. Plant hormones that are important for cell division and, therefore, plant growth. They work in conjunction with auxins.


Ethylene


A gas produced by plant cells that stimulates fruit ripening and induces aging and senescence.