Biology 11a - Endocrine System
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90 terms
Terms | Definitions |
|---|---|
 Endocrine System | - acts as a means of internal communication - coordinates the activities of the organ systems |
| Endocrine Glands | - synthesize and secrete hormones directly into the circulatory system |
| Exocrine Glands | - secrete substances that are transported by ducts - ex: the gall bladder |
| Hormones | - chemical substances - regulate the function of target organs or tissues |
| Examples of Endocrine Glands | a) pituitary b) hypothalamus c) thyroid d) parathyroids e) adrenals f) pancreas g) testes i) ovaries j) pineal k) kidneys l) gastrointestinal glands m) heart n) thymus |
| Pituitary Gland | - or "hypophysis" - is a small, trilobed gland lying at the base of the brain - has two main lobes: anterior and posterior |
| Anterior Pituitary | - secretes direct hormones and tropic hormones - hormonal secretions of the anterior pituitary are regulated by hypothalamic secretions called the releasing/inhibiting hormones or factors |
| Direct Hormones | a) growth hormone (GH, somatotropin) b) Prolactin |
| Growth Hormone (GH, somatotropin) | - promotes bone and muscle growth - inhibits the uptake of glucose by certain cells - stimulates the breakdown of fatty acid, thus conserving glucose - stimulated by the hypothalamic releasing hormone GHRH - inhibited by somatostatin - secretion is also under neural and metabolic control - deficiency = dwarfism; overproduction = gigantism & acromegaly |
| Acromegaly | - a disorder caused by overproduction of growth hormone - characterized by a disproportionate overgrowth of bone - localized especially in the skull, jaw, feet and hands |
| Prolactin | - stimulates milk production and secretion in female mammary glands |
| Tropic Hormones | a) adrenocorticotropic hormone (ACTH) b) thyroid-stimulating hormone (TSH) c) luteinizing hormone (LH) d) follicle-stimulating hormone (FSH) |
| Adrenocorticotropic Hormone (ACTH) | - stimulates the adrenal cortex to synthesize and secrete glucocorticoids - is regulated by the releasing hormone corticotropin releasing factor (CRF) |
| Thyroid-Stimulating Hormone (TSH) | - stimulates the thyroid gland to absorb iodine and then synthesize and release thyroid hormone - is regulated by the releasing hormone TRH |
| Luteinizing Hormone (LH) | - in females: stimulates ovulation and formation of the corpus luteum - in males: stimulates the interstitial cells of the testes to synthesize testosterone - regulated by estrogen, progesterone and gonadotropin releasing hormone (GnRH) |
| Follice-Stimulating Hormone (FSH) | - in females: casues maturation of ovarian follicles - in males: stimulates maturation of the seminiferous tubules and sperm production - is regulated by estrogen and GnRH |
| Tip to remember the six hormones of the anterior pituitary | FLAT and PIG FSH LH ACTH TSH Prolactin I(gnore) GH |
| Posterior Pituitary | - doesn't synthesize hormones - stores and releases the hormones oxytocin and ADH, which are produced by the neurosecretory cells of the hypothalamus - hormone secretion is stimulated by action potentials descending from the hypothalamus |
| Oxytocin | - is secreted during childbirth - increases the strength and frequency of uterine muscle contractions - induced by suckling - stimulates milk secretion in the mammary glands |
| Antidiuretic Hormone (ADH, vasopressin) | - increases the permeability of the nephron's collecting duct to water - therefore promoting water reabsorption and increasing blood volume - is secreted when plasma osmolarity increases, as sensed by the osmoreceptors in the hypothalamus or when blood volume decreases, as sensed by baroreceptors in the circulatory system |
| Hypothalamus | - is part of the forebraind - is located directly above the pituitary gland - receives neural transmissions from other parts of the brain and from peripheral nerves that trigger specific responses from its neurosecretory cells |
| Neurosecretory Cells | - regulate pituitary gland secretions via negative feedback mechaisms and through the actions of inhibiting and releasing hormones |
| Hypothalamus' Interaction with Anterior Pituitary | - hypothalamic releasing hormones stimulate or inhibit the secretions of the anterior pituitary - ex: GnRH stimulates the anterior pituitary to secrete FSH and LH - releasing hormones are secreted into the hypothalamic-hypophyseal portal system |
| Hypothalamic-Hypophyseal Portal System | - a circulatory pathway - blood from the capillary bed in the hypothalamus flows through a portal vein into the anterior pituitary, where it diverges into a second capillary network - this way releasing hormones can immediately reach the anterior pituitary |
| Negative Feedback | - a preventive mechanism - to prevent over secretion of hormones, since this is potentially harmful to an organism - a high hormone level inhibits further production of that hormone - ex: CRF stimulates ACTH secretion, which stimulates adrenal cortical hormones. When there is too much cortisol, CRF is inhibited by negative feedback |
| Hypothalamus' Interaction with Posterior Pituitary | - neurosecretory cells in the hypothalamus synthesize both oxytocin and ADH and transport them via their axons into the posterior pituitary for storage and secretion |
| Thyroid Gland | - is a bilobed structure located on the ventral surface of the trachea - produces and secretes thyroxine, triiodothyronine (the thyroid hormones) and calcitonin |
| Thyroid Hormones: Thyroxine (T4) and Triiodothyronine (T3) | - T4 and T3 are derived from the iodination of the amino acid tyrosine - thyroid hormones are necessary for growth and neorological development in children - in adults they increase the rate of cellular respiration and rate of protein + fatty acid synthesis, as well as degradation in many tissues - high levels of thyroid hormones inhibit TRH and TSH |
| Hypothyroidism | - caused by inflammation of the thyroid or iodine deficiency - lack of thyroid hormones or none produced at all - common symptoms: slowed heart + respiratory rate, fatigue, cold intolerance and weight gain - in newborn infants is called cretisism (mental retardation & short stature) |
| Hyperthyroidism | - thyroid is overstimulated - oversecretion of the thyroid hormones - common symptoms: increased metabolic rate, feelings of excessive warmth, profues sweating, palpitations, weight loss and protruding eyes |
| Goiter | - a bulge in the neck due to thyroid enlargement - due to hypo and hyperthyroidism |
| Calcitonin | - decreases plasma Ca²⁺ concentration by inhibiting the relsease of Ca²⁺ from bone - secretion is regulated by plasma Ca²⁺ levels |
| Parathyroid Glands | - are four small pea-shaped structures embedded in the posterior surface of the thyroid - synthesize and secrete parathyroid hormone (PTH) |
| Parathyroid Hormone (PTH) | - together with calcitonin and vitamin D, regulates plasma Ca²⁺ concentration - plasma Ca²⁺ concentration regulates PTH too through negative feedback mechanism - PTH raises Ca²⁺ concentration in the blood by stimulating Ca²⁺ release from bone and decrease Ca²⁺ excretion in the kidneys - PTH converts vitamin D into its active form, which stimulates intestinal calcium absorption |
| Hormones affecting Ca²⁺ | - PTH increases Ca²⁺ - calcitonin decreases Ca²⁺ (calciTONIN tones down Ca²⁺) |
| Adrenal Glands | - are located on top of the kidneys - consists of the adrenal cortex and adrenal medulla |
| Adrenal Cortex | - stimulated by ACTH - synthesize and secrete steroid hormones known as corticosteroids |
| Corticosteroids | - derived from cholesterol - produced in adrenal cortex - include: a) glucocorticoids b) mineralocorticoids c) cortical sex hormones |
| Glucocorticoids | - a type of corticosteroids - includes cortisol and cortisone - are involved in glucose regulation and protein metabolism - raise blood glucose levels by promoting gluconeogenesis and decrease protein synthesis - reduce body's immunological and inflammatory responses - cortisol secretion is governed by a negative feedback mechanism |
| Mineralocorticoids | - a type of corticosteroids - ex: aldosterone - regulate plasma levels of sodium and postassium - regulate total extracellular water volume |
| Aldosterone | - causes active reabsorption of sodium and passive reabsorption of water in the nephron - this results in a rise in blood volume and blood pressure - stimulates the secretion of potassium ion and hydrogen ion into the nephron and later excretion in urine - secretion is regulated by renin-angiotensin system |
| Aldosterone Regulated by Renin-Angiotensin System | - when blood volume falls, juxtaglomerular cells of the kidney produce renin - renin converts the plasma protein angiotensinogen to angiotensin I - angiotensin I is converted to angiotensin II, which stimulates the adrenal cortex to secrete aldosterone - aldosterone helps restore blood volume by increasing sodium reabsorption at the kidney, which increase water reabsorption - this removes the initial need for renin production |
| Renin | - an enzyme - converts the plasma protein angiotensinogen to angiotensin I |
| Cortical Sex Hormones | - the adrenal cortex secretes small amount of androgens (male sex hormones) in both males and females - in males most of the androgens are produced by the testes, so cortical androgen has minimal effect - in females, overproduction of the adrenal androgens may have masculinizing effects (like excessive facial hair) |
| Adrenal Medulla | - produces epinephrine (adrenaline) and norepinephrine ( noradrenaline) - both hormones belong to a class of amino acid derived compounds called catecholamines - both hormones are also neurotransmitters |
| Flight or Flight Response | - elicited by sympathetic nervous system in due to stress - epinephrine increases the conversion of glycogen to glucose in liver and muscle tissue, causing a rise in blood glucose levels and an increase in the basal metabolic rate - both epi and norepinephrine increase the rate and strength of the heartbeat and dilate and constrict blood vessels - increase the blood supply to skeletal muscle, heart, brain - decrease blood supply to the kidneys, skin and digestive tract |
| Pancreas | - is both an exocrine and an endocrine organ - exocrine function is performed by the cells that secrete digestive enzymes into the small intestine via a series of ducts - endocrine function is performed by the islets of Langerhans - produce glucagon, insulin, somatostatin |
| Islets of Langerhans | - small, glandular structues - composed of alpha, beta and delta cells - alpha cells produce and secrete glucagon - beta cells produce and secrete insulin - delta cells produce and secrete somatostatin |
| Glucagon | - function: a) stimulates protein and fat degradation b) convert glycogen to glucose c) gluconeogenesis - all the above increase blood glucose levels - glucagon secretion is stimulated by a decrease in blood glucose and by gastrointestinal hormones (CCK and gastrin) - is inhibited by high plasma glucose levels - actions are largely antagonistic to insulin's actions |
| Insulin | - is a protein hormone secreted in response to a high blood glucose concentration - stimulates the uptake of glucose by muscle and adipose cells - stimulates storage of glucose as glycogen in muscle and liver cells, thus lowering glucose level in the blood - stimulates synthesis of fats from glucose - stimulates uptake of amino acids - actions are antagonistic from glucagon and glucocorticoids - regulated by blood glucose levels |
| Hypoglycemia | - low blood glucose levels |
| Hyperglycemia | - high blood glucose levels - leads to excretion of glucose and water loss - underproduction or insensitivity of insulin leads to diabetes mellitus |
| Diabetes Mellitus | - underproduction or insensitivity of insulin - is associated with weakness and fatigue - may lead to ketoacidosis |
| Ketoacidosis | - a dangerous lowering of blood pH due to excess keto acids and fatty acids in the plasma |
| Somatostatin | - secretion is increased by high blood gluose or high amino acid levels - this leads to decreased insulin and glucagon secretion - is regulated by CCK and GH levels - is always inhibitory regardless of where it acts |
| Plasma Glucose Synopsis | - insulin decreases plasma glucose - glucagon increases plasma glucose - groth hormone, glucocorticoids and epinephrine are also capable of increasing plasma glucose |
| Testes | - intersitital cells produce and secrete androgens (testosterone) |
| Testosterone | - induces embryonic sexual differentiation and male sexual development at puberty - maintains secondary sex characteristics - secretion is controlled by a negative feedback mechanism involving FSH and LH - insensitivity to testosterone results in testicular feminization |
| Testicular Feminization | - insensitivity to testosterone - a genetic mall (XY) has female secondary sexual characteristics |
| Ovaries | - synthesize and secrete estrogens + progesterone - the secretion of these hormones is regulated by LH and FSH, which in turn are regulated by GnRH |
| Estrogens | - are steroid hormones necessary for normal female maturation - secreted by the ovarian follicles and the corpus luteum - stimulate development of female reproductive tract - contribute to the development of secondary sexual characteristics and sex drive - responsible for the thickening of the endometrium (uterine wall) |
| Progesterone | - is a steroid hormone secreted by the corpus luteum during the luteal phase of the menstrual cycle - stimulates the development and the maintainance of the endometrial walls in preparation for implantation |
| The Menstrual Cycle | - the hormones secreted by the ovaries, the hypothalamus and the pituitary play important roles in the female reproductive cycle - menstrual cycle can be divided into the follicular phase, ovulation, the luteal phase and menstruation |
| Follicular Phase | - begins with the cessation of the menstrual flow from previous cycle - FSH and LH act together to promote the development of several ovarian follicles, which grown and begin secreting estrogen - rising levels of estrogen in the latter half of this phase stimulate GnRH secretion, which in turn further stimulates LH secretion |
| Ovulation | - a mature ovarian follicle bursts and releases and ovum - occurs midway through the cycle - is caused by a surge in LH which is preceded by and in part caused by a peak in estrogen levels |
| Luteal Phase | - after ovulation, LH icause the ruptured follicle to develop into the corpus luteum, which secretes estrogen and progesterone - progesterone causes the glands of the endometrium to mature and produce secretions that prepare it for the implantation of an embryo - progesterone and estrogen are essential for the maintenance of endometrium - progesterone and estrogen together inhibit secretion of GnRH, there foe inhibiting LH and FSH secretion - this prevents the maturation of additional follicles during the remainder of the cycle |
| Menstruation | - if the ovum isn't fertilized, the corpus luteum atrophies - progesterone and esterogen levels drop - this cause endometrium to slough off - progesterone and estrogen levels decline and GnRH is no longer inhibited - GnRH re-stimulates LH and FSH secretion, so the cycle begins anew - if ovum is fertilized, menstruation ceases for the duration of the pregnancy |
| Pregancy | - during the first trimester, the corpus luteum is preserved by human chorionic gonadotropin - progesterone and estrogen secretion by the corpus luteum is maintained during the first trimester - during the second trimester, HCG decline, but progesterone and estrogen levels rise because they're now secreted by the placenta itself - high levels of progesterone and estrogen inhibit GnRH secretion, thus preventing FSH and LH secretion and the onset of a new menstrual cycle |
| Human Chorionic Gonadotropin (HCG) | - is a hormone produced by the blastocysts and the developing placenta - urine pregnancy tests are designed to test for the presence of HCG in the urine - HCG can be detected in the urine one to two weeks after conception |
| Menopause | - is the period in a woman's life (age 45-55) when menstruation first becomes irregular and eventually stops - is the result of a progressive decline decline in the functioning of the ovaries with advancing age - some follicles fail to rupture, ovulation doesn't occur and less estrogen is produced by the ovaries - hormonal regulation of other glands is disrupted - symptoms: bloating, hot flashes and headaches |
| Pineal Gland | - is a tiny structure at the base of the brain - secretes the hormone melatonin |
| Melatonin | - role is unclear, but it's believed to play a role in the regulation of circadian rhythms - secretion is regulated by light and dark cycles in the environment |
| Circadian Rhythms | - physiological cycles lasting 24 hours |
| Other Endocrine Organs | a) stomach and intestines b) kidneys c) heart and brain d) thymus gland |
| Other Endocrine Organs: Stomach and Intestines | - glandular tissue is found throughout the mucosa of the stomach and intestines - primary stimulus for gastrointestinal hormone release is the presence of food in the gut (neural input and exposure to other hormones affect release too) - over 20 gastrointestinal peptides are known - important examples: gastrin, secretin & CCK |
| Other Endocrine Organs: Kidneys | - primary function is urine formation - secrete renin and erthropoietin |
| Renin | - an enzyme secreted by the kidney - is involved in the regulation of aldosterone secretion |
| Erythropoietin | - secreted by the kidney - secreted in response to decreased renal oxygen levels - stimulates bone marrow to produce red blood cells - patients with chronic kidney disease can become anemic due to impaired erythropoietin production, causing inadequate red cell production from the bone marrow - this can be fixed with genetically engineered erythropoietin to stimulate bone marrow to produce more red blood cells |
| Other Endocrine Organs: Heart and Brain | - release atrial natriuretic hormone (ANH) and brain natriuretic peptide (BNP) from heart and brain respectively - both are involved in the regulation of salt and water balance |
| Other Endocrine Organs: Thymus Gland | - is located in the front neck region - secretes hormones like thymosin during childhood - atrophies by adulthood, after the immune system has fully developed |
| Thymosin | - secreted by the thymus gland - stimulates T lymphocyte development and differentiation |
| Types of Hormones | - hormones are classified on the basis of their chemical structure a) peptide hormones b) steroid hormones c) amino acid-derived hormones |
| Two ways hormones affect the activities of their target cells | a) via extracellular receptors b) via intracellular receptors |
| Peptides: Secondary Messenger | - range from simple short peptides (amino acid chains, such as ADH) to complex polypeptides such as insulin - act as first messengers - bind to sepcific receptors on the surface of target cells - this triggers a series of enzymatic reactions within each cell |
| Peptides: Synthesis | - begins with the synthesis of a large polypeptide - it's cleaved int o smaller protein units - transported to the golgi apparatus where it's modified to the active hormone - then it's packaged into secretory vesicles and stored until it's released by the cell through exocytosis |
| Peptides: Triggering of Enzymatic Reactions | - conversion of ATP to cyclic adenosine monophosphate (cAMP) - this reaction is catalyzed by the membrane-bound enzyme adenylate cyclase - cyclic AMP acts as a second messenger, relaying messages from extracellular peptide hormone to cytoplasmic enzymes & initiating a series of successive reactions in the cell. - this is an example of a cascade effect - cyclic AMP activity is inactivated by the cytoplasmic enzyme phosphodiesterase |
| Cascade Effect | - with each step, the hormone's effects are amplified |
| Steroids: Primary Messenger | - ex: estrogen and aldosterone - belongs to a class of lipid-dervied molecules iwth a characteristic ring structure - are produced by testes, ovaries, placenta and adrenal cortex - precursors already present in the cell during synthesis, undergo enzymatic reaction to convert to active hormones - pass through cell membrane with ease because they're lipid-soluable - not stored, but are secreted at a rate determined by their rate of synthesis |
| Steroids: Primary Messenger (continued) | - enter target cells directly - bind to specific receptor proteins in the cytoplasm - this receptor-hormone complex enters the nucleus & directly activates the expression of specific genes by binding to receptors on the chromatin - this induces a change in mRNA transcription and protein synthesis |
| Amino Acid Derivatives | - are hormones composed of one or two modified amino acids - are synthesized in the cytoplasm of glandular cells - some are further modified & stored in granules until the cell is stimulated to release them - others are initially synthesized as component parts of larger molecules and stored - some like epinephrine activate their target cells as peptide hormones do (via second messengers) - others like thyroxine act like steroid hormones, entering the nucleus of target cells & regulating gene expression |
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