Endocrinology

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1

endocrinology

study of hormones and disorders of these hormones

2

endocrine system

hypothalamus and pituitary, thyroid and parathyroid, kidney, adrenals, gonads: ovaries and testicles, and Islets of Langerhans

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hormone

any substance normally produced by specialized cells in some part of the body, carried by the blood stream to another part, where it effects the body as a whole; vehicles for intracellular and extracellular communication

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hormone characteristics

specificity, multiple actions, variable forms, excretion rates

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specificity

hormones only target specific cells for response

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variable half-life

dependent on the weight of the hormone

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excretion rates

diurnal variation, cyclic patterns, and stimulus response of hormone

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hormone functions

maintain homeostasis, regulate growth and development, promote sexual maturation, sexual rhythms and facilitate reproduction, regulate energy production, adapt and adjust body to stressful and emergency situations, and promote and inhibit production or release or other hormones

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peptides and proteins

polypeptides or glycoproteins, soluble in plasma, interact with target cell membrane receptors to trigger a second messenger to complete the specific action of the hormone; short term effects

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amines

amino acid derivatives, poorly soluble in plasma, interact with membrane receptors of target cells, and provide long and short term effects

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steroids

composed of lipids (cholesterol), can transverse through the cell membrane; produced by ovaries, testis, placenta, and adrenal cortex; insoluble in water; long-lasting

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tropic

originate from anterior pituitary gland; specific for another endocrine gland

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non-tropic or direct effector

secreted by non-pituitary endocrine glands; act directly on peripheral tissue; exert a feedback effect on the hypothalamus or anterior pituitary gland

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hormone receptors

located on cell membrane or within cell cytoplasm; binding of hormone to receptor initiates a signal; results in changes in gene expression; ultimately causes a biological response

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negative feedback control

an increase in the product causes a decrease in the system; serves to stabilize a process; primary means of hormone regulation

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positive feedback control

an increase in the product causes an increase in the activity of the system

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regulation and control

occurs by controlling the rate of synthesis rather than the rate of degradation

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hypothalamus

the primary control; small gland next to pituitary gland connected to the pituitary by the pituitary stalk

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pituitary gland

releases both tropic and effector hormones

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thyrotropin releasing hormone

releases TSH and prolactin

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gonadotropin releasing hormone

releases LH and FSH

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corticotropin releasing hormone

releases ACTH

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growth hormone releasing hormone

releases GH

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somatostatin

inhibits GH and TSH release

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dopamine

inhibits prolactin release

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oxytocin

promotes uterine contraction and milk let down released in posterior pituitary

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anti-diuretic hormone

affects water volume

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anterior pituitary (adenohypophysis)

hormones which target other endocrine glands; forms the lactotrophs, somatotropin, throtrophs, corticotrophins and gonadotrophs

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intermediate lobe (pars intermedialis)

little functional capacity

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posterior pituitary (neurohypophysis)

stores and releases oxytocin and vasopressin (ADH)

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luteinizing hormone (LH)

targets gonads: ovaries, testes; tropic; sex steroid feedback; regulates ovulation, testosterone production

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follicle stimulating hormone (FSH)

targets ovary; tropic; inhibin feedback; regulates ovarian recruitment

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thyroid stimulating hormone (TSH)

targets thyroid; tropic; thyroid hormone feedback (T4/T3); stimulates thyroid hormone production

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adrenocorticotropin hormone (ACTH)

targets adrenal cortex; tropic; cortisol feedback; stimulates synthesis and secretion of glucocorticoid hormones

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growth hormone (somatotropin)

targets multiple glands; peptide with direct effector; insulin-like growth factor feedback; stimulates tissue growth; amphibolic

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prolactin

targets breasts; direct effector; unknown feedback hormone; functions in secretion

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amphibolic

influences both anabolic and catabolic processes

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growth hormone

allows effective transition from fed to fasting state without substrate shortage; directly antagonizes insulin effects on glucose metabolism; provides hepatic gluconeogenesis; stimulates lipolysis; enhances protein synthesis in skeletal muscle and other tissues; stimulates production of insulin-like growth factors

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growth hormone stimulators

meals, exercise, sleep, and hypoglycemia

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growth hormone inhibitors

glucose loading, epinephrine, emotional and psychogenic stress, nutritional deficiencies, and insulin deficiency

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growth hormone testing

based on dynamic physiology of growth hormone axis; testing for autonomous production of growth hormone relies on normal suppression of growth hormone by oral glucose loading

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GH stimulation

insulin-induced hypoglycemia (outdated method); combination infusions of GHRH and amino acid L-arginine; infusion of L-arginine coupled with oral L-DOPA

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acromegaly

results from pathologic or autonomous growth hormone excess; usually caused by a pituitary tumor; causes gigantism, bony and soft tissue overgrowth, progressive enlargement of hands, feet, mandible, and skill, arthritis, diabetes, hypertension, atherosclerosis, muscle weakness, sleep apnea, and shortened life expectancy; greater risk of developing cancer

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growth hormone deficiency

occurs in both children and adults; genetic or tumor caused with growth failure in children or result of structural or functional pituitary abnormalities in adults; recessive mutation in GHRH gene, failure of GH secretion, loss of GH gene, GH insensitivity, and structural lesions of pituitary or hypothalamus

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prolactin

functions in relation to reproduction, breast growth during pregnancy, milk secretion, direct effector, stimulated by thyrotropin-releasing hormone; inhibited by dopamine

46

posterior pituitary

does not synthesize hormones; stores and releases hormones made by the hypothalamus to be transported along the hypothalamohypophyseal tract; oxytocin and antidiuretic hormone or vasopressin

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oxytocin

released from posterior pituitaryfunctions in lactation stimulating milk let down and stimulating smooth muscle in the uterus; synthetic is Pitocin used to induce or enhance labor contractions

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ADH/ vasopressin

regulates water excretion in the renal tubules where the receptors are found; assists in water balance; hypothalamic osmoreceptors and vascular basoceptors regulate release from posterior pituitary

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ADH deficiency

hormone imbalance of diabetes insipidus with symptoms of >2.5L per day urinary output, excessive thirst, and dehydration

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water deprivation test

monitors ADH and urine osmolality levels

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syndrome of inappropriate antidiuretic hormone secretion (SIADH)

increased ADH with low plasma osmolality levels; urine Na increases, plasma Na decreases

52

hypopituitarism

failure of either pituitary or hypothalamus results in loss of anterior pituitary function; associated with low or normal levels of tropic hormone; both tropic and target hormone levels should be measured under suspicion of pituitary failure; if one secondary deficiency is documented, other deficiency states and cause of pituitary failure must be found

53

panhypopituitarism

complete loss of function

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mono tropic hormone deficiency

loss of only a single hormone