Endocrine System Pt.2 Flashcards
Thyroid gland is composed of…
-isthmus
-composed of follicles that produce glycoprotein thyroglobulin
-colloid (fluid with thyroglobulin + iodine) fills lumen of follicles and is precursor for TH
-parafollicular cells produce hormone calcitonin
Isthmus
2 lateral lobes connected by median mass
Thyroid hormone (TH) includes
Thyroxine (T4) and triiodothyronine (T3) which increase rate of cellular metabolism. Consequently, oxygen use and heat production rise
Effects of T3 and T4 on basal metabolic rate (BMR)/ temp. Regulation
Normal: promotes normal o2 use and BMR; calorigenesis; enhances effects of SNS
Hypo: BMR below normal; decreases body temp, cold intolerance; decreases appetite; weight gain; reduced sensitivity to catecholamine
Hyper: BMR above normal; increased body temp., heat intolerance; increased appetite; weight loss
Effects of T4 and T3 on carb/lipid/protein metabolism
Normal: promotes glucose catabolism; mobilizes fats: essential for protein synthesis: enhances liver’s synthesis of cholesterol
Hypo: decreases glucose metabolism; elevated cholesterol/triglyceride levels in blood; decreases protein synthesis; edema
Hyper: enhanced catabolism of glucose, proteins, and fats; weight loss; loss of muscle mass
Effects of T4 and T3 on NS
Normal: promotes normal development of NS in fetus and infant; promotes normal adult NS production
Hypo: in infant, slowed/deficient brain development, intellectual disability; in adults, mental dulling, depression, paresthesias, memory impairment, hypoactive reflexes
Hyper: irritability, restlessness, insomnia, personality changes exophthalmos (in Graves’ disease)
Effects of T4 and T3 on NS
Normal: promotes normal development of NS in fetus and infant; promotes normal adult NS production
Hypo: in infant, slowed/deficient brain development, intellectual disability; in adults, mental dulling, depression, paresthesias, memory impairment, hypoactive reflexes
Hyper: irritability, restlessness, insomnia, personality changes exophthalmos (in Graves’ disease)
Thyroid Hormone (TH)
-2 related compounds:
-T4 (thyroxine); has 3 tyrosine molecules + 4 bound iodine atoms
-T3 (triiodothyronine), has 2 tyrosines + 3 bound iodine atoms
-major metabolic hormone
-increases metabolic rate and heat production (calorigenic effect)
-regulation of tissue growth and development:
-development of skeletal and NS
-Reproductive capabilities
-maintenance of blood pressure
Effects of T4 and T3 on ❤️ system
Normal: promotes normal functioning of the ❤️
Hypo: decreased efficiency of ❤️s pumping action; low ❤️ rate and blood pressure
Hyper: increased sensitivity to catecholamines can lead to rapid ❤️ rate, palpitations, high blood pressure, and ❤️ failure
Synthesis of TH
-thyroid gland stores hormone extra cellularly
-thyroidglobulin synthesizedand discharged into follicle lumen
-iodides (I-) actively taken into cell and released into lumen
-iodides oxidized to iodine (I2)
-iodine attaches to tyrosine, mediated by perioxidase
-iodinated tyrosines link together to form T3 and T4
-colloid is endocystosed and vesicle is combined with a lysosome
-T3 and T4 are cleaved and diffused into bloodstream
Effects of T4 and T3 on muscular system
Normal: promotes normal muscular development and function
Hypo: sluggish muscle action; muscle cramps; myalgia
Hyper: muscle atrophy and weakness
Transport and regulation of TH
-T4 and T3 transported in the body by thyroxine-binding globulins (TBGs)
-both bind to target receptors, but T3 is 10x more active than T4
-peripheral tissues convert T4 to T3
-(-) feedback regulation of TH:
-rising TH levels provide (-) feedback inhibition on release of TSH
-hypothalamic thyrotropin-releasing hormone (TRH) can overcome (-) feedback during pregnancy or exposure to cold
Effects of T4 and T3 on Skeletal system
Normal: promotes normal growth and maturation of skeleton
Hypo: in child, growth retardation, skeletal stunting and retention of child’s body proportions; in adults: joint pain
Hyper: in child: excessive skeletal growth, initially, followed by early epiphyseal closure and short stature; in adult: demineralization of skeleton
Homeostatic imbalances of TH
-Hypo in adults:
-pts are cold, fatigued and overweight
-myxedema; goiter if due to lack of iodine
-hashimotos- TSH receptor is blacked by abnormal antibody
-hypo in infants- cretinism
-hyper- graves:
-underweight, hot, anxious with voracious appetite
-exophthalmos
-can have goiter
-can be caused by abnormal antibody (long acting thyroid stimulator; LATS)
-also promotes excessive thyroid growth by binding to TSH receptor
Effects of T4 and T3 in GI system
Normal: promotes normal GI motility and tone; increases secretion of digestive juices
Hypo: depressed GI motility, tone, and secretory activity; constipation
Hyper: excessive GI motility; diarrhea
Effects of T4 and T3 in GI system
Normal: promotes normal GI motility and tone; increases secretion of digestive juices
Hypo: depressed GI motility, tone, and secretory activity; constipation
Hyper: excessive GI motility; diarrhea
Calcitonin
-produced by parafollicular (c) cells
-no known physiological role in humans
-antagonist to parathyroid hormone (PTH)
-at higher than normal doses:
-inhibits osteoclast activity and release of Ca2+ from bone matrix
-stimulates Ca2+ uptake and incorporation into bone matrix
Calcitonin
-produced by parafollicular (c) cells
-no known physiological role in humans
-antagonist to parathyroid hormone (PTH)
-at higher than normal doses:
-inhibits osteoclast activity and release of Ca2+ from bone matrix
-stimulates Ca2+ uptake and incorporation into bone matrix
Effects of T4 and T3 on. Reproductive system
Normal: promotes normal female reproductive ability and lactation
Hypo: depressed ovarian function: sterility; depressed lactation
Hyper: in females: depressed ovarian function; in males; impotence
Effects of T4 and T3 on integumentary system
Normal: promotes normal hydration and secretory activity of skin
Hypo: skin pale, thick, and dry; facial edema; hair coarse and thick
Hyper: skin flushed, this, and moist; hair fine and soft; nails soft and thin
Parathyroid glands
-4-8 tiny glands embedded in posterior aspect of thyroid
-Contain oxyphil cells (function unknown) and parathyroid cells that secrete parathyroid hormone (PTH) or parathormone
-PTH—most important hormone in Ca2+ homeostasis
Secretion of thyroid hormone, promoted by TSH, requires…
Follicular cells to take up the stored colloid and split the hormones from the colloid for release. Rising levels of TH feedback to inhibit the anterior pituitary and hypothalamus
Parathyroid hormone
Functions
• Stimulates osteoclasts to digest bone matrix and release Ca2+ to:
-Enhances reabsorption of Ca2+ and secretion of phosphate by kidneys
-Promotes activation of vitamin D (by kidneys); increases absorption of Ca2+ by intestinal mucosa
• Negative feedback control: rising Ca2+ in blood inhibits PTH release
Homeostatic imbalances of PTH
-Must regulate Ca2+ levels very closely
-Hyperparathyroidism due to tumor
-Bones soften and deform
-Elevated Ca2+ depresses nervous system and contributes to formation of kidney stones
-Hypoparathyroidism following gland trauma or removal or dietary magnesium deficiency
-Results in tetany, respiratory paralysis
What is the difference between T3 and T4? Which one of these is referred to as thyroxine?
T4 has 4 bound iodine atoms, and T3 has 3. T4 is the major hormone secreted, but T3 is more potent. T4=thyroxine
Why does TH require plasma proteins in order to move through blood? Where are the receptors for TSH located?
TH must be carried through🩸by plasma proteins b/c it is lipid soluble and so does not readily dissolve in 🩸, which is mostly💧. The receptors for TSH are located on plasma membrane of the thyroid follicle cells (on the sides facing away from colloid- TSH is 💧-soluble hormone from anterior pituitary)
Adrenal (suprarenal) glands
-Paired, pyramid-shaped organs atop kidneys
-Structurally and functionally are two glands in one
-Adrenal medulla—nervous tissue; part of sympathetic nervous system
-Adrenal cortex—three layers of glandular tissue that synthesize and secrete corticosteroids
Parathyroid glands
-Located on dorsal aspect of thyroid gland
-secrete PTH- increases 🩸calcium levels
-targets bone, kidneys, and small intestine (indirectly via Vit D activation)
-PTH= key hormone for calcium homeostasis
Adrenal cortex
-Three layers and corticosteroids produced
1) Zona glomerulosa—mineralocorticoids
2) Zona fasciculata—glucocorticoids
3) Zona reticularis—gonadocorticoids
PTH release and inhibit
Falling 🩸calcium levels trigger PTH release; rising 🩸 calcium levels inhibit its release
Mineralocorticoids
-Regulate electrolytes (primarily Na+ and K+) in ECF
-Importance of Na+: affects ECF volume, blood volume, blood pressure, levels of other ions
-Importance of K+: sets RMP
-Aldosterone most potent mineralocorticoid
-Stimulates Na+ reabsorption and water retention by kidneys; elimination of K+
-Increases blood volume
-Increases blood Na+
-Decreases blood K+
Hyperparathyroidism results in…
Hypercalcemia and extreme bone wasting
Hypoparathyroidism leads to…
Hypocalcemia, evidenced by tetany and respiratory paralysis
Aldosterone
Release triggered by:
• Decreasing blood volume and blood pressure
• Rising blood levels of K+
Paired adrenal (suprarenal) glands
Sit atop the kidneys. Each adrenal gland has 2 functional portions, the cortex and medulla
Indicated general functions of parathyroid hormone
-raises 🩸 calcium
-stimulates release of calcium from bones
-indirectly increases activity of AND # of osteoclasts
-stimulates reabsorption of calcium by kidneys
-stimulates final conversion of vit d in kidneys
-calcidiol into calcitriol
-calcitriol aids calcium absorption in small intestines
-decreases 🩸 phosphate
-stimulates release of phosphate from bones and absorption of phosphate in the gut
-stimulates secretion of phosphate by kidneys
-amount secreted by kidneys exceeds the amount being released/reabsorbed, leading to OVERALL decrease in 🩸 phosphate levels
Mechanisms of aldosterone secretion
Renin-angiotensin-aldosterone mechanism: decreased blood pressure stimulates kidneys to release renin, triggers formation of angiotensin II, potent stimulator of aldosterone release
• Plasma concentration of K+: increased K+ directly influences zona glomerulosa cells to release aldosterone
• ACTH: causes small increases of aldosterone during short-term stress
• Atrial natriuretic peptide (ANP): blocks renin and aldosterone secretion to decrease BP
What is the major effect of TH? PTH? Calcitonin?
TH: increase basal metabolic rate (and heat production) in the body.
PTH: increases 🩸 Ca2+ levels in variety of ways
Calcitonin at high levels (pharmacological) has Ca2+- lowering, bone-sparing effects (at normal levels, no effects on humans)
Homeostatic imbalances of aldosterone
Aldosteronism—hypersecretion due to adrenal tumors
• Hypertension and edema due to excessive Na+
• Excretion of K+ leading to abnormal function of neurons and muscle
Name the cells that release TH, PTH, and calcitonin?
-thyroid follicular cells release TH
-parathyroid cells in parathyroid gland release PTH
-parafollicular (C) cells in the thyroid gland release calcitonin
Glucocorticoids
-Keep blood glucose levels relatively constant
-Maintain blood pressure by increasing action of vasoconstrictors
-Cortisol (hydrocortisone)
-Cortisone
-Corticosterone
-Normal levels maintained by negative feedback
Glucocorticoids
-Keep blood glucose levels relatively constant
-Maintain blood pressure by increasing action of vasoconstrictors
-Cortisol (hydrocortisone)
-Cortisone
-Corticosterone
-Normal levels maintained by negative feedback
List hormones produced by adrenal gland and their physiological effects
Aldosterone- helps kidneys control their amount of salt in the 🩸 and tissues in the body
Cortisol- helps the body manage and use carbs, proteins, and fats.
Adrenaline
List the 3 classes of hormones released from the adrenal cortex and briefly state the major effects of each?-
Glucocorticoids are stress hormones that, among many effects, increase 🩸 glucose.
Mineralocortoids increase 🩸 Na+ (and 🩸 pressure) and decrease 🩸 K+
Gonadcorticoids are male and female sex hormones that are thought to have a variety of effects
Glucocorticoids: cortisol
Released in response to ACTH, patterns of eating and activity, and stress
• Prime metabolic effect is gluconeogenesis—formation of glucose from fats and proteins
-Promotes rises in blood glucose, fatty acids, and amino acids
• “Saves” glucose for brain
• Enhances vasoconstriction à rise in blood pressure to quickly distribute nutrients to cells
• Powerful anti-inflammatory – reduces effects of histamine
• Suppresses the immune system – reduces the activity of T and B cells
• Inhibits healing
• Alters mood
• Increases appetite
Mineralocortoids (chiefly aldosterone) regulation of release
Stimulates by renin-angiotensin-aldosterone mechanism (activated by decreasing 🩸volume or 🩸 pressure), elevated 🩸 K+ levels, and ACTH (minor influence)
Mineralocortoids (chiefly aldosterone/ adrenocortical hormones) regulation of release
Stimulates by renin-angiotensin-aldosterone mechanism (activated by decreasing 🩸volume or 🩸 pressure), elevated 🩸 K+ levels, and ACTH (minor influence)
Inhibited by increasing 🩸 pressure, decreases 🩸 K+ levels
Homeostatic imbalances of glucocorticoids
-Hypersecretion—Cushing’s syndrome/disease
-Depresses cartilage and bone formation
-Inhibits inflammation
-Depresses immune system
-Disrupts cardiovascular, neural, and gastrointestinal
-Fat redistribution
-Buffalo hump
-Hyposecretion—Addison’s disease
-Decrease in glucose and Na+ levels
-Difficulty handling chronic stress
-Extreme fatigue
-Weight loss
-Hyperpigmentation
-Also involves deficits in mineralocorticoids
-Decreased Na+ levels
-Severe dehydration, and hypotension
Homeostatic imbalances of glucocorticoids
-Hypersecretion—Cushing’s syndrome/disease
-Depresses cartilage and bone formation
-Inhibits inflammation
-Depresses immune system
-Disrupts cardiovascular, neural, and gastrointestinal
-Fat redistribution
-Buffalo hump
-Hyposecretion—Addison’s disease
-Decrease in glucose and Na+ levels
-Difficulty handling chronic stress
-Extreme fatigue
-Weight loss
-Hyperpigmentation
-Also involves deficits in mineralocorticoids
-Decreased Na+ levels
-Severe dehydration, and hypotension
Mineralcorticoids target organ and effects
Kidneys: increase 🩸 levels of Na+ and b decrease 🩸 levels of K+
Since 💧 reabsorption usually accompanies sodium retention, 🩸 volume and 🩸 pressure rise
Gonadocorticoids (Sex Hormones)
-Most weak androgens (male sex hormones) converted to testosterone in tissue cells, some to estrogens
-May contribute to:
-Onset of puberty
-Appearance of secondary sex characteristics
-Sex drive in women
Gonadocorticoids (Sex Hormones)
-Most weak androgens (male sex hormones) converted to testosterone in tissue cells, some to estrogens
-May contribute to:
-Onset of puberty
-Appearance of secondary sex characteristics
-Sex drive in women
Mineralocorticoids effects of hyper and hypo secretion
Hyper: aldosteronism
Hypo: Addison’s disease