Endocrine - Physiology Flashcards
What does this hypothalamic hormone induces/inhibits: TRH
+ TSH, prolactin
What does this hypothalamic hormone induces/inhibits: Dopamine
- Prolactin
What does this hypothalamic hormone induces/inhibits: CRH
+ ACTH, MSH, beta-endorphin
What does this hypothalamic hormone induces/inhibits: GHRH
+ GH
What does this hypothalamic hormone induces/inhibits: Somatostatin
- GH, TSH
What does this hypothalamic hormone induces/inhibits: GnRH
+ FSH, LH
What does this hypothalamic hormone induces/inhibits: Prolactin
- GnRH
Describe prolactin regulation
Prolactin is tonically inhibited by dopamine from hypothalamus
It inhibits own secretion by increasing dopamine synthesis and secretion
TRH also increases prolactin secretion
Function of Prolactin (2)
- Stimulates milk production in breast
2. Inhibits ovulation/spermatogenesis by inhibiting GnRH synthesis and release
What pharmacological substances can promote or inhibit prolactin secretion?
Inhibit prolactin: dopamine agonist (bromocriptine)
Promote prolactin: dopamine antagonists (most antipsychotics), estrogens (OCPs, pregnancy) stimulate prolactin secretion
Functions of growth hormone (2)
- Stimulates linear growth and muscle mass through IGF1/somatomedin secretion
- increases insulin resistance (diabetogenic)
Regulation of growth hormone. What promotes or inhibits secretion?
Released in pulses in response to GHRH
Promoted by exercise, sleep
Inhibited by glucose, somatostatin
In the first step of adrenal steroids, what is cholesterol converted to, facilitated by what enzyme?
Cholesterol to Pregnenolone
by Desmolase
What can promote or inhibit desmolase activity?
ACTH +
Ketoconazole -
Function of 17alpha-hydroxylase
- Pregnenolone -> 17-hydroxypregnenolone
2. Progesterone -> 17-hydroxyprogesterone
Function of 3beta-hydroxysteroid dehydrogenase
- Pregnenolone -> Progesterone
- 17-hydroxypregnenolone -> 17-hydroxyprogesterone
- DHEA -> Androstenedione
Function of 21-hydroxylase
- Progesterone -> 11-deoxycorticosterone
2. 17-hydroxyprogesterone -> 11-deoxycortisol
Function of 11beta-hydroxylase
- 11-deoxycorticosterone -> Corticosterone
2. 11-deoxycortisol -> Cortisol
Function of aromatase
- Androstenedione -> estrone
2. Testosterone -> estradiol
Function of 5alpha-reductase
Testosterone -> DHT
Function of Aldosterone synthase
Corticosterone -> Aldosterone
Activated by Angiotensin II
Describe level adrenal steroids in: 17alpha-hydroxylase deficiency
Mineralcorticoid: High
Cortisol: Low
Sex hormone: Low
Presentation: hypertension, hypokalemia
XY: pseudohermaphroditism (low DHT)
XX: lacks secondary sex characteristics
Describe level adrenal steroids in: 21-hydroxylase deficiency
Mineralcorticoid: Low
Cortisol: Low
Sex hormone: High
Presentation: hypotension, hyperkalemia, high renin, volume depletion
Masculinization; pseudohermaphroditism in females
Describe level adrenal steroids in: 11beta-hydroxylase deficiency
Mineralcorticoid: High (11-deoxycorticosterone)
Cortisol: Low
Sex hormone: High
Presentation: Masculinization
Why do all congenital adrenal enzme deficiencies have enlargement of both adrenal glands?
Increased ACTH from low cortisol
What is cortisol bound to?
Corticosteroid-binding globulin (CBG)
Functions of cortisol (6)
- maintains blood pressure (upregulates alpha1-receptors on arterioles which increases sensitivity to NE/E)
- decreases bone formation
- anti-inflammatory/immunosuppressive
- increases insulin resistance (diabetogenic)
- Increases gluconeogensis, lipolysis, proteolysis (during stress)
- inhibits fibroblasts (causes striae)
What is impact of chronic stress on HPA axis?
Prolonged secretion
Describe cortisol regulation
CRH (hypothalamus) stimulates ACTH release (pituitary), causing cortisol production in adrenal zona fasciculata.
Excess cortisol suppresses CRH, ACTH and cortisol secretion
Cortisol effects on the immune system (5)
- Inhibits production of leukotrienes/prostaglandins
- inhibits leukocyte adhesion (neutrophilia)
- blocks histamine release from mast cells
- reduces eosinophils
- blocks IL-2 production
Source of PTH
Chief cells in parathyroid
Functions of PTH (4)
- Increases bone resorption of calcium and phosphate
- increase kidney reabsorption of calcium in distal convoluted tubule
- decrease reabsorption of phosphate in proximal convoluted tubule
- increase 1alpha-hydroxylase activity in kidney (increases 1,25-(OH)2 D3 (calcitriol)
Increased serum Calcium, decrease serum phosphate, and increase urine phosphate
Mechanism of bone resoprtion by PTH
Increases production of M-CSF and RANK-L in osteoblasts, which stimulates osteoclasts
What increases or decreases PTH secretion
Low calcium and magnesium stimulates PTH
Very low magnesium inhibits PTH
Common causes of low magnesium (4)
Diarrhea Aminoglycosides Diuretics Alcohol abuse Citrate (in whole blood or packed RBC transfusion) can chelate Ca2+/Mg2
Function of vitamin D
Increase absorption of dietary calcium and phosphate
Decrease bone resorption of calcium and phosphate
Pathway of Vitamin D synthesis
From Skin: 7-dehydrocholesterol is converted to cholecalciferol (D3) or dietary intake of D2 from plates)
Both converted to 25-OH in liver -> 1,25-(OH)2 in kidney
What is the active and inative forms of vitamin D
Active: 1,25-(OH)2
Inactive: 24,25-(OH)2
What regulates vitamin D?
Increased PTH
1,25-(OH)2 feedback inhibits its own production
Source of calcitonin
C cells (parafollicular cells) of thyroid
Function of calcitonin
Decrease bone resoprtion of calcium
Opposes PTH, but not important in normal calcium homeostasis
Regulation of calcitonin
Increased serum Ca2+ causes calcitonin secretion.
What endocrine hormones signal through cAMP? (12)
[FLAT ChAMP]
FSH, LH, ACTH, TSH, CRH, hCG, ADH-V2, MSH, PTH, calcitonin, GHRH, glucagon
What endocrine hormones signal through cGMP? (2)
ANP, NO (EDRF)
What endocrine hormones signal through IP3?
[GGOAT]
GnRH, GHRH, Oxytocin, ADH-V1, TRH, histamine-H1, angiotensin II, gastrin
What endocrine hormones signal through steroid receptors?
[VETTT CAP]
Vitamin D, Estrogen, Testosterone, T3/T4, Cortisol, Aldosterone, Progesterone
What endocrine hormones signal through intrinsic tyrosine kinse? (MAPK pathway)
Insulin, IGF-1, FGF, PDGF, EGF
What endocrine hormones signal through receptor-associated tyrosine kinase? (JAK/STAT pathway)
[PIG]
Prolactin, Immunomodulators (cytokines, IL-2, IL-6, IL-8, IFN), GH
What happens if there is increased/decreased sex hormone-binding globulin in males and females?
(Increased SHBG) Decreased free testosterone -> gynecomastia (males)
(Decreased SHBG) Increased free testosterone -> hirsutism in females
SHBG levels increase during pregnancy
Source of T3/T4
Follicles of thyroid
Most T3 formed in target tissues
Functions of thyroid hormone (5)
- Bone growth (synergistic with GH)
- CNS maturation
- increase beta-1 receptors in heart (increase CO, HR, SV, contractility)
- increase basal metabolic rate through increased Na/K ATPase activity (increase O2 consumption, RR, body temperature)
- increase glycogenolysis, gluconeogenesis, lipolysis
How does thyroid hormone increase heart rate, SV, and contractility in the heart?
Increased beta-1 receptors in heart
How does thyroid hormone increase basal metabolic rate?
Increase Na/K ATPase activity
What can increase or decrease TBG level?
Decreased: hepatic failure
Increased: pregnancy, OCP (estrogen)
Function of peroxidase
Oxidation and organification of iodide
Coupling of MIT and DIT
Function of 5’-deiodinase
Converts T4 to T3 in peripheral tissue (T3 binds receptor with greater affinity)
Regulation of thyroid hormone
Negative feedback by free T3 to anterior pituitary decreases sensitivity to TRH
What is the Wolff-Chaikoff effect?
Excess iodine inhibits thyroid peroxidase -> decrease iodine organification -> decreases T3/T4
What inhibits iodine transport into follicular cells?
Anions (perchlorate, pertechnetate)
Functions of oxytocin
Uterine contraction during labor
Release of breast milk (let-down) in lactating mothers
