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USMLE > Endocrine - Physiology > Flashcards

Endocrine - Physiology Flashcards

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USMLE® Step 1 flashcards
1
Q

What does this hypothalamic hormone induces/inhibits: TRH

A

+ TSH, prolactin

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2
Q

What does this hypothalamic hormone induces/inhibits: Dopamine

A
  • Prolactin
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3
Q

What does this hypothalamic hormone induces/inhibits: CRH

A

+ ACTH, MSH, beta-endorphin

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4
Q

What does this hypothalamic hormone induces/inhibits: GHRH

A

+ GH

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5
Q

What does this hypothalamic hormone induces/inhibits: Somatostatin

A
  • GH, TSH
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6
Q

What does this hypothalamic hormone induces/inhibits: GnRH

A

+ FSH, LH

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7
Q

What does this hypothalamic hormone induces/inhibits: Prolactin

A
  • GnRH
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8
Q

Describe prolactin regulation

A

Prolactin is tonically inhibited by dopamine from hypothalamus

It inhibits own secretion by increasing dopamine synthesis and secretion

TRH also increases prolactin secretion

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9
Q

Function of Prolactin (2)

A
  1. Stimulates milk production in breast

2. Inhibits ovulation/spermatogenesis by inhibiting GnRH synthesis and release

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10
Q

What pharmacological substances can promote or inhibit prolactin secretion?

A

Inhibit prolactin: dopamine agonist (bromocriptine)

Promote prolactin: dopamine antagonists (most antipsychotics), estrogens (OCPs, pregnancy) stimulate prolactin secretion

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11
Q

Functions of growth hormone (2)

A
  1. Stimulates linear growth and muscle mass through IGF1/somatomedin secretion
  2. increases insulin resistance (diabetogenic)
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12
Q

Regulation of growth hormone. What promotes or inhibits secretion?

A

Released in pulses in response to GHRH

Promoted by exercise, sleep
Inhibited by glucose, somatostatin

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13
Q

In the first step of adrenal steroids, what is cholesterol converted to, facilitated by what enzyme?

A

Cholesterol to Pregnenolone

by Desmolase

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14
Q

What can promote or inhibit desmolase activity?

A

ACTH +

Ketoconazole -

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15
Q

Function of 17alpha-hydroxylase

A
  1. Pregnenolone -> 17-hydroxypregnenolone

2. Progesterone -> 17-hydroxyprogesterone

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16
Q

Function of 3beta-hydroxysteroid dehydrogenase

A
  1. Pregnenolone -> Progesterone
  2. 17-hydroxypregnenolone -> 17-hydroxyprogesterone
  3. DHEA -> Androstenedione
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17
Q

Function of 21-hydroxylase

A
  1. Progesterone -> 11-deoxycorticosterone

2. 17-hydroxyprogesterone -> 11-deoxycortisol

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18
Q

Function of 11beta-hydroxylase

A
  1. 11-deoxycorticosterone -> Corticosterone

2. 11-deoxycortisol -> Cortisol

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19
Q

Function of aromatase

A
  1. Androstenedione -> estrone

2. Testosterone -> estradiol

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20
Q

Function of 5alpha-reductase

A

Testosterone -> DHT

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21
Q

Function of Aldosterone synthase

A

Corticosterone -> Aldosterone

Activated by Angiotensin II

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22
Q

Describe level adrenal steroids in: 17alpha-hydroxylase deficiency

A

Mineralcorticoid: High
Cortisol: Low
Sex hormone: Low

Presentation: hypertension, hypokalemia
XY: pseudohermaphroditism (low DHT)
XX: lacks secondary sex characteristics

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23
Q

Describe level adrenal steroids in: 21-hydroxylase deficiency

A

Mineralcorticoid: Low
Cortisol: Low
Sex hormone: High

Presentation: hypotension, hyperkalemia, high renin, volume depletion
Masculinization; pseudohermaphroditism in females

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24
Q

Describe level adrenal steroids in: 11beta-hydroxylase deficiency

A

Mineralcorticoid: High (11-deoxycorticosterone)
Cortisol: Low
Sex hormone: High

Presentation: Masculinization

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25
Q

Why do all congenital adrenal enzme deficiencies have enlargement of both adrenal glands?

A

Increased ACTH from low cortisol

26
Q

What is cortisol bound to?

A

Corticosteroid-binding globulin (CBG)

27
Q

Functions of cortisol (6)

A
  1. maintains blood pressure (upregulates alpha1-receptors on arterioles which increases sensitivity to NE/E)
  2. decreases bone formation
  3. anti-inflammatory/immunosuppressive
  4. increases insulin resistance (diabetogenic)
  5. Increases gluconeogensis, lipolysis, proteolysis (during stress)
  6. inhibits fibroblasts (causes striae)
28
Q

What is impact of chronic stress on HPA axis?

A

Prolonged secretion

29
Q

Describe cortisol regulation

A

CRH (hypothalamus) stimulates ACTH release (pituitary), causing cortisol production in adrenal zona fasciculata.

Excess cortisol suppresses CRH, ACTH and cortisol secretion

30
Q

Cortisol effects on the immune system (5)

A
  1. Inhibits production of leukotrienes/prostaglandins
  2. inhibits leukocyte adhesion (neutrophilia)
  3. blocks histamine release from mast cells
  4. reduces eosinophils
  5. blocks IL-2 production
31
Q

Source of PTH

A

Chief cells in parathyroid

32
Q

Functions of PTH (4)

A
  1. Increases bone resorption of calcium and phosphate
  2. increase kidney reabsorption of calcium in distal convoluted tubule
  3. decrease reabsorption of phosphate in proximal convoluted tubule
  4. increase 1alpha-hydroxylase activity in kidney (increases 1,25-(OH)2 D3 (calcitriol)

Increased serum Calcium, decrease serum phosphate, and increase urine phosphate

33
Q

Mechanism of bone resoprtion by PTH

A

Increases production of M-CSF and RANK-L in osteoblasts, which stimulates osteoclasts

34
Q

What increases or decreases PTH secretion

A

Low calcium and magnesium stimulates PTH

Very low magnesium inhibits PTH

35
Q

Common causes of low magnesium (4)

A 
Diarrhea
Aminoglycosides
Diuretics
Alcohol abuse
Citrate (in whole blood or packed RBC transfusion) can chelate Ca2+/Mg2
36
Q

Function of vitamin D

A

Increase absorption of dietary calcium and phosphate

Decrease bone resorption of calcium and phosphate

37
Q

Pathway of Vitamin D synthesis

A

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

38
Q

What is the active and inative forms of vitamin D

A

Active: 1,25-(OH)2
Inactive: 24,25-(OH)2

39
Q

What regulates vitamin D?

A

Increased PTH

1,25-(OH)2 feedback inhibits its own production

40
Q

Source of calcitonin

A

C cells (parafollicular cells) of thyroid

41
Q

Function of calcitonin

A

Decrease bone resoprtion of calcium

Opposes PTH, but not important in normal calcium homeostasis

42
Q

Regulation of calcitonin

A

Increased serum Ca2+ causes calcitonin secretion.

43
Q

What endocrine hormones signal through cAMP? (12)

A

[FLAT ChAMP]

FSH, LH, ACTH, TSH, CRH, hCG, ADH-V2, MSH, PTH, calcitonin, GHRH, glucagon

44
Q

What endocrine hormones signal through cGMP? (2)

A

ANP, NO (EDRF)

45
Q

What endocrine hormones signal through IP3?

A

[GGOAT]

GnRH, GHRH, Oxytocin, ADH-V1, TRH, histamine-H1, angiotensin II, gastrin

46
Q

What endocrine hormones signal through steroid receptors?

A

[VETTT CAP]

Vitamin D, Estrogen, Testosterone, T3/T4, Cortisol, Aldosterone, Progesterone

47
Q

What endocrine hormones signal through intrinsic tyrosine kinse? (MAPK pathway)

A

Insulin, IGF-1, FGF, PDGF, EGF

48
Q

What endocrine hormones signal through receptor-associated tyrosine kinase? (JAK/STAT pathway)

A

[PIG]

Prolactin, Immunomodulators (cytokines, IL-2, IL-6, IL-8, IFN), GH

49
Q

What happens if there is increased/decreased sex hormone-binding globulin in males and females?

A

(Increased SHBG) Decreased free testosterone -> gynecomastia (males)

(Decreased SHBG) Increased free testosterone -> hirsutism in females

SHBG levels increase during pregnancy

50
Q

Source of T3/T4

A

Follicles of thyroid

Most T3 formed in target tissues

51
Q

Functions of thyroid hormone (5)

A
  1. Bone growth (synergistic with GH)
  2. CNS maturation
  3. increase beta-1 receptors in heart (increase CO, HR, SV, contractility)
  4. increase basal metabolic rate through increased Na/K ATPase activity (increase O2 consumption, RR, body temperature)
  5. increase glycogenolysis, gluconeogenesis, lipolysis
52
Q

How does thyroid hormone increase heart rate, SV, and contractility in the heart?

A

Increased beta-1 receptors in heart

53
Q

How does thyroid hormone increase basal metabolic rate?

A

Increase Na/K ATPase activity

54
Q

What can increase or decrease TBG level?

A

Decreased: hepatic failure
Increased: pregnancy, OCP (estrogen)

55
Q

Function of peroxidase

A

Oxidation and organification of iodide

Coupling of MIT and DIT

56
Q

Function of 5’-deiodinase

A

Converts T4 to T3 in peripheral tissue (T3 binds receptor with greater affinity)

57
Q

Regulation of thyroid hormone

A

Negative feedback by free T3 to anterior pituitary decreases sensitivity to TRH

58
Q

What is the Wolff-Chaikoff effect?

A

Excess iodine inhibits thyroid peroxidase -> decrease iodine organification -> decreases T3/T4

59
Q

What inhibits iodine transport into follicular cells?

A

Anions (perchlorate, pertechnetate)

60
Q

Functions of oxytocin

A

Uterine contraction during labor

Release of breast milk (let-down) in lactating mothers

USMLE (13 decks)

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