Endocrine Physiology - BRS & Guyton and Hall Flashcards Preview

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Flashcards in Endocrine Physiology - BRS & Guyton and Hall Deck (56)
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1

ADH

1. Originates primarily in supraoptic nuclei of hypothalamus

2. Inc. H2O permeability (aquaporin 2, AQP2) of principal cells of late distal tubule and collecting duct (via V2 receptor and adenylate cyclase-cAMP mech)

3. Constriction of vsm (via V1 receptor and IP3/Ca2+ mech)

2

Aldosterone

Inc. renal Na+ reabsorption
Inc. renal K+ secretion
Inc. renal H+ secretion

Under tonic control by ACTH but separately regulated by RAAS and K+

Decrease in blood volume --> dec. renal perfusion pressure --> inc. renin secretion --> catalyzes A to AI --> AI to AII by ACE --> AII acts on zone glomerulosa of adrenal cortex to inc. conversion of corticosterone to aldosterone --> aldosterone inc. renal Na+ reabsorption, thereby restoring extracellular fluid volume and blood volume to normal

Hyperkalemia increases aldosterone secretion (aldosterone increases renal K+ secretion)

3

A 41-year-old woman has hypocalcemia, hyperphosphatemia, and decreased urinary phosphate excretion. Injection of PTH causes an increase in urinary cyclic adenosine monophosphate (cAMP). The most likely diagnosis is:

A. Primary hyperparathyroidism
B. Vitamin D intoxication
C. Vitamin D deficiency
D. Hypoparathyroidism after thyroid surgery
E. Pseudohypoparathyroidism

D. Hypoparathyroidism after thyroid surgery

- Vitamin D intoxication would cause hypercalcemia
- Vitamin D deficiency would cause hypocalcemia and hypophosphatemia
- Not pseudohypoparathyroidism (defective Gs in kidney and bone causes PTH resistance) b/c corrected by exogenous PTH

4

A 38-year-old man who has galactorrhea is found to have prolactinoma. He is treated with bromocriptine, which eliminates the galactorrhea. What is the basis for the therapeutic action of bromocriptine?

Bromocriptine = dopamine agonist

Secretion of prolactin by anterior pituitary is tonically inhibited by secretion of dopamine from hypothalamus - thus, dopamine agonist acts just like dopamine (inhibits prolactin secretion)

5

What function of Sertoli cells mediates negative feedback control of FSH secretion?

Synthesis of inhibin

Note: Leydig cells synthesize testosterone which is aromatized in the ovaries

6

What substance is derived from pro-opiomelanocortin (POMC)?

ACTH

POMC = parent molecule in anterior pituitary for ACTH and intermediary lob for MSH

MSH, a component of POMC and ACTH, stimulates melatonin production.

7

Which of the following inhibits the secretion of growth hormone by the anterior pituitary?

a. Sleep
b. Stress
c. Puberty
d. Somatomedins
e. Starvation
f. Hypoglycemia

Somatomedin are generated with GH acts on its target tissues; they inhibit GH secretion by the anterior pituitary, both directly and indirectly (by stimulating somatostatin release)

8

What explains the suppression of let down during pregnancy?

Blood levels of estrogen and progesterone are high.

Although high circulating levels of estrogen stimulate prolactin secretion (lactation) doing pregnancy, milk let down is inhibited by progesterone and estrogen.

After birth, progesterone and estrogen levels fall dramatically. Prolactin can then interact with its receptors in the breast, and lactation continues to proceed if initiated by suckling.

Milk let-down via oxytocin is also initiated by suckling.

9

Which step in steroid hormone biosynthesis, if inhibited, blocks the production of all androgenic compounds but does not block the production of glucocorticoids?

Conversion of 17-hydroxypregnenolone to dehydroepiandrosterone (as well as conversion of 17-hydroxyprogesterone to androstenedione) is catalyzed by 17,20-lyase.

If this process is inhibited, synthesis of androgens is stopped.

10

A 46-year-old woman has hirsutism, hyperglycemia, obesity, muscle wasting, and increased circulating levels of ACTH. The most likely cause of her symptoms is:

a. primary adrenocortical insufficiency (Addison's disease)
b. primary overproduction of ACTH (Cushing's disease)
d. treatment with exogenous glucocorticoids

b. Cushing's disease
- Elevation of ACTH stimulates overproduction of glucocorticoids and androgens

Treatment with exogenous glucocorticoids would produce similar symptoms but you would get decreased levels of ACTH b/c of negative feedback.

Addison's would produce high levels of ACTH due to loss of negative feedback inhibition but symptoms would be of glucocorticoid deficit, not excess.

11

Cushing's disease vs. syndrome

Disease - pituitary issue causing over secretion of ACTH --> high levels of cortisol

Syndrome - high levels of cortisol but exerts negative feedback on pituitary to result in low levels of ACTH

Use dex suppression test to distinguish... if you give high levels of dex, and ACTH levels decrease --> Cushing's disease

12

Blood levels of which of the following substances is decreased in Graves' disease?

a. Triiodothyronine (T3)
b. Thyroxine (T4)
c. Diiodotyrosine (DIT)
d. TSH
e. Iodide (I-)

In Graves' disease (hyperthyroidism), the thyroid is stimulated to produce and secrete high levels of thyroid hormones as a result of stimulation by thyroid-stimulating Igs [antibodies to TSH receptors on thyroid gland]

B/c of high circulating levels of thyroid hormones, anterior pituitary secretion of TSH will be turned off (negative feedback).

13

Which step in steroid hormone biosynthesis is stimulated by ACTH?

Cholesterol --> pregnenolone

14

The source of estrogen during the second and third trimesters of pregnancy?

Fetal adrenal gland synthesizes DHEA-S, which is hydroxylated in fetal liver, and then transferred to placenta, where it is aromatized to estrogen

In the first trimester, CL is the source of both estrogen and progesterone

15

Secretion of oxytocin is increased by:

a. milk ejection
b. dilation of the cervix
c. increased prolactin levels
d. increased ECF volume
e. increased serum osmolarity

b. Suckling and dilation of cervix = stimuli for oxytocin secretion

Milk let-down = RESULT of oxytocin action, not cause of secretion

prolactin secretion is also stimulated by suckling, but prolactin does not directly cause oxytocin secretion

increased ECF and hyperosmolarity = stimuli for other posterior pituitary hormone, ADH

16

Propylthiouracil can be used to reduce the synthesis of thyroid hormones in hyperthyroidism because it inhibits oxidation of:

a. T3
b. T4
c. DIT
d. TSH
e. Iodide (I-)

E. Iodide

For iodide (I-) to be incorporated into thyroid hormone, it must be oxidized to I2 which is accomplished by a peroxidase enzyme in the thyroid follicular cell membrane. Propylthiouracil inhibits peroxidase and therefore, halts synthesis of thyroid hormones.

17

A 39-year-old man with untreated DM type I is brought to the ER. An injection of insulin would be expected to cause an increase in his:

a. urine glucose concentration
b. blood glucose concentration
c. blood K+ concentration
d. blood pH
e. breathing rate

DM symptoms pre-insulin:
- Hyperglycemia
- Glycosuria
- Hyperkalemia
- Metabolic acidosis with compensatory hyperventilation

Insulin treatment would decrease blood glucose (by increasing uptake of glucose into cells), decrease urinary glucose (secondary to decreasing blood glucose), decrease blood K+ (shifting K+ into cells), and correct metabolic acidosis (by decreasing production of ketoacids)

Correction in metabolic acidosis will lead to increase in blood pH and will reduce compensatory hyperventilation

18

What results from the action of PTH on the renal tubule?

Stimulates both renal calcium reabsorption in the renal distal tubule and the 1 alpha-hydroxylase enzyme.

PTH inhibits phosphate reabsorption in the proximal tubule (which is associated with an increase in urinary cAMP).

19

Which step in steroid hormone biosynthesis occurs in the accessory sex target tissues of the male and is catalyzed by 5alpha-reductase?

Conversion of testosterone --> DHT

20

A 16-year-old seemingly normal female is diagnosed with androgen insensitivity disorder. She has never had a menstrual cycle and is found to have a blind-ending vagina; no uterus, cervix, or ovaries; a 46 XY genotype; and intraabdominal testes.

Her serum testosterone is elevated. Which of the following characteristics is caused by lack of androgen receptors?

a. 46 XY genotype
b. testes
c. elevated serum testosterone
d. lack of uterus and cervix
e. lack of menstrual cycles

c. elevated serum testosterone is due to lack of AR on anterior pituitary (which normally would mediate negative feedback by testosterone)

presence of testes due to male genotype

lack of uterus and cervix is due to antimullerian hormone (secreted by fetal testes), which suppressed differentiation of the mullein ducts into internal female genital tract

lack of menstrual cycles is due to absence of female reproductive tract

21

Which hormone stimulates the conversion of testosterone to 17beta-estradiol in ovarian granulosa cells?

Testosterone is synthesized from cholesterol in ovarian theca cells and diffuses to ovarian granulosa cells, where it is converted to estradiol by the action of aromatase (CYP19). FSH stimulates aromatase enzyme and increases the production of estradiol.

22

Which hormone causes constriction of vsm through an inositol 1,4,5-triphosphate (IP3) second messenger system?

a. ADH
b. aldosterone
c. dopamine
d. oxytocin
e. PTH

ADH causes constriction of vsm by activating V1 receptor that uses IP3 and Ca2+ second messenger system.

When hemorrhage or ECF volume contraction occurs, ADH secretion by posterior pituitary is stimulated via volume receptors. Resulting increase in ADH levels causes increased water reabsorption by collecting ducts (V2R) and vasoconstriction (V1R) to help restore blood pressure

23

Somatostatin inhibits the secretion of which of the following hormones?

a. ADH
b. Insulin
c. oxytocin
d. prolactin
e. TH

insulin

Somatostatin actions are diverse.

1. Secreted by hypothalamus to inhibit GH secretion by anterior pituitary
2. Secreted by cells of GI tract to inhibit secretion of GI hormones
3. Secreted by delta cells of pancreas to inhibit secretion of insulin and glucagon by beta and alpha cells

24

Inhibition of which enzyme in the steroid hormone synthetic pathway reduces the size of the prostate?

a. aldosterone synthase
b. aromatase
c. cholesterol desmolase
d. 17,20-lyase (CYP17)
e. 5alpha-reductase

5alpha-reductase catalyzes testosterone --> DHT

DHT = active androgen in several male accessory sex tissues (e.g. prostate)

25

Seven days after ovulation, pituitary secretion of LH decreases rapidly. What is the cause of this decrease in secretion?

Secretion of estrogen and progesterone by the CL suppresses hypothalamic secretion of GnRH and anterior pituitary secretion of LH.

26

Which of the following statements about ADH is true?

a. It is synthesized in the posterior pituitary gland.
b. It increases salt and water reabsorption in the collecting tubules and ducts.
c. It stimulates thirst.
d. It has opposite effects on urine and plasma osmolality.

d. It has opposite effects on urine and plasma osmolality.

- Synthesized in supraoptic and paraventricular nuclei of the hypothalamus
- Increases water reabsorption ONLY (hence plasma osmolality dec. while urine osmolality inc.)
- no direct effect on thirst center

27

A baby is born with a penis, a scrotum with no testes, no vagina, and XX chromosomes. This condition is referred to as hermaphroditism. What could cause this abnormality?

a. The presence of a testosterone-secreting tumor in the mother's right adrenal gland
b. Abnormally high levels of LH in the material blood
c. Abnormally low rates of estrogen production by the placenta

a. The presence of a testosterone-secreting tumor in the mother's right adrenal gland

V high conc. of testosterone in a female embryo will induce formation of male genitalia

28

A young woman is given daily injections of a substance beginning on the 16th day of her normal menstrual cycle and continuing for 3 weeks. As long as the injections continue, she does not menstruate. What could the injected substance be?

HCG has same stimulatory effect as LH on CL.

If you give HCG, the CL will continue to secrete estrogen and progesterone, preventing degradation of the endometrium and onset of menstruation.

29

Which of the following could inhibit the initiation of labor?

a. Administration of an progesterone antagonist
b. Administration of LH
c. Administration of prostaglandin E2 antagonist
d. Mechanically dilating and stimulating cervix
e. Administration of oxytocin

c. PGE2 strongly stimulates uterine smooth muscle contraction and is formed in increasing rate by the placenta late in gestation

a, d, e - all initiate labor

b. LH no effect

30

If a radioimmunoassay is properly conducted and the amount of radioactive hormone bound to antibody is low, what would this indicate?

Plasma levels of endogenous hormone are high