Endocrine Physiology - BRS & Guyton and Hall Flashcards
ADH
- Originates primarily in supraoptic nuclei of hypothalamus
- Inc. H2O permeability (aquaporin 2, AQP2) of principal cells of late distal tubule and collecting duct (via V2 receptor and adenylate cyclase-cAMP mech)
- Constriction of vsm (via V1 receptor and IP3/Ca2+ mech)
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)
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
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)
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
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.
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)
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.
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.
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.
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
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).
Which step in steroid hormone biosynthesis is stimulated by ACTH?
Cholesterol –> pregnenolone
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
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
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.
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
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).
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
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
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.
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