Question 1

Which of the following hormones acts by an inositol 1,4,5-triphosphate ( $\left.\mathrm{IP}_{3}\right)-\mathrm{Ca}^{2+}$ mechanism of action?

Accepted Answer

[Table 7.2]. Gonadotropin-releasing hormone (GnRH) is a peptide hormone that acts on the cells of the anterior pituitary by an inositol 1,4,5-triphosphate $\left(\mathrm{IP}_{3}\right)-\mathrm{Ca}^{2+}$ mechanism to cause the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). 1,25-Dihydroxycholecalciferol and progesterone are steroid hormone derivatives of cholesterol that act by inducing the synthesis of new proteins. Insulin acts on its target cells by a tyrosine kinase mechanism. Parathyroid hormone (PTH) acts on its target cells by an adenylate cyclase-cyclic adenosine monophosphate (cAMP) mechanism.

Question 2

Which step in steroid hormone biosynthesis is stimulated by adrenocorticotropic hormone (ACTH)?

Accepted Answer

[V A 2 a (2)]. The conversion of cholesterol to pregnenolone is catalyzed by cholesterol desmolase. This step in the biosynthetic pathway for steroid hormones is stimulated by adrenocorticotropic hormone (ACTH).

Question 3

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

Accepted Answer

[ $\mathrm{X}$ F 3]. During the second and third trimesters of pregnancy, the fetal adrenal gland synthesizes dehydroepiandrosterone-sulfate (DHEA-S), which is hydroxylated in the fetal liver and then transferred to the placenta, where it is aromatized to estrogen. In the first trimester, the corpus luteum is the source of both estrogen and progesterone.

Question 4

Which of the following causes increased aldosterone secretion?

Accepted Answer

[V A 2 b]. Decreased blood volume stimulates the secretion of renin (because of decreased renal perfusion pressure) and initiates the renin-angiotensinaldosterone cascade. Angiotensin-converting enzyme (ACE) inhibitors block the cascade by decreasing the production of angiotensin II. Hyperosmolarity stimulates antidiuretic hormone (ADH) (not aldosterone) secretion. Hyperkalemia, not hypokalemia, directly stimulates aldosterone secretion by the adrenal cortex.

Question 5

Secretion of oxytocin is increased by

Accepted Answer

[III C 2]. Suckling and dilation of the cervix are the physiologic stimuli for oxytocin secretion. Milk ejection is the result of oxytocin action, not the cause of its secretion. Prolactin secretion is also stimulated by suckling, but prolactin does not directly cause oxytocin secretion. Increased extracellular fluid (ECF) volume and hyperosmolarity are the stimuli for the secretion of the other posterior pituitary hormone, antidiuretic hormone (ADH).

Question 6

A 61-year-old woman with hyperthyroidism is treated with propylthiouracil. The drug reduces the synthesis of thyroid hormones because it inhibits oxidation of

Accepted Answer

[IV A 2]. For iodide ( $\mathrm{I}^{-}$) to be "organified" (incorporated into thyroid hormone), it must be oxidized to $\mathrm{I}_{2}$, which is accomplished by a peroxidase enzyme in the thyroid follicular cell membrane. Propylthiouracil inhibits peroxidase and, therefore, halts the synthesis of thyroid hormones.

Question 7

A 39-year-old man with untreated diabetes mellitus type I is brought to the emergency room. An injection of insulin would be expected to cause an increase in his

Accepted Answer

[VI C 3; Table 7.7]. Before the injection of insulin, the woman would have had hyperglycemia, glycosuria, hyperkalemia, and metabolic acidosis with compensatory hyperventilation. The injection of insulin would be expected to decrease her blood glucose (by increasing the uptake of glucose into the cells), decrease her urinary glucose (secondary to decreasing her blood glucose), decrease her blood $\mathrm{K}^{+}$(by shifting $\mathrm{K}^{+}$into the cells), and correct her metabolic acidosis (by decreasing the production of ketoacids).
The correction of the metabolic acidosis will lead to an increase in her blood $\mathrm{pH}$ and will reduce her compensatory hyperventilation.

Question 8

Which of the following results from the action of parathyroid hormone (PTH) on the renal tubule?

Accepted Answer

[VII B 2]. Parathyroid hormone (PTH) stimulates both renal $\mathrm{Ca}^{2+}$ reabsorption in the renal distal tubule and the $1 \alpha$-hydroxylase enzyme. PTH inhibits (not stimulates) phosphate reabsorption in the proximal tubule, which is associated with an increase in urinary cyclic adenosine monophosphate (cAMP). The receptors for PTH are located on the basolateral membranes, not the luminal membranes.

Question 9

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

Accepted Answer

[IX A]. Some target tissues for androgens contain $5 \alpha$-reductase, which converts testosterone to dihydrotestosterone, the active form in those tissues.

Question 10

Which of the following pancreatic secretions has a receptor with four subunits, two of which have tyrosine kinase activity?

Accepted Answer

[VI C 2]. The insulin receptor in target tissues is a tetramer. The two $\beta$ subunits have tyrosine kinase activity and autophosphorylate the receptor when stimulated by insulin.

Question 11

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 $46 \mathrm{XY}$ genotype; and intra-abdominal testes. Her serum testosterone is elevated. Which of the following characteristics is caused by lack of androgen receptors?

Accepted Answer

[IX C]. The elevated serum testosterone is due to lack of androgen receptors on the anterior pituitary (which normally would mediate negative feedback by testosterone). The presence of testes is due to the male genotype. The lack of uterus and cervix is due to anti-müllerian hormone (secreted by the fetal testes), which suppressed differentiation of the müllerian ducts into the internal female genital tract. The lack of menstrual cycles is due to the absence of a female reproductive tract.

Quiz 7: Endocrine Physiology

Which of the following hormones acts by an inositol 1,4,5-triphosphate ( $\left.\mathrm{IP}_{3}\right) -\mathrm{Ca}^{2+}$ mechanism of action?

Which step in steroid hormone biosynthesis is stimulated by adrenocorticotropic hormone (ACTH) ?

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

Which of the following causes increased aldosterone secretion?

Secretion of oxytocin is increased by

A 61-year-old woman with hyperthyroidism is treated with propylthiouracil. The drug reduces the synthesis of thyroid hormones because it inhibits oxidation of

A 39-year-old man with untreated diabetes mellitus type I is brought to the emergency room. An injection of insulin would be expected to cause an increase in his

Which of the following results from the action of parathyroid hormone (PTH) on the renal tubule?

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

Which of the following pancreatic secretions has a receptor with four subunits, two of which have tyrosine kinase activity?

Quiz 7: Endocrine Physiology

Which of the following hormones acts by an inositol 1,4,5-triphosphate ( IP3) −Ca2+\left.\mathrm{IP}_{3}\right) -\mathrm{Ca}^{2+}IP3​) −Ca2+ mechanism of action?

Which step in steroid hormone biosynthesis is stimulated by adrenocorticotropic hormone (ACTH) ?

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

Which of the following causes increased aldosterone secretion?

Secretion of oxytocin is increased by

A 61-year-old woman with hyperthyroidism is treated with propylthiouracil. The drug reduces the synthesis of thyroid hormones because it inhibits oxidation of

A 39-year-old man with untreated diabetes mellitus type I is brought to the emergency room. An injection of insulin would be expected to cause an increase in his

Which of the following results from the action of parathyroid hormone (PTH) on the renal tubule?

Which step in steroid hormone biosynthesis occurs in the accessory sex target tissues of the male and is catalyzed by 5α5 \alpha5α -reductase?

Which of the following pancreatic secretions has a receptor with four subunits, two of which have tyrosine kinase activity?

Which of the following hormones acts by an inositol 1,4,5-triphosphate ( $\left.\mathrm{IP}_{3}\right) -\mathrm{Ca}^{2+}$ mechanism of action?

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