Pretest Endocrinology Questions

Question 1

461. A 43-year-old male develops a brain tumor that impinges on the supraoptic nucleus in the hypothalamus. As a result, the secretion of which of the following hormones is affected?
     a. Adrenocorticotropic hormone (ACTH)
     b. Antidiuretic hormone (ADH)
     c. Follicle-stimulating hormone (FSH)
     d. Growth hormone (GH)
     e. Prolactin

Answer 1

461. The answer is b. (Ganong, pp 234–236, 242–250.) Antidiuretic hor- mone (ADH), also called arginine vasopressin (AVP), is secreted from the posterior lobe of the pituitary gland (neurohypophysis) into the general circulation from the endings of supraoptic neurons in the hypothalamus. ACTH, FSH, GH, and prolactin are all secreted by the anterior pituitary gland (adenohypophysis) into the portal hypophysial circulation from the endings of arcuate and other hypothalamic neurons.

Question 2

462. Following neck surgery, a patient develops circumoral paresthesia and a long QT interval on the electrocardiogram consistent with hypocalcemia resulting from injury to the parathyroid glands. Which of the following is true regarding parathyroid hormone (PTH)?

a. It is synthesized and secreted from the oxyphil cells in the parathyroid glands
b. Secretion is increased in response to an increase in plasma-free Ca2+ concentration
c. It acts directly on bone cells to increase Ca2+ resorption and mobilize Ca2+
d. It acts directly on intestinal cells to increase Ca2+ absorption
e. It increases phosphate reabsorption in the renal proximal tubular cells

Answer 2

C.

462. The answer is c. (Ganong, pp 390–392. Stead et al., pp 88–89, 232–233.) PTH, secreted by the chief cells of the parathyroid gland, is essential for life. PTH has a direct effect on bone to increase bone resorp- tion and mobilze Ca2+; this effect is mediated by increasing intracellular cAMP levels in osteoblasts. PTH also increases calcium absorption from the gut, although that effect is the result of PTH-mediated increases in renal 1,2,5-dihydroxy-cholecalciferol. PTH has a phosphaturic action due to a decrease in phosphate reabsorption in the proximal tubules. The secretion of PTH is inversely related to the circulating levels of ionized calcium.

Question 3

463. A 39-year-old man with an enlarged head, hands, and feet, osteoarthritic vertebral changes and hirsutism presents with a complaint of gynecomastia and lactation. The patient is most likely suffering from a tumor in which of the following locations?

a. Hypothalamus
b. Anterior pituitary
c. Posterior pituitary
d. Adrenal cortex
e. Breast

Answer 3

B.

463. The answer is b. (Ganong, pp 399–402, 409. Stead et al., pp 74–75, 233.) Tumors of the somatotropes of the anterior pituitary gland secrete large amounts of growth hormone, leading to acromegaly in adults. When the epiphyses have not yet fused to the long bones, growth is stimulated by excess growth hormone leading to gigantism in children. Once the epiphy- ses have closed, linear growth is no longer possible, and growth hormone produces the pattern of bone and soft tissue abnormalities typical of acromegaly. Hypersecretion of growth hormone is accompanied by hyper- secretion of prolactin in up to 40% of patients with acromegaly. Human growth hormone also has intrinsic lactogenic activity. Acromegaly can be caused by hypothalamic tumors that secrete growth hormone-releasing hormone (GRH), but these are rare.

Question 4

464. A major league baseball player takes human growth hormone to increase his performance. Which of the following is true regarding human growth hormone?

a. Secretion is stimulated by somatostatin and inhibited by ghrelin
b. It has a long half-life
c. It inhibits protein synthesis
d. It decreases lipolysis
e. It stimulates production of somatomedins (insulin-like growth factors I and II)
by the liver, cartilage, and other tissues

Answer 4

e.

Growthhormone (GH) exerts many of its effects on growth and metabolism by stimulating the production and release of polypeptide growth factors called somatomedins from the liver, cartilage, and other tissues. In humans, the principal circu- lating somatomedins are insulin-like growth factor I (IGF-I, somatomedin C) and IGF-II. GH release is stimulated by growth hormone-releasing hor- mone (GHRH) and ghrelin and inhibited by somatostatin. All of these pep- tides are synthesized and released by the hypothalamus, though the main site of ghrelin synthesis and secretion is the stomach. GH increases lipoly- sis; the resultant increase in free fatty acids, which takes several hours to develop, provides a ready source of energy for the tissues during hypo- glycemia, fasting, and stressful stimuli. GH also has a protein anabolic effect. GH is metabolized rapidly; the half-life of circulating GH in humans is 6 to 20 minutes.

Question 5

465. A 28-year-old woman develops a posterior pituitary tumor. Which of the following hormones is secreted by the posterior pituitary gland?

a. a-Melanocyte-stimulating hormone (a-MSH)
b. b-Lipotropin (b-LPH)
c. Leutinizing hormone (LH)
d. Oxytocin
e. Thyroid-stimulating hormone (TSH)

Answer 5

d.

Oxytocin is secreted from the posterior lobe of the pituitary gland (neurohypophysis) into the general circulation from the endings of paraventricular neurons in the hypothala- mus. LH, TSH, and b-lipotropin are all secreted by the anterior pituitary gland (adenohypophysis). a-MSH is released from the intermediate lobe of the pituitary.

Question 6

466. A 36-week pregnant mother has a decrease in urinary estriol excretion, indicating a decline in fetal adrenal cortical activity. Which of the following is the principal steroid secreted by the fetal adrenal cortex?

a. Cortisol
b. Corticosterone
c. Dehydroepiandrosterone
d. Progesterone
e. Pregnenolone

Answer 6

C.

Because it lacks 3b-hydroxysteroid dehydrogenase, the enzyme that converts pregnenolone to progesterone (the initial step in both glucocorticoid and mineralocorti- coid synthesis), the fetal cortex synthesizes primarily dehydroepiandros- terone. This steroid is released as its sulfate and is metabolized further to estrogen and androgen by the placenta. During fetal life, the adrenal cortex consists of a thin subcapsular rim, which eventually gives rise to the adult cortex, and a thick inner fetal cortex, which constitutes 80% of the gland. This zone undergoes rapid involution after birth.

Question 7

467. A 22-year-old woman presents with a recurrent vaginal candidiasis that is refractory to nystatin treatment. Diabetes screening shows elevated fasting blood glucose, and the patient is started on 25 units of insulin per day. Which aspect of glucose transport is enhanced by insulin?

a. Transport into adipocytes
b. Transport across the tubular epithelium of the kidney
c. Transport into the brain
d. Transport through the intestinal mucosa
e. Transport against a concentration gradient

Answer 7

A

Insulin increases glucose uptake by adipocytes. Transport of glucose into cells is by facilitated diffusion. Insulin increases the number of transporters available for glucose uptake in many cells, including adipocytes, skeletal, and cardiac muscle, and some smooth muscle. Insulin does not enhance glucose transport into brain cells, intestinal mucosal cells, or renal tubular epithelial cells. Diabetics have increased susceptibility to infections due to decreased efficacy of granulocytes despite a normal number. Type 1 dia- betes mellitus patients must use insulin. They cannot use oral hypo- glycemic agents because they do not have any functional pancreatic b cells.

Question 8

468. A 52-year-old woman with a chief complaint of snoring is referred for a sleep study. As shown in the graph below, the concentration of a hor- mone varied over the 24-hour period of study. This diurnal variation in plasma level results from the secretion of which of the following hormones?

a. Thyroxine
b. Insulin
c. Parathyroid hormone
d. Cortisol
e. Estrogen

Answer 8

d

Cortisol is the only hormone that has a diurnal variation, as shown in the graph accompanying the question. Plasma cortisol levels rise sharply during sleep, peaking soon after awakening, and sinking to a low level approxi- mately 12 hours later. This pattern is intimately related to the secretory rhythm of ACTH, which governs, and in turn is partly governed by, plasma concentration of cortisol.

Question 9

469. A 24-year-old pregnant woman and her 3-year-old child are seen in a medical mission clinic in Sudan. The child is short in stature, has a pot- belly and enlarged protruding tongue, and is developmentally delayed. Iodine is prescribed for mother and child, with the hope of preventing mental retardation in the developing fetus. Iodides are stored in the thyroid follicles mainly in the form of which of the following?

a. Thyroxine
b. Triiodothyronine
c. Thyroglobulin
d. Monoiodotyrosine
e. Thyroid peroxidase

Answer 9

B.

The thyroid gland stores iodide primarily as thyroglobulin. The thyroid gland has a specialized active transport system that very efficiently traps iodide from circulating blood and can accumulate iodide against a large con- centration gradient. Within the thyroid, the iodide rapidly undergoes organi- fication by which it is oxidized and covalently linked to tyrosine residues in thyroglobulin. The iodinated tyrosine residues gradually become coupled to form thyroxine, the major secretion product of the thyroid. Children who are hypothyroid from birth or before are called cretins. Worldwide, congenital hypothyroidism is one of the most common causes of preventable mental retardation. Outside of the United States and most other developed countries, maternal iodine deficiency is a major cause of congenital hypothyroidism.

Question 10

470. A 15-year-old girl presents with loss of the outer one-third of her eyebrows. Physical examination demonstrates slight enlargement of the thyroid gland and delayed relaxation phase of deep tendon reflexes. Blood work shows an elevation in creatine phosphokinase (CPK) and thyroid- stimulating hormone (TSH). Thyroid hormone therapy is ordered. Physiologically active thyroxine exists in which of the following forms?

a. Bound to albumin
b. Bound to prealbumin
c. Bound to globulin
d. As a glucuronide
e. Unbound

Answer 10

E

Only the free unbound form of thyroxine is physiologically active. Circulating thyroxine can be bound to albumin, thyroxine-binding prealbumin (TBPA), or thyroxine-binding globulin (TBG). Most thyroxine is bound, and, despite the large available pool of albumin, most of it is bound to TBG. This reflects the relatively greater affinity of TBG for thyroxine.

Question 11

471. A patient with uncontrolled diabetes has an increase in the plasma concentration of free fatty acids that parallels his increase in plasma glucose. Which of the following is correct regarding activation of hormone- sensitive lipase in adipocytes?

a. It causes increased hydrolysis of cholesterol esters.
b. It is mediated by a cyclic AMP-dependent protein kinase.
c. It is prevented by cortisol.
d. It is stimulated by insulin.
e. It results in accumulation of monoglycerides and diglycerides in adipocytes.

Answer 11

b

Hormone-sensitive lipase is a cytoplasmic enzyme in adipocytes that catalyzes the complete hydrolysis of triglyceride to fatty acids and glycerol. It is activated by a cyclic AMP- dependent protein kinase that phosphorylates the enzyme, converting it to its active form. Because no accumulation of monoglycerides or diglycerides is detected in adipocytes following the action of hormone-sensitive lipase, it is the initial hydrolysis of triglyceride to fatty acid and diglyceride that is the rate-limiting step. Hormone-sensitive lipase is sensitive to several hormones in vitro, but it appears to be regulated in vivo primarily by epinephrine and glucagon, which activate it by increasing cyclic AMP, and insulin, which inhibits it by preventing cyclic AMP-dependent phosphorylation. Cortisol enhances lipolysis indirectly by promoting increased enzyme synthesis.

Question 12

472. A patient with DiGeorge’s congenital thymic aplasia presents with a seizure. An elevated serum phosphorus and low serum calcium confirm a hypoparathyroid state. Plasma levels of calcium can be increased most rapidly by the direct action of PTH on which of the following?

a. Kidney
b. Intestine
c. Thyroid gland
d. Bones
e. Skeletal musculature

Answer 12

D

PTH increases plasma calcium levels primarily by mobilizing bone calcium. The main function of the parathyroid gland is to maintain a constant ionized calcium level in the extracellular fluid. To do this, PTH stimulates increased plasma calcium levels, chiefly by mobilizing calcium from bones. Although PTH can also increase renal tubular reab- sorption of calcium and intestinal absorption of calcium, these effects depend on adequate dietary ingestion of calcium and thus occur more slowly.

Question 13

473. A 20-year-old male medical student presents with increasing daytime somnolence. A 24-hour sleep study showing a sudden onset of REM sleep without previous slow-wave sleep, confirms a diagnosis of narcolepsy. REM sleep decreases the secretion of growth hormone. The physiological secretion of growth hormone is increased by which of the following?

a. Hypoglycemia
b. Hyperglycemia
c. Free fatty acids
d. Somatostatin
e. Growth hormone

Answer 13

A. Hypoglycemia

Synthesis and secretion of growth hormone (GH) by the anterior pituitary is regulated by a variety of metabolic factors, many of which act to alter the balance between release of growth hormone-releasing hormone (GRH) and somatostatin (SS) from the hypothalamus. Among the stimuli that increase GH secretion are: (1) conditions in which there is a deficiency of energy substrate (e.g., hypoglycemia, exercise, and fasting); (2) stressful stimuli (e.g., fever, various psychological stresses); (3) an increase in arginine and some other amino acids (e.g., protein meal, infusion of arginine); (4) glucagon; (5) L-Dopa and dopamine receptor agonists; (6) estrogens and androgens; and (7) going to sleep. Stimuli that decrease GH secretion include somatostatin, REM sleep, glucose, cortisol, free fatty acids, and GH itself.

Question 14

474. A 50-year-old male alcoholic presents with cirrhotic liver disease and chronic pancreatitis. He has been nauseated for the past several days, and not eating. Blood glucagon levels are elevated with which of the following results?

a. Stimulation of glycogenolysis in muscle
b. Inhibition of insulin secretion
c. Stimulation of gluconeogenesis in the liver
d. Inhibition of adenylate cyclase
e. Inhibition of phospholipase C

Answer 14

C

The primary action of glucagon is to increase blood glucose concentration, which it accomplishes by promoting gluco- neogenesis and glycogenolysis in the liver but not in muscle. These effects are mediated by cyclic AMP, which is produced by hepatic adenylate cyclase following interaction of glucagon with its plasma membrane receptor. Interaction of glucagon with different hepatic plasma membrane receptors activates phospholipase C, which results in a rise in concentration of intra- cellular Ca2+, which further stimulates glycogenolysis. Although glucagon opposes the action of insulin, it does not directly affect insulin secretion.

Question 15

475. A patient in hyperkalemic renal failure is given an infusion of glucose and insulin. The actions of insulin include which of the following?

a. Converting glycogen to glucose
b. Stimulating gluconeogenesis
c. Increasing plasma amino acid concentration
d. Enhancing potassium entry into cells
e. Reducing urine formation

Answer 15

d.

One of insulin’s major effects is the stimulation of the Na+-K+ pump, which increases potassium entry into cells, with a resultant lowering of the extracellular K+ concentra- tion. Insulin given along with glucose, to prevent hypoglycemia, is often used as a treatment for hyperkalemia. Insulin’s major effect on metabolism is the synthesis of proteins and lipids and the storage of glucose as glyco- gen. Insulin stimulates the uptake of amino acids and glucose by most cells of the body and decreases the rate of gluconeogenesis. Insulin has no effect on urine formation, but in diabetes, when glucose levels increase to a level at which the kidney can no longer reabsorb the filtered glucose, glucose acts as an osmotic diuretic and increases the formation of urine.

Question 16

476. A 47-year-old woman with an anterior pituitary tumor presents with poor wound healing and hypertension. The endogenous secretion of ACTH is correctly described in which of the following statements?

a. It shows a circadian rhythm in humans.
b. It is decreased during periods of stress.
c. It is inhibited by aldosterone.
d. It is stimulated by glucocorticoids.
e. It is stimulated by epinephrine.

Answer 16

A

The secretion of ACTH occurs in several irregular bursts during the day; the peak occurs early in the morning prior to awakening and thus is not due to the stress of arising. This circadian rhythm, maximum secretion in early morning and minimum secretion in the evening, is regulated by the hypothalamus through the secretion of corticotropin-releasing hormone (CRH) into the hypothalamic-hypophyseal portal capillary system. In addi- tion to the basal rhythm, physical or mental stress will lead to increased ACTH secretion within minutes. ACTH is also regulated as a result of feed- back inhibition by the hormones whose synthesis it stimulates, such as glu- cocorticoids. Aldosterone is a mineralocorticoid and is not controlled by ACTH. Epinephrine does not appear to have any effect on ACTH secretion.

Question 17

477. A patient with tuberculosis becomes confused and complains of muscle cramps and nausea. Lab results show a plasma sodium concentration of 125 mEq/L, serum osmolarity of 200 mOsm/kg, urine osmolarity of 1500 mOsm/kg, urine sodium of 400 mEq/day, and a normal blood volume. These clinical findings are consistent with which of the following?

a. Increased secretion of atrial natriuetic peptide
b. Decreased secretion of aldosterone
c. Increased secretion of aldosterone
d. Decreased secretion of antidiuretic hormone
e. Increased secretion of antidiuretic hormone

Answer 17

E. HELP!!!!

An increase in antidi- uretic hormone is associated with isovolemic, hypotonic hyponatremia, and an increase in both urine osmolarity and urine sodium. The etiology of syndrome of inappropriate antidiuretic hormone secretion (SIADH) includes idiopathic overproduction of ADH that is often associated with disorders of the CNS (encephalitis, stroke, head trauma) and pulmonary disease (TB, pneumonia). Hyperaldosteronism leads to decreased sodium (and water) excretion and thus hypernatremia and an increase in extracel- lular fluid volume. A decrease in aldosterone would be associated with hypovolemic hyponatremia. A decrease in ANP would lead to decreased sodium and water excretion.

Question 18

478. A 29-year-old male recovering from a viral upper respiratory tract infection develops a tender, enlarged thyroid gland and subacute thyroiditis, requiring hormone therapy. Injection of thyroid hormone into a human subject will result in which of the following?

a. Decrease the rate of oxygen consumption
b. Increase muscle protein synthesis
c. Decrease the need for vitamins
d. Increase the plasma concentration of cholesterol
e. Decrease the rate of lipolysis

Answer 18

b

Thyroid hormone affects all aspects of metabolism; it increases calorigene- sis in every tissue in the body. The hormone stimulates protein synthesis, which may be directly responsible for a portion of its calorigenic effect. Thyroid hormone affects both synthesis and degradation of lipids; the net effect is a decrease in lipid stores. By increasing the mechanisms by which cholesterol is eliminated from the body, thyroid hormone decreases plasma cholesterol levels. Because of its stimulatory effect on metabolic processes, thyroid hormone increases the demand for coenzymes and vitamins.

Question 19

479. An abdominal computed tomography (CT) in a patient with Conn’s syndrome (primary hyperaldosteronism) shows multiple small adrenocortical masses. Which of the following clinical findings are most likely present?

a. Hypertension
b. Hyperkalemia
c. Decreased extracellular fluid volume
d. Increased concentrating ability of the kidney
e. Increased hematocrit

Answer 19

A

The symptoms of primary hyperaldosteronism (Conn’s syndrome) develop from chronic excess secretion of aldosterone from the zona glomerulosa of the adrenal cortex. Patients are hypertensive and have an expanded blood volume with a decreased hematocrit. They are not markedly hypernatremic because of a renal escape phenomenon. Patients are severely depleted of potassium and, as a consequence, suffer kidney damage, with a resulting loss in concentrating ability.

Question 20

480. A 75-year-old female with primary hyperparathyroidism presents at her physician’s office with dehydration and malaise. Which of the following plasma levels are most likely to be decreased?

a. Phosphate
b. Sodium
c. Calcium
d. Potassium
e. Calcitonin

Answer 20

a

Parathyroid hormone (PTH) is essential for maintaining plasma calcium and phosphate levels. It is released in response to decreased plasma calcium and acts to increase calcium reabsorption and phosphate excretion. Thus, hyperparathyroidism is characterized by hypophos- phatemia and hypercalcemia.

Question 21

481. A patient undergoes adrenalectomy to remove a tumor. Adrenalectomy is associated with which of the following?

a. Euphoria
b. Increased mobilization and utilization of fatty acids
c. Hyperglycemia with decreased insulin sensitivity
d. Improved resistance to infection or shock
e. Augmented water excretion by the kidneys and sodium loss in the urine

Answer 21

c

Removal of the adrenal glands produces the clinical picture known as Addison’s disease, a disorder associated with deprivation of adrenocortical hormones. A lack of glucocorticoids diminishes the body’s ability to syn- thesize glucose by gluconeogenesis. Mineralocorticoid deprivation pro- duces diuresis, natriuresis, and decreased potassium secretion leading to excessive potassium plasma levels and acidosis.

Question 22

A 37-year-old female presents with exophthalmus and an enlarged thyroid gland. The levels of free thyroxine and triiodothyronine in her blood are elevated. Other clinical findings of Graves’ disease include which of the following?

a. Anorexia
b. Increased basal metabolic rate
c. Bradycardia
d. Increased weight gain
e. Decreased sweating

Answer 22

B

Hyperthyroidism can increase the basal metabolic rate 60 to 100% above normal. Thyroid hormone causes nuclear transcription of large numbers of genes in virtually all cells of the body. The result is a generalized increase in functional cell activity and metabolism. The increased metabolic activity of patients with hyperthyroidism is accompanied by increased food intake. Nevertheless, their body weight decreases. The generalized increase in cel- lular activity results in increased sweat production and increased heart rate. The latter sign is often used by physicians to determine whether a patient has increased thyroid hormone production.

Question 23

483. A 20-year-old diabetic male forgets to take his insulin prior to the start of the National Collegiate Athletic Association (NCAA) swimming championships. Insulin-independent glucose uptake occurs in which of the following sites?

a. Adipose tissue
b. Cardiac muscle
c. Skeletal muscle
d. The brain
e. The uterus

Answer 23

A and C

WHY IS IT D?

Insulin does not promote glucose uptake by most brain cells. Insulin does increase glucose uptake inskeletal muscle, cardiac muscle, smooth muscle, adipose tissue, leuko- cytes, and the liver. In most insulin-sensitive tissues, insulin acts to pro- mote glucose transport by enhancing facilitated diffusion of glucose down a concentration gradient. In the liver, where glucose freely permeates the cell membrane, glucose uptake is increased as a result of its phosphoryla- tion by glucokinase. Formation of glucose-6-phosphate reduces the intra- cellular concentration of free glucose and maintains the concentration gradient favoring movement of glucose into the cell.

Question 24

484. A 46-year-old woman on lithium therapy for her bipolar disorder, presents with complaints of weakness, arthralgia, and constipation. Blood work reveals hypercholesterolemia, increased levels of thyroid-stimulating hormone (TSH), and decreased T4 and T3 levels. Which of the following is also likely to be associated with her hypothyroid state?

a. Tachycardia
b. Increased metabolic rate
c. Heat intolerance
d. Sleepiness
e. Decreased body mass index

Answer 24

D

Sleepiness is common in patients with hypothyroidism. Hypothyroidism is a condition usually characterized by low levels of T3 and T4, owing to atrophy of the thyroid gland. In very rare cases there is resistance to the effects of thyroid hormones. A deficiency of thyroid hormones or their effects results in bradycardia, which is due to decreased sympathetic activity, and a decreased metabolic rate with its associated sleepiness, weight gain, and cold intolerance. Excess thyroid hormone increases metabolic rate, which increases heat production, stimulates the appetite, and causes weight loss even in the face of increased intake of food. Heat intolerance is characteristic of hyperthyroidism.

Question 25

485. A multisystem trauma patient develops hyperpyrexia, severe tachycardia, and high-output congestive heart failure with volume depletion, consistent with thyroid storm. Which of the following is the most appropriate treatment for the exaggerated hyperthyroidism? a. T3 administration to induce negative feedback inhibition of T4 b. Aspirin to treat the fever c. Propylthiouracil to block synthesis of new thyroid hormone d. b2-adrenergic agents to mediate vasodilation and bronchodilation e. Iodine followed by propylthiouracil to block release and synthesis of thyroid hormone

Answer 25

C Thyroid storm is an exaggerated manifestation of hyperthyroidism. Thyroid storm is a medical emergency and mortality is high (20–50%) even with the correct treatment. After primary stabilization of the airway, breathing and oxygenation, circulation, and fluid balance, treatment includes propylthiouracil (PTU) or methimazole to block the synthesis of new thyroid hormone and b-blockers to block adrenergic effects. Iodine should not be given until after PTU has taken effect (~1.5) or more thyroid hormone will be produced. Aspirin displaces T4 from thyroid binding protein, and therefore should not be used to treat fever. T3 and T4 inhibit the release of thyrotropin-releasing hormone (TRH) from the hypothalamus, which regulates thyroid-stimulating hormone (TSH) secretion from the anterior pituitary gland.

Question 26

486. A 5-year-old boy presents with sexual precocity. Twenty-four hour melatonin concentrations are found to be lower than normal. Which of the following is true regarding melatonin? a. It is synthesized in the anterior pituitary gland. b. It regulates skin pigmentation in humans. c. Its secretion is increased by darkness. d. Its secretion is inhibited by norepinephrine from the sympathetic nervous system. e. It is synthesized from the amino acid L-arginine.

Answer 26

c Synthesis and secretion of melatonin are increased in the dark via input from norepinephrine secreted by postganglionic sympathetic neurons. Melatonin is synthesized in the pineal gland from the amino acid tryptophan. Pinealomas (tumors of the pineal gland) that destroy the pineal gland and reduce secretion of melatonin and cause hypothalamic damage may cause precocious puberty by removing the inhibitory effect of melatonin on the pituitary response to gonadotropin-releasing hormone. Melatonin causes amphibian skin to become lighter in color but has no role in the regulation of skin color in humans.

Question 27

487. A patient presents with Whipple’s triad, including plasma glucose

Answer 27

e The islets of Langerhans, which constitute 1 to 2% of the pancreatic weight, secrete insulin, glucagon, somatostatin, and pancreatic polypeptide. Each is secreted from a distinct cell type, A, B, D, and F, respectively. The islets are scattered throughout the pancreas, but are more plentiful in the tail than in the body or head.

Question 28

488. A 59-year-old man is brought to his physician’s office by his wife. She reports that he has been weak, nauseated, and urinates frequently. She has also noticed a fruity odor on her husband’s breath. A urine sample is strongly positive for ketones and the finger-stick glucose is high, leading to a presumptive bedside diagnosis of diabetes. As a result of insulin deficiency, which of the following will most likely occur? a. Increased cellular uptake of glucose b. Decreased intracellular a-glycerophosphate in liver and fat cells c. Enhanced glucose uptake and use except by brain tissue d. Decreased fatty acid release from adipose tissue e. Indirect depression of glucose utilization due to excess fatty acids in the blood

Answer 28

B a-Glycerophosphate is produced in the course of normal use of glucose. In the absence of adequate quantities of a-glycerophosphate, a normal accep- tor of free fatty acids in triglyceride synthesis, lipolysis will be the predom- inant process in adipose tissue. As a result, fatty acids will be released into the blood. The prevailing insulin level is decisive in the selection of sub- strate by a tissue for the production of energy. Insulin promotes use of car- bohydrate, and a lack of the hormone causes use of fat mainly to the exclusion of uptake and use of glucose, except by brain tissue. Indirect depression of glucose utilization due to excess fatty acids is a result, and not a contributing cause, of increased use of fat.

Question 29

489. A 24-year-old woman presents with a slightly elevated blood pressure. She has high plasma levels of T3, cortisol, and renin activity, but no symptoms or signs of thyrotoxicosis or Cushing’s syndrome. Which of the following is the most likely explanation? a. She has been treated with ACTH and TSH. b. She has been treated with T3 and cortisol. c. She has an adrenocortical tumor. d. She is in the third trimester of pregnancy. e. She has been subjected to chronic stress.

Answer 29

D Thyroxin- binding globulin (TBG) is increased in estrogen-treated patients and dur- ing pregnancy, increasing the total plasma levels of T3 and T4, but with a normal level of the free thyroid hormones, such that the clinical state is euthyroid. Cortisol levels also increase during pregnancy and parturition due to increased production of corticotropin-releasing hormone (CRH) by the placenta (as well as the fetal hypothalamus). Although tissue renin con- tributes little to the circulating renin pool, pregnancy is associated with increased renin levels that may arise from components of the tissue renin- angiotensin system found in the uterus, the placenta, and the fetal mem- branes. Amniotic fluid contains large amounts of prorenin.

Question 30

490. Which of the following hormones initiates its biological effects by activation of cell membrane receptors? a. Progesterone b. Estrogens c. Cortisol d. Thyroxine e. Epinephrine

Answer 30

E Due to their relatively low sol- ubility within the lipid portions of the cell membrane, peptide hormones and catecholamines (epinephrine) must interact with receptors located on the cell membrane. Activation of the receptor is followed by the generation of intracellular second messengers that ultimately mediate the biological response to the hormone. Steroid hormones and thyroid hormones readily pass through the cell surface membrane and interact with intracellular receptors to produce their effects by regulating gene expression within the nucleus.

Question 31

491. A 13-year-old female presents for her annual sports physical. Her height is measured at 50 inches (>3 SD below the mean for her age), and the history suggests that the girl may be suffering from anorexia nervosa. Which of the following statements about growth and development is correct? a. Growth hormone activates the JAK2-STAT pathway b. Linear growth ceases earlier in boys than in girls c. Serum IGF-I levels decrease throughout childhood d. Growth hormone is essential for prenatal linear growth e. Normal growth during puberty is independent of thyroid function

Answer 31

A Growth hor- mone activates many different intracellular enzyme cascades, including the JAK2-STAT pathway, which also mediates the effects of various growth fac- tors and prolactin. Secretion of insulin-like growth factor I (IGF-I) increases throughout childhood and stimulate cell proliferation and growth in many different cell types, including chondrocytes within growth plates. Linear growth ends earlier in girls than in boys. IGF-II is largely indepen- dent of growth hormone and plays a role in the growth of the fetus before birth. Thyroid hormones are essential for normal linear growth and skele- tal development. The growth-promoting effects of thyroid hormones occur via a synergistic effect with growth hormone.

Question 32

492. Which of the following hormones interacts with a cytoplasmic receptor and then localizes in the nucleus and directs protein and nucleotide synthesis? a. Thyrotropin-releasing hormone b. Epinephrine c. Luteinizing hormone d. Cortisol e. Insulin

Answer 32

d Cortisol, like other steroid hormones, diffuses into target cells and interacts with intracellular receptors. The steroid-receptor complex has a high affinity for the steroid- responsive element of DNA. Once bound to DNA, the hormone-receptor complex acts as a transcription factor to regulate gene expression and for- mation of specific messenger RNAs.

Question 33

493. A patient with chronic asthma is started on glucocorticoid therapy. The treatment may result in bone loss because glucocorticoids do which of the following? a. Inhibit bone formation b. Increase calcium absorption from the GI tract c. Increase osteoblast growth d. Inhibit bone resorption e. Suppress vitamin D activation

Answer 33

a (check this explanation though, for error. Cortisol should increase Ca by inhibiting OPG)... Glucocorticoids lower plasma Ca2+ levels by inhibiting osteoclast formation and activity. Over long periods of time, glucocorticoids cause osteoporosis by decreasing bone formation and increasing bone resorption. They decrease bone formation by inhibiting protein synthesis in osteoblasts. Glucocorticoids also decrease the absorption of Ca2+ and PO43– from the intestine and increase the renal excretion of these ions. Vitamin D formation is facilitated when plasma Ca2+ levels are low.

Question 34

494. A 29-year-old woman presents with paroxysmal episodes of headaches, anxiety, and palpitations. The physician suspects an anxiety disorder, but orders laboratory studies to rule out underlying disease. The lab findings of hypercalcemia and elevated urinary catecholamines suggest the possibility of Type II multiple endocrine neoplasia (MEN II). Which of the following is the hallmark of pheochromocytoma? a. Hypoglycemia b. Weight gain c. Dry skin d. Lethargy e. Hypertension

Answer 34

E The hallmark of pheochromocytoma is either sustained or paroxysmal hypertension. Pheochromocytoma is a rare catecholamine-secreting tumor of the adrenal chromaffin cells. Patients with the disease often have associated episodes of sweating, anxiety or nervousness, palpitations, headache, diaphoresis, and hyperglycemia. In adults, approximately 80% of pheochromocytomas are unilateral and solitary. The 10% rule applies to pheochromocytomas, as follows: 10% in adults are bilateral, 10% are extraadrenal, 10% are malignant, and 10% are familial, inherited as an autosomal dominant trait either alone or in combination with MEN 2 (though recent evidence suggests that 25% of patients with pheochromocytoma may have an inherited form of the disease).

Question 35

495. A 36-year-old male computer programmer works for a company that has just been acquired in a corporate take-over. He experiences symptoms of tachycardia, palpitations, and an irregular heart beat, particularly at night. His plasma catecholamine levels are found to be increased, which may result from which of the following? a. An increase in blood pressure b. An increase in blood volume c. An increase in plasma cortisol d. An increase in blood glucose e. Changing from the standing to the supine position

Answer 35

C. Phenylethanolamine-N- methyltransferase (PNMT), the enzyme that catalyzes the formation of epinephrine from norepinephrine, is found in appreciable quantities only in the brain and the adrenal medulla. Adrenal medullary PNMT is induced by glucocorticoiods and glucocorticoids are necessary for the normal develop- ment of the adrenal medulla. Circumstances that increase sympathetic nerve input to the adrenal medulla increase catecholamine secretion. Major stressors include decreased intravascular volume or pressure, fear or rage, a change in posture from supine to standing, and hypoglycemia.

Question 36

496. An 18-year-old man with hemophilia A suffered multiple internal injuries from a motorcycle accident. He is now presenting with dizziness, abdominal pain, dark patches on his elbows and knees, and cravings for chips and french fries. He is referred to an endocrinologist who makes the diagnosis of Addison’s disease, and prescribes cortisol. Cortisol administration to a patient with adrenal insufficiency will result in which of the following? a. Increased insulin sensitivity in muscle b. Enhanced wound healing c. Increased corticotropin-releasing hormone secretion d. Increased ACTH secretion e. Increased gluconeogenesis

Answer 36

e Cortisol is defined as a glucocorticoid because it promotes the conversion of amino acids to glucose (gluconeogenesis). It also decreases glucose uptake by muscle and adipocytes by decreasing the sensitivity of the cells to insulin. The net result is to provide more glucose to non-insulin-requiring cells. Cortisol retards wound healing. It also decreases CRH and ACTH secretion by feedback inhibition.

Question 37

497. An 80-year-old man reports increasing dyspnea, which worsens with exertion. Echocardiography indicates that the ejection fraction is within normal limits, but the cardiologist orders blood levels of brain natriuretic peptide and atrial natriuretic peptide to evaluate possible congestive heart failure. Which of the following statements about atrial natriuretic peptide (ANP) are correct? a. ANP enhances antidiuretic hormone (ADH) secretion. b. ANP constricts afferent renal arterioles. c. ANP acts only on the distal nephron to increase urine flow. d. ANP secretion increases when central venous pressure increases. e. ANP secretion is stimulated by hyponatremia.

Answer 37

d. Atrial natriuretic pep- tide (ANP) is synthesized, stored, and secreted by cardiac atrial muscle, the latter in response to increased central venous pressure or increased plasma sodium concentrations. ANP increases glomerular filtration by simultane- ous dilation of afferent and constriction of efferent renal arterioles. It decreases salt and water reabsorption along the entire length of the kidney. The excretion of water is enhanced by inhibition of ADH.

Question 38

498. A patient with multiple endocrine neoplasia Type I (MEN I) and acromegaly is found to have a deletion of the 11q13 region of chromosome 11, a suppressor gene for growth hormone. Growth hormone excess results in which of the following? a. Decreased gluconeogenesis b. Hypoglycemia c. Insulin resistance d. Decreased protein synthesis e. Decreased lipolysis

Answer 38

C. Patients with acromegaly have insulin resistance. In addition, they manifest increased lipolysis and increased gluconeogenesis due to their high growth hormone levels. The combination of enhanced glucose production and insulin resistance can produce hyperglycemia and diabetes mellitus. Protein synthesis increases to support tissue growth and proliferation.

Question 39

499. Sulfonylurea treatment in a diabetic patient causes a fall in the patient’s plasma glucose concentration to 45 mg/dL. Which of the following is a sign and symptom of hypoglycemia? a. Dry skin b. Bradycardia c. Insomnia d. Loss of fine motor skills e. Satiety

Answer 39

D. Hypoglycemia can lead to loss of fine motor skills. Hypoglycemia refers to abnormally low blood glucose levels and is dangerous because glucose is the primary energy source for brain cells. Dysfunction of the nervous system can lead to dizziness, headache, mental confusion, convulsion, and loss of consciousness. Increased sympathetic activity can produce sweating, tachycardia, hunger, and anxiety.

Question 40

500. Radiation treatment for a pituitary tumor in an 8-year-old boy results in the complete loss of pituitary function. As a result, the child is likely to experience which of the following symptoms? a. Hypothyroidism and goiter b. Absent sexual maturation c. Accelerated growth spurts d. Increased ACTH e. Increased TSH levels

Answer 40

B. Radiation treatment likely produced panhypopituitarism in the young child. Sexual maturation and growth during development will not occur because of low levels of GH, FSH, LF, ILGF1, TSH and thyroid hormones, and gonadal hormones. The cortisol response to stress is decreased due to low ACTH levels. A goiter cannot develop in the absence of TH.

Question 41

501. A 49-year-old male patient with AIDS and declining CD4 counts has an increased frequency of systemic infections and develops sick euthyroid syndrome with a decline in T4 and T3 levels. With normal thyroid function, which of the following is correct? a. TSH initiates thyroid hormone secretion via activation of nuclear receptors in thyroid gland cells. b. Secretion of TSH is regulated primarily by the pituitary level of T3 c. TSH is secreted from the posterior pituitary d. T4 is the physiologically active hormone e. T4 is formed from T3 by the process of monodeiodination.

Answer 41

B Secretion of TSH is regulated primarily by the pituitary levels of T3. As plasma thyroid hormone levels increase, pituitary T3 levels rise and lead to inhibition of TSH synthesis and secretion. TSH stimulates thyroid gland function by binding to specific cell membrane receptors and increasing the intracellular levels of cAMP. The thyroid gland secretes thyroxine (T4) and triiodothyronine (T3); the latter is the physiologically active hormone. The majority of T3 is formed in the peripheral tissues by deiodination of T4.

Question 42

502. The second year medical students started a hunger strike to protest the reduction in library hours. After 3 days of fasting, the students will most likely manifest which of the following? a. Decreased lipolysis b. Increased urinary excretion of nitrogen c. Decreased gluconeogenesis d. Increased glucose utilization by the brain e. Increased secretion of insulin

Answer 42

C With prolonged fasting of 3 days or more, gluconeogenesis is decreased partly due to increased ketogenesis and lipolysis. The increased availability of ketones and fatty acids as a source of fuel for brain cells decreases the demand by the brain for glucose. The decreased gluconeogenesis is reflected in a nitrogen excre- tion level at or below normal values. Insulin levels decrease beginning as early as 24 hour after a meal.