Question 1

After extensive testing, a 60-year-old man is found to have a pheochromocytoma that secretes mainly epinephrine. Which of the following signs would be expected in this patient? (A) Decreased heart rate (B) Decreased arterial blood pressure (C) Decreased excretion rate of 3-methoxy-4-hydroxymandelic acid (VMA) (D) Cold, clammy skin

Accepted Answer

The answer is D [Chapter 2, I C; Table 2.2]. Increased circulating levels of epinephrine from the adrenal medullary tumor stimulate both α-adrenergic and β-adrenergic receptors. Thus, heart rate and contractility are increased and, as a result, cardiac output is increased. Total peripheral resistance (TPR) is increased because of arteriolar vasoconstriction, which leads to decreased blood flow to the cutaneous circulation and causes cold, clammy skin. Together, the increases in cardiac output and TPR increase arterial blood pressure. 3-Methoxy-4-hydroxymandelic acid (VMA) is a metabolite of both norepinephrine and epinephrine; increased VMA excretion occurs in pheochromocytomas.

Question 2

After extensive testing, a 60-year-old man is found to have a pheochromocytoma that secretes mainly epinephrine. Symptomatic treatment would be best achieved in this man with (A) phentolamine (B) isoproterenol (C) a combination of phentolamine and isoproterenol (D) a combination of phentolamine and propranolol (E) a combination of isoproterenol and phenylephrine

Accepted Answer

The answer is D [Chapter 2, I; Table 2.3]. Treatment is directed at blocking both the α-stimulatory and β-stimulatory effects of catecholamines. Phentolamine is an α-blocking agent; propranolol is a β-blocking agent. Isoproterenol is a β1 and β2 agonist. Phenylephrine is an α1 agonist.

Question 3

The principle of positive feedback is illustrated by the effect of (A) PO2 on breathing rate (B) glucose on insulin secretion (C) estrogen on follicle-stimulating hormone (FSH) secretion at midcycle (D) blood [Ca2+] on parathyroid hormone (PTH) secretion (E) decreased blood pressure on sympathetic outflow to the heart and blood vessels

Accepted Answer

The answer is C [Chapter 7, I D; X E 2]. The effect of estrogen on the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by the anterior lobe of the pituitary gland at midcycle is one of the few examples of positive feedback in physiologic systems—increasing estrogen levels at midcycle cause increased secretion of FSH and LH. The other options illustrate negative feedback. Decreased arterial PO2 causes an increase in breathing rate (via peripheral chemoreceptors). Increased blood glucose stimulates insulin secretion. Decreased blood [Ca2+] causes an increase in parathyroid hormone (PTH) secretion. Decreased blood pressure decreases the firing rate of carotid sinus nerves (via the baroreceptors) and ultimately increases sympathetic outflow to the heart and blood vessels to return blood pressure to normal.

Question 4

A negative free-water clearance (CH2O) would occur in a person (A) who drinks 2 L of water in 30 minutes (B) after overnight water restriction (C) who is receiving lithium for the treatment of depression and has polyuria that is unresponsive to antidiuretic hormone (ADH) administration (D) with a urine flow rate of 5 mL/min, a urine osmolarity of 295 mOsm/L, and a serum osmolarity of 295 mOsm/L (E) with a urine osmolarity of 90 mOsm/L and a serum osmolarity of 310 mOsm/L after a severe head injury

Accepted Answer

The answer is B [Chapter 5, VII D; Table 5.6]. A person with a negative free-water clearance (CH2O) would, by definition, be producing urine that is hyperosmotic to blood (CH2O = V - Cosm). After overnight water restriction, serum osmolarity increases. This increase, via hypothalamic osmoreceptors, stimulates the release of antidiuretic hormone (ADH) from the posterior lobe of the pituitary. This ADH circulates to the collecting ducts of the kidney and causes reabsorption of water, which results in the production of hyperosmotic urine. Drinking large amounts of water inhibits the secretion of ADH and causes excretion of dilute urine and a positive CH2O . Lithium causes nephrogenic diabetes insipidus by blocking the response of ADH on the collecting duct cells, resulting in dilute urine and a positive CH2O . In option D, the calculated value of CH2O is zero. In option E, the calculated value of CH2O is positive.

Question 5

CO2 generated in the tissues is carried in venous blood primarily as ``` (A) CO2 in the plasma (B) H2CO3 in the plasma (C) HCO3 − in the plasma (D) CO2 in the red blood cells (RBCs) (E) carboxyhemoglobin in the RBCs ```

Accepted Answer

The answer is C [Chapter 4, V B; Figure 4.9]. CO2 generated in the tissues enters venous blood and, in the red blood cells (RBCs), combines with H2O in the presence of carbonic anhydrase to form H2CO3. H2CO3 dissociates into H+ and HCO3 −. The H+ remains in the RBCs to be buffered by deoxyhemoglobin, and the HCO3 − moves into plasma in exchange for Cl−. Thus, CO2 is carried in venous blood to the lungs as HCO3 −. In the lungs, the reactions occur in reverse: CO2 is regenerated and expired.

Question 6

In a 35-day menstrual cycle, ovulation occurs on day ``` (A) 12 (B) 14 (C) 17 (D) 21 (E) 28 ```

Accepted Answer

The answer is D [Chapter 7, X E 2]. Menses occurs 14 days after ovulation, regardless of cycle length. Therefore, in a 35-day menstrual cycle, ovulation occurs on day 21. Ovulation occurs at the midpoint of the menstrual cycle only if the cycle length is 28 days.

Question 7

Which of the following hormones stimulates the conversion of testosterone to 17β-estradiol in ovarian granulosa cells? ``` (A) Adrenocorticotropic hormone (ACTH) (B) Estradiol (C) Follicle-stimulating hormone (FSH) (D) Gonadotropin-releasing hormone (GnRH) (E) Human chorionic gonadotropin (HCG) (F) Prolactin (G) Testosterone ```

Accepted Answer

The answer is C [Chapter 7, X A]. 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. Follicle-stimulating hormone (FSH) stimulates the aromatase enzyme and increases the production of estradiol.

Question 8

Which gastrointestinal secretion is hypotonic, has a high [HCO3 −], and has its production inhibited by vagotomy? (A) Saliva (B) Gastric secretion (C) Pancreatic secretion (D) Bile

Accepted Answer

The answer is A [Chapter 6, IVA 2–4 a]. Saliva has a high [HCO3 −] because the cells lining the salivary ducts secrete HCO3 −. Because the ductal cells are relatively impermeable to water and because they reabsorb more solute (Na+ and Cl−) than they secrete (K+ and HCO3 −), the saliva is rendered hypotonic. Vagal stimulation increases saliva production, so vagotomy (or atropine) inhibits it and produces dry mouth.

Question 9

A 53-year-old man with multiple myeloma is hospitalized after 2 days of polyuria, polydipsia, and increasing confusion. Laboratory tests show an elevated serum [Ca2+] of 15 mg/dL, and treatment is initiated to decrease it. The patient' s serum osmolarity is 310 mOsm/L. The most likely reason for polyuria in this man is (A) increased circulating levels of antidiuretic hormone (ADH) (B) increased circulating levels of aldosterone (C) inhibition of the action of ADH on the renal tubule (D) stimulation of the action of ADH on the renal tubule (E) psychogenic water drinking 13. The treatment drug is administered in error and produces a further increase in the patient's serum [Ca2+]. That drug is (a) a thiazide diuretic (B) a loop diuretic (C) calcitonin (d) mithramycin (e) etidronate disodium 14. Which of the following substances acts on its target cells via an inositol 1,4,5-triphosphate (IP3)–Ca2+ mechanism? (a) Somatomedins acting on chondrocytes (B) Oxytocin acting on myoepithelial cells of the breast (C) Antidiuretic hormone (ADH) acting on the renal collecting duct (d) Adrenocorticotropic hormone (ACTH) acting on the adrenal cortex (e) Thyroid hormone acting on skeletal muscle

Accepted Answer

The answer is C [Chapter 5, VII D 3; Table 5.6]. The most likely explanation for this patient's polyuria is hypercalcemia. With severe hypercalcemia, Ca2+ accumulates in the inner medulla and papilla of the kidney and inhibits adenylate cyclase, blocking the effect of ADH on water permeability. Because ADH is ineffective, the urine cannot be concentrated and the patient excretes large volumes of dilute urine. His polydipsia is secondary to his polyuria and is caused by the increased serum osmolarity. Psychogenic water drinking would also cause polyuria, but the serum osmolarity would be lower than normal, not higher than normal.

Question 10

A 53-year-old man with multiple myeloma is hospitalized after 2 days of polyuria, polydip-sia, and increasing confusion. Laboratory tests show an elevated serum [Ca2+] of 15 mg/dL, and treatment is initiated to decrease it. The patient' s serum osmolarity is 310 mOsm/L. The treatment drug is administered in error and produces a further increase in the patient's serum [Ca2+]. That drug is ``` (A) a thiazide diuretic (B) a loop diuretic (C) calcitonin (D) mithramycin (E) etidronate disodium ```

Accepted Answer

The answer is A [Chapter 5, VI C]. Thiazide diuretics would be contraindicated in a patient with severe hypercalcemia because these drugs cause increased Ca2+ reabsorption in the renal distal tubule. On the other hand, loop diuretics inhibit Ca2+ and Na+ reabsorption and produce calciuresis. When given with fluid replacement, loop diuretics can effectively and rapidly lower the serum [Ca2+]. Calcitonin, mithramycin, and etidronate disodium inhibit bone resorption and, as a result, decrease serum [Ca2+].

Question 11

Which of the following substances acts on its target cells via an inositol 1,4,5-triphosphate (IP3)–Ca2+ mechanism? (A) Somatomedins acting on chondrocytes (B) Oxytocin acting on myoepithelial cells of the breast (C) Antidiuretic hormone (ADH) acting on the renal collecting duct (D) Adrenocorticotropic hormone (ACTH) acting on the adrenal cortex (E) Thyroid hormone acting on skeletal muscle

Accepted Answer

The answer is B [Chapter 7; Table 7.2]. Oxytocin causes contraction of the myoepithelial cells of the breast by an inositol 1,4,5-triphosphate (IP3)–Ca2+ mechanism. Somatomedins (insulin-like growth factor [IGF]), like insulin, act on target cells by activating tyrosine kinase. Antidiuretic hormone (ADH) acts on the V2 receptors of the renal collecting duct by a cyclic adenosine monophosphate (cAMP) mechanism (although in vascular smooth muscle it acts on V1 receptors by an IP3 mechanism). Adrenocorticotropic hormone (ACTH) also acts via a cAMP mechanism. Thyroid hormone induces the synthesis of new protein (e.g., Na+,K+-adenosine triphosphatase [ATPase]) by a steroid hormone mechanism.

Question 12

A key difference in the mechanism of excitation–contraction coupling between the muscle of the pharynx and the muscle of the wall of the small intestine is that (A) slow waves are present in the pharynx, but not in the small intestine (B) adenosine triphosphate (ATP) is used for contraction in the pharynx, but not in the small intestine (C) intracellular [Ca2+] is increased after excitation in the pharynx, but not in the small intestine (D) action potentials depolarize the muscle of the small intestine, but not of the pharynx (E) Ca2+ binds to troponin C in the pharynx, but not in the small intestine, to initiate contraction

Accepted Answer

The answer is E [Chapter 1, VI B; VII B; Table 1.3]. The pharynx is skeletal muscle, and the small intestine is unitary smooth muscle. The difference between smooth and skeletal muscle is the mechanism by which Ca2+ initiates contraction. In smooth muscle, Ca2+ binds to calmodulin, and in skeletal muscle, Ca2+ binds to troponin C. Both types of muscle are excited to contract by action potentials. Slow waves are present in smooth muscle but not skeletal muscle. Both smooth and skeletal muscle require an increase in intracellular [Ca2+] as the important linkage between excitation (the action potential) and contraction, and both consume adenosine triphosphate (ATP) during contraction.

Question 13

A 40-year-old woman has an arterial pH of 7.25, an arterial Pco2 of 30 mm Hg, and serum [K+] of 2.8 mEq/L. Her blood pressure is 100/80 mm Hg when supine and 80/50 mm Hg when standing. What is the cause of her abnormal blood values? (A) Vomiting (B) Diarrhea (C) Treatment with a loop diuretic (D) Treatment with a thiazide diuretic

Accepted Answer

The answer is B [Chapter 5, IX D; Table 5.9]. The arterial blood values and physical findings are consistent with metabolic acidosis, hypokalemia, and orthostatic hypotension. Diarrhea is associated with the loss of HCO3− and K+ from the gastrointestinal (GI) tract, consistent with the laboratory values. Hypotension is consistent with extracellular fluid (ECF) volume contraction. Vomiting would cause metabolic alkalosis and hypokalemia. Treatment with loop or thiazide diuretics could cause volume contraction and hypokalemia, but would cause metabolic alkalosis rather than metabolic acidosis.

Question 14

Secretion of HCl by gastric parietal cells is needed for ``` (A) activation of pancreatic lipases (B) activation of salivary lipases (C) activation of intrinsic factor (D) activation of pepsinogen to pepsin (E) the formation of micelles ```

Accepted Answer

The answer is D [Chapter 6, V B 1 c]. Pepsinogen is secreted by the gastric chief cells and is activated to pepsin by the low pH of the stomach (created by secretion of HCl by the gastric parietal cells). Lipases are inactivated by low pH.

Question 15

Which of the following would cause an increase in glomerular filtration rate (GFR)? (A) Constriction of the afferent arteriole (B) Constriction of the efferent arteriole (C) Constriction of the ureter (D) Increased plasma protein concentration (E) Infusion of inulin

Accepted Answer

The answer is B [Chapter 5, II C 6; Table 5.3]. Glomerular filtration rate (GFR) is determined by the balance of Starling forces across the glomerular capillary wall. Constriction of the efferent arteriole increases the glomerular capillary hydrostatic pressure (because blood is restricted in leaving the glomerular capillary), thus favoring filtration. Constriction of the afferent arteriole would have the opposite effect and would reduce the glomerular capillary hydrostatic pressure. Constriction of the ureter would increase the hydrostatic pressure in the tubule and, therefore, oppose filtration. Increased plasma protein concentration would increase the glomerular capillary oncotic pressure and oppose filtration. Infusion of inulin is used to measure the GFR and does not alter the Starling forces.

Question 16

Fat absorption occurs primarily in the ``` (A) stomach (B) jejunum (C) terminal ileum (D) cecum (E) sigmoid colon ```

Accepted Answer

The answer is B [Chapter 6, V C 1, 2]. First, fat absorption requires the breakdown of dietary lipids to fatty acids, monoglycerides, and cholesterol in the duodenum by pancreatic lipases. Second, fat absorption requires the presence of bile acids, which are secreted into the small intestine by the gallbladder. These bile acids form micelles around the products of lipid digestion and deliver them to the absorbing surface of the small intestinal cells. Because the bile acids are recirculated to the liver from the ileum, fat absorption must be complete before the chyme reaches the terminal ileum.

Question 17

Which of the following hormones causes constriction of vascular smooth muscle through an inositol 1,4,5-triphosphate (IP3) second messenger system? ``` (A) Antidiuretic hormone (ADH) (B) Aldosterone (C) Dopamine (D) Oxytocin (E) Parathyroid hormone (PTH) ```

Accepted Answer

The answer is A [Chapter 7, III C 1 b]. Antidiuretic hormone (ADH) causes constriction of vascular smooth muscle by activating a V1 receptor that uses the inositol 1,4,5-triphosphate (IP3) and Ca2+ second messenger system. When hemorrhage or extracellular fluid (ECF) volume contraction occurs, ADH secretion by the posterior pituitary is stimulated via volume receptors. The resulting increase in ADH levels causes increased water reabsorption by the collecting ducts (V2 receptors) and vasoconstriction (V1 receptors) to help restore blood pressure.

Question 18

A 30-year-old woman has the anterior lobe of her pituitary gland surgically removed because of a tumor. Without hormone replacement therapy, which of the following would occur after the operation? (A) Absence of menses (B) Inability to concentrate the urine in response to water deprivation (C) Failure to secrete catecholamines in response to stress (D) Failure to secrete insulin in a glucose tolerance test (E) Failure to secrete parathyroid hormone (PTH) in response to hypocalcemia

Accepted Answer

The answer is A [Chapter 7, III B]. Normal menstrual cycles depend on the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. Concentration of urine in response to water deprivation depends on the secretion of antidiuretic hormone (ADH) by the posterior pituitary. Catecholamines are secreted by the adrenal medulla in response to stress, but anterior pituitary hormones are not involved. Anterior pituitary hormones are not involved in the direct effect of glucose on the beta cells of the pancreas or in the direct effect of Ca2+ on the chief cells of the parathyroid gland.

Question 19

Which of the following responses occurs as a result of tapping on the patellar tendon? (A) Stimulation of Ib afferent fibers in the muscle spindle (B) Inhibition of Ia afferent fibers in the muscle spindle (C) Relaxation of the quadriceps muscle (D) Contraction of the quadriceps muscle (E) Inhibition of α-motoneurons

Accepted Answer

The answer is D [Chapter 2, III C 1; Figure 2.9]. When the patellar tendon is stretched, the quadriceps muscle also stretches. This movement activates Ia afferent fibers of the muscle spindles, which are arranged in parallel formation in the muscle. These Ia afferent fibers form synapses on α-motoneurons in the spinal cord. In turn, the pool of α-motoneurons is activated and causes reflex contraction of the quadriceps muscle to return it to its resting length.

Question 20

A 5-year-old boy has a severe sore throat, high fever, and cervical adenopathy. It is suspected that the causative agent is Streptococcus pyogenes. Which of the following is involved in producing fever in this patient? (A) Increased production of interleukin-1 (IL-1) (B) Decreased production of prostaglandins (C) Decreased set-point temperature in the hypothalamus (D) Decreased metabolic rate (E) Vasodilation of blood vessels in the skin

Accepted Answer

The answer is A [Chapter 2, VI C]. Streptococcus pyogenes causes increased production of interleukin-1 (IL-1) in macrophages. IL-1 acts on the anterior hypothalamus to increase the production of prostaglandins, which increase the hypothalamic set-point temperature. The hypothalamus then “reads” the core temperature as being lower than the new set-point temperature and activates various heat-generating mechanisms that increase body temperature (fever). These mechanisms include shivering and vasoconstriction of blood vessels in the skin.

Question 21

A 5-year-old boy has a severe sore throat, high fever, and cervical adenopathy. Before antibiotic therapy is initiated, the patient is given aspirin to reduce his fever. The mechanism of fever reduction by aspirin is (A) shivering (B) stimulation of cyclooxygenase (C) inhibition of prostaglandin synthesis (D) shunting of blood from the surface of the skin (E) increasing the hypothalamic set-point temperature

Accepted Answer

The answer is C [Chapter 2, VI C 2]. By inhibiting cyclooxygenase, aspirin inhibits the production of prostaglandins and lowers the hypothalamic set-point temperature to its original value. After aspirin treatment, the hypothalamus “reads” the body temperature as being higher than the set-point temperature and activates heat-loss mechanisms, including sweating and vasodilation of skin blood vessels. This vasodilation shunts blood toward the surface skin. When heat is lost from the body by these mechanisms, body temperature is reduced.

Question 22

Arterial pH of 7.52, arterial Pco2 of 26 mm Hg, and tingling and numbness in the feet and hands would be observed in a (A) patient with chronic diabetic ketoacidosis (B) patient with chronic renal failure (C) patient with chronic emphysema and bronchitis (D) patient who hyperventilates on a commuter flight (E) patient who is taking a carbonic anhydrase inhibitor for glaucoma (F) patient with a pyloric obstruction who vomits for 5 days (G) healthy person

Accepted Answer

The answer is D [Chapter 5, IX D 4; Table 5.9]. The blood values are consistent with acute respiratory alkalosis from hysterical hyperventilation. The tingling and numbness are symptoms of a reduction in serum ionized [Ca2+] that occurs secondary to alkalosis. Because of the reduction in [H+], fewer H+ ions will bind to negatively charged sites on plasma proteins, and more Ca2+ binds (decreasing the free ionized [Ca2+]).

Question 23

Albuterol is useful in the treatment of asthma because it acts as an agonist at which of the following receptors? ``` (A) α1 Receptor (B) β1 Receptor (C) β2 Receptor (D) Muscarinic receptor (E) Nicotinic receptor ```

Accepted Answer

The answer is C [Chapter 2, I C 1 d]. Albuterol is an adrenergic β2 agonist. When activated, the b2 receptors in the bronchioles produce bronchodilation.

Question 24

Which of the following hormones is converted to its active form in target tissues by the action of 5α-reductase? ``` (A) Adrenocorticotropic hormone (ACTH) (B) Aldosterone (C) Estradiol (D) Prolactin (E) Testosterone ```

Accepted Answer

The answer is E [Chapter 7, IX A; Figure 7.16]. Testosterone is converted to its active form, dihydrotestosterone, in some target tissues by the action of 5α-reductase.

Question 25

If an artery is partially occluded by an embolism such that its radius becomes one-half the preocclusion value, which of the following parameters will increase by a factor of 16? (A) Blood flow (B) Resistance (C) Pressure gradient (D) Capacitance

Accepted Answer

The answer is B [Chapter 3, II C, D]. A decrease in radius causes an increase in resistance, as described by the Poiseuille relationship (resistance is inversely proportional to r4). Thus, if radius decreases twofold, the resistance will increase by (2)4 or 16-fold.

Question 26

If heart rate increases, which phase of the cardiac cycle is decreased? (A) Atrial systole (B) Isovolumetric ventricular contraction (C) Rapid ventricular ejection (D) Reduced ventricular ejection (E) Isovolumetric ventricular relaxation (F) Rapid ventricular filling (G) Reduced ventricular filling

Accepted Answer

The answer is G [Chapter 3, V; Figure 3.15]. When heart rate increases, the time between ventricular contractions (for refilling of the ventricles with blood) decreases. Because most ventricular filling occurs during the “reduced” phase, this phase is the most compromised by an increase in heart rate.

Question 27

A 17-year-old boy is brought to the emer-gency department after being injured in an automobile accident and sustaining signifi-cant blood loss. He is given a transfusion of 3 units of blood to stabilize his blood pressure. Before the transfusion, which of the following was true about his condition? (A) His total peripheral resistance (TPR) was decreased (B) His heart rate was decreased (C) The firing rate of his carotid sinus nerves was increased (D) Sympathetic outflow to his heart and blood vessels was increased

Accepted Answer

The answer is D [Chapter 3, IX C; Table 3.6; Figure 3.21]. The blood loss that occurred in the accident caused a decrease in arterial blood pressure. The decrease in arterial pressure was detected by the baroreceptors in the carotid sinus and caused a decrease in the firing rate of the carotid sinus nerves. As a result of the baroreceptor response, sympathetic outflow to the heart and blood vessels increased, and parasympathetic outflow to the heart decreased. Together, these changes caused an increased heart rate, increased contractility, and increased total peripheral resistance (TPR) (in an attempt to restore the arterial blood pressure).

Question 28

A 17-year-old boy is brought to the emer-gency department after being injured in an automobile accident and sustaining signifi-cant blood loss. He is given a transfusion of 3 units of blood to stabilize his blood pressure. Which of the following is a consequence of the decrease in blood volume in this patient? (A) Increased renal perfusion pressure (B) Increased circulating levels of angiotensin II (C) Decreased renal Na+ reabsorption (D) Decreased renal K+ secretion

Accepted Answer

The answer is B [Chapter 3, IX C; Table 3.6; Figure 3.21; Chapter 5 IV C 3 b (1)]. The decreased blood volume causes decreased renal perfusion pressure, which initiates a cascade of events, including increased renin secretion, increased circulating angiotensin II, increased aldosterone secretion, increased Na+ reabsorption, and increased K+ secretion by the renal tubule.

Question 29

A 37-year-old woman suffers a severe head injury in a skiing accident. Shortly thereafter, she becomes polydipsic and polyuric. Her urine osmolarity is 75 mOsm/L, and her serum osmolarity is 305 mOsm/L. Treatment with 1-deamino-8-d-arginine vasopressin (dDAVP) causes an increase in her urine osmolarity to 450 mOsm/L. Which diagnosis is correct? ``` (A) Primary polydipsia (B) Central diabetes insipidus (C) Nephrogenic diabetes insipidus (D) Water deprivation (E) Syndrome of inappropriate antidiuretic hormone (SIADH) ```

Accepted Answer

The answer is B [Chapter 5, VII C; Table 5.6]. A history of head injury with production of dilute urine accompanied by elevated serum osmolarity suggests central diabetes insipidus. The response of the kidney to exogenous antidiuretic hormone (ADH) (1-deamino-8-d-arginine vasopressin [dDAVP]) eliminates nephrogenic diabetes insipidus as the cause of the concentrating defect.

Question 30

Which diuretic inhibits Na+ reabsorption and K+ secretion in the distal tubule by acting as an aldosterone antagonist? (A) Acetazolamide (B) Chlorothiazide (C) Furosemide (D) Spironolactone

Accepted Answer

The answer is D [Chapter 5, IV C 3 b (1); Table 5.11]. Spironolactone inhibits distal tubule Na+ reabsorption and K+ secretion by acting as an aldosterone antagonist.

Question 31

Which gastrointestinal secretion has a component that is required for the intestinal absorption of vitamin B12? (A) Saliva (B) Gastric secretion (C) Pancreatic secretion (D) Bile

Accepted Answer

The answer is B [Chapter 6, V E 1 c; Table 6.3]. Gastric parietal cells secrete intrinsic factor, which is required for the intestinal absorption of vitamin B12.

Question 32

Secretion of which of the following hormones is stimulated by extracellular fluid volume expansion? ``` (A) Antidiuretic hormone (ADH) (B) Aldosterone (C) Atrial natriuretic peptide (ANP) (D) 1,25-Dihydroxycholecalciferol (E) Parathyroid hormone (PTH) ```

Accepted Answer

The answer is C [Chapter 3, VI C 4]. Atrial natriuretic peptide (ANP) is secreted by the atria in response to extracellular fluid volume expansion and subsequently acts on the kidney to cause increased excretion of Na+ and H2O.

Question 33

Which step in the steroid hormone synthetic pathway is stimulated by angiotensin II? ``` (A) Aldosterone synthase (B) Aromatase (C) Cholesterol desmolase (D) 17,20-Lyase (E) 5α-Reductase ```

Accepted Answer

The answer is A [Chapter 7, V A 2 b; Figure 7.11]. Angiotensin II increases production of aldosterone by stimulating aldosterone synthase, the enzyme that catalyzes the conversion of corticosterone to aldosterone.

Question 34

Which of the following is the first step in the biosynthetic pathway for thyroid hormones that is inhibited by propylthiouracil? ``` (A) Iodide (I−) pump (B) I− →I2 (C) I2 + tyrosine (D) Diiodotyrosine (DIT) + DIT (E) Thyroxine (T4)→triiodothyronine (T3) ```

Accepted Answer

The answer is B [Chapter 7, IV A 2]. The oxidation of I− to I2 is catalyzed by peroxidase and inhibited by propylthiouracil, which can be used in the treatment of hyperthyroidism. Later steps in the pathway that are catalyzed by peroxidase and inhibited by propylthiouracil are iodination of tyrosine, coupling of diiodotyrosine (DIT) and DIT, and coupling of DIT and monoiodotyrosine (MIT).

Question 35

Arterial pH of 7.29, arterial [HCO3 −] of 14 mEq/L, increased urinary excretion of NH4 +, and hyperventilation would be observed in a (A) patient with chronic diabetic ketoacidosis (B) patient with chronic renal failure (C) patient with chronic emphysema and bronchitis (D) patient who hyperventilates on a commuter flight (E) patient who is taking a carbonic anhydrase inhibitor for glaucoma (F) patient with a pyloric obstruction who vomits for 5 days (G) healthy person

Accepted Answer

The answer is A [Chapter 5, IX D 1; Table 5.9]. The blood values are consistent with metabolic acidosis, as would occur in diabetic ketoacidosis. Hyperventilation is the respiratory compensation for metabolic acidosis. Increased urinary excretion of NH4 + reflects the adaptive increase in NH3 synthesis that occurs in chronic acidosis. Patients with metabolic acidosis secondary to chronic renal failure would have reduced NH4+ excretion (because of diseased renal tissue).

Question 36

Activation of which of the following receptors increases total peripheral resistance (TPR)? ``` (A) α1 Receptor (B) β1 Receptor (C) β2 Receptor (D) Muscarinic receptor (E) Nicotinic receptor ```

Accepted Answer

The answer is A [Chapter 2, I C 1 a]. When adrenergic α1 receptors on the vascular smooth muscle are activated, they cause vasoconstriction and increased total peripheral resistance (TPR).

Question 37

The receptor for this hormone has tyrosine kinase activity. ``` (A) Adrenocorticotropic hormone (ACTH) (B) Antidiuretic hormone (ADH) (C) Aldosterone (D) Insulin (E) Parathyroid hormone (PTH) (F) Somatostatin ```

Accepted Answer

The answer is D [Chapter 7; Table 7.2]. Hormone receptors with tyrosine kinase activity include those for insulin and for insulin-like growth factors (IGF). The β subunits of the insulin receptor have tyrosine kinase activity and, when activated by insulin, the receptors autophosphorylate. The phosphorylated receptors then phosphorylase intracellular proteins; this process ultimately results in the physiologic actions of insulin.

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