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65 Cards in this Set
- Front
- Back
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Which of the following would be present in a patient with a small-cell carcinoma of the lung that autonomously secretes vasopressin?
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A. Blood volume contraction
B. Decreased plasma atrial natriuretic peptide C. Hypernatremia D. Inappropriately concentrated urine E. Increased thirst The correct answer is D. A tumor that ectopically secretes vasopressin can produce a disorder called the syndrome of inappropriate antidiuretic hormone (SIADH). Hypovolemia physiologically stimulates ADH (vasopressin) secretion, so the diagnosis of SIADH is made only if the patient is euvolemic. A hallmark of this disorder is excessive renal retention of free water with resultant hypervolemia, not blood volume contraction (choice A), and dilutional hyponatremia, not hypernatremia (choice C). The volume expansion leads to increased, not decreased (choice B), secretion of atrial natriuretic peptide (ANP) by atrial myocytes. The increased ANP is one of the factors that causes the kidney to increase sodium excretion and produce an inappropriately concentrated urine. Urine is typically hypertonic to plasma in this disorder. The volume expansion also tends to suppress renin secretion, and the resultant decrease in serum aldosterone may also contribute to the increased renal sodium excretion. The dilutional hypotonicity would inhibit, not stimulate (choice E), hypothalamic thirst mechanisms. |
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On stimulating the afferent portions of the glossopharyngeal and vagus nerves, which of the following outcomes would most likely occur?
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A. Bradycardia with hypertension
B. Bradycardia with hypotension C. Sinus arrhythmia with hypotension D. Tachycardia with hypertension E. Tachycardia with hypotension The correct answer is B. The glossopharyngeal nerve (CN IX) and the vagus nerve (CN X) carry afferent information to the medulla from the carotid sinus and aortic arch baroreceptors, respectively. The firing rate of these neurons increases with increasing blood pressure. By artificially increasing the firing rate of these nerves, the medulla therefore receives a false signal that indicates that the blood pressure is too high. This elicits a baroreceptor reflex, resulting in a decrease in sympathetic outflow and an increase in parasympathetic outflow, which leads to bradycardia and hypotension. Physiologically the glossopharyngeal nerve innervates the sensory nuclei of the medulla oblongata. The somatic motor portion innervates the muscles involved with swallowing. The visceral motor portion affects the parotid salivary gland by way of the otic ganglion. The vagus nerve innervates the sensory fibers to sensory nuclei and autonomic centers of the medulla oblongata. The visceral motor fibers go to muscles of the palate, pharynx, digestive, respiratory, and cardiovascular systems in the thoracic and abdominal cavities. |
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Which of the following controls the salivary secretion?
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A. Parasympathetic nervous system
B. Gastrin C. Secretin D. CCK The correct answer is A. Salivary secretion is almost entirely under control of the parasympathetic system. Sympathetic stimulation causes transient minor stimulation. Parotid secretion is stimulated by parasympathetic stimulation from CN IX, whereas submandibular and sublingual secretion is stimulated by parasympathetic stimulation from CN VII. Choice B - Gastric secretion is stimulated by gastrin. Choice C - Pancreatic secretion is stimulated by secretin. Choice D - CCK stimulates bile secretion. |
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Erythropoietin stimulates which of the following intermediates in hematopoiesis?
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A. Basophilic erythroblasts
B. Colony forming units-erythroid (CFU-E) C. Multipotential stem cells D. Proerythroblasts E. Reticulocytes The correct answer is B. The colony forming unit-erythroid (CFU-E) is a unipotential stem cell that develops from a burst forming unit-erythroid (BFU-E), which develops eventually from the multipotential stem cell. The BFU-E is somewhat responsive to erythropoietin, but the CFU-E is completely dependent on erythropoietin. Erythropoietin is normally released from the kidney in response to hypoxic or anemic conditions. The basophilic erythroblast (choice A) differentiates from the proerythroblast. It is recongnizable by light microscopy and has a dark basophilic staining due to hemoglobin synthesis. It is not directly affected by erythropoietin, but is instead indirectly increased by the increase in precursor cells from the increase in CFU-E earlier in development. The multipotential stem cell (choice C) appears earlier in development than CFU-E and does not increase with erythropoietin. The development of all major components of blood (RBC, WBC, and platelets) begins with the multipotential stem cell (CFU-S). This cell is noncommitted and can self-renew. It is located in the bone marrow and is not recognizable by light microscopy. The proerythroblast (choice D), which is the first recognizable cell in the red cell lineage, develops from the CFU-E cell. It is not affected directly by erythropoietin, but instead increases in number from the increased CFU-E cells. The reticulocyte (choice E) is the enucleated cell just before the mature red blood cell. Reticulocytes enter the peripheral circulation but continue to synthesize hemoglobin. This cell is not directly stimulated by erythropoietin, but increases in number as a result of the increase in precursors. |
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In a controlled experiment, radiolabeled ATP is injected into an isolated muscle. The muscle is stimulated and allowed to contract for 10 seconds. An autoradiogram from a biopsy of the muscle will show radiolabeled ATP bound to
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A. actin
B. myosin C. sarcoplasmic reticulum D. tropomyosin E. troponin C The correct answer is B. During the contraction cycle, ATP binds to myosin, causing the dissociation of myosin from actin. Actin (choice A) forms cross-bridges with myosin but does not bind to ATP. The sarcoplasmic reticulum (choice C) is involved in storing and releasing Ca2+ for muscle contraction. Tropomyosin (choice D) is a thin filament that runs alongside actin. In the absence of calcium, tropomyosin lies in the groove of the actin filament and blocks actin's myosin-binding sites. Troponin C (choice E) is the calcium-binding subunit of the troponin complex. When troponin C binds calcium, a conformational change causes tropomyosin to shift, thereby exposing the myosin-binding sites on actin. |
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Which of the following would shift the oxygen-hemoglobin dissociation curve to the right?
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A. Carbon monoxide poisoning
B. Decreased PCO2 C. Decreased pH D. Decreased temperature E. Decreased 2,3-DPG The correct answer is C. The loading of O2 is facilitated when the oxygen dissociation curve shifts to the left, and the unloading of O2 is facilitated when the oxygen dissociation curve shifts to the right. A good way to remember the conditions that promote dissociation of O2 is to think of exercising muscle, which has decreased pH (choice C) because of the accumulation of lactic acid, increased PCO2 (compare with choice B) because of the increased rate of aerobic metabolism, increased temperature (compare with choice D), and increased 2,3-DPG (2,3-diphosphoglycerate; compare with choice E) because of increased glycolysis. Carbon monoxide poisoning (choice A) left-shifts the oxygen dissociation curve, which interferes with the unloading of O2. Carbon monoxide also strongly binds to available sites on hemoglobin. |
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After a total gastrectomy, which of the following digestive enzymes will be produced in inadequate amounts?
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A. Amylase
B. Chymotrypsin C. Lipase D. Pepsin E. Trypsin The correct answer is D. Gastrectomy is removal of the entire stomach. Pepsin is secreted (in an inactive, or zymogen, form, as pepsinogen) by the chief cells of the stomach. Pepsinogen is activated by contact with stomach acid. Although protein digestion usually begins with the actions of hydrochloric acid and pepsin, pancreatic enzymes complete the job as the food passes into the small intestine. Amylases (choice A) hydrolyze 1, 4 glycosidic linkages of starches to produce oligosaccharides, maltose, maltotriose, and dextrins. Amylases are produced by the pancreas and salivary glands. Chymotrypsin (choice B) is a proteolytic enzyme released by the pancreas as the inactive proenzyme, chymotrypsinogen. Lipases (choice C) are mostly released by the pancreas and serve to digest various lipids, including triacylglycerols. Trypsin (choice E) is a proteolytic enzyme released by the pancreas as the inactive proenzyme trypsinogen. |
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Which of the following cardiovascular changes is most likely to occur when changing from a standing to a supine position?
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A. Decreased myocardial contractility
B. Decreased total peripheral resistance C. Dilation of large veins D. Increased pulse E. Increased renal blood flow The correct answer is D. Baroreceptors detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts. The baroreceptor mechanism is important for maintaining arterial pressure when a person sits or stands from a lying position. When a person suddenly stands, the blood pressure in the brain and upper body tends to fall, which initiates a strong sympathetic discharge throughout the body aimed at returning blood pressure to normal. Increasing sympathetic stimulation to the heart causes an increase in heart rate, conduction velocity, and myocardial contractility (compare with choice A). The sympathetic stimulation also causes constriction of nearly all the arterioles in the body, which greatly increases the total peripheral resistance (compare with choice B). Sympathetic stimulation of the renal vasculature leads to a decrease in renal blood flow (compare with choice E). Constriction of large veins (compare with choice C) increases venous return to the heart, causing the heart to pump increased amounts of blood. |
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A man competing in a weightlifting competition lifts 325 lb over his head and holds it there for 5 seconds. Suddenly, his arms give way and he drops the weight to the floor. Which of the following receptors is responsible for this sudden muscle relaxation?
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A. Free nerve endings
B. Golgi tendon organ C. Merkel disk D. Muscle spindle E. Pacinian corpuscle The correct answer is B. Normally, stretching of muscle results in a reflex contraction: the harder the stretch, the stronger the contraction. At a certain point, when the tension becomes too great, the contracting muscle suddenly relaxes. The reflex that underlies this sudden muscle relaxation is called the Golgi tendon organ (GTO) reflex, also known as the inverse stretch reflex or autogenic inhibition. The GTO is an extensive arborization of nerve endings that is connected in series with the extrafusal skeletal muscle fibers. As a result, GTOs respond to muscle tension rather than muscle length. Increased tension leads to stimulation of Ib afferents, which inhibit the homonymous muscle by way of spinal interneurons. Free nerve endings (choice A) are unmyelinated, unencapsulated nerve endings that penetrate the epidermis. These types of receptors respond to pain and temperature. Merkel disks (choice C) are composed of specialized tactile epidermal cells and their associated nerve endings. They are located in the basal layer of the epithelium and are slowly adapting receptors that respond to touch and pressure. Muscle spindles (choice D) are spindle-shaped bundles of muscle fibers (intrafusal fibers) that are arranged in parallel with extrafusal skeletal muscle fibers, so they sense the length of the muscle. They are innervated by Group Ia and II sensory afferent neurons. Pacinian corpuscles (choice E) are unmyelinated nerve endings surrounded by thin, concentric layers of epithelioid fibroblasts. In transverse section, this receptor resembles a sliced onion. They are found primarily in the deep layer of the dermis, loose connective tissue, male and female genitalia, mesentery, and visceral ligaments. They are rapidly adapting receptors that respond to touch and pressure. |
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During the early stages of infection, which of the following compounds exert the most powerful chemotactic effect on neutrophils, causing them to migrate into an inflamed area?
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A. C5a and IL-8
B. IL-1 and tumor necrosis factor C. LTC4 and LTD4 D. PGI2 and PGD2 E. Thromboxane and platelet activating factor The correct answer is A. The most important chemotactic factors for neutrophils are the complement factor C5a and the interleukin IL-8. The cytokines IL-1 and tumor necrosis factor (choice B) have complex, similar actions, including stimulation of production of many acute-phase reactions, stimulation of fibroblasts, and stimulation of endothelium. Leukotrienes LTC4 and LTD4 (choice C) cause increased vascular permeability. Prostaglandins PGI2 and PGD2 (choice D) mediate vasodilation and pain. Thromboxane and platelet activating factor (choice E) induce platelet changes. |
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Which of the following is decreased as a result of hyperventilation?
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A. Arterial oxygen content
B. Arterial oxygen tension (PO2) C. Arterial pH D. Cerebral blood flow E. Cerebrovascular resistance The correct answer is D. The key symptom is hyperventilation, which occurs if the rate and depth of respiration exceeds the demands for oxygen delivery and carbon dioxide removal. Hyperventilation results in hypocapnia, alkalosis, increased cerebrovascular resistance, and decreased cerebral blood flow. Carbon dioxide plays an important role in the control of cerebral blood flow. An increase in arterial PCO2 dilates blood vessels in the brain and a decrease in PCO2 causes vasoconstriction. The anxious, hyperventilating woman is "blowing off" carbon dioxide, which lowers her arterial PCO2, causing the cerebrovascular resistance (choice E) to increase, thereby decreasing cerebral blood flow. The decrease in cerebral blood flow has caused the woman to feel faint and to have blurred vision. Other symptoms commonly associated with the hyperventilation of anxiety states are feelings of tightness in the chest and a sense of suffocation. Hyperventilation increases the arterial oxygen content (choice A) and PO2(choice B) in a normal person. A decrease in arterial PCO2 causes the arterial pH (choice C) to increase (i.e., the patient becomes alkalotic). |
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Following electrical stimulation of the raphe nuclei, which of the following neurotransmitter levels would be expected to increase?
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A. Acetylcholine
B. Dopamine C. Gamma-amino-butyric acid (GABA) D. Norepinephrine E. Serotonin The correct answer is E. Serotonin is the primary neurotransmitter of the raphe nuclei. Ascending serotonin projections from the dorsal and median raphe nuclei distribute diffusely throughout the brain. Other raphe nuclei provide descending serotonin projections to the spinal cord and brainstem. Cell bodies that contain acetylcholine (choice A) are found in the basal nucleus of Meynert (which degenerates in Alzheimer disease), in the medial septum and diagonal band complex, and in the striatum. Dopamine- (choice B) containing cell bodies are found in the midbrain (in the substantia nigra pars compacta and in the ventral tegmental area). The cell bodies in the hypothalamus contribute to the tuberoinfundibular pathway. GABA (choice C) is the primary inhibitory neurotransmitter of the brain and is therefore located throughout the brain. Norepinephrine- (choice D) containing neurons are found predominantly in the locus ceruleus of the pons and midbrain. |
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A boy is found to have multiple arteriovenous fistulas involving small cutaneous and subcutaneous arteries and veins of the right leg. Which of the following would be increased in a blood sample taken from the boy's right femoral vein?
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A. Carbon dioxide content
B. Hematocrit C. Oxygen content D. Plasma sodium concentration E. Total protein concentration The correct answer is C. Congenital arteriovenous fistulas are often associated with limb swelling and hypertrophy, visible pulsations when the fistulas are large, cosmetic changes when the fistulas are in the subcutaneous tissues and skin, and varicose veins. The venous pressure is frequently increased and the skin is often warmer compared with the opposite extremity. Because blood flowing through the fistulas has by-passed the tissues of the extremity, the oxygen content of venous blood from the involved limb is elevated as compared with the opposite limb, which is the pathognomonic sign of arteriovenous fistula. Because much of the femoral venous blood has bypassed the tissues, its carbon dioxide content (choice A) is expected to be lower compared with venous blood of the opposite extremity (i.e., it should be closer to that of arterial blood). The venous hematocrit (choice B) is normally slightly greater compared with arterial hematocrit because of a "chloride shift" into red blood cells as they pass through the microcirculation. This small increase in hematocrit is attenuated with arteriovenous fistula as venous blood is diluted with arterial blood that has bypassed the microcirculation. There is no reason for sodium concentration (choice D) or total protein concentration (choice E) to be affected by arteriovenous fistula, as these are normally similar in arterial and venous blood. |
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In the event of carbon monoxide poisoning, the blood sample taken from a systemic artery reveals
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A. normal hemoglobin level and normal oxygen content
B. normal hemoglobin level with reduced oxygen content C. reduced hemoglobin level with reduced oxygen content D. increased hemoglobin level with increased oxygen content The correct answer is B. Oxygen content is the total amount of oxygen carried in blood, that is, ml oxygen/100 ml of blood. CO competes for oxygen binding sites on Hb, thus decreasing the oxygen binding capacity of hemoglobin and decreasing the oxygen content of blood. Because CO does not destroy or damage the hemoglobin molecule itself, the Hb level will remain normal despite the reduction of oxygen carried by it. Choice A - Normal condition when no pathology is present. Choice C - Hb concentration and oxygen content are decreased in anemia, as less hemoglobin is produced. Choice D - Both Hb and oxygen content are increased in polycythemia. |
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An increase in which of the following is the most likely stimulus for the proliferation a large number of blood vessels in an abdominal tumor?
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A. Angiostatin
B. Growth hormone C. Thrombospondin D. Vascular endothelial growth factor E. Tissue oxygen partial pressure The correct answer is D. Vascular endothelial growth factor (VEGF) is a heparin-binding glycoprotein that increases endothelial cell proliferation in vitro and increases capillary growth (i.e., angiogenesis) in vivo. Unlike most other growth factors, VEGF has unique target cell specificity for vascular endothelial cells. VEGF is overexpressed in solid tumors and in ischemic areas of the heart and retina. Levels are also reversibly increased in a variety of normal and transformed cells exposed to a hypoxic environment. These characteristics of VEGF make it an ideal candidate as a regulator of angiogenesis in physiologic and pathophysiologic situations in which vessel growth is preceded by deficient perfusion of the tissues. Angiostatin (choice A) is an antiangiogenic factor expressed by tumors that tends to inhibit angiogenesis. Growth hormone (choice B) has a general effect that causes growth of almost all tissues of the body, but does not appear to stimulate angiogenesis to a significant extent in solid tumors. Thrombospondin (choice C) is a multifunctional glycoprotein that interferes with tumor growth, angiogenesis, and metastasis. An increase in tissue oxygen partial pressure (choice E) is unlikely to be the stimulus for new vessel growth because (1) solid tumors are invariably hypoxic or ischemic (i.e., the partial pressure of oxygen is low), and (2) an increase in the partial pressure of oxygen in a tumor would tend to decrease the expression of VEGF, thereby decreasing the amount of angiogenesis in the tissues. |
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Measurement of the blood pressure of a 65-year-old man reveals a systolic pressure of 190 mm Hg and a diastolic pressure of 100 mm Hg. His pulse is 74/min and pulse pressure is 90 mm Hg. A decrease in which of the following is the most likely explanation for the high pulse pressure?
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A. Arterial compliance
B. Cardiac output C. Myocardial contractility D. Stroke volume E. Total peripheral resistance The correct answer is A. A decrease in arterial compliance indicates that the arterial wall is stiffer (i.e., less distensible). When the compliance of the arterial system decreases, the rise in arterial pressure becomes greater for a given stroke volume pumped into the arteries. In the normal young adult, the systolic blood pressure is approximately 120 mm Hg and the diastolic blood pressure is approximately 80 mm Hg. Because the pulse pressure is the difference between the systolic and diastolic blood pressures, the normal pulse pressure is approximately 40 mm Hg in a healthy young adult. In older adults, however, the pulse pressure sometimes increases as much as two times normal because the arteries become hardened by arteriosclerosis. The cardiac output (choice B) itself has no direct effect on the pulse pressure; however, if a decrease in cardiac output is associated with a decrease in stroke volume, the pulse pressure would be expected to decrease. Cardiac output = stroke volume x pulse. A decrease in myocardial contractility (choice C) would be expected to decrease stroke volume, and therefore cause the pulse pressure to decrease. A decrease in stroke volume (choice D) causes the pulse pressure to decrease because a smaller amount of blood enters the arterial system with each heartbeat, and the increase and decrease of pressure during systole and diastole is decreased. This would cause cardiac output to decrease. A decrease in total peripheral resistance (choice E) (i.e., vasodilation) does not have a significant effect on the pulse pressure of the major arteries under normal conditions. |
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Which of the following hormones is most important in initiating gall bladder contraction?
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A. Cholecystokinin (CCK)
B. Gastric inhibitory peptide (GIP) C. Gastrin D. Secretin E. Vasoactive intestinal polypeptide (VIP) The correct answer is A. Cholecystokinin, or CCK, is synthesized in the duodenal and jejunal mucosa and stimulates gall bladder contraction and pancreatic enzyme secretion. Other functions include slowing of gastric emptying, an atrophic effect on the pancreas, and secretion of antral somatostatin that in turn decreases gastric acid secretion. Gastric inhibitory peptide, or GIP (choice B), stimulates pancreatic insulin secretion at physiologic doses and inhibits gastric acid secretion and gastric motility at pharmacologic doses. Gastrin (choice C) prepares the stomach and small intestine for food processing, including stimulating secretion of HCl, histamine, and pepsinogen. It also increases gastric blood flow, lower esophageal sphincter tone, and gastric contractions. Secretin (choice D) stimulates secretion of bicarbonate-containing fluid from the pancreas and biliary ducts. Vasoactive intestinal polypeptide, or VIP (choice E), relaxes intestinal smooth muscle and stimulates gut secretion of water and electrolytes. |
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What is the most common cause of an atrial septal congenital heart malformation?
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A. Failure of formation of the septum primum
B. Failure of formation of the septum secundum C. Incomplete adhesion between the septum primum and septum secundum D. Malformation of the membranous interventricular septum E. Malformation of the muscular interventricular septum The correct answer is C. The most common form of atrial septal defect is located near the foramen ovale (not to be confused with a patent foramen ovale, which is of little or no hemodynamic significance). They result from incomplete adhesion between the septum primum and the septum secundum during development. Atrial septal defect is usually asymptomatic until middle age. Right ventricular lift and S2 widely split and fixed is noted. A grade T-III/VI systolic ejection murmur at the pulmonary area is often noted. Atrial septal defects less commonly result from failures of formation of the septum primum (choice A) and septum secundum (choice B). Malformations of the interventricular septum (choices D and E) cause ventricular septal defects rather than atrial septal defects. |
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Aspirin reduces fever and cause anticoagulation by inhibiting which of the following pathways?
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A. Phospholipase A2
B. Lipoxygenase C. Prostacyclin D. Cyclogenase The correct answer is D. Aspirin and other NSAIDs inhibit cyclooxygenase, thereby inhibiting the production of prostaglandins. This then decreases the set-point temperature. Inhibition of phospholipase A2 (choice A) inhibits arachidonic acid. Inhibition of lipoxygenase (choice B) blocks leukotrienes production. Blocking prostacyclin (choice C) does not decrease platelet aggregation. |
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Which of the following directly inhibits insulin secretion?
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A. Alpha2-adrenergic agonist
B. Beta2-adrenergic agonist C. Cholecystokinin D. Glucagon E. Ingestion of a high-sugar meal The correct answer is A. Alpha2-receptor agonists directly inhibit pancreatic insulin secretion. Beta2-adrenergic agonists (choice B) stimulate insulin secretion. Cholecystokinin (choice C) is a hormone that causes not only gallbladder contraction, but also insulin secretion from the pancreas. Pancreatic glucagon release (choice D) acts as a paracrine stimulus for insulin secretion. Ingestion of high-sugar meals (choice E) is a stimulus for the secretion of insulin from the pancreas. |
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Which of the following urinary constituents is probably present in abnormally high concentration and accounts for bubbles in the urine and generalized edema, especially noticeable in dependent regions and under the eyes?
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A. Albumin
B. Chloride C. Glucose D. Sodium E. Urea The correct answer is A. The combination of edema and frothy urine suggests nephrotic syndrome. Urine with high protein content is more able to form stable bubbles than is normal urine, and may be a clue that a patient (or parent) notices. The edema is caused by loss of albumin from the plasma, lending to fluid loss from plasma to interstitial space. Chloride (choice B) in urine cannot be detected grossly and would not cause frothy urine. Some people can detect a sweet smell to urine that contains large amounts of glucose (choice C), and Greek physicians were known to taste urine to diagnose diabetes, but the presentation suggests nephrotic syndrome. Sodium (choice D) in urine cannot be detected grossly and would not cause frothy urine. Very concentrated urine with a high urea (choice E) content looks darker in color and is not necessarily frothy. |
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Carbon dioxide is transported in blood by a variety of mechanisms. Which of the following is quantitatively the most important method for transporting CO2?
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A. As carbaminohemoglobin
B. As CO2 in gas bubbles C. As CO2 in physical solution D. As sodium bicarbonate in red cells E. As sodium bicarbonate in serum The correct answer is E. Red blood cells (and many other blood cells) contain the enzyme carbonic anhydrase, which catalyzes the intracellular conversion of CO2 to bicarbonate and H+ ion. Most of the bicarbonate in the red cell is exchanged across the plasmalemma for chloride ion. This means that although the bulk of the production of bicarbonate occurs in the red cell (choice D), the bulk of the actual transport occurs in serum. Carbonic anhydrase is not present in serum. Bicarbonate can be produced in serum by nonenzymatic means, but the process is slow. CO2 is also carried as carbaminohemoglobin (choice A), which forms when CO2 binds to an NH2 side group of the hemoglobin protein, rather than to the heme iron (Fe2+) as with carbon monoxide and oxygen. CO2 is not transported in the form of bubbles (choice B), which is a good thing, because gas bubbles are effectively emboli, which can lead to considerable morbidity or death. Some CO2 is carried directly dissolved in blood (choice C). It is 20 times more soluble in blood than is O2. |
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Disease of which of the following structures would most likely cause a large difference in blood pressure between a patient's legs and arms?
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A. Aortic valve
B. Descending aorta C. Left atrium D. Left ventricle E. Mitral valve The correct answer is B. A patient that has a large difference in blood pressure between his legs and arms suggests disease of the aorta distal to the arch, where the vessels supplying the arms arise. In younger individuals, coarctation of the aorta is the most probable diagnosis. In older individuals, severe atherosclerosis of the abdominal aorta, iliac system, or femoral system is the most probable diagnosis. Disease of the aortic valve (choice A), left atrium (choice C), left ventricle (choice D), or mitral valve (choice E) would not produce selective effects on the blood pressure of the arms or legs. |
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When a given substance is injected into an experimental animal, it increases intracellular Ca+ through the formation of inositol 1,4,5-triphosphate. On which of the following receptors does the given substance act?
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A. Beta-1 receptor
B. Beta-2 receptor C. Alpha-1 receptor D. Alpha-2 receptor E. M2 receptor The correct answer is C. Phenylephrine acts on the alpha-1 receptor to increase intracellular Ca+ through formation of inositol 1,4,5-triphosphate. Isoproterenol acts on the beta-1 and beta-2 receptors (choices A and B, respectively) through the activation of adenylate cyclase and production of cAMP. Clonidine (choice D) acts on the alpha-2 receptor through the inhibition of adenylate cyclase and decreases cAMP. ACH acts on the M2 receptor, which is inhibitory in the heart and decreases heart rate and conduction velocity in AV node. |
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In the event of propagation of an action potential, the conduction velocity is increased by
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A. decrease in fiber size
B. increase in fiber size C. unmyelinated fiber D. increased internal resistance The correct answer is B.Propagation of action potentials occurs by the spread of local currents to adjacent areas of membrane that are then depolarized to threshold and generate action potentials. Increasing fiber size increases conduction velocity. The greater the diameter, the greater the conduction velocity. Choices A and D - Decreasing the diameter of nerve fiber results in increased internal resistance, thus conduction velocity decreases. Choice C - Myelin acts as an insulator around nerve axons and increases the conduction velocity. The greater the myelination, the greater the conduction velocity. |
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During an experiment, the loss of a portion of the adrenal gland, which is controlled by the autonomic nervous system, results in a decreased capacity of the individual to mobilize glycogen or fat during exercise. Which of the following hormones of respective regions should be absent to match the outcome of this experiment?
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A. Epinephrine - medulla
B. Epinephrine - zona reticularis C. Cortisol and androgen - zona reticularis and zona fasciculata D. Aldosterone - zona glomerulosa E. Aldosterone - Medulla The correct answer is A.The major hormone of the adrenal medulla is epinephrine, a catecholamine regulated by the autonomic nervous system. Its absence produces the above-mentioned effect. Epinephrine is not a hormone of the cortex (choice B), and aldosterone is not a hormone of the medulla (choice E). Cortisol and androgen (choice C), the hormones of the adrenal cortex, zona fasciculata, and reticularis, are regulated by ACTH. Absence of cortisol could cause severe problems under stressful conditions. Catecholamines do not exert vasoconstriction without cortisol, leading to circulatory failure. Mineralocorticoid aldosterone, the hormone of the zona glomerulosa (choice D), is under the control of angiotensin-2. Its absence could result in circulatory shock and death. Therefore, it is necessary for survival. |
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Which of the following substances is most responsible for the constancy in plasma sodium concentration when large amounts of sodium are ingested?
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A. Aldosterone
B. Angiotensin II C. Antidiuretic hormone (ADH) D. Atrial natriuretic factor (ANF) E. Epinephrine The correct answer is C. A 5-fold increase in sodium intake causes the plasma sodium concentration to increase by less than 1%, indicating the existence of a powerful mechanism for maintaining extracellular sodium concentration at a constant level. When the ADH-thirst mechanism is blocked, however, a 5-fold increase in sodium intake causes the plasma sodium concentration to increase by more than 10%. The major mechanism for controlling extracellular sodium concentration (and extracellular osmolarity) therefore is the ADH-thirst mechanism. You should recall that ADH increases the permeability of the late distal tubule and collecting duct to water, which allows water to be retained by the body and a concentrated urine to be excreted. Aldosterone (choice A) and angiotensin II (choice B) are powerful salt-retaining hormones. They regulate the total amount of sodium in the body, but have relatively little effect on plasma sodium concentration under normal conditions for the following reasons: (1) they increase reabsorption of sodium and water to an equal extent, and (2) any tendency for sodium concentration to change is immediately compensated for by changes in ADH levels, which return sodium concentration to a normal value. Atrial natriuretic factor (choice D) is released from the atria when blood volume increases. It acts on the kidneys to increase the excretion of sodium and water. ANF, however, does not play an important role in regulating plasma sodium concentration because any tendency for sodium concentration (and osmolarity) to change is immediately compensated for by changes in ADH levels, as discussed previously. Epinephrine (choice E) does not play an important role in regulating extracellular sodium concentration. |
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To minimize chronic rejection injury to transplanted organs, immunosuppressive therapy is aimed at downregulating which of the following components of the immune response?
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A. Autoantibody production
B. Complement protein synthesis C. HLA antigen expression D. Mast cell degranulation E. T-lymphocyte activity The correct answer is E. Before any immune response can occur, such as a graft rejection, T cells can be activated by exposure to an antigen. Chronic rejection of any solid organ entails cellular injury to endothelial cells, resulting in intimal proliferation, fibrosis, and eventually ischemic injury to the graft. Immunosuppressive therapy is directed at controlling lymphocyte activity and minimizing cellular rejection. Autoantibodies (choice A) are not involved in organ transplant rejection. The antibodies produced are alloantibodies directed only to the graft, not to the host. Complement proteins (choice B) are involved in the humoral component of acute rejection, and complement binding to alloantibodies increases graft damage. Complement protein production, however, is not affected by immunosuppressive therapy. HLA antigen expression (choice C) is central to recognition of foreign cells in grafted tissue. HLA antigens are expressed constitutively by all normal cells, and immunosuppression does not affect their production. Mast cell degranulation (choice D) is a component of the anaphylactic response (Type I hypersensitivity). Graft rejection is a Type IV hypersensitivity response and does not involve mast cell degranulation. |
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Which of the following laboratory parameters could be used to assess glycemic control over the past 2-3 months for a patient with type 2 diabetes?
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A. Blood glucose
B. Blood insulin levels C. Blood ketones D. Glycosylated hemoglobin E. Urinary glucose The correct answer is D. The range of normal for the HbA1c or glycosylated hemoglobin is 3.9-6.9%. This is directly related to the level of glucose in the blood. Because HbA1c is a stable product, its concentration reflects glucose levels over the past 2-3 months. HbA1c forms as a result of nonenzymatic glycosylation, a fundamental biochemical abnormality that accounts for most of the histopathologic alterations in diabetes mellitus. At first, glucose forms reversible glycosylation products with proteins by formation of Schiff bases. Rearrangement of Schiff bases leads to more stable, but still reversible, Amadori products and subsequently to irreversible advanced glycosylation end products (AGE), of which HbA1c is an example. Blood ketones, blood glucose, urinary glucose, and blood insulin do not reflect longstanding metabolic abnormalities of diabetes mellitus and cannot be used to assess long-term glycemic control. Blood glucose (choice A) is elevated in type 1 and type 2 diabetes mellitus. Hyperglycemia is the diagnostic feature of diabetes mellitus and leads to glycosuria (choice E) when blood glucose exceeds 160-180 mg/dL. Blood insulin (choice B) is absent in untreated type 1 diabetes and normal or even slightly increased in type 2 diabetes, depending on the state of the type 2 diabetes. Blood ketones (choice C) (acetoacetic acid and beta-hydroxybutyric acid) are synthesized from free fatty acids in response to severe insulin deficiency. Accumulation of ketone bodies in the blood is a crucial pathogenetic factor in ketoacidosis, which occurs primarily in type 1 diabetics or type 2 diabetics with advanced disease who are improperly treated. |
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Daily serum samples from a woman with a normal menstrual cycle reveal decreasing progesterone and 17-estradiol levels. Serum LH and FSH levels are low, and begin rising. Basal body temperature begins falling. Within three days, which of the following events would be expected to occur?
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A.Markedly increased inhibin levels
B. Menstruation C. Ovulation D. Rapidly decreased LH levels E. Significantly increased basal body temperature The correct answer is B. A typical menstrual cycle lasts around 26-30 days. The luteal phase (post-ovulation) generally lasts fourteen days; the length of the follicular phase (pre-ovulation) is far more variable, and accounts for most of the variability observed in the length of the menstrual cycle. Just before menstruation, sex steroid levels are low, but gonadotropin levels (especially FSH) begin rising slightly. Basal body temperature remains high during the luteal phase of the menstrual cycle, but falls precipitously a few days before the onset of menstruation. Markedly increased inhibin levels (choice A) are seen in the middle of the luteal phase, dropping to low levels just before menstruation. LH levels peak approximately 36 hours before ovulation (choice C), then decrease rapidly (choice D) within a few days to a low level during the mid-luteal phase, gradually decreasing until menstruation. The basal body temperature significantly increases (choice E) shortly after ovulation, due to the metabolic effects of progesterone produced by the corpus luteum. |
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Antigens processed by the exogenous antigen presentation pathway are presented in association with which of following?
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A. Fc receptors
B. IgG heavy chains C. MHC class I molecules D. MHC class II molecules E. T cell receptor (TCR) The correct answer is D. When pathogenic organisms are phagocytized and degraded in the exogenous antigen presentation pathway, the antigenic molecules are presented on the surface of the antigen-presenting cell by MHC class II molecules to a CD4+ T lymphocyte with a specific TCR for the specific antigenic epitope. The Fc (choice A) portion of an antibody molecule is the part of the immunoglobulin that attaches to the Fc receptors on phagocytic cell surfaces. When a Fab portion of the antibody is attached to the pathogen and the Fc attaches to the phagocytic cell surface, the phagocyte can destroy the pathogen more efficiently. The IgG molecule (choice B) is an immunoglobulin that reacts with the antigen after it has been destroyed and presented to the T cell. The IgG immunoglobulin is never involved in antigen presentation. In the endogenous antigen presentation pathway (e.g., a virus infecting a cell), the cell would display epitopes from the virus in association with class I molecules (choice C) to the CD8+ cytotoxic T cell. The TCR (choice E) is the area of the mature T cell that reacts with the antigen epitope that is presented by the antigen-presenting cell. |
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Most of the testosterone secreted by the testes exists in the plasma in the form of
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A. dihydrotestosterone bound to gonadal steroid-binding hormone
B. free dihydrotestosterone C. free testosterone D. testosterone bound to albumin E. testosterone bound to sex-steroid-binding globulin The correct answer is E. Most circulating testosterone is bound to plasma protein (approximately 98%), rather than existing in free form (choice C). Of this, most is bound to a specific sex (or gonadal) steroid-binding protein (choice E), and a minority is bound to albumin (choice D). Dihydrotestosterone is produced from testosterone in the tissues by a specific enzyme, 5-alpha-reductase, rather than circulating in bound (choice A) or free (choice B) form. Testosterone is the principal androgen produced by the interstitial cells of the testes. |
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During a surgical procedure, cranial nerves IX and X are accidentally cut bilaterally. What would be the immediate change in the patient's hemodynamic condition?
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A. Bradycardia with hypertension
B. Bradycardia with hypotension C. Sinus arrhythmia with hypotension D. Tachycardia with hypertension E. Tachycardia with hypotension The correct answer is D. The glossopharyngeal nerve (CN IX) and the vagus nerve (CN X) carry afferent information to the medulla from the carotid sinus and aortic arch baroreceptors, respectively. The firing rate of these neurons increases with increasing blood pressure. Severing these nerves therefore sends the medulla a false signal that the patient has suddenly lost all blood pressure. This elicits a baroreceptor reflex, resulting in an increase in sympathetic outflow and leading to tachycardia and hypertension. Remember physiologically the glossopharyngeal nerve routes to sensory nuclei of the medulla oblongata. The somatic motor portion destination is the pharyngeal muscles involved in swallowing. The visceral portion innervates the parotid salivary gland by way of the otic ganglion. The vagus nerve routes to the sensory fibers to sensory nuclei and autonomic centers of the medulla oblongata. The visceral fibers innervate the motor fibers and muscles of the palate, pharynx, and digestive, respiratory, and cardiovascular systems in the thoracic and abdominal cavities. |
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A patient with severe anemia may have which of the following symptoms?
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A. Bradycardia
B. Cyanosis C. Low stroke volume D. Warm hands E. Wide pulse pressure The correct answer is E. The normal blood hemoglobin concentration is approximately 15-16 g/dL for a man and 13-14 g/dL for a woman. A person is considered to be severely anemic when the hemoglobin concentration decreases to less than 7.5 g/dL. In severely anemic, the resting cardiac output is significantly increased with an increase in pulse and stroke volume (choice C). The increase in stroke volume causes a widening of the pulse pressure, because when a greater amount of blood is ejected during each systole, the blood pressure increases and decreases to a greater extent. Bradycardia (choice A) is said to occur when the pulse decreases to less than 60/min. Severely anemic exhibit tachycardia, which is defined as a pulse greater than 100/min. The increase in pulse is because the body is trying to increase oxygen perfusion to tissues by increasing the heart rate. Cyanosis (choice B) refers to a bluish color of the skin and mucous membranes that results from the presence of deoxygenated hemoglobin in the blood vessels, especially the capillaries. Cyanosis does not occur in severely anemic despite widespread hypoxia in the tissues because 5 grams of deoxygenated hemoglobin must be present in each 100 mL of blood to produce overt cyanosis. In other words, the hemoglobin concentration is too low for a severely anemic to become cyanotic. The hands of anemic are often cold (choice D) because of decreased blood flow and oxygen perfusion to the skin. |
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Radiographic studies of a 2-year-old child reveal a new fracture of the humerus and evidence of multiple old fractures in ribs and long bones of the extremities. Physical examination reveals that the toddler has "peculiar teeth," a blue tinge to the sclera, and unusually mobile joints. The disease that the physician suspects the child has is characterized by an abnormality of which of the following biochemical functions?
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A. Collagen type I synthesis
B. Collagen type II synthesis C. Collagen type III synthesis D. Collagen type IV synthesis E. Collagen type V synthesis The correct answer is A. The child has the most common variant (type I) of osteogenesis imperfecta, which is an autosomal dominant genetic defect in the synthesis of type I collagen, because of decreased synthesis of the procollagen alpha1(1) amino acid chain. This defect (unlike that of the perinatal, lethal, type II form of osteogenesis imperfecta) is compatible with survival, but does cause skeletal fragility, dentinogenesis imperfecta (abnormal teeth), blue sclera, joint laxity, and hearing impairment. Spontaneous fractures occur in utero and in childhood. Unfortunately, many families of children with this defect have had their children removed because of "abuse," only to find that the broken bones continue in the new environment. Type I collagen is found in skin, bone, tendons, and most other organs. This causes severe osteoporosis. Less severe mutations in type I collagen are common, resulting in collagen disarray and predisposing to hypogonadal (e.g., menopausal) or idiopathic osteoporosis. Type II collagen (choice B) is found in cartilage and vitreous humor. Type III collagen (choice C) is found in blood vessels, uterus, and skin. Type IV collagen (choice D) makes basement membranes. Type V collagen (choice E) is a minor component of interstitial tissues and blood vessels. There are also type VI-XI collagens, which are minor constituents of various tissues. |
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Which of the following neurotransmitters is most important for the induction of REM sleep?
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A. Acetylcholine
B. Dopamine C. Epinephrine D. Norepinephrine E. Serotonin The correct answer is A. Acetylcholine is the neurotransmitter of primary importance for the induction of REM sleep. Some of the other neurotransmitters do function in sleep, but REM sleep can occur in their absence. In the CNS, ACH synapses are throughout the brain and spinal cord. In the PNS, ACH is found at the neuromuscular junctions, preganglionic synapses of the ANS, neuroeffector junctions of parasympathetic division, and in the sympathetic division of the ANS. Dopamine (choice B) is a neurotransmitter with a role in voluntary movement, mood, cognition, and regulation of prolactin release. Epinephrine (choice C) is important in sympathetic nervous system responses. It is also a CNS neurotransmitter. Norepinephrine (choice D) is important in sympathetic nervous system responses. It is also a CNS neurotransmitter involved in attention, arousal, and mood. Serotonin (choice E) is a CNS neurotransmitter that plays an important role in mood and sensation. In the periphery, it is involved in vascular regulation and digestive function. |
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The primary metabolic effect of the principal hormone secreted by the alpha cells of the pancreas is
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A. augmentation of calcium deposition in bone
B. increase of amino acid storage in the liver C. promotion of lipogenesis in liver and adipose tissue D. inhibition of gluconeogenesis E. stimulation of glycogenolysis The correct answer is E. Glucagon is released from the alpha cells of the pancreas in response to hypoglycemia and stimulates glycogenolysis to increase serum glucose. Augmented calcium deposition in bone (choice A) is achieved by calcitonin, which is secreted by the C-cells in the thyroid gland. Glucagon plays no role in calcium metabolism. Glucagon favors amino acid conversion to glucose (gluconeogenesis) rather than storage in the liver (choice B). Insulin (which generally has opposite effects of glucagon) promotes lipogenesis in the liver and in adipose tissue (choice C), and also promotes glycogen synthesis. Glucagon stimulates gluconeogenesis (choice D). |
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Compensation for high altitude will result in which of the following physiologic changes?
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A. Decreased production of erythropoietin
B. Decreased 2,3-diphosphoglycerate (2,3-DPG) C. Increased renal excretion of H+ ions D. Increased renal excretion of HCO3- E. Pulmonary vasodilation The correct answer is D. Compensation for high altitude includes an increase in the renal excretion of bicarbonate. The diminished barometric pressure found at high altitude causes arterial hypoxia, which is sensed by peripheral chemoreceptors. The ventilation rate increases, thereby causing a respiratory alkalosis. The kidney then compensates by increasing the excretion of HCO3-. Erythropoietin is increased, not decreased in chronic hypoxia and at high altitude (choice A). Increased erythropoietin leads to an increased hematocrit. Another adaptation to high altitude is increased 2,3-DPG (compare with choice B), which shifts the oxygen dissociation curve to the right. This facilitates the release of O2 in the tissue. High altitude leads to respiratory alkalosis. The renal compensation is a metabolic acidosis characterized by decreased H+ excretion and increased HCO3- excretion. Respiratory acidosis is normally compensated with a metabolic alkalosis that would include increases in H+ excretion (choice C). Pulmonary vasoconstriction, not vasodilation (choice E), occurs in response to alveolar hypoxia, such as would occur at high altitudes. |
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A decrease in which of the following parameters would tend to increase the glomerular capillary hydrostatic pressure?
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A. Afferent arteriolar resistance
B. Bowman's capsular hydrostatic pressure C. Capillary filtration coefficient D. Efferent arteriolar resistance E. Plasma colloid osmotic pressure The correct answer is A. The glomerular filtration rate is the rate of filtrate formation at the glomerulus. It is commonly used to assess renal function. A decrease in the resistance of the afferent arteriole (i.e., arteriolar dilation) directly increases glomerular capillary hydrostatic pressure by lessening the decrease in blood pressure that normally occurs along the vasculature proximal to the glomerulus. (Recall that the afferent arteriole is upstream from the glomerulus; the efferent arteriole is downstream from the glomerulus.) The glomerular capillary hydrostatic pressure is the determinant of glomerular filtration rate most subject to physiologic control. Bowman's capsular hydrostatic pressure (choice B), capillary filtration coefficient (choice C), and plasma colloid osmotic pressure (choice E) are important determinants of GFR but they do not have any direct effect to increase or decrease the glomerular capillary hydrostatic pressure. A decrease in efferent arteriolar resistance (choice D) would tend to decrease the glomerular capillary hydrostatic pressure because the efferent arteriole is downstream from the glomerular capillaries. |
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Exogenous therapy with which of the following hormones would be most likely to slow or prevent osteoporosis?
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A. Cortisol
B. Epinephrine C. Estrogen D. Thyroxine E. Vasopressin The correct answer is C. Estrogen replacement in postmenopausal women seems to play an important role in preventing or limiting development of osteoporosis in postmenopausal women. Osteoporosis can be asymptomatic or may involve severe backache and spontaneous fractures. There is often a loss of height. Serum parathyroid hormone, calcium, phosphorus, and 25(OH)D2 are often normal. Demineralization of the spine, hip, and pelvis are common. Cortisol (choice A) excess, as in endogenous or exogenous Cushing syndrome, is a contributing cause of osteoporosis. Increased cortisol will worsen the condition. Epinephrine (choice B) concentrations seem to be unrelated to osteoporosis. Increased levels will increase pulse and blood glucose level. Thyroxine (choice D) excess (e.g., in thyrotoxicosis) may contribute to bone loss in some cases of osteoporosis. Vasopressin (choice E) concentrations seem to be unrelated to osteoporosis. Vasopressin or antidiuretic hormone will decrease the amount of water loss from the kidneys. |
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A type 1 diabetic is noncompliant with his required insulin therapy and develops hyperglycemia. The release of which of the following intestinal hormones would be stimulated?
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A. Gastic inhibitory peptide (GIP)
B. Gastrin C. Motilin D. Secretin E. Somatostatin The correct answer is A. Gastric inhibitory peptide (GIP) is produced in the duodenal and jejunal mucosa by K cells and is released in response to intraluminal glucose and fatty acids. GIP is sometimes called glucose-dependent insulinotropic peptide because it stimulates pancreatic insulin secretion in the presence of hypergylcemia. Note that although GIP release would be stimulated, the hormone would not have a pronounced effect in this type 1 diabetic, whose pancreatic islet cells do not produce adequate amounts of insulin. Gastrin (choice B) is synthesized and stored primarily in the G cells of the stomach and TG cells of the stomach and small intestine. The stimuli for gastrin secretion include increased vagal discharge, digestive products, calcium salts, and gastric distention. Gastrin stimulates HCl secretion by parietal cells, histamine release from enterochromaffin cells, pepsinogen secretion by chief cells, gastric blood flow, and contraction of gastric circular smooth muscle. It has a trophic effect on gastric and small intestinal mucosa and the pancreas, increases lower esphageal sphincter (LES) tone, and is a weak stimulus for the secretion of pancreatic enzymes and bicarbonate. Motilin (choice C) is produced in the M and enterochromaffin cells of the duodenum and jejunum. Secretion occurs during fasting. Motilin acts to regulate the migrating myoelectric complex (MMC). Secretin (choice D) is synthesized and stored in the S cells of the mucosa of the upper intestine. Acidification of the duodenal mucosa and the presence of fat and protein degradation produced in the duodenum stimulate its secretion. The main role of secretin is to stimulate bicarbonate secretion from the pancreas and liver. Somatostatin (choice E) is synthesized and stored in the D cells of the pancreatic islets, in the gastric antrum, and throughout the intestine. It is also present in the hypothalamus. It inhibits the release of gastrin, cholecystokinin (CCK), and most other gastrointestinal hormones. In brief, it shuts off the gut. Somatostatin inhibits the release of glucagon by pancreatic alpha cells, as well as the release of insulin by the pancreatic beta cells (of the islets of Langerhans). |
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Which of the following is most likely to decrease in skeletal muscles during exercise?
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A. Arteriolar resistance
B. Carbon dioxide concentration C. Lactic acid concentration D. Sympathetic nervous activity E. Vascular conductance The correct answer is A. The increase in muscle blood flow that occurs during exercise is caused by dilation of the arterioles (i.e., decreased arteriolar resistance). In normal skeletal muscles, blood flow can increase as much as 20-fold during strenuous exercise. Most of this increase in blood flow can be attributed to the dilatory actions of metabolic factors (e.g., adenosine, lactic acid, carbon dioxide) produced by the exercising muscles. Exercise causes the concentration of carbon dioxide (choice B) and lactic acid (choice C) to increase in the muscles. Mass discharge of the sympathetic nervous system (choice D) occurs throughout the body during exercise, causing arterioles to constrict in most tissues. The arterioles in the exercising muscles, however, are strongly dilated by vasodilator substances released from the muscles. A decrease in vascular conductance (choice E) occurs when the vasculature is constricted. Resistance and conductance are inversely related, so that a decrease in arteriolar resistance is associated with an increase in arteriolar conductance. |
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A. Arteriolar resistance
B. Carbon dioxide concentration C. Lactic acid concentration D. Sympathetic nervous activity E. Vascular conductance The correct answer is A. The increase in muscle blood flow that occurs during exercise is caused by dilation of the arterioles (i.e., decreased arteriolar resistance). In normal skeletal muscles, blood flow can increase as much as 20-fold during strenuous exercise. Most of this increase in blood flow can be attributed to the dilatory actions of metabolic factors (e.g., adenosine, lactic acid, carbon dioxide) produced by the exercising muscles. Exercise causes the concentration of carbon dioxide (choice B) and lactic acid (choice C) to increase in the muscles. Mass discharge of the sympathetic nervous system (choice D) occurs throughout the body during exercise, causing arterioles to constrict in most tissues. The arterioles in the exercising muscles, however, are strongly dilated by vasodilator substances released from the muscles. A decrease in vascular conductance (choice E) occurs when the vasculature is constricted. Resistance and conductance are inversely related, so that a decrease in arteriolar resistance is associated with an increase in arteriolar conductance. |
A. Arteriolar resistance
B. Carbon dioxide concentration C. Lactic acid concentration D. Sympathetic nervous activity E. Vascular conductance The correct answer is A. The increase in muscle blood flow that occurs during exercise is caused by dilation of the arterioles (i.e., decreased arteriolar resistance). In normal skeletal muscles, blood flow can increase as much as 20-fold during strenuous exercise. Most of this increase in blood flow can be attributed to the dilatory actions of metabolic factors (e.g., adenosine, lactic acid, carbon dioxide) produced by the exercising muscles. Exercise causes the concentration of carbon dioxide (choice B) and lactic acid (choice C) to increase in the muscles. Mass discharge of the sympathetic nervous system (choice D) occurs throughout the body during exercise, causing arterioles to constrict in most tissues. The arterioles in the exercising muscles, however, are strongly dilated by vasodilator substances released from the muscles. A decrease in vascular conductance (choice E) occurs when the vasculature is constricted. Resistance and conductance are inversely related, so that a decrease in arteriolar resistance is associated with an increase in arteriolar conductance. |
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Which of the following is likely to be decreased in a patient with severe anemia (Hb less than 7 g/dL)?
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A. Arterial O2 content
B. Arterial O2 saturation C. Arterial PO2 D. Cardiac output E. Pulse The correct answer is A. A decrease in the hemoglobin concentration of the blood causes a proportional decrease in the oxygen-carrying capacity of the blood. Each gram of hemoglobin can normally carry a total of 1.34 grams of oxygen. Thus, each 100 mL of arterial blood can normally carry approximately 20 mL oxygen at a normal hemoglobin concentration of 15 g/dL blood. With a hemoglobin concentration of 7 g/100 mL, each 100 mL of blood can carry only 9.4 mL oxygen. The oxygen saturation of hemoglobin in the arterial blood (choice B) and the arterial PO2 (choice C) are virtually unaffected by the hemoglobin concentration of the blood. The reduced oxygen-carrying capacity of the severely anemic patient is associated with a compensatory increase in cardiac output during resting conditions and especially during exercise. The elevation in cardiac output helps to maintain oxygen delivery to the tissues at an adequate level. The increase in cardiac output (choice D) is caused by an increase in pulse (choice E). |
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Maximal ventricular Na+ channel conductance occurs during which phase of the ECG?
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A. P wave
B. QRS interval C. ST interval D. T wave E. U wave The correct answer is B. Phase 0 of the cardiac muscle action potential (AP) corresponds to the opening of voltage-dependent sodium channels, causing a transient but large increase in sodium conductance during ventricular depolarization. The shape of the QRS complex of the ECG is determined by the spread of the combined phase 0 (depolarization) of all the ventricular muscle of the heart. The P wave (choice A) corresponds to atrial depolarization. The ST interval (choice C) represents the time interval during which all ventricular cells are in phase 2 of their AP. Phase 2 is dominated by a high, prolonged calcium conductance through slow channels. The length of the ST interval corresponds closely to the AP duration in ventricular muscle. The T wave (choice D) corresponds to ventricular repolarization. The U wave (choice E) is found only occasionally in ECGs and is presumed to be caused by the repolarization of papillary muscle. |
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During normal diastole, which of the following is most important in preventing over-distension of the ventricles?
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A. Adjacent lungs
B. Aortic valve C. Diaphragm D. Fibrous pericardium E. Mitral valve The correct answer is D. The fibrous pericardium, which surrounds the heart, does not simply separate the heart from other chest structures, but has the important physiologic role of limiting the distension of the heart during diastole. This helps keep the (normal) heart functioning in a useful part of Starling's curve. In congestive heart failure, the slow enlargement of the heart also enlarges the fibrous pericardium, and this protective function may be lost. The lungs (choice A) and diaphragm (choice C) do not usually significantly limit cardiac expansion during diastole. Shutting and opening of the aortic (choice B) and mitral valves (choice E) are mechanical events that occur secondary to the changes in pressure in the cardiac chambers. |
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Physical examination of a pregnant woman in her second trimester reveals a slightly enlarged, nontender thyroid gland and a normal cardiac examination. The serum thyroxine (T4) level is increased; however, the serum thyroid-stimulating hormone (TSH) is normal. Which of the following best explains the laboratory findings in this patient?
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A. Decreased estrogen
B. Increased free thyroxine (T4) C. Increased progesterone D. Increased serum triiodothyronine (T3) E. Increased thyroid-binding globulin (TBG) The correct answer is E. The total serum thyroxine (T4) represents the sum of the T4 bound to thyroid-binding globulin (TBG) and the free T4. An increased total T4 may be caused by an increase in TBG or an increase in free T4, the latter leading to signs of thyrotoxicosis. In a euthyroid state, one third of the binding sites on TBG are occupied by T4. An increase in estrogen (pregnancy, birth control pills) increases the synthesis of TBG. The T4 bound to the additional TBG increases the total serum T4. The extra TBG, however, does not alter the free T4 level because of the equilibrium between the serum concentration of T4 and thyroid gland T4 production. Because the free T4 level is normal, there is no stimulus to release thyroid-stimulating hormone (TSH) from the pituitary gland. Regarding the patient's enlarged thyroid gland, heat intolerance, and palpitations, these are normal findings in pregnancy and do not indicate an overactive thyroid gland. Estrogen is increased (not decreased) in pregnancy (choice A). The serum free T4 (choice B) is normal in pregnancy. This explains why the serum TSH is normal in the presence of an elevated serum T4, which reflects the increase in TBG normally occurring in pregnancy. The increase in progesterone (choice C) during pregnancy has no effect on TBG levels. Although the serum T3 (choice D) concentration is increased in pregnancy for the same reason as serum T4 (more T3 is bound to TBG), it is not responsible for the increase in synthesis of TBG that leads to the increase in serum T4. |
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Administration of an experimental drug that acts on peripheral nervous system (PNS) myelin is shown to increase the space constant of an axon in a peripheral nerve. Action potentials traveling down the axon would be predicted to be
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A. faster
B. larger C. slower D. smaller E. unchanged The correct answer is A. The space constant of an axon reflects the amount of passive or electrotonic spread of current within the axon. The larger the space constant, the further the current can spread, allowing action potentials to propagate faster. This is why myelin increases the conduction velocity of action potentials down an axon. Conversely, demyelination decreases the space constant and slows action potential conduction. |
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Respiratory rate: 15/min; Arterial pressure: 120/80mm Hg; Cardiac output: 5L/min; Heart rate: 50/min
Basal measurements are shown above. What is the stroke volume during resting conditions (in mL/min)? |
A. 50
B. 75 C. 100 D. 125 E. 150 The correct answer is C. The cardiac output (CO) is equal to the volume of blood ejected from the heart during each beat of the heart (SV, stroke volume) multiplied by the number of times the heart beats each minute (HR, heart rate). That is, CO = SV x HR. Therefore, SV = CO/HR, and since CO = 5000 mL/min, and HR = 50/min, SV = 5000/50 = 100 mL. Note that some of the data listed are irrelevant to the solution of the problem |
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The drug used in the induction of anesthesia facilitates which of the following receptors action, which increases chloride conduction?
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A. GABA-B
B. Glycine C. GABA-A D. Glutamate The correct answer is C. Barbiturates facilitate GABA-A action by increasing the duration of chloride-channel opening, thus decreasing neuron firing. GABA-B receptor (choice A) increases K+ conductance. Glycine (choice B) is an inhibitory neurotransmitter that increases Cl- conductance. Glutamate (choice D) is an excitatory neurotransmitter in the brain. The kainite receptor for glutamate is an ion channel for Na+ and K+. |
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A 45-year-old man with acromegaly has an MRI revealing the presence of a 1.5-cm tumor in the anterior pituitary. Which of the following endocrine abnormalities is likely to be present?
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A. Decreased plasma growth hormone concentration
B. Decreased plasma IGF-1 concentration C. Decreased plasma insulin concentration D. Impaired glucose tolerance The correct answer is D. The patient probably has acromegaly caused by a growth hormone-secreting adenoma in the anterior pituitary. Hypersecretion of growth hormone in an adult will not cause an increase in stature, because the epiphyses of long bones have already fused. Overgrowth of bone in the face and skull, however, produces the characteristic protruding jaw and forehead observed in this disorder. Soft tissue proliferation leads to a coarsening of facial features. The hands and feet are particularly affected, producing large and thickened spade-like fingers and toes. Excessive growth hormone decreases the sensitivity of peripheral tissues to insulin ("anti-insulin" effect). This tends to raise blood glucose and produce a compensatory hyperinsulinemia (not decreased plasma insulin, choice C) that functions to limit the hyperglycemia. Approximately 50% of patients with acromegaly show impaired glucose tolerance. Plasma levels of growth hormone (choice A) and IGF-1 (choice B) are both increased in acromegaly. |
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Which of the following is a characteristic of steroid hormones?
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A. Activation of adenylate cyclase
B. Activation of protein kinases C. Plasma membrane receptors D. Stimulation of cellular protein synthesis E. Termination of effects by phosphodiesterase The correct answer is D. Peptide/protein hormones and steroid hormones act by very different mechanisms. Steroid hormones circulate in the bloodstream, then leave the bloodstream by dissolving in the lipid-rich plasma membrane. Steroids cross the plasma membrane and enter the cytoplasm, where they bind to a mobile protein receptor. The hormone/receptor complex then enters the nucleus and triggers RNA synthesis, leading to protein synthesis, thereby changing the cellular response. Hormones such as cortisol and aldosterone are steroid hormones. In contrast, protein and amine hormones bind to specific receptors on the outer surface of the plasma membrane (choice C), but do not enter the cytoplasm. Many activate adenylate cyclase (choice A) and thereby increase cAMP. The increased cAMP stimulates protein kinases (choice B), which change the target cell responses by phosphorylating intracellular proteins. Hydrolysis of cAMP by phosphodiesterases (choice E) terminates the effect of the hormone. |
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Stimulating glossopharyngeal afferent fibers that supply the carotid sinus would most likely cause which of the following changes?
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A. Hypertension with bradycardia
B. Hypertension with tachycardia C. Hypotension with bradycardia D. Hypotension with tachycardia E. No changes in blood pressure or heart rate The correct answer is C. The glossopharyngeal nerve (CN IX) and the vagus nerve (CN X) carry afferent information to the medulla from the carotid sinus and aortic arch baroreceptors, respectively. The firing rate of these neurons increases with increasing blood pressure. Stimulation of the glossopharyngeal nerve therefore sends the medulla a false signal that the animal has suddenly had an increase in blood pressure. This elicits a baroreceptor reflex resulting in a decrease in sympathetic outflow and an increase in parasympathetic outflow, leading to hypotension and bradycardia. |
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What is the role of the macrophage during antibody formation?
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A. Activation of cytotoxic CD8 T cells
B. Delayed hypersensitivity reaction C. Lysis of virus-infected cells D. Processing antigen and presenting it to T helper CD4 cells E. Synthesis of immunoglobulin The correct answer is D. The macrophage is a phagocytic cell of the monocyte-macrophage system. The macrophage phagocytizes exogenous antigens (e.g., a bacterium), degrading the antigen into small epitopes and presenting them, on MHC class II molecules on its surface, to CD4 T helper cells. Macrophages do not activate cytotoxic CD8 T lymphocytes (choice A). The major activator of cytotoxic CD8 T lymphocytes is IL-2 from CD4+ THl cells. Delayed hypersensitivity reactions (choice B) are the results of CD4+ THl cells. These cells do not produce antibody. They secrete gamma interferon and interleukin 2 (IL-2), stimulating more cells to become involved in the delayed hypersensitivity reaction. The cells that participate in lysis of virus infected cells (choice C) are cytotoxic CD8+ T lymphocytes that react with MHC class I molecules containing epitopes of the virus from the infected cell. Macrophages do not participate in this activity. Macrophages never synthesize antibody (choice E). B cells initially produce antibody, then are converted to plasma cells or memory B cells. The stimulus for the production of this antibody comes from T helper cells that were stimulated by epitopes presented to them by macrophages. |
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Which of the following is most important for maintaining adequate cardiac output early in the course of exercise?
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A. Decreased cardiac index
B. Decreased diastolic blood pressure C. Increased heart rate D. Increased stroke volume E. Increased systematic vascular resistance The correct answer is D. At the beginning of aerobic (isotonic) exercise, increased stroke volume is the most important adjustment for maintaining adequate cardiac output (CO = HR x SV) or cardiac output = heart rate x stroke volume. There is an increased, not decreased, cardiac index (choice A) during isotonic exercise. Diastolic blood pressure usually remains unchanged during isotonic exercise; it is not decreased (choice B). In contrast, systolic blood pressure usually rises during isotonic exercise. Increased heart rate (choice C) becomes more important later in isotonic exercise (beyond 50% of maximal work capacity). There is decreased, not increased, systemic vascular resistance (choice E) during isotonic exercise. |
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Which of the following regions of the nephron is capable of the greatest level of sodium reabsorption?
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A. Collecting duct
B. Distal convoluted tubule C. Proximal convoluted tubule D. Thick ascending limb of the loop of Henle The correct answer is C. About 70% of the sodium entering the proximal convoluted tubule is actively reabsorbed. Chloride and water follow passively. The collecting duct (choice A) reabsorbs about 3% to 5% of the entering sodium, via aldosterone-regulated, electrogenic Na+-channel pumps. Antidiuretic hormone (ADH) increases H2O permeability and reabsorption in this region. The distal convoluted tubule (choice B) reabsorbs about 5% of the entering sodium via Na+/K+/2Cl- cotransport. This region is relatively impermeable to water. The ascending limb of the loop of Henle (choice D) reabsorbs about 20% of the entering sodium via Na+/K+/2Cl- cotransport. This region is relatively impermeable to water. |
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An infant has a coarctation of the aorta that reduces renal blood flow to 50% lower than normal. Which of the following is increased in this infant?
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A. Blood flow in the lower body
B. Glomerular filtration rate C. Plasma levels of angiotensin II D. Renal excretion of sodium E. Renal excretion of water The correct answer is C. The lower than normal pressure at the level of the kidneys causes renin to be secreted and angiotensin to be formed. Renin is released by the kidney because of (1) sympathetic stimulation and (2) a decline in renal blood flow. When renin acts on angiotensinogen, a plasma protein produced in the liver, it converts angiotensinogen to angiotensin I. Angiotensin I is converted to angiotensin II by the enzyme ACE (angiotensin converting enzyme). The angiotensin causes salt and water retention so that within a few days to weeks the arterial pressure in the lower body (at the level of the kidneys) increases. Blood flow in the lower body (choice A) is lower rather than increased, because of the blockage. Blood flow, however, can be normal, above, and below the constriction if the body is able to compensate fully. The decrease in blood pressure at the level of the kidneys causes the glomerular filtration rate (choice B) to decrease. Increased plasma levels of angiotensin II cause salt and water retention; thus, salt and water excretion (choices D and E) are decreased. |
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A patient with small-cell bronchogenic carcinoma of the lung complains of muscle weakness, fatigue, confusion, and weight gain. Serum sodium is found to be elevated and the tumor is secreting ectopic ADH. Which of the following abnormal laboratory results would also be expected?
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A. Decreased plasma atrial natriuretic peptide (ANP) concentration
B. Decreased plasma vasopressin concentration C. Decreased serum osmolarity D. Decreased urinary sodium concentration E. Increased plasma aldosterone concentration The correct answer is C. Bronchogenic carcinomas can secrete ectopic vasopressin (ADH), leading to the syndrome of inappropriate ADH (SIADH). As long as water intake is not decreased, the increased plasma vasopressin (not decreased, choice B) causes excessive water reabsorption by the renal distal tubule and collecting duct. The increased total body water can explain the weight gain. Edema is usually absent because the extra free water is distributed to intracellular and extracellular volumes. The extra plasma water produces a dilutional hyponatremia, which can explain the weakness, fatigue, and confusion. There will also be a dilutional decrease in serum osmolarity. With SIADH, the urine sodium is usually increased (not decreased, choice D) compared with normal. This leads to an inappropriately concentrated urine. The volume expansion resulting from the excessive water retention may be responsible for the increased urinary sodium. Volume expansion would increase plasma ANP (not decrease, choice A) and increase renal sodium excretion. The volume expansion would also inhibit renin secretion from the kidney with subsequent decrease in plasma aldosterone (not increase, choice E). Decreased plasma aldosterone would then allow for increased renal excretion of sodium. |
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A decrease in which of the following parameters would tend to increase the glomerular capillary hydrostatic pressure?
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A. Afferent arteriolar resistance
B. Bowman's capsular hydrostatic pressure C. Capillary filtration coefficient D. Efferent arteriolar resistance E. Plasma colloid osmotic pressure The correct answer is A. A decrease in the resistance of the afferent arteriole (i.e., arteriolar dilation) directly increases glomerular capillary hydrostatic pressure by lessening the drop in blood pressure that normally occurs along the vasculature proximal to the glomerulus. [Recall that the afferent arteriole turns into the glomerulus; the efferent arteriole drains the glomerulus.] The glomerular capillary hydrostatic pressure is the determinant of glomerular filtration rate most subject to physiologic control. Bowman's capsular hydrostatic pressure (choice B), capillary filtration coefficient (choice C), and plasma colloid osmotic pressure (choice E) are important determinants of GFR, but they do not have any direct effect to increase or decrease the glomerular capillary hydrostatic pressure. A decrease in efferent arteriolar resistance (choice D) would tend to decrease the glomerular capillary hydrostatic pressure because it would allow blood to more easily flow out of the glomerulus. |
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Which of the following lung volumes or capacities cannot be measured directly using simple spirometry?
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A. Expiratory reserve volume
B. Functional residual capacity C. Inspiratory reserve volume D. Tidal volume E. Vital capacity The correct answer is B. The functional residual capacity is the amount of air left in the lungs after a normal expiration. Because this volume cannot be expired in its entirety, it cannot be measured by spirometry. Essentially, lung volume that contains the residual volume, which is the amount of air remaining after maximal expiration (e.g., functional residual capacity and total lung capacity), cannot be measured by spirometry. These volumes can be determined using helium dilution techniques coupled with spirometry or body plethysmography. The expiratory reserve volume (choice A) is the volume of air that can be expired after expiration of a tidal volume. The inspiratory reserve volume (choice C) is the volume of air that can be inspired after inspiration of a tidal volume. Tidal volume (choice D) is the amount of air inspired or expired with each normal breath. Vital capacity (choice E) is the volume of air expired after a maximal inspiration. |
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Which of the following would be expected to increase in response to hemorrhage resulting in loss of 600 mL of blood?
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A. Arteriolar diameter in skeletal muscle
B. Sodium excretion C. Sympathetic nerve activity D. Vagal nerve activity E. Water excretion The correct answer is C. The decrease in blood pressure caused by hemorrhage activates the baroreceptor reflex, which tends to increase sympathetic nerve activity and decrease parasympathetic (vagal) nerve activity (choice D). The increase in sympathetic nerve activity constricts arterioles in skeletal muscle (choice A) and elsewhere in the body. The fact the patient has lost 600 mL blood and yet her blood pressure has decreased only slightly from a normal value of approximately 120/80 mm Hg may be attributed to the following compensatory responses: baroreceptor epinephrine released from the adrenal medulla, formation of angiotensin II, formation of vasopressin, and the capillary fluid shift mechanism. Activation of the renin angiotensin system during hemorrhage also plays an important role in maintaining blood pressure. Angiotensin II increases blood pressure acutely by constricting arterioles throughout the body (choice A), and chronically by decreasing the renal excretion of salt (choice B) and water (choice E). The decrease in salt and water excretion returns blood volume to a normal value. |
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Which of the following areas of the adrenal gland would be expected to increase in activity in a patient subjected to salt restriction?
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A. Adrenal medulla
B. Zona fasciculata of the adrenal cortex C. Zona glomerulosa of the adrenal cortex D. Zona reticularis of the adrenal cortex The correct answer is C. This question requires you to equate salt restriction with an increased synthesis of aldosterone (aldosterone promotes sodium reabsorption) and then to remember that aldosterone is produced in the zona glomerulosa (the outermost layer) of the adrenal cortex. The adrenal medulla (choice A) secretes catecholamines. The zona fasciculata (choice B) is the middle layer of the adrenal cortex. It primarily secretes glucocorticoids. The zona reticularis (choice D) is the innermost layer of the adrenal cortex. It primarily secretes androgens such as dehydroepiandrosterone (DHEA). |
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A middle-aged patient develops acromegaly. Which of the following pair of hormones normally regulates the hormone responsible for the symptoms seen with this disease?
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A. Dopamine and norepinephrine
B. LH and hCG C. Prolactin and FSH D. Somatostatin and GHRH E. TSH and ACTH The correct answer is D. Acromegaly is typically produced by a growth hormone-secreting pituitary adenoma. Growth hormone synthesis is predominantly regulated by hypothalamic GHRH (growth hormone releasing hormone), and its pulsatile secretion is predominantly regulated by hypothalamic somatostatin. Note that the question asks for regulating hormones, not the hormone directly responsible for the disease. Dopamine and norepinephrine are catecholamines that regulate smooth muscle tone and cardiac function (choice A). Luteinizing hormone (LH) regulates sex steroid hormone production by testes and ovaries. Human chorionic gonadotropin (hCG) is produced by the placenta and has actions similar to LH (choice B). Prolactin regulates menstruation and lactation. Follicle stimulating hormone (FSH) regulates ovarian and testicular function (choice C). Thyroid stimulating hormone (TSH) regulates secretion of thyroid hormones. Adrenocorticotropin (ACTH) regulates glucocorticoid secretion (choice E). |
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If the luminal diameter of the right renal artery is decreased by approximately 50%, which of the following is most likely increased?
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A. Afferent arteriolar resistance
B. Glomerular filtration rate C. Glomerular hydrostatic pressure D. Interlobar artery pressure E. Secretion of renin The correct answer is E. The decrease in renal artery diameter causes a reduction in arterial pressure within the kidney, which results in an initial decrease in glomerular hydrostatic pressure (choice C) and glomerular filtration rate (choice B). The decrease in glomerular filtration rate decreases the amount of sodium chloride that is delivered to the macula densa; in turn, the juxtaglomerular cells secrete renin, and angiotensin II is formed. The angiotensin then mainly constricts the efferent arterioles, which increases glomerular hydrostatic pressure and glomerular filtration rate back toward normal. This macula densa feedback mechanism also attempts to return glomerular hydrostatic pressure (and therefore glomerular filtration rate) to a normal level by decreasing afferent arteriolar resistance (choice A). An obstruction of the renal artery would decrease blood pressure in the interlobar arteries (choice D). |
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Serum chemistry studies of a patient reveal that her aspartate aminotransferase (AST) is markedly elevated, whereas her alanine aminotransferase (ALT), gamma-glutamyl transpeptidase (GGT), and alkaline phosphatase are all within normal limits. Disease of which of the following organs would be most likely to cause this serum enzyme pattern?
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A. Colon
B. Duodenum C. Heart D. Pancreas E. Stomach The correct answer is C. Myocardial infarction (MI) can cause AST elevation without accompanying elevation of ALT or other liver enzymes. This is an important fact to remember because it may be the first clue for heart disease in a patient who has an atypical presentation of MI (as is common in women with MI). MI can be confirmed with measurement of the MB fraction of creatine phosphokinase (CPK-MB). In addition, Troponin T and Troponin I can be diagnostic. Unfortunately, diseases of the tubular organs of the gastrointestinal tract, including colon (choice A), duodenum (choice B), and stomach (choice E), do not produce distinctive serum enzyme patterns. Damage to the pancreas (choice D) is associated with elevated amylase levels. |
