Kaplan Physiology Flashcards
- 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?
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.
- A newborn infant has multiple hemorrhages. Clotting studies demonstrate an elevated
prothrombin time and elevated INR. An abnormality of which of the following biochemical
processes is likely present in this patient?
A. Conversion of homocysteine to methionine
B. Conversion of methylmalonyl CoA to succinyl CoA
C. Degradation of cystathionine
D. Formation of gamma-carboxyglutamate residues
E. Hydroxylation of proline
The correct answer is D. Deficiency of vitamin K produces a clotting disorder characterized by an
elevated prothrombin time and easy bleeding, particularly in neonates (hemorrhagic disease of the
newborn). The biochemical basis for this hemorrhagic tendency is that glutamate residues on Factors
II (Thrombin), VII, IX, and X must be converted to gamma-carboxyglutamate residues (in a vitamin Krequiring
reaction) for optimal activity.
The conversion of homocysteine to methionine (choice A) requires vitamin B12. Vitamin B12
deficiency can result in the development of pernicious anemia. Conversion of methylmalonyl CoA to
succinyl CoA (choice B) requires vitamin B12.
Degradation of cystathionine (choice C) requires vitamin B6 and can result in the development of
mouth soreness, glossitis, cheilosis, and weakness.
Hydroxylation of proline (choice E) requires vitamin C. Vitamin C deficiency can cause easy bruising,
but will not prolong the prothrombin time. Vitamin C deficiency is commonly known as scurvy.
3. Where are the body's temperature regulation centers located? A. Midbrain B. Pons C. Medulla D. Hypothalamus
The correct answer is D. Temperature regulation centers and thirst and food intake regulatory
centers are located in the hypothalamus. Choice A - Midbrain contains the micturation center. Choice
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B - Pneumotaxic centers are located in the pons. Choice C - The medulla contains the vasomotor
center, respiratory center, vomiting, swallowing, and coughing centers.
4. An animal is made diabetic by injection of a drug that destroys pancreatic ß cells. Removal of which of the following organs would most likely produce a decrease in blood glucose concentration in this animal? A. Anterior pituitary B. Colon C. Gonads D. Kidney E. Pancreas
The correct answer is A. The anterior pituitary produces the following hormones: thyroid-stimulating
hormone (TSH), adrenocorticotropic hormone (ACTH), follicle stimulating hormone (FSH), leutinizing
hormone (LH), prolactin, and growth hormone (GH). Two of these secretions (GH, ACTH) affect the
sensitivity of peripheral tissues to the action of insulin. Growth hormone has a direct effect on liver and
muscle to decrease insulin sensitivity. This may be partly through a growth hormone-induced decline
in insulin receptors or to unknown postreceptor defects. In excess, growth hormone is “diabetogenic,”
and approximately 25% of patients with acromegaly have diabetes. ACTH indirectly has antiinsulin
effects by virtue of the cortisol secretion it evokes. Like growth hormone, cortisol also decreases
insulin sensitivity in peripheral tissues. A third anterior pituitary hormone, TSH, also tends to increase
blood glucose levels. In this case, the effect is probably mediated mostly through increased glucose
absorption by the gut. Patients with hyperthyroidism can sometimes exhibit a postprandial glucosuria
because of excessive intestinal glucose absorption. In diabetic animals, the removal of the anterior
pituitary may lower blood glucose by increasing tissue sensitivity to whatever insulin remains.
Removal of the colon (choice B) should have little effect on blood glucose because dietary glucose is
absorbed in the small intestine.
Sex steroids secreted by the gonads (choice C) have little effect on blood glucose concentration.
The kidney (choice D) plays an important role in reabsorbing filtered glucose. In diabetes, the tubular
reabsorption maximum is exceeded and glucose spills over into the urine. The loss of glucose in the
urine helps to reduce the severity of the plasma hyperglycemia. Removal of the kidneys would, if
anything, make the hyperglycemia worse. Pancreatectomy (choice E) would make the hyperglycemia
worse by removing the source of any remaining insulin.
5. Which of the following is most likely to decrease in the skeletal muscles of a healthy 22- year-old woman during exercise? 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) attributed to the dilatory actions of
metabolic factors (e.g., adenosine, lactic acid, carbon dioxide) produced by the exercising muscles. In
normal skeletal muscles, the blood flow can increase as much as 20-fold during strenuous exercise.
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.
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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.
6. Which of the following parameters is expected to increase in response to a 50% reduction in sodium intake for a 2-month period? A. Arterial pressure B. Atrial natriuretic peptide release C. Extracellular fluid volume D. Renin release E. Sodium excretion
The correct answer is D. Renin is an enzyme released by the juxtaglomerular cells when renal blood
pressure or pO2 declines. Renin converts angiotensinogen to angiotensin I. A reduction in sodium
intake leads to a decrease in extracellular fluid volume (choice C) and therefore a decrease in arterial
pressure (choice A). The decrease in arterial pressure stimulates renin release that in turn leads to
an increase in the formation of angiotensin II. The angiotensin II increases the renal retention of salt
and water (i.e., decreases sodium excretion, choice E), which returns the extracellular fluid volume
nearly back to normal.
Atrial natriuretic peptide (choice B) is released from the two atria of the heart as a result of an
increase in the extracellular fluid volume. A decrease in sodium intake therefore would tend to
decrease the release of atrial natriuretic peptide.
7. Which of the following hormones is most important in the initiation of gallbladder contraction following a fatty meal? A. CCK B. Gastrin C. GIP D. Secretin E. VIP
The correct answer is A. Cholecystokinin, or CCK, is synthesized in the duodenal and jejunal
mucosa and stimulates gallbladder contraction and pancreatic enzyme secretion. Other functions
include slowing of gastric emptying, an atrophic effect on the pancreas, and secretion of antral
somatostatin, which in turn decreases gastric acid secretion.
Gastrin (choice B) prepares the stomach and small intestine for food processing, including
stimulating secretion of HCl, histamine, and pepsinogen, increasing gastric blood flow, lower
esophageal sphincter tone, and gastric contractions. Gastric inhibitory peptide, or GIP (choice C),
stimulates pancreatic insulin secretion at physiologic doses and inhibits gastric acid secretion and
gastric motility at pharmacologic doses. Secretin (choice D) stimulates secretion of bicarbonatecontaining
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.
8. During spermatogenesis, crossing over occurs during the meiotic division of which of the following cells? A. Primary spermatocytes B. Secondary spermatocytes C. Spermatids D. Spermatogonia E. Spermatozoa
The correct answer is A. Crossing over, a transposition of genetic information, occurs during the
first meiotic (reduction) division, when the primary spermatocyte divides to form two secondary
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spermatocytes. This division does not consist of separation of sister chromatids after DNA replication,
but rather involves the separation of previously paired, homologous chromosomes. Crossing over
occurs during prophase of meiosis I.
The secondary spermatocyte (choice B) undergoes the second meiotic division, which results in four
spermatids (choice C), each with the haploid number of chromosomes. The spermatids are located
adjacent to the lumen of the seminiferous tubules and are distinguished by their small size. These
cells undergo no further division, but become transformed into mature spermatozoa (choice E)
through the prcess of spermiogenesis.
The spermatogonia (choice D) are the primitive germ cells. These cells give rise to the primary
spermatocytes through repeated mitotic divisions.
Remember the sequence of spermatogenesis:
Spermatogonia (2n) ? REPEATED MITOSES ? Primary spermatocytes (2n) ? FIRST MEIOTIC
DIVISION ? Secondary spermatocytes (n) ? SECOND MEIOTIC DIVISION ? Spermatids (n) ?
SPERMIOGENESIS ? Spermatozoa (n)
- A decrease in which of the following is the most likely cause of peripheral edema in a
patient with long-term alcoholism and liver disease?
A. Capillary hydrostatic pressure
B. Interstitial colloid osmotic pressure
C. Interstitial hydrostatic pressure
D. Plasma colloid osmotic pressure
E. Precapillary arteriolar resistance
The correct answer is D. Osmotic pressure of a solution is an indicator of the force of water
movement resulting from its solute concentration. The higher the solute concentration of a solution,
the greater its osmotic pressure. The plasma colloid osmotic pressure is often low in alcoholics with
chronic liver disease (cirrhosis). The diseased liver cannot produce adequate amounts of albumin,
which leads to a decrease in the concentration of albumin in the plasma (i.e., hypoalbuminemia).
Because approximately 75% of the plasma colloid osmotic pressure can be attributed to the presence
of albumin in the plasma, the decrease in plasma albumin concentration that occurs in the latter
stages of cirrhosis often leads to peripheral edema. Cirrhosis also causes excess fluid to accumulate
in the peritoneal cavity as ascites. In the case of ascites, the edema results not only from
hypoalbuminemia, but also from portal vein obstruction (which increases capillary hydrostatic
pressure) and the obstruction of lymphatic drainage of the liver. In fact, ascites is observed more often
than peripheral edema in liver disease.
A decrease in capillary hydrostatic pressure (choice A) would tend to decrease fluid loss from the
capillaries, and thereby oppose the development of edema. A decrease in the colloid osmotic
pressure of the interstitial fluid (choice B) would decrease fluid loss from the capillaries, thereby
opposing the development of edema. A decrease in interstitial hydrostatic pressure (choice C) would
tend to increase fluid loss from the capillaries, but this cannot be considered a primary cause of
edema because the interstitial hydrostatic pressure actually increases when a tissue becomes
edematous. A decrease in precapillary arteriolar resistance (choice E), which means arteriolar
dilation, would increase capillary hydrostatic pressure and tend to cause edema. Decreased
precapillary arteriolar resistance in the peripheral vasculature, however, is not associated with
cirrhosis.
- The medical record of a patient indicates a systolic murmur due to increase in afterload,
producing a pressure gradient between the ventricle and aorta during ejection. Which of the
following best describes the condition?
A. Aortic insufficiency
B. Aortic stenosis
C. Mitral insufficiency
D. Mitral stenosis
The correct answer is B.Aortic stenosis increases afterload and produces a pressure gradient
between ventricle and aorta during ejection. Aortic insufficiency (choice A) increases preload and
produces retrograde flow from the aorta to the ventricle, leading to a diastolic murmur. Mitral
insufficiency (choice C) increases volume and pressure in the atrium and ventricle, producing a
systolic murmur. Mitral stenosis (choice D) increases left-atrial volume and pressure, producing a
diastolic murmur.
11. At 25 weeks of pregnancy, an unidentified infection greatly compromises the viability of a developing fetus. The level of which of the following hormones in the mother's blood is most likely to be affected? A. Estriol B. Free thyroxine C. Human chorionic gonadotropin D. Human chorionic somatomammotropin E. Progesterone
The correct answer is A. Plasma levels of maternal estrogens during pregnancy depend on a
functioning fetus. The fetal adrenal cortex and liver produce the weak androgens, DHEA-S and 16-OH
DHEA-S, which are carried to the placenta by the fetal circulation. The placenta then desulfates the
androgens and aromatizes them to estrogens (16-OH DHEA-S, estriol) before delivery to the maternal
circulation. Estradiol and estrone increase approximately 50-fold during pregnancy, but estriol
increases approximately 1,000 fold. When estriol is assayed daily, a significant drop may be a
sensitive early indicator of fetal jeopardy. Total serum thyroxine concentration may be increased in
pregnancy because of an increase in circulating TBG resulting from increased estrogen. Free
thyroxine, however, (choice B) remains within the normal range because of feedback regulation. The
decline in estrogen with fetal compromise may gradually decrease serum thyroxine, but the free
thyroxine will remain unchanged. Human chorionic gonadotropin (choice C) and human chorionic
somatomammotropin (choice D) are both secreted by syncytiotrophoblasts of the placenta. As long
as placental function is intact, blood levels of these two hormones should not change with fetal
compromise. Placental secretion of progesterone (choice E) during pregnancy is also independent of
any fetal contribution. The placenta relies on maternal cholesterol for progesterone production. Fetal
death has no immediate influence on progesterone production by the placenta.
- A healthy 20-year-old man deprived of water for several days has a plasma concentration
of antidiuretic hormone (ADH) 5 times greater than normal. Which of the following is the most
likely explanation for the increase in ADH concentration?
A. Decreased plasma aldosterone
B. Decreased plasma renin activity
C. Increased extracellular fluid volume
D. Increased left atrial pressure
E. Increased plasma osmolality
The correct answer is E. An obligatory loss of water from the body continues to occur even when a
person is deprived of water. This loss of water from the body tends to concentrate the extracellular
fluid, causing it to become hypertonic. Both the decrease in extracellular fluid (compare with choice
C) and the increase in osmolarity act as stimuli for increased thirst and increased secretion of ADH.
The decrease in extracellular fluid volume also tends to decrease arterial pressure that in turn
increases plasma renin activity (compare with choice B) and aldosterone levels in the plasma
(compare with choice A). Water deprivation tends to decrease left atrial pressure (compare with
choice D).
- Which of the following indices would be expected to be decreased in a kidney donor after
full recovery from the removal of the kidney?
A. Creatinine clearance
B. Creatinine production
C. Daily excretion of sodium
D. Plasma creatinine concentration
E. Renal excretion of creatinine
The correct answer is A.Because creatinine is freely filtered by the glomerulus but not secreted or
reabsorbed to a significant extent, the renal clearance of creatinine is approximately equal to the
glomerular filtration rate. In fact, creatinine clearance is commonly used to assess renal function in the
clinical setting. When a kidney is removed, the total glomerular filtration rate decreases because 50%
of the nephrons have been removed, which causes the creatinine clearance to decrease. In turn, the
plasma creatinine concentration (choice D) increases until the rate of creatinine excretion by the
kidneys (choice E) is equal to the rate of creatinine production by the body. Recall that creatinine
excretion = GFR x plasma creatinine concentration. Creatinine excretion is therefore normal when
GFR is decreased following removal of a kidney because the plasma concentration of creatinine is
elevated. Creatinine is a waste product of metabolism. Creatinine production (choice B) is directly
related to the muscle mass of an individual, but is independent of renal function. The daily excretion of
sodium (choice C) is unaffected by the removal of a kidney. The amount of sodium excreted each
day by the remaining kidney exactly matches the amount of sodium entering the body in the diet.
14. An elevated level of which of the following substances would identify a specimen as plasma rather than serum? A. Albumin B. Erythrocytes C. Fibrinogen D. Granulocytes E. Serotonin
The correct answer is C. This is simply a definition What is the difference between serum and
plasma? Essentially, serum is derived from plasma by the extraction of fibrinogen and coagulation
factors II, V, and VIII. This can be achieved by allowing whole blood to clot, then removing the clot.
Albumin (choice A) is present in serum and plasma. Neither erythrocytes (choice B) nor
granulocytes (choice D) are present in either serum or plasma. Serotonin (choice E) levels may be
increased in serum because of the platelet breakdown that occurs during the extraction process.
Serotonin is normally found in the highest concentration in platelets, and in the enterochromaffin cells
and myenteric plexus of the gastrointestinal tract. The brain and the retina contain smaller amounts.
- A dietary deficiency of which of the following is most strongly associated with a neural
tube defect at the base of the fetus’s spine?
A. Calcium
B. Folate
C. Iron
D. Vitamin C
E. Vitamin K
The correct answer is B. Neural tube defects most commonly occur in the lumbosacral region, typically resulting in motor and sensory deficits in the lower extremities, and bowel and bladder dysfunction. This condition is now known to be associated with low maternal folate during the first 3-4 weeks of pregnancy, a time when many women may be unaware of their pregnancy. It is now recommended that all women of childbearing age consume at least 400 grams of folic acid daily. Calcium deficiency (choice A) can cause osteoporosis and osteopenia. Iron deficiency (choice C) can cause iron deficiency anemia. Vitamin C deficiency (choice D) can cause scurvy. Vitamin K deficiency (choice E) can cause a bleeding diathesis.
16. Which of the following substances can be converted to glucose to supply the needs of the brain during starvation? A. Acetoacetate B. Acetone C. Amino acids D. Beta-hydroxybutyrate E. Fatty acids
The correct answer is C. During starvation, the diet is inadequate to provide sufficient glucose to
maintain the brain, yet the brain requires glucose as an energy source. Glucose used in the brain
during starvation is synthesized from amino acids, primarily derived from muscle protein. This use of
amino acids in starvation leads to profound muscle wasting.
The ketone bodies (acetoacetate, choice A; acetone, choice B; and beta-hydroxybutyrate, choice D)
produced during starvation and diabetic ketoacidosis are derived from adipose triacylglycerols.
Although these compounds can be used in biochemical pathways in the brain, they cannot completely
replace glucose in that organ. Furthermore, glucose cannot be synthesized from these precursors.
Fatty acid (choice E) degradation cannot be used to produce glucose. It can be used, however, to
produce ketone bodies that can be used by the brain as a source of intermediates for some synthetic
pathways.
17. Absence of which of the following cell types is responsible for loss of vitamin B12 absorption? A. Chief cells B. G cells C. Goblet cells D. Mucous neck cells E. Parietal cells
The correct answer is E. The parietal cells of the stomach produce intrinsic factor, a glycoprotein
that binds vitamin B12 in the lumen of the stomach and facilitates its absorption in the terminal ileum.
Patients without a stomach and those with pernicious anemia (autoimmune destruction of parietal
cells) require B12 replacement therapy. Recall that B12 deficiency will lead to megaloblastic anemia
and a blood smear with hypersegmented neutrophils. Note that parietal cells also synthesize and
secrete HCl. Chief cells (choice A) are responsible for secreting pepsinogen, the precursor to pepsin.
G cells (choice B) secrete gastrin, which stimulates secretion of acid by the parietal cells found in the
body and fundus of the stomach. Zollinger-Ellison syndrome is caused by a pancreatic or duodenal
tumor that secretes gastrin (a gastrinoma). It is characterized by the development of severe peptic
ulcer disease. Goblet cells (choice C) are part of the mucosa of the small intestine, not the stomach.
They produce glycoproteins (mucins) that protect and lubricate the lining of the intestine. Mucous
neck cells (choice D) secrete mucus and are located in the necks of the gastric glands.
- Which of the following is most likely to relieve the symptoms caused by hyperventilation?
A. Breathing a 10% oxygen/90% nitrogen mixture
B. Breathing 100% nitrogen
C. Breathing in and out of a plastic bag
D. Intravenous administration of bicarbonate
E. Lying down
The correct answer is C. Hyperventilation os often associated with states of anxiety and can lead to
feelings of faintness, suffocation, tightness in the chest, and blurred vision. Individuals undergoing
such an attack may not be aware of overbreathing. The anxious, hyperventilating patient is “blowing
off” carbon dioxide, which lowers the arterial PCO2. Many of the symptoms associated with anxiety
attacks are probably caused by a decrease in cerebral blood flow secondary to low arterial PCO2.
Recall that carbon dioxide is a major regulator of cerebral blood flow, i.e., carbon dioxide dilates the
brain vasculature, and conversely, the vasculature constricts when carbon dioxide levels are low. The
decrease in cerebral blood flow leads to cerebral hypoxia, which is probably responsible for the
fainting and blurred vision. An attack may be terminated by breathing in and out of a plastic bag
because this can increase carbon dioxide levels in the blood. Inhaling a 5% carbon dioxide mixture
would also be effective. Breathing a mixture of 10% oxygen/90% nitrogen (choice A) or 100%
nitrogen (choice B) can decrease oxygen delivery to the brain and thereby worsen the symptoms
caused by hyperventilation. Hyperventilation results in hypocapnia (low PCO2), which causes
alkalosis (high blood pH). Bicarbonate (choice D) should not be administered to an alkalotic patient.
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The feelings of faintness and blurred vision resulting from hyperventilation are not relieved by lying
down (choice E).
- A student volunteers to have his lung volumes and capacities measured. He is instructed
to breathe several times until the helium has equilibrated between the spirometer and his
lungs, and then exhale as much air as he possibly can. Calculations are made to determine the
amount of air remaining in his lungs, which is called the
A. expiratory reserve volume
B. functional residual capacity
C. inspiratory capacity
D. inspiratory reserve volume
E. residual volume
The correct answer is E. There are two ways to arrive at the correct answer to this question. The
first is to simply remember the definition of residual volume (RV): the amount of air remaining in the
lungs after maximal exhalation. The second way is to recall that the helium dilution technique
described above is used to measure functional residual capacity (FRC) and RV, which narrows the
reasonable option choices to B and E. All of the other volumes and capacities can be directly
measured with spirometry because they are blown into the spirometer. Only FRC and RV represent
amounts of air that remain in the lungs. Expiratory reserve volume (choice A) is the volume expelled
by an active expiratory effort after passive expiration. Functional residual capacity (choice B) is
defined as the amount of air remaining in the lungs after passive expiration. Inspiratory capacity
(choice C) is the maximal amount of air inspired after a passive expiration. Inspiratory reserve volume
(choice D) is the amount of air inspired with a maximal inspiratory effort over and above the tidal
volume.
- Which of the following characteristics is similar for spermatogenesis and oogenesis?
A. Age at which meiosis begins
B. Amount of cytoplasm retained
C. DNA replication during meiosis
D. Length of prophase I
E. Transmission to fetus of mitochondrial DNA
The correct answer is C. The actual process of manipulation of DNA and chromosomes during
meiosis is very similar in spermatogenesis and oogenesis. The processes also differ in many other
respects, however:
In oogenesis, the process of meiosis begins before birth and arrests between birth and puberty in
prophase I. In contrast, spermatogenesis does not begin until puberty (choice A).
The egg retains a large volume of cytoplasm (choice B), where nearly all the cytoplasm is stripped
during formation of a sperm. As noted, in oogenesis, meiosis is arrested in prophase I, which is
consequently very prolonged in the female. In spermatogenesis, meiosis is completed in a much
shorter time (choice D). Both the egg and the sperm have mitochondria, but those of the sperm are
left outside when the sperm nucleus enters the egg and consequently do not contribute to the
mitochondrial genome of the fetus. Instead, the mitochondria are transmitted from the egg to the fetus
(choice E). Traits coded for by mitochondrial DNA are therefore inherited in a matrilineal fashion.
- Increases in which of the following normal physiological parameters may have contributed
to the formation of acute gastric stress ulcers?
A. Bicarbonate transport
B. Epithelial regenerative capacity
C. Mucosal blood flow
D. Mucus secretion
E. Pepsin production
The correct answer is E. Pepsin is produced in the chief cells in the stomach. This proteolytic
enzyme functions most effectively at a strong acid pH of 1.5 - 2.0. Pepsin production is a normal
physiologic activity of the stomach that, in conditions of stress, may overwhelm the stomach’s
weakened defenses and result in gastric ulceration. Gastric acid production is another condition that
may increase and cause acute ulceration. Furthermore, these two factors may remain unchanged and
still result in gastric ulcers if the gastric defenses are weakened by stress. All of the other choices
represent normal defensive forces in the stomach.
Increased bicarbonate transport (choice A) would protect the gastric epithelium from the potentially
harmful acidity of the gastric contents. The adherent mucus is relatively alkaline, providing local
protection to the superficial mucosa.
Gastric epithelial cells can normally replicate rapidly, allowing mucosal defects to be rapidly repaired.
Increasing the regenerative capacity of the epithelium (choice B) would have a protective effect
against ulceration.
The gastric mucosa is richly supplied with blood, providing the epithelial cells with an ample supply of
nutrients, oxygen, and bicarbonate to contend with the harsh gastric microenvironment. Stress ulcers
are associated with compromised gastric blood flow, not increased flow (choice C).
Mucus protects the gastric epithelium by virtue of being water insoluble, impermeable to pepsin, and
slowly permeated by acid (H+). Increasing mucus production (choice D) has a protective effect for the
gastric mucosa.
22. Inhibition of which of the following could be responsible for impotence as a side effect of a medication? A. Conversion of DHT to testosterone B. Forward motility factor C. Nitric oxide synthase (NOS) D. Oxytocin E. Prostaglandins
The correct answer is C. Penile erection is mediated by the parasympathetic nervous system. The
neurons involved are termed nonadrenergic, noncholinergic (NANC) autonomic neurons, and they
release nitric oxide (NO). NO binds to the iron in the heme molecule of guanylate cyclase, activating it
to form cGMP. This results in a decrease in intracellular calcium and subsequent smooth muscle
relaxation and vasodilation in the corpus cavernosa, producing erection. Nitric oxide synthase (NOS)
is the enzyme required for the formation of NO from circulating arginine, and androgens are
necessary to maintain normal amounts of this enzyme. Inhibition of this enzyme could result in
impotence. Inhibition of the conversion of testosterone to DHT, not DHT to testosterone (choice A),
would be accomplished by a 5-alpha-reductase inhibitor. This could cause impotence by its
antiandrogen effect. In fact, finasteride, a clinically used 5-alpha-reductase inhibitor, produces drastic
decreases in libido in some men. Inhibition of forward motility factor (choice B) would hamper sperm
motility and result in infertility, not impotence. Inhibition of oxytocin (choice D) or prostaglandins
(choice E) would result in failure to ejaculate (ejaculatory incompetence), not impotence.
- A research physiologist decides to use a marker to measure the volume of total body water
in a volunteer. Which of the following substances would he most likely use?
A. Antipyrine
B. Cresyl violet
C. Evans blue
D. I131-albumin
E. Inulin
The correct answer is A. Antipyrine and tritium are both markers for total body water. Cresyl violet
(choice B) is a histologic dye used to stain Missl substance in neurons. It stains cell bodies. Evans
blue (choice C) is used to measure the plasma compartment.
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I131-albumin (choice D) is used to measure the plasma compartment. Inulin (choice E) is used to
measure the extracellular fluid compartment.
24. Which of the following vascular structures contains the largest proportion of the total blood volume in a normal individual? A. Aorta and large arteries B. Arterioles C. Capillaries D. Chambers of the heart E. Venules and veins
The correct answer is E. The total blood volume of the body is approximately 5000 mL. The
systemic veins contain approximately 64% of this volume or approximately 3200 mL. No other
segment of the circulation comes close to the amount of blood contained by the systemic veins: the
chambers of the heart (choice D) contain approximately 350 mL; the aorta and large arteries (choice
A) together contain approximately 650 mL; and the arterioles and capillaries (choices B and C)
together contain approximately 350 mL. Although the capillaries contain less than 7% of the total
blood volume, they have a very large surface area that facilitates diffusion exchange of nutrients and
metabolites between the blood and tissue spaces.
- Which of the following substances is likely to be present in significant amounts in urine
that has a stable, frothy, white foam on top?
A. Bilirubin
B. Blood
C. Glucose
D. Ketones
E. Protein
The correct answer is E. In this case, you need to know that a stable froth on urine is usually caused
by proteinuria (more than several grams per 24 hours). High levels of bilirubin (choice A) in urine can
cause an unusual yellow foam. Blood in the urine (choice B) might be present in some forms of renal
disease, but would not explain the stable foam. High levels of glucose (choice C) in urine can cause it
to develop a sweet smell and taste; smelling and tasting urine was an ancient method of diagnosing
diabetes mellitus, but is no longer recommended. Ketones (choice D) may give urine an acetone-like
odor.
- Tissue taken from a fracture site of a patient with end stage renal failure is noted to have
increased osteoclastic activity, with notable tunnel-like dissection by osteoclasts into the bony
trabeculae. Increased levels of which of the following hormones is most likely to be
responsible for this lesion?
A. Calcitonin
B. Cortisol
C. Erythropoietin
D. Glucagon
E. Parathyroid hormone
The correct answer is E. The histological picture suggests hyperparathyroidism, a well-recognized
sequela of chronic renal failure. This condition is caused by high levels of serum phosphate and low
serum calcium, which stimulate the release of parathyroid hormone (PTH) in an effort to normalize the
calcium/phosphate ratio. PTH stimulates osteoblasts to become osteoclasts, which dissolve the bone
reservoir of calcium and release it into the blood. This condition, known as renal osteodystrophy, may
lead to osteomalacia and osteitis fibrosa cystica, which is classically associated with dissecting
osteitis, as described in this question. With respect to parathyroid hormone physiology, the following
apply. The PTH has 5 effects: (1) stimulates osteoclasts; (2) inhibits osteoblasts; (3) promotes
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intestinal absorption of calcium and phosphate ions; (4) reduces urinary excretion of calcium; (5)
stimulates formation and secretion of calcitrol at the kidneys.
Calcitonin (choice A), which serves to lower serum calcium levels, is produced in small quantities in
chronic renal failure, as serum calcium is already pathologically low.
Excess cortisol (choice B; Cushing’s syndrome) may produce osteoporosis and pathologic fractures,
but there is no relationship between chronic renal failure and cortisol excess. Cushing’s syndrome is
generally secondary to adrenal or pituitary adenomas or primary adrenal hyperfunction.
Erythropoietin (choice C) production is often deficient in chronic renal failure. Excess erythropoietin
activates erythrocyte precursors, but does not activate osteoclasts.
Glucagon (choice D) excess is a very rare entity, occurring in a minority of islet cell tumors, and is not
associated with renal failure. High glucagon produces a transitory skin rash, anemia, and a form of
diabetes mellitus.
- Nonfunctioning of complement component C36 would be expected to interfere with which
of the following biologic functions?
A. Decreased appetite
B. Fever
C. Increased collagen synthesis by fibroblasts
D. Increased leukocyte adherence to endothelium
E. Opsonization to facilitate phagocytosis
The correct answer is E. C3b acts as an opsonin, together with IgG, to facilitate phagocytosis. None
of the other functions listed in the answer choices is attributable to C3b. Instead, all of the other
answer choices are functions of the cytokines interleukin-1 (IL-1) and tumor necrosis factor (TNF).
Tumor necrosis factor is produced by macrophages and activated T-cells, whereas many different cell
types (including macrophages) produce IL-1.
Decreased appetite (choice A) is typical during an acute illness (such responses are called acute
phase reactions). Other acute phase reactions include fever (choice B), increased sleep, shock,
leukocytosis, and increased serum acute phase proteins.
Fibroblasts proliferate and increase their synthesis of collagen (choice C), collagenase, protease, and
prostaglandin E in response to IL-1 and TNF.
Effects of IL-1 and TNF on endothelium include increased synthesis of mediators (prostaglandins, IL-
1, IL- 8, platelet-derived growth factor), increased leukocyte adherence (choice D), and increased
procoagulant activity with decreased anticoagulant activity.
- If a creatinine clearance of 100 mL/min changes to 50 mL/min over 1 year, assuming that
there has been no change in diet, which of the following physiologic changes can be
expected?
A. A 2-fold decrease in blood urea nitrogen concentration
B. A 2-fold decrease in creatinine excretion rate
C. A 2-fold increase in creatinine excretion rate
D. A 2-fold increase in creatinine reabsorption
E. A 2-fold increase in plasma creatinine concentration
The correct answer is E. Creatinine clearance is used clinically to estimate glomerular filtration rate
(GFR). The 50% decrease in creatinine clearance in this patient therefore suggests that GFR has
decreased by 50% over the past year. Because creatinine is freely filtered but not reabsorbed (choice
D), the filtration rate and excretion rate of creatinine are equal during steady state conditions. When
GFR decreases, the rate of creatinine excretion will also decrease, causing the rate of creatinine
excretion to decrease to below the rate of creatinine production. The result is an increase in plasma
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creatinine concentration. When plasma creatinine levels have increased by 2-fold, normal amounts of
creatinine can then again be excreted (compare with choices B and C) because the excretion rate of
creatinine is equal to the product of GFR and plasma creatinine concentration. In summary, when
GFR decreases, the plasma creatinine concentration continues to increase until the rate of creatinine
filtration (and excretion) becomes equal to the rate of creatinine production by the body.
The blood urea nitrogen concentration (choice A) increases when GFR is reduced.
- A cell biologist wants to activate protein kinase C in cultured cells. Stimulation of which of
the following receptor types would most likely produce the greatest activation?
A. Alpha 1 adrenergic
B. Beta 1 adrenergic
C. Dopamine-2 (D2)
D. Gamma-aminobutyric acid, type A (GABAA)
E. Nicotinic cholinergic
The correct answer is A. It is a good idea to know the mechanism of action of various receptors.
Alpha-1 adrenergic receptors are coupled to the G protein, Gq. This G protein causes breakdown of
the membrane phospholipid phosphatidylinositol bisphosphate (PIP2), forming the products
diacylglycerol, which stimulates protein kinase C, and inositol triphosphate (IP3), which releases
calcium from the endoplasmic reticulum. It is important to note that cyclic AMP activates protein
kinases by dissociating the complex of regularity and catalytic subunits, which results in activation of
the cellular response.
Beta-1 adrenergic receptors (choice B), like all beta receptors, are coupled to the Gs G protein,
leading to the activation of adenylate cyclase. This increases intracellular concentrations of cAMP by
converting ATP to cAMP. cAMP in turn stimulates protein kinase A, also known as cAMP-dependent
protein kinase.
Dopamine-2 receptors (choice C) are coupled to Gi. Stimulation of these receptors inhibits adenylate
cyclase, thus lowering cAMP levels and protein kinase A activity.
Gamma-aminobutyric acid, type A (GABAA) receptors (choice D) are not G-protein-coupled
receptors, but are instead ligand-gated ion channel receptors. Stimulation of these inhibitory receptors
causes a chloride flux, thus stabilizing the membrane potential of the cell.
Nicotinic cholinergic receptors (choice E) are not G-protein-coupled receptors, but are instead ligandgated
ion channel receptors. Stimulation of these receptors causes sodium influx, leading to excitation
of the cells.
30. which type of blood vessel is the mean linear velocity of a red blood cell the lowest? A. Aorta and large arteries B. Arterioles C. Capillaries D. Small arteries E. Vena cavae and large veins
The correct answer is C. The same volume of blood flows through each of the different types of
blood vessels each minute. Because the capillaries have the largest cross-sectional area (averaging
2500-5000 cm2), and the velocity of blood flow is inversely related to cross-sectional area, the mean
linear velocity of a red blood cell is lowest in the capillaries. Under resting conditions, the mean linear
velocity of a red blood cell in the capillaries is 0.3-0.6 mm/sec, whereas the velocity in the aorta
(choice A) is approximately 200 mm/sec. This low velocity of red blood cells in the capillary network
allows plenty of time for oxygen to diffuse to the tissues.
The velocity of blood flow is ranked from highest to lowest as follows: aorta (choice A) > vena cavae
(choice E) > large veins (choice E) > small arteries (choice D) > arterioles (choice B) > capillaries.
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When the vena cavae are partially collapsed, however, (which occurs often) they have a lower crosssectional
area and a higher velocity of blood flow compared with the aorta.
31 cells that have a low affinity for MHC class I molecules differentiate in the thymus to become which type of cell? A. CD8+ cytotoxic lymphocyte B. Gamma-delta T cell C. Natural killer cell D. T helper 1 cell E. T helper 2 cell
The correct answer is A. CD8 cells are generated after mature T cells interact with certain foreign
antigens. They are responsible for defense against intracellular pathogens, tumor immunity, and
organ graft rejection. CD8+ cytotoxic T lymphocytes are positively selected in the thymus because
they have low affinity for MHC class I molecules. If they had possessed high affinity for the MHC class
I molecules, they would have been eliminated (negative selection) because of the danger of
autoimmune disease. Also, cells with no affinity for MHC class I molecules would be eliminated.
The gamma-delta designation in a T cell (choice B) refers to type of receptor on the cell. Most T-cell
receptors are alpha-beta receptors, but some are of a different isotype termed gamma-delta.
Natural killer cells (choice C) are large granular lymphocytes that are part of the innate immune
response. Natural killer cell function does not depend on MHC class I or class II molecules; it simply
kills tumor cells or virally infected cells.
T helper 1 (choice D) and T helper 2 cells (choice E) would have a low affinity for class II MHC
molecules to survive in the thymus. If they had no affinity or strong affinity for these molecules, they
would have been eliminated.
32. Maintenance of the corpus luteum during the first trimester of pregnancy is accomplished principally by the secretion of A. antidiuretic hormone (ADH) B. follicle stimulating hormone (FSH) C. human chorionic gonadotropin (hCG) D. luteinizing hormone (LH) E. progesterone
The correct answer is C. The corpus luteum secretes estrogens, progesterone, and relaxin. hCG,
secreted by the syncytiotrophoblast lining the placental villi, maintains the corpus luteum during the
first trimester of pregnancy. hCG appears in the maternal blood stream soon after implantation
occurs. This hormone, in addition to maintaining the corpus luteum, also promotes the continued
secretion of progesterone. As a result, the endometrial lining remains functional and menses does not
occur. Antidiuretic hormone (vasopressin; choice A) does not play a significant role during
pregnancy. FSH (choice B) acts on granulosa cells to promote the conversion of androstenedione to
estradiol. LH (choice D) acts on theca cells to promote androstenedione secretion. Progesterone
(choice E) is important for maintaining the pregnancy, however, it does not act to maintain the corpus
luteum.
33. Metabolism of 100 grams of fat will yield approximately how many kilocalories? A. 200 B. 400 C. 600 D. 900 E. 1200
The correct answer is D. Carbohydrates contain approximately 3.4 kcal of energy and proteins
contain 4 kcal of energy per gram. Fats are the more energy-efficient storage form, containing 9 kcal
of energy per gram. A quantity of 100 grams of fat would therefore yield 900 kcal of energy.
34. Which of the following hormones of pregnancy is most likely to be significantly decreased compared with normal in the blood sample of a woman whose fetus has died during the second trimester? A. Estriol B. Human chorionic gonadotropin C. Human chorionic somatomammotropin D. Progesterone E. Prolactin
The correct answer is A. Maternal blood levels of estriol, a weak estrogen, depend on a viable fetus.
The fetal adrenal cortex and liver produce the weak androgen, 16-OH dehydroepiandrosterone sulfate
(16-OH DHEA-S) that is carried by the fetal circulation to the placenta, where it is converted to estriol
and secreted into the maternal circulation. Although maternal blood levels of estradiol and estrone
increase by 50-fold during pregnancy, maternal blood levels of estriol increase 1,000-fold. Increasing
maternal blood levels of estriol is the best indicator of fetal well-being. A significant drop in maternal
estriol may indicate fetal jeopardy.
Human chorionic gonadotropin (hCG, choice B) is secreted by syncytiotrophoblast cells and does not
depend on a viable fetus. Human chorionic gonadotropin (hCG) is in the same hormone family as
TSH, FSH, and LH. The maternal blood or urinary level of hCG is used to confirm the presence of
pregnancy. Its function is to “rescue” the corpus luteum and maintain the pregnancy until the placenta
can produce sufficient estrogen and progesterone.
Human chorionic somatomammotropin (hCS; choice C) is secreted by syncytiotrophoblast cells and
does not depend on the presence of a viable fetus. It is also known as human placental lactogen, and
is in the same hormone family as growth hormone and prolactin. Its function in pregnancy is not
completely understood, but it may serve to reduce maternal glucose use and allow for “shunting” of
glucose to the fetus.
Maternal progesterone (choice D) depends on a viable placenta, but does not depend on a fetal
contribution. The precursor for placental secretion of progesterone is maternal (not fetal) cholesterol.
Prolactin (choice E) levels steadily increase during pregnancy. This contributes to the final
development of a mature mammary gland. It is secreted by the anterior pituitary and does not require
a fetal contribution.
- With time, blood stored in a blood bank tends to become relatively depleted of 2,3-
diphosphoglycerate (2,3-DPG). What effect does this have on the hemoglobin-oxygen
dissociation curve?
A. Shifts the curve to the left, so that the hemoglobin has a decreased oxygen affinity
B. Shifts the curve to the left so that the hemoglobin has an increased oxygen affinity
C. Shifts the curve to the right, so that the hemoglobin has a decreased oxygen affinity
D. Shifts the curve to the right, so that the hemoglobin has an increased oxygen affinity
E. Does not change the dissociation curve
The correct answer is B. 2,3-diphosphoglycerate (2,3-DPG) is produced in red cells (RBCs) by a
variation on the glycolytic pathway, and levels diminish when glycolysis by the RBCs slows. The
depletion of 2,3-DPG in stored blood causes the hemoglobin dissociation curve to shift to the left,
leading to an increase in oxygen affinity. This increase is helpful in the picking up of oxygen by
hemoglobin from the lungs, but it can be very problematic in the release of oxygen from the blood to
the tissues. This is not just a theoretical point: considerable effort has been expended in developing
improved solutions for storing packed RBCs and methods for “restoring” older stored cells so that the
2,3-DPG levels are adequate. In practice, in otherwise reasonably healthy patients, older transfused
blood will quickly regenerate 2,3-DPG when placed in the glucose-containing environment of the
serum; however, even transiently decreased 2,3-DPG levels in a severely compromised patient can
be dangerous.
- Under normal conditions, the main drive for respiration is the
A. arterial PCO2 acting through central chemoreceptors
B. arterial PCO2 acting through peripheral chemoreceptors
C. arterial pH acting through central chemoreceptors
D. arterial pH acting through peripheral chemoreceptors
E. arterial PO2 acting through central chemoreceptors
The correct answer is A. The most important factor in the control of minute-to-minute ventilation is
arterial PCO2, which influences chemoreceptors located near the ventral surface of the medulla. As
arterial PCO2 rises, CO2 diffuses from cerebral blood vessels into the CSF. Carbonic acid is formed
and dissociates into bicarbonate and protons. Protons directly stimulate these central
chemoreceptors, resulting in hyperventilation. Hyperventilating reduces the PCO2 in the arterial blood
and subsequently in the CSF.
Peripheral chemoreceptors located in the carotid and aortic bodies respond to increases in
PCO2(choice B), but are less important than the central chemoreceptors. It is estimated that when a
normal subject hyperventilates in response to inhalation of CO2, less than 20% of the response can
be attributed to the peripheral receptors. However, they respond more quickly than their central
counterparts and are thought to play a role in regulating ventilation after abrupt changes in PCO2.
There are no known central chemoreceptors that respond to either arterial pH (choice C) or arterial
PO2(choice E).
Carotid chemoreceptors (choice D) cause hyperventilation in response to decreases in arterial pH;
however, CO2 acting through central chemoreceptors is the most important regulator of ventilation
under normal conditions.
37. Which of the following types of nerve fibers carry pain that is aching, burning, sometimes throbbing, and poorly localized? A. Group II fibers B. Group III fibers C. Type C fibers D. Substance P
The correct answer is C. Slow pain as described in this question is carried by type C fibers. Choice-
A - The dorsal column system consists of type II fibers that carry touch and pressure sensation.
Choice B - Fast pain is carried by group III fibers. It has a rapid onset and offset and is localized. The
anterolateral system, which processes sensations of temperature, pain, and light touch, consists
primarily of group III and group IV fibers. Choice D - Pain is associated with detection and perception
of noxious stimuli (nociception). The neurotransmitters for nociceptors include substance P. Inhibition
of the release of substance P is the basis of pain relief by opioids.
- If a drug is taken that stimulates sympathetic cholinergic neurons, which of the following
responses is expected?
A. Bradycardia
B. Bronchoconstriction
C. Diaphoresis
D. Increased gastrointestinal motility
E. Increased peripheral vascular resistance
The correct answer is C. Sympathetic cholinergic neurons are sympathetic postganglionic neurons
that happen to release acetylcholine instead of norepinephrine. The vast majority of sweat glands in
the body are innervated by sympathetic cholinergic neurons (choice C). Bradycardia (choice A),
bronchoconstriction (choice B), and increased gastrointestinal motility (choice D) would all result
from stimulating parasympathetic cholinergic neurons.
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Increased peripheral vascular resistance (choice E) would result from stimulating sympathetic
adrenergic neurons.
- A 3-year-old child has inhaled a peanut that has lodged in the right mainstem bronchus,
largely occluding it. The child is cyanotic, with a PO2 of 60 mm Hg. Which of the following
mechanisms best accounts for the child’s hypoxemia?
A. Decreased capacity of pulmonary diffusion
B. Decreased PO2 in inspired air
C. Hypoventilation of central origin
D. Hypoventilation of peripheral origin
E. Inequalities of ventilation and perfusion
The correct answer is E. Inequalities of ventilation and perfusion contribute to hypoxia in many
settings. In this case, blood goes to both lungs (perfusion), but air is prevented from entering one of
the lungs (ventilation). Because the right lung is being perfused, but not ventilated, hypoxemia ensues
when the deoxygenated blood from the right lung mixes with oxygenated blood from the left lung. If
the inadequate ventilation of the lung persists long enough, the lung tissue itself can be damaged,
causing a secondary local dilation of arterioles, making the problem even worse. Peanuts are
notorious for producing this type of problem in young children because of their size and shape, which
allow them to lodge in the trachea or main bronchus after aspiration.
Decreased diffusion capacity (choice A) can occur when the blood-gas barrier is thickened (e.g.,
diffuse interstitial fibrosis, sarcoidosis, asbestosis, respiratory distress syndrome), when the surface
area of the blood-gas barrier is reduced (e.g., pneumonectomy, emphysema), or when less
hemoglobin is available to carry oxygen (e.g., anemia, pulmonary embolism).
Decreased PO2 in inspired air (choice B) is seen at high altitudes and when the settings are wrong
during artificial ventilation.
Hypoventilation of central origin (choice C) is seen in morphine and barbiturate overdose.
Hypoventilation of peripheral origin (choice D) is seen in poliomyelitis and chest trauma.
- One hour before a dental procedure a patient receives four 500-mg amoxicillin capsules.
On arriving at the dental office the dentist notices that the patient has maculopapular rash and
is wheezing. The effector cell in this type of hypersensitivity is a(n)
A. eosinophil
B. mast cell
C. megakaryocyte
D. neutrophil
E. TH1 CD4+ lymphocyte
The correct answer is B. This patient is experiencing the early phase of type I hypersensitivity,
characterized by bronchospasm and development of a maculopaplar rash. Other potential symptoms
of this allergic drug reaction include pruritus and watery discharge from the nose, mucus secretion in
the airways, and a wheal-and-flare response with pruritus in the skin. The mechanism of
hypersensitivity involves prior sensitization of a population of TH2 cells that produced cytokines,
including interleukin-4. The interleukin-4 causes B cells to switch their heavy chain class from IgM to
IgE. The IgE molecules then attach to mast cells or basophils. With subsequent antigen (allergen)
challenge, the mast cells degranulate and release mediators, including histamine, which produces the
anaphylactic response.
Eosinophils (choice A) are involved in late-phase type I hypersensitivity reactions and type II
antibody-dependent cell cytotoxicity reactions directed against parasites. Eosinophils enter the area of
the reaction because of the release of eosinophil chemotactic factor (eotaxin) and the beta-chemokine
RANTES released from TH2 CD4+ cells and mast cells. Eosinophils are recruited into the tissues as
17
part of the late-phase reaction of type I hypersensitivity. Their survival in tissue is dependent on IL-3,
IL-5, and granulocyte-monocyte colony stimulating factor (GM-CSF) released from TH2 cells.
Megakaryocytes (choice C) are bone marrow cells that produce platelets. They are not involved in
type I hypersensitivity.
Neutrophils (choice D) are not a cell type that is key to the development of type I hypersensitivity.
TH1 CD 4+ lymphocytes (choice E) are associated with delayed type hypersensitivity reactions such
as contact dermatitis involving exposure to poison ivy or poison oak.
41. An increase in which of the following is the most likely explanation for the swelling in the legs seen with congestive heart failure? A. Interstitial colloid osmotic pressure B. Lymph flow C. Plasma colloid osmotic pressure D. Right atrial pressure E. Stroke volume
The correct answer is D. Congestive heart failure typically develops when the heart becomes
damaged (usually as a result of myocardial infarction) and the cardiac output cannot be maintained at
a normal level. A low cardiac output has profound effects on the kidneys, causing salt and water
retention. If the heart is not damaged too badly, the increase in blood volume caused by the fluid
retention can increase venous return sufficiently to totally compensate for the diminished pumping
capacity of the heart. The increase in venous return causes the right atrial pressure to increase, which
elevates venous pressure throughout the body. This increase in venous pressure can cause
excessive fluid loss from the microcirculation and the development of peripheral edema. The labored
breathing experienced by the patient is indicative of mild pulmonary edema caused by increased
pressure in the pulmonary microvasculature.
The increase in fluid loss from the microcirculation would be expected to literally wash protein
molecules out of the interstitial compartment and thereby decrease the interstitial colloid osmotic
pressure (choice A), and increase the flow of lymph (choice B) from the tissue as a consequence
rather than a cause of the edema.
Increased plasma colloid osmotic pressure (choice C) would tend to decrease the development of
edema. Also, fluid retention by the kidneys tends to dilute the plasma and thus decrease the plasma
colloid osmotic pressure.
Stroke volume (choice E) has no direct role in the formation of peripheral edema.
42. An increase in which of the following best explains the mechanism by which the cardiac output increases in severe anemia? A. Arteriolar diameter B. Blood viscosity C. Peripheral vascular resistance D. Splanchnic blood flow E. Tissue oxygen tension
The correct answer is A. Anemia is present in adults if the hematocrit is less than 41% in men and
37% in women. Poor diet and pathologic bleeding can lead to the development of folic acid deficiency
and iron deficiency anemia, respectively. In severe anemia, diminished transport of oxygen in the
blood leads to hypoxia in the tissues. The hypoxia (compare with choice E) causes small arteries and
arterioles to dilate, which allows greater than normal amounts of blood to return to the heart. In severe
anemia, the viscosity of blood (choice B) may decrease by 50% or more because blood viscosity
depends largely on the concentration of red blood cells. This decrease in viscosity lowers the
18
resistance to blood flow in the peripheral tissues (i.e., decreases peripheral vascular resistance,
choice C) allowing even greater amounts of blood to return to the heart.
Blood is often shunted away from the splanchnic vascular bed (choice D) in anemia, which can cause
gastrointestinal problems.
43. Which of the following is found in the respiratory zone of the lung? A. Goblet cells B. Main bronchi C. Mucous cells D. Terminal bronchioles E. Type I epithelial cells
The correct answer is E. There are two zones in the lung: the conducting zone (where there is no
gas exchange) and the respiratory zone (where gas exchange takes place). Of all of the structures
listed, only type I epithelial cells are located in the respiratory zone. Type I epithelial cells are the
primary structural cells of the alveolar wall. Type II epithelial cells, also located in the alveoli, produce
surfactant. Goblet cells (choice A), which are mucus-secreting cells, are present in the conducting
airways. The main bronchi (choice B) are part of the conducting airways. Mucous cells (choice C),
which are mucus-secreting cells, are also present in the conducting airways. Terminal bronchioles
(choice D) are the most distal part of the conducting airways. Respiratory bronchioles, which are just
distal to the terminal bronchioles, are part of the respiratory zone. These two types of bronchioles can
be differentiated from each other by whether they have alveoli budding from their walls. Respiratory
bronchioles have alveoli, terminal bronchioles do not.
44. Laboratory studies of an automobile accident victim show a significant elevation of creatine kinase (CK). Which of the following tissues is most likely to be the source of the enzyme? A. Bone B. Brain C. Heart D. Kidney E. Skeletal muscle
The correct answer is E. Creatine kinase occurs in several different forms, or isoenzymes, in the
body. Most tissues contain a mix of creatine kinase isoenzymes, but one species often predominates.
The MB isoenzyme of creatine kinase is associated with heart damage; the MM isoenzyme is
associated with muscle damage; and the BB isoenzyme is associated with brain damage. Surgery
and general trauma are commonly implicated as causes of sufficient skeletal muscle trauma to
markedly elevate creatine kinase by way of the CK-MM (skeletal muscle isoenzyme) isoenzyme.
Bone (choice A) is not a significant source of CK. Brain (choice B) can occasionally be a source of
creatine kinase (BB isoenzyme), but would not usually be the major source following an automobile
accident. Heart damage (choice C), as in myocardial infarction, can elevate creatine kinase, but
would not usually be the major source in an automobile accident. If the dilemma arises as to whether
an automobile accident was possibly secondary to a myocardial infarction, the ratio of CK-MB to total
CK may be helpful in demonstrating a cardiac contribution (CK-MB is characteristic of heart muscle).
Kidney (choice D) is not a major source of creatine kinase.
45. Which of the following binds to von Willebrand factor at the platelet membrane? A. Adenosine diphosphate (ADP) B. Calcium C. Glycoprotein GPIb D. Platelet factor 3 (PF3) E. Prostacyclin
The correct answer is C. Glycoprotein GPIb on the platelet membrane binds von Willebrand factor, a
plasma protein that circulates in a complex with factor VIII. ADP (choice A) is a powerful inducer of
platelet aggregation and strengthens the platelet plug by the addition of more activated platelets.
Calcium (choice B) is essential for increasing the degree of platelet aggregation and strengthening
the platelet plug. It is also a necessary cofactor in the coagulation cascade (required for the
conversion of factors IX to IXa, X to Xa, V to Va, and prothrombin [factor II] to thrombin [factor IIa]).
Platelet factor 3 (PF3; choice D) is involved in platelet plug formation. Prostacyclin (choice E) is
synthesized by blood vessel endothelial cells and inhibits platelet aggregation.
- Which of the following statements about Troponin C is true? Troponin C
A. inhibits the interaction of actin and myosin
B. attaches the troponin complex to tropomyosin
C. permits the interaction of actin and myosin
D. is located at the junction of A band and I band
The correct answer is C. Troponin C is the calcium binding protein that when bound to calcium
permits the interaction of actin and myosin. Cross bridges continue as long as calcium is bound to
troponin C. Choice A - Troponin I inhibits the interaction of actin and myosin. Choice B - Troponin T
attaches the troponin complex to tropomyosin. Choice D - T tubules are the extensive tubular network
that carry the depolarization from sarcolemmal membrane to the cell interior. These are located at the
junction of A band and I band.
47 .Which of the following can be determined by calculation of the clearance of paraaminohippuric acid (PAH)? A. Extracellular fluid (ECF) volume B. Effective renal plasma flow (ERPF) C. Glomerular filtration rate (GFR) D. Plasma volume E. Total body water (TBW)
The correct answer is B. At less than saturating concentrations, PAH is completely secreted into the
proximal tubule and excreted into the urine. The volume of plasma cleared of PAH is therefore
approximately equal to the volume of plasma flowing through the peritubular capillaries, also called
the effective renal plasma flow, or ERPF. The ECF volume (choice A) can be calculated by
measuring the volume of distribution of solutes that move freely across capillary walls but cannot
permeate cell membranes (e.g., inulin and mannitol). GFR (choice C) is best calculated using a
substance that is freely filtered at the glomerulus, not reabsorbed, and only minimally secreted into
the urine. Creatinine fits the bill and is used clinically to measure the GFR (inulin also works and is
used experimentally). Although the creatinine excretion exceeds filtration by 10-20% (because of the
secretion), creatinine clearance is still a good approximation for GFR because the error caused by
secretion is balanced by an overestimation of plasma creatinine inherent in the measurement
technique. The plasma volume (choice D) can be measured by measuring the volume of distribution
of radioactively labeled serum albumin or of Evans blue dye (binds to albumin). Total body water
(TBW; choice E) can be measured by measuring the volume of distribution of tritium, deuterium, or
antipyrine.
- The clearance of several substances was measured at a constant glomerular filtration rate
and constant urine flow rate, but at increasing plasma concentrations of the substance. Under
these conditions, clearance will increase at high plasma concentrations for which of the
following substances?
A. Creatinine
B. Mannitol
C. Penicillin
D. Phosphate
E. Urea
The correct answer is D. Clearance of a substance will change with increasing plasma
concentration if that substance is secreted or reabsorbed by a facilitated mechanism. As the
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concentration of the substance increases, the transporter becomes saturated, and its contribution to
excretion changes, changing the clearance. If the substance is reabsorbed by a facilitated
mechanism, clearance will eventually increase with increasing plasma concentrations. Approximately
80% of filtered phosphate is reabsorbed in the proximal tubule by a sodium-phosphate cotransporter,
which is a facilitated mechanism. The phosphate buffer system consists of an anion, H2PO4, that is a
weak acid. The basic operation of the phosphate buffer system resembles that of the carbonic acidbicarbonate
buffer system.
49. Gastrin stimulates the secretion of HCl. Which of the following cell types located at the fundus of the stomach produces HCl? A. Parietal cells B. Chief cells C. G cells D. Mucous cells
The correct answer is A. Parietal cells located in the body of the stomach secrete HCl and intrinsic
factor. Stimuli for secretion are gastrin, histamine, and Ach. Parietal cells secrete HCl into the lumen
of the stomach and concurrently absorb bicarbonate into the blood stream. Choice B - Chief cells,
located in fundus, secrete pepsinogen under vagal stimulation. Choice C - Vagal stimulation secretes
gastrin from the G cells of the antrum of the stomach. Choice D - Mucous cells, located in the antrum
of the stomach, secrete mucus and pepsinogen under vagal stimulation.
- Adrenocorticotropic hormone (ACTH) promotes the production of cortisol by stimulating
which of the following reactions?
A. 11-Deoxycortisone to cortisol
B. 17-Hydroxyprogesterone to 11-deoxycortisol
C. Cholesterol to pregnenolone
D. Pregnenolone to progesterone
E. Progesterone to 17-hydroxyprogesterone
The correct answer is C. All of the choices listed are reactions that occur in the synthetic pathway
from cholesterol to cortisol. ACTH stimulates the first reaction in the pathway: cholesterol to
pregnenolone. This reaction is catalyzed by the enzyme cholesterol desmolase.
The next step in the pathway is pregnenolone to progesterone (choice D); progesterone is then
converted to 17-hydroxyprogesterone (choice E); 17-hydroxyprogesterone is converted to 11-
deoxycortisol (choice B) by the enzyme 21 beta-hydroxylase; and the 11-deoxycortisol is then
converted to cortisol (choice A).
- Laboratory studies for an alcoholic patient indicate that serum magnesium is depressed.
Which of the following findings would be most consistent with this information?
A. Decreased serum calcium
B. Decreased serum phosphate
C. Increased bone density
D. Increased plasma parathyroid hormone concentration
The correct answer is A. Malnutrition associated with chronic alcoholism can lead to a severe
magnesium deficiency. The effect of low serum magnesium on parathyroid hormone secretion (PTH)
depends on severity and duration. An acute decrease in serum magnesium will increase PTH
secretion, whereas a prolonged severe deficiency results in decreased PTH secretion. There is also
evidence that the action of PTH is decreased with chronic magnesium deficiency. Hence, this patient
is suffering from “functional” hypoparathyroidism, causing low serum calcium (choice A) that can
produce weakness, tremors, muscle fasciculations, and seizures. In patients with magnesium
deficiency, magnesium administration will produce a prompt increase in plasma PTH with subsequent
restoration of serum calcium concentration to normal.
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With functional hypoparathyroidism bone density would be decreased (not increased, choice C). The
combination of decreased PTH secretion (not increased, choice D) and decreased effectiveness of
PTH produce hypocalcemia and hyperphosphatemia (not hypophosphatemia, choice B).
Phosphorous is needed for development of high-energy compounds, nucleic acids, and bone matrix.
Respiratory rate 15; blood pressure 120/80 mm Hg; cardiac output 5 L/min; pulse 50
52. 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 systole (i.e., the stroke volume; SV) multiplied by the number of times the heart
beats each minute (heart rate; HR). In other words, CO = SV x HR. Therefore, SV = CO/HR, and
because CO = 5,000 mL/min and HR = 50 beats/min, SV = 5,000/50 = 100 mL/beat.
In the examination of a single cardiac cycle, stroke volume is the most important factor to consider. In
the consideration of cardiac function over time, clinicians are concerned with cardiac output (the
volume of blood ejected in 1 minute). Physiologically, cardiac output is precisely regulated so that
peripheral tissues receive an adequate circulatory supply under a variety of conditions; for example,
stroke volume can almost triple when neccessary.
- Which of the following would most likely be an associated finding during fasting for a
patient with an insulin-secreting tumor that is localized to the tail of the pancreas?
A. Glycosylated hemoglobin level is increased
B. Plasma concentration of C peptide is decreased
C. Plasma concentration of glucagon is decreased
D. Plasma concentration of glucose is increased
E. Plasma concentration of proinsulin is increased
The correct answer is E. Hypersecretion of insulin by a pancreatic cell tumor is a major cause of
fasting hypoglycemia (plasma glucose is not increased, choice D). Symptoms are related to
neuroglycopenia and could include recurrent central nervous system dysfunction during fasting or
exercise. Although proinsulin only makes up approximately 20% of plasma immunoreactive insulin in
normal individuals, in patients with an insulinoma it contributes 30-90% of the immunoreactive insulin.
The increased secretion of insulin by the tumor will also lead to an increase in C peptide secretion
(not decreased, choice B) since ß cells secrete insulin and C peptide on a one-to-one molar ratio.
Given the prolonged hypoglycemia, the amount of glycosylated hemoglobin may also be decreased,
although this is not a universal finding. Certainly an increase in glycosylated hemoglobin would not be
expected (choice A). Glucagon secretion is increased by hypoglycemia and its plasma level in a
patient with an insulinoma would be expected to be increased compared with normal (not decreased,
choice C).
- Physical examination of a woman with advanced, metastatic lung cancer demonstrates
hyperpigmentation of skin, even in areas protected from the sun. ACTH levels are found to be
elevated. Tumor inducement of which endocrine organ is most likely?
A. Adrenal gland
B. Endocrine pancreas
C. Ovaries
D. Pituitary gland
E. Thyroid gland
The correct answer is A. This is Addison disease, in which severe adrenal disease produces
adrenocortical insufficiency. Causes include autoimmune destruction, congenital adrenal hyperplasia,
hemorrhagic necrosis, and replacement of the glands by either tumor (usually metastatic) or
granulomatous disease (usually tuberculosis). The symptoms can be subtle and nonspecific (such as
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those listed). Skin hyperpigmentation is a specific clue that may be present on physical examination,
suggesting excess pituitary ACTH secretion. Most patients have symptoms (fatigue, gastrointestinal
distress) related principally to glucocorticoid deficiency. In some cases, however, mineralocorticoid
replacement may also be needed for symptoms of salt wasting with lower circulating volume.
Except in the case of primary pancreatic cancer, complete tumor replacement of the endocrine
pancreas (choice B) would be uncommon. In any event, pancreatic involvement would be associated
with diabetes mellitus.
Involvement of the ovaries (choice C) by metastatic tumor (classically gastric adenocarcinoma) would
produce failure of menstruation.
Involvement of the pituitary gland (choice D) could produce Addisonian symptoms, but the pigmented
skin suggests a primary adrenal problem rather than pituitary involvement.
Replacement of the thyroid gland (choice E) by tumor would cause hypothyroidism with lesser
degrees of fatigue and cold intolerance; this is an unusual cause of hypothyroidism.
- The resultant decrease in blood flow causes by partial obstruction of the renal artery by an
atherosclerotic plaque increases release of an enzyme from which of the following structures?
A. Afferent arterioles
B. Arcuate arteries
C. Juxtaglomerular cells
D. Kupffer cells
E. Proximal convoluted tubule
The correct answer is C. The juxtaglomerular cells are in the wall of the afferent arteriole, close to
the glomerulus. Together the macula densa and juxtaglomerular cells form the juxtaglomerular
apparatus. In response to decreased blood pressure, they secrete renin, an enzyme that converts
angiotensinogen to angiotensin I. Angiotensin converting enzyme, found in the lungs, converts
angiotensin I to angiotensin II. Angiotensin II increases peripheral vascular resistance directly and
stimulates aldosterone secretion, resulting in increased reabsorption of sodium and water in the distal
convoluted tubules.
The afferent arteriole (choice A) carries blood from the interlobular arteries to the glomerulus.
Filtration of blood occurs in the glomerulus, with the filtrate entering Bowman’s capsule.
The arcuate arteries (choice B) are branches of the interlobar arteries of the kidney. The arcuate
arteries lie in the corticomedullary junction of the kidney and give rise to interlobular arteries, which
enter the cortex of the kidney and supply the glomeruli.
Kupffer cells (choice D) are found in the liver, along the sinusoids. They are phagocytic cells that are
part of the reticuloendothelial system.
The proximal convoluted tubule (choice E) is directly continuous with Bowman’s capsule. Most of the
resorption of the glomerular filtrate occurs in this part of the nephron.
56. In a person weighing 75 kg, the volume of total body water is 45 L. What is the interstitial volume and plasma volume? A. 4 L, 12 L B. 12 L, 4 L C. 8 L, 8 L D. 5 L, 10 L
The correct answer is B. Interstitial volume = 12 L and plasma volume = 4 L. The calculation is
based on the following estimates: of total body weight, approximately 60% is water. One third of this
water is extracellular, and two thirds is intracellular. Of the one third that is extracellular, approximately
one quarter is plasma volume, and the other three quarters is interstitial volume. Using the figures in
the problem:
57. When a 10-day-old infant jumps and jerks his arms to his chest in response to a noice, the infant is exhibiting the A. Babinski reflex B. deep tendon reflex C. Moro reflex D. palmar reflex E. tonic neck reflex
The correct answer is C. The identification of reflexes is an important part of human physiology. The
Moro reflex can be elicited in the infant by any startling event; it consists of extension and abduction of
the arms, followed by flexion and adduction of the arms. This is a normal reflex that appears between
the ages of 25 and 36 weeks of gestation, and will normally disappear between 3-6 months of age.
The Babinski reflex (choice A) is elicited when the lateral surface of the sole of the foot is stroked
resulting in the great toe going up and the other toes fanning. It normally disappears at 1 year of age.
Deep tendon reflexes (choice B) can be elicited by tapping a tendon with a reflex hammer, which
stretches the tendon, producing contraction in the corresponding muscle. These are present
throughout life.
The palmar grasp reflex (choice D) is characterized by the infant’s hand closing over an object that is
placed in the palm of the hand. This reflex normally disappears at 2 months of age.
The tonic neck reflex (choice E) consists of extension of the ipsilateral leg and flexion of the
contralateral arm and leg when the head is turned. This reflex normally disappears between 7-8
months of life.
58. Which of the following is the primary opsonin in the complement system? A. C1q B. C3b C. C5 D. C5a E. Factor B
The correct answer is B. Complement consists of 11 plasma proteins that interact in a chain reaction
following exposure to activated antibodies or surfaces of certain pathogens. Complement promotes
cell lysis, phagocytosis, and often defense mechanisms. C3b is the most critical molecule in both the
classical and alternative complement pathways. C3, the most abundant protein of all the complement
proteins, is cleaved into C3a and C3b. C3b attaches to bacterial surfaces for opsonization by
phagocytes. C3a binds to mast cells and basophils, activating them and producing histamine release.
C1q (choice A) is a complement component in the classical pathway. It binds to the constant heavy
domain of an IgG molecule that has reacted with the bacterial surface epitope. C1q is not involved in
opsonization as it simply functions as an enzyme in the early complement cascade.
- Constriction of which of the following types of blood vessels is most important for
minimizing the decrease in mean systemic filling pressure caused by loss of 1 liter of blood?
A. Aorta and large arteries
B. Arterioles
C. Capillaries
D. Small arteries
E. Venules and veins
The correct answer is E. The venous system serves as an important blood reservoir for the
circulation. When blood is lost from the body and blood pressure begins to decrease, pressure
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reflexes are elicited that send sympathetic nerve signals to venules and veins causing them to
constrict. By “tightening” the circulation and taking up much of the “slack” caused by the blood loss,
nearly normal function can usually be restored with up to a 20% loss of blood volume.
Constriction of the arterial system has relatively little effect on mean systemic filling pressure because
the arterial system (choices A, B, and D) contains a relatively small volume of blood.
Capillaries do not constrict because they do not contain smooth muscle cells in their walls (choice C).
- Which of the following regulates the frequency of gastrointestinal slow waves?
A. Circadian rhythms
B. Dietery intake of fiber
C. Intrinsic pacemaker regions within the smooth muscle
D. Local levels of cholecystokinin secretion
E. Systemic levels of catecholamines and corticosteroids
The correct answer is C. Slow waves are oscillating membrane potentials that are generated locally
within the gastrointestinal smooth muscle. In each region of the gastrointestinal tract, intrinsic
pacemaker cells within the smooth muscle independently generate slow waves. Slow-wave
frequencies are relatively constant and are characteristic of each region of the gut.
There is no evidence that either circadian rhythms (choice A) or dietary fiber intake levels (choice B)
have any effect on gastrointestinal slow wave frequencies.
Cholecystokinin (choice D), corticosteroids, and sympathetic stimulation (choice E) may modify the
frequency of action potentials and contractions by affecting the amplitude, rather than the frequency,
of the slow waves.
- A 72-year-old woman with mild heart failure is treated overzealously with a thiazide
diuretic. A few days later, the woman complains of muscle weakness, and laboratory tests
demonstrate hypokalemia. Which of the following is most likely increased in this woman?
A. Arterial H+ concentration
B. Plasma aldosterone
C. Plasma sodium
D. Potassium retention
E. Sodium retention
The correct answer is B. Aldosterone is a minerlocorticoid produced by the zona glomerulosa or the
adrenal cortex. It stimulates sodium and water conservation at the kidneys. This hormone is secreted
in response to the presence of angiotensin II. Diuretics lead to aldosterone excess and hypokalemia
by a variety of mechanisms. (1) Diuretic induces volume depletion stimulated the formation of
angiotensin II, which, in turn, causes a secondary increase in plasma aldosterone concentration. This
increase in plasma aldosterone stimulates potassium excretion, contributing to the hypokalemia. (2)
The saline diuresis increases sodium delivery to the collecting tubule. The increased availability of
sodium along with the elevated plasma aldosterone augments sodium reabsorption in the collecting
tubule, thereby raising luminal negativity. This high luminal negativity in the collecting tubule promotes
secretion of cations, especially hydrogen ions, which raises bicarbonate reabsorption. (3) The saline
diuresis causes rapid fluid flow in the distal tubule, which, in turn, keeps luminal potassium
concentration low by carrying it away and thus preventing the assimilation of any potassium that
enters the lumen. This low luminal concentration of potassium creates a steep concentration gradient
for additional potassium losses in the urine. The treatment of edema with thiazide or loop diuretics is
the most common cause of metabolic alkalosis. Arterial pH is increased and arterial H+ concentration
(choice A) is decreased with metabolic alkalosis.
Sodium depletion tends to decrease plasma sodium (choice C) levels, although the effect is usually
small. Overuse of the thiazide diuretic has caused depletion of sodium and potassium by the kidneys,
not retention of sodium and potassium (choices D and Choice E).
62. Increasing urine flow rate from 1 mL/min to 10 mL/min will significantly increase the clearance of A. creatinine B. inulin C. penicillin D. phosphate E. urea
The correct answer is E. Urine flow rate is controlled primarily by antidiuretic hormone (ADH), which
regulates the amount of pure water retained in the urine. ADH also controls the reabsorption of urea in
the papillary collecting duct. High urine flow rates indicate low ADH, which increases urea clearance.
In contrast, low urine flow rates indicate high ADH, which results in a greater reabsorption of urea and
a lower urea clearance.
The concentration (and osmolarity) of all other solutes (choices A, B, C, and D) varies inversely with
urine flow rate, resulting in no change in clearance. Recall that clearance = (urine concentration x
urine flow rate)/plasma concentration.
- A 3-year-old boy with chronic granulomatous disease (CGD) has a culture of a purulent
discharge from an abscess that shows Staphylococcus aureus. Immunoglobulin and
complement levels are normal. The boy received all of the standard immunizations without any
adverse effects. His immune deficiency most likely involves which of the following?
A. B cells
B. Chemotaxis
C. IgG subclass 2
D. Phagocytic cells
E. T cells
The correct answer is D. This patient has chronic granulomatous disease (CGD), which is
associated with defective phagocytes. CGD is inherited as an X-linked or autosomal recessive trait
and consists of a group of heterogenous disorders of oxidative metabolism affecting the normal
respiratory burst, consisting of increased oxygen consumption, leading to the generation of
intracellular hydrogen peroxide and superoxide radicals by phagocytic cells. The hydrogen peroxide
and superoxide radicals are required for the killing of ingested intracellular organisms. The reaction is
catalyzed by an NADPH oxidase that seems to be defective in the phagocytes of patients with CGD.
In CGD patients, the engulfment process by the phagocytic cells is normal; however, the pathogenic
organism is not killed, but persists within the cell. The patients suffer from infections with organisms
that are normally considered of low virulence (e.g., Staphylococcus aureus, Aspergillus, Candida,
Escherichia coli, and Serratia marcescens). The nitroblue tetrazolium (NBT) test is used to screen for
CGD. B cells (choice A) are responsible for antibody-mediated immunity, and the immunoglobulin
levels in this patient were normal. Chemotaxis (choice B) is important in the migration of the
phagocytic cell toward the site of infection, not in intracellular killing. IgG subclass 2 (choice C) is the
most important immunoglobulin in the protection against encapsulated organisms. T cells (choice E)
are important in the host response to viruses, fungi, and intracellular bacterial organisms. The patient
was immunized normally (including the live, attenuated MMR vaccine), making T-cell dysfunction
unlikely.
- Which of the following indices would be expected to be higher in an individual living at sea
level versus an individual living in the mountains?
A. Diameter of pulmonary vessels
B. Erythropoietin production
C. Mitochondrial density in a muscle biopsy
D. Renal bicarbonate (HCO3-) excretion
E. Respiratory rate
The correct answer is A. Several physiologic changes occur in a person living at high altitude. The
diminished barometric pressure at high altitude causes alveolar hypoxia and arterial hypoxia.
Pulmonary vasoconstriction occurs in response to alveolar hypoxia; therefore, the diameter of the
pulmonary vessels would be greater in the brother living at sea level. All the other choices describe
physiologic processes that would be enhanced by living at high altitude.
Increased erythropoietin production (choice B) caused by arterial hypoxia leads to increases in
hematocrit and increased oxygen carrying capacity in people living at high altitude.
Mitochondrial density increases (choice C) in people chronically exposed to the hypoxemia caused
by living at high altitude.
At high altitudes, the ventilation rate increases, causing a respiratory alkalosis. The kidney then
compensates by increasing the excretion of HCO3- (choice D).
Increasing the rate of respiration (choice E) is a very useful adaptation to the hypoxic conditions of
high altitude. The primary stimulus is the hypoxic stimulation of peripheral chemoreceptors.
