Exam 2

Question 1

1. Which is a false statement about skeletal muscle structure?
   a. A myofibril is composed of multiple muscle fibers.
   b. Most skeletal muscles attach to bones by connective-tissue tendons.
   c. Each end of a thick filament is surrounded by six thin filaments.
   d. A cross-bridge is a portion of the myosin molecule.
   e. Thin filaments contain actin, tropomyosin, and troponin.

Answer 1

A - A single skeletal muscle fiber, or cell, is composed of many myofibrils.

Question 2

2. Which is correct regarding a skeletal muscle sarcomere?
   a. M lines are found in the center of the I band.
   b. The I band is the space between one Z line and the next.
   c. The H zone is the region where thick and thin filaments overlap.
   d. Z lines are found in the center of the A band.
   e. The width of the A band is equal to the length of a thick filament.

Answer 2

E - The dark stripe in a striated muscle that constitutes the A band results from the aligned thick filaments within myofibrils, so thick filament length is equal to A-band width.

Question 3

3. When a skeletal muscle fiber undergoes a concentric isotonic contraction:
   a. M lines remain the same distance apart.
   b. Z lines move closer to the ends of the A bands.
   c. A bands become shorter.
   d. I bands become wider.
   e. M lines move closer to the end of the A band.

Answer 3

B - As filaments slide during a shortening contraction, the I band becomes narrower, so the distance between the Z line and the thick filaments (at the end of the A band) must decrease.

Question 4

4. During excitation-contraction coupling in a skeletal muscle fiber:
   a. the Ca2+-ATPase pumps calcium into the T-tubule.
   b. action potentials propagate along the membrane of the sarcoplasmic reticulum.
   c. calcium floods the cytosol through the dihydropyridine (DHP) receptors.
   d. DHP receptors trigger the opening of lateral sac ryanodine receptor calcium channels.
   e. acetylcholine opens the DHP receptor channel.

Answer 4

D - DHP receptors act as voltage sensors in the T-tubule membrane and are physically linked to ryanodine receptors in the sarcoplasmic reticulum membrane. When an action potential depolarizes the T-tubule membrane, DHP receptors change conformation and trigger the opening of the ryanodine receptors. This allows calcium to flood from the interior of the sarcoplasmic reticulum into the cytosol.

Question 5

5. Why is the latent period longer during an isotonic twitch of a skeletal muscle fiber than it is during an isometric twitch?
   a. Excitation-contraction coupling is slower during an isotonic twitch.
   b. Action potentials propagate more slowly when the fiber is shortening, so extra time is required to activate the entire fiber.
   c. In addition to the time for excitation-contraction
   coupling, it takes extra time for enough cross-bridges to attach to make the tension in the muscle fiber greater than the load.
   d. Fatigue sets in much more quickly during isotonic contractions, and when muscles are fatigued the crossbridges move much more slowly.
   e. The latent period is longer because isotonic twitches only occur in slow (Type I) muscle fi bers.

Answer 5

C - In an isometric twitch, tension begins to rise as
soon as excitation-contraction is complete and the
first cross-bridges begin to attach. In an isotonic
twitch, excitation-contraction coupling takes the
same amount of time, but the fiber is delayed from
shortening until after enough cross-bridges have
attached to move the load.

Question 6

6. What prevents a drop in muscle fiber ATP concentration during the first few seconds of intense contraction?
   a. Because cross-bridges are pre-energized, ATP is not needed until several cross-bridge cycles have been completed.
   b. ADP is rapidly converted back to ATP by creatine phosphate.
   c. Glucose is metabolized in glycolysis, producing large quantities of ATP.
   d. The mitochondria immediately begin oxidative
   phosphorylation.
   e. Fatty acids are rapidly converted to ATP by oxidative glycolysis.

Answer 6

B - In the first few seconds of exercise, mass-action
favors transfer of the high-energy phosphate from
creatine phosphate to ADP by the enzyme creatine
kinase.

Question 7

7. Which correctly characterizes a “fast-oxidative” type of skeletal muscle fiber?
   a. few mitochondria and high glycogen content
   b. low myosin ATPase rate and few surrounding capillaries
   c. low glycolytic enzyme activity and intermediate contraction velocity
   d. high myoglobin content and intermediate glycolytic enzyme activity
   e. small fiber diameter and fast onset of fatigue

Answer 7

D - Fast-oxidative-glycolytic fibers are an intermediate type that are designed to contract rapidly but to resist fatigue. They utilize both aerobic and anaerobic energy systems, and thus they are red fibers with high myoglobin (which facilitates production of ATP by oxidative phosphorylation), but they also have a moderate ability to generate ATP through glycolytic pathways.

Question 8

8. Which is false regarding the structure of smooth muscle?
   a. The thin filament does not include the regulatory protein troponin.
   b. The thick and thin filaments are not organized in sarcomeres.
   c. Thick filaments are anchored to dense bodies instead of Z lines.
   d. The cells have a single nucleus.
   e. Single-unit smooth muscles have gap junctions connecting individual cells

Answer 8

C - In smooth muscle cells, dense bodies serve the

same functional role as Z lines do in striated muscle cells—they serve as the anchoring point for the thin filaments.

Question 9

9. The role of myosin light-chain kinase in smooth muscle is to:
   a. bind to calcium ions to initiate excitation-contraction coupling.
   b. phosphorylate cross-bridges, thus driving them to bind with the thin filament.
   c. split ATP to provide the energy for the power stroke of the cross-bridge cycle.
   d. dephosphorylate myosin light chains of the cross-bridge, thus relaxing the muscle.
   e. pump calcium from the cytosol back into the sarcoplasmic reticulum.

Answer 9

B - When myosin light-chain kinase transfers a
phosphate group from ATP to the myosin light
chains of the cross-bridges, binding and cycling of
cross-bridges is activated.

Question 10

10. Single-unit smooth muscle differs from multiunit smooth muscle because:
    a. single-unit muscle contraction speed is slow, while multiunit is fast.
    b. single-unit muscle has T-tubules, multiunit muscle does not.
    c. single-unit muscles are not innervated by autonomic nerves.
    d. single-unit muscle contracts when stretched, whereas multiunit muscle does not.
    e. single-unit muscle does not produce action potentials spontaneously, but multiunit muscle does.

Answer 10

D - Stretching a sheet of single-unit smooth muscle
cells opens mechanically gated ion channels, which
causes a depolarization that propagates through
gap junctions, followed by calcium entry and
contraction. This does not occur in multiunit
smooth muscle.

Question 11

11. Which of the following describes a similarity between cardiac and smooth muscle cells?
    a. An action potential always precedes contraction.
    b. The majority of the calcium that activates contraction comes from the extracellular fluid.
    c. Action potentials are generated by pacemaker potentials.
    d. An extensive system of T-tubules is present.
    e. Calcium release and contraction strength are graded.

Answer 11

E - The amount of calcium released during a typical
resting heart beat exposes less than half of the thin
filament cross-bridge binding sites. Autonomic
neurotransmitters and hormones can increase or
decrease the amount of calcium released to the
cytosol during EC coupling.

Question 12

1. Which of the following contains blood with the lowest oxygen content?
   a. aorta
   b. left atrium
   c. right ventricle
   d. pulmonary veins
   e. systemic arterioles

Answer 12

C - Blood in the right ventricle is relatively

deoxygenated after returning from the tissues.

Question 13

2. If other factors are equal, which of the vessels below would have the lowest resistance?
   a. length = 1 cm, radius = 1 cm
   b. length = 4 cm, radius = 1 cm
   c. length = 8 cm, radius = 1 cm
   d. length = 1 cm, radius = 2 cm
   e. length = 0.5 cm, radius = 2 cm

Answer 13

E - Resistance decreases as the fourth power of an
increase in radius, and in direct proportion to a
decrease in vessel length.

Question 14

3. Which of the following correctly ranks pressures during isovolumetric contraction of a normal cardiac cycle?
   a. left ventricular > aortic > left atrial
   b. aortic > left atrial > left ventricular
   c. left atrial > aortic > left ventricular
   d. aortic > left ventricular > left atrial
   e. left ventricular > left atrial > aortic

Answer 14

D

Question 15

4. Which of the following is not characteristic of the body’s capillaries?
   a. large total surface area
   b. small individual diameter
   c. thin walls
   d. high blood velocity
   e. highly branched

Answer 15

D - The large total cross-section of capillaries results in very slow blood velocity.

Question 16

5. Which of the following would not result in tissue edema?
   a. an increase in the concentration of plasma proteins
   b. an increase in the pore size of systemic capillaries
   c. an increase in venous pressure
   d. blockage of lymph vessels
   e. a decrease in the protein concentration of the plasma

Answer 16

A - Increasing colloid osmotic pressure would decrease filtration of fluid from capillaries into the tissues.

Question 17

6. Which statement comparing the systemic and pulmonary circuits is true?
   a. The blood flow is greater through the systemic.
   b. The blood flow is greater through the pulmonary.
   c. The absolute pressure is higher in the pulmonary.
   d. The blood flow is the same in both.
   e. The pressure gradient is the same in both.

Answer 17

D - Pressures are higher in the systemic circuit, but

because the cardiovascular system is a closed loop, the flow must be the same in both.

Question 18

7. What is mainly responsible for the delay between the atrial and ventricular contractions?
   a. the shallow slope of AV node pacemaker potentials
   b. slow action potential conduction velocity of AV node cells
   c. slow action potential conduction velocity along atrial muscle cell membranes
   d. slow action potential conduction in the Purkinje network of the ventricles
   e. greater parasympathetic nerve fi ring to the ventricles than to the atria

Answer 18

B - The AV node is the only conduction point between atria and ventricles, and the slow propagation through it delays the beginning of ventricular contraction.

Question 19

9. Which of the following would help restore homeostasis in the first few moments after a person’s mean arterial pressure became
   elevated?
   a. a decrease in baroreceptor action potential frequency
   b. a decrease in action potential frequency along
   parasympathetic neurons to the heart
   c. an increase in action potential along sympathetic neurons to the heart
   d. a decrease in action potential frequency along sympathetic neurons to arterioles
   e. an increase in total peripheral resistance

Answer 19

D - Reduced firing to arterioles would reduce total
peripheral resistance and thus reduce mean arterial
pressure toward normal.

Question 20

10. Which is false about L-type calcium channels in cardiac ventricular muscle cells?
    a. They are open during the plateau of the action potential.
    b. They allow calcium entry that triggers sarcoplasmic reticulum calcium release.
    c. They are found in the T-tubule membrane.
    d. They open in response to depolarization of the membrane.
    e. They contribute to the pacemaker potential

Answer 20

E - Ventricular muscle cells do not have a pacemaker potential, and the L-type calcium channel is not open during this phase of the action potential even in autorhythmic cells

Question 21

11. Which correctly pairs an ECG phase with the cardiac event responsible?
    a. P-wave: Depolarization of the ventricles
    b. P-wave: Depolarization of the AV node
    c. QRS-wave: Depolarization of the ventricles
    d. QRS-wave: Repolarization of the ventricles
    e. T-wave: Repolarization of the atria

Answer 21

C

Question 22

12. When a person engages in strenuous, prolonged exercise:
    a. blood fl ow to the kidneys is reduced.
    b. cardiac output is reduced.
    c. total peripheral resistance increases.
    d. systolic arterial blood pressure is reduced.
    e. blood fl ow to the brain is reduced.

Answer 22

A - Increased sympathetic nerve fi ring and
norepinephrine release during exercise constricts
vascular beds in the kidneys, GI tract, and other
tissues to compensate for the large dilation of muscle vascular beds.

Question 23

13. Hematocrit is increased
    a. when a person has a vitamin B12 defi ciency.
    b. by an increase in secretion of erythropoietin.
    c. when the number of white blood cells is increased.
    d. following a hemorrhage.
    e. in response to excess oxygen delivery to the kidneys.

Answer 23

B - Reduced oxygen delivery to the kidneys
increases the secretion of erythropoietin, which
stimulates bone marrow to increase production of
erythrocytes.

Question 24

14. The principal site of erythrocyte production is
    a. the liver.
    b. the kidneys.
    c. the bone marrow.
    d. the spleen.
    e. the lymph nodes.

Answer 24

C

Question 25

15. Which is not part of the cascade leading to formation of a blood clot?
    a. contact between the blood and collagen found outside the blood vessels
    b. prothrombin converted to thrombin
    c. formation of a stabilized fi brin mesh
    d. activated platelets
    e. secretion of tissue plasminogen activator (t-PA) by endothelial cells

Answer 25

E - t-PA is part of the fi brinolytic system that dissolves clots.

Question 26

4. Which of the following will increase alveolar PO2?
   a. Increase in metabolism and no change in alveolar ventilation
   b. Breathing air with 15 percent oxygen at sea level
   c. Increase in alveolar ventilation matched by an increase in
   metabolism
   d. Increased alveolar ventilation with no change in metabolism
   e. Carbon monoxide poisoning

Answer 26

D - An increase in alveolar PO2 results from an increase in alveolar ventilation (supply of oxygen) relative to metabolic rate (consumption of oxygen).

Question 27

5. Which of the following will cause the largest increase in systemic arterial oxygen saturation in the blood?
   a. An increase in red cell concentration (hematocrit) of 20 percent
   b. Breathing 100 percent O2 in a normal subject at sea level
   c. An increase in arterial PO2 from 40 to 60 mmHg
   d. Hyperventilation in a healthy subject at sea level

Answer 27

C - The relationship between arterial PO2 and arterial oxygen saturation is described by the oxygen hemoglobin dissociation curve. The greatest increase in oxygen saturation for the same change in PO2 occurs at the steepest part of the curve—between a PO2 of 40 and 60 mmHg.

Question 28

7. Which of the following is not true about asthma?
   a. The basic defect is chronic airway inflammation.
   b. It is always caused by an allergy.
   c. The airway smooth muscle is hyperresponsive.
   d. It can be treated with inhaled steroid therapy.
   e. It can be treated with bronchodilator therapy.

Answer 28

B - There are forms of asthma that are not primarily due to the presence of allergens. Examples are exerciseor cold-air-induced asthma.

Question 29

8. Which of the following is true?
   a. Peripheral chemoreceptors increase fi ring with low arterial PO2 but are not sensitive to an increase in arterial PCO2.
   b. The primary stimulus to the central chemoreceptors is low arterial PO2.
   c. Peripheral chemoreceptors increase fi ring during a metabolic alkalosis.
   d. The increase in ventilation during exercise is due to a decrease in arterial PO2.
   e. Peripheral and central chemoreceptors both increase firing when arterial PCO2 increases.

Answer 29

E - Respiratory acidosis (increase in blood PCO2 and decrease in pH) is a major stimulus to ventilation— this is mediated both by afferents from the peripheral chemoreceptors and by an increase in central chemoreceptor activity.

Question 30

9. Ventilation-perfusion inequalities lead to hypoxemia because:
   a. the relationship between PCO2 and the content of CO2 in blood is sigmoidal.
   b. a decrease in ventilation-perfusion matching in a lung region causes pulmonary arteriolar vasodilation in that region.
   c. increases in ventilation cannot fully restore O2 content in areas with low ventilation-perfusion matching.
   d. increases in ventilation cannot normalize PCO2.
   e. pulmonary blood vessels are not sensitive to changes in PO2.

Answer 30

C - Because of the shape of the oxygen-hemoglobin
dissociation curve, small increases in PO2 due
to increases in ventilation cannot fully saturate
hemoglobin. When the desaturated blood mixes
with saturated blood, the average is still hypoxemic.

Question 31

10. After the expiration of a normal tidal volume, a subject breathes in as much air as possible. The volume of air inspired is the:
    a. inspiratory reserve volume.
    b. vital capacity.
    c. inspiratory capacity.
    d. total lung capacity.
    e. functional residual capacity.

Answer 31

C - Remember that a lung capacity is the sum of at least two volumes. Inspiratory capacity is the sum of tidal volume and inspiratory reserve volume.

Question 32

1. Which of the following will lead to an increase in glomerular fluid filtration in the kidney?
   a. An increase in the protein concentration in the plasma.
   b. An increase in the fluid pressure in Bowman’s space.
   c. An increase in the glomerular capillary blood pressure.
   d. A decrease in the glomerular capillary blood pressure.
   e. Constriction of the afferent arteriole.

Answer 32

C - The main driving force favoring fl uid fi ltration
from the glomerular capillary to Bowman’s space is
glomerular capillary blood pressure (PGC).

Question 33

2. Which of the following is true about renal clearance?
   a. It is the amount of a substance excreted per unit time.
   b. A substance with clearance >GFR undergoes only filtration.
   c. A substance with clearance >GFR undergoes filtration and secretion.
   d. It can be calculated knowing only the filtered load of a substance and the rate of urine production.
   e. Creatinine clearance approximates renal plasma flow.

Answer 33

C - In order for a substance to appear in the urine at
a faster rate than its filtration rate, it must also be
actively secreted into the tubular fluid.

Question 34

3. Which of the following will not lead to a diuresis?
   a. excessive sweating
   b. central diabetes insipidus
   c. nephrogenic diabetes insipidus
   d. excessive water intake
   e. uncontrolled diabetes mellitus

Answer 34

A - Excessive sweating will decrease blood volume. This will lead to compensatory mechanisms to preserve total body water, including a decrease in urine production (antidiuresis).

Question 35

4. Which of the following contributes directly to the generation of:
   a hypertonic medullary interstitium in the kidney?
   a. active sodium transport in the descending limb of Henle’s loop
   b. active water reabsorption in the ascending limb of Henle’s loop
   c. active sodium reabsorption in the distal convoluted tubule
   d. water reabsorption in the cortical collecting duct
   e. secretion of urea into Henle’s loop

Answer 35

E - Urea is trapped in the medullary interstitium and
is an osmotically active particle. The resultant
increase in tonicity helps to maintain the gradient for medullary passive water reabsorption.

Question 36

5. An increase in renin is caused by:
   a. a decrease in sodium intake.
   b. a decrease in renal sympathetic nerve activity.
   c. an increase in blood pressure in the renal artery.
   d. an aldosterone-secreting adrenal tumor.
   e. essential hypertension.

Answer 36

A - A decrease in sodium intake stimulates renin because of the decrease in sodium delivery to the macula densa. This is detected and results in an increase in renin release from the juxtaglomerular cells.

Question 37

6. An increase in parathyroid hormone will
   a. increase plasma 25(OH) D.
   b. decrease plasma 1,25-(OH)2D.
   c. decrease calcium excretion.
   d. increase phosphate reabsorption.
   e. increase calcium reabsorption in the proximal tubule.

Answer 37

C - Parathyroid hormone stimulates calcium
reabsorption in the distal tubules of the nephron,
thereby decreasing calcium excretion. Because
parathyroid hormone is increased in hypocalcemic
states, the resulting decrease in calcium excretion
helps to restore blood calcium to normal.

Question 38

7. Which of the following is a component of the renal response to metabolic acidosis?
   a. reabsorption of hydrogen ions
   b. secretion of bicarbonate into the tubular lumen
   c. secretion of ammonium into the tubular lumen
   d. secretion of glutamine into the interstitial fl uid
   e. carbonic anhydrase-mediated production of HPO4

Answer 38

C - Secretion of ammonium into the renal tubule is
one way to rid the body of excess hydrogen ion
(metabolic acidosis).

Question 39

8. Which of the following is consistent with respiratory alkalosis?
   a. an increase in alveolar ventilation during mild exercise
   b. hyperventilation
   c. an increase in plasma bicarbonate
   d. an increase in arterial CO2
   e. urine pH

Answer 39

B - Increases in ventilation greater than metabolic rate “blow off” CO2 and results in a decrease in arterial PCO2. Because of the buffering of bicarbonate, this increases arterial pH (respiratory alkalosis).

Question 40

9. Which is true about the difference between cortical and juxtamedullary nephrons?
   a. Most nephrons are juxtamedullary.
   b. The efferent arterioles of cortical nephrons give rise to most of the vasa recta.
   c. The afferent arterioles of the juxtamedullary nephrons give rise to most of the vasa recta.
   d. All cortical nephrons have a loop of Henle.
   e. Juxtamedullary nephrons generate a hyperosmotic medullary interstitium.

Answer 40

E - Cortical nephrons either have short or absent
Henle’s loops. Only juxtamedullary nephrons have
long Henle’s loops, which plunge into the renal
medulla and create a hyperosmotic interstitium via
countercurrent multiplication.

Question 41

10. Which of the following is consistent with untreated chronic renal failure?
    a. proteinuria
    b. hypokalemia
    c. increased plasma 1,25-(OH)2D
    d. increased plasma erythropoeitin
    e. increased plasma bicarbonate

Answer 41

A - When the renal corpuscles become diseased, they greatly increase their permeability to protein.
Furthermore, diseased proximal tubules cannot
remove the filtered protein from the tubular lumen.
This results in increased protein in the urine
(proteinuria).