a. 5 mg/h
b. 10 mg/h
c. 15 mg/h
d. 20 mg/h
e. 30 mg/h
10. A 43-year-old pregnant woman develops preeclampsia at 32 weeks’ gestation. Intravenous labetalol is given to reduce blood pressure, and magnesium sulfate, which blocks N-methyl-D-aspartate (NMDA) receptors in the central nervous system, is ordered for the prevention of eclamptic seizures until the fetus can be delivered. Which of the following activates the NMDA receptor?
a. Acetylcholine
b. Gamma-aminobutyric acid (GABA)
c. Glutamate
d. Glycine
e. Kainate
11. A 56-year-old woman presents with fatigue and malaise. Hepatomegaly and mild jaundice are evident upon physical examination. Blood tests reveal an increase in aspartate aminotransferase and the presence of anti–smooth muscle antibodies, suggestive of autoimmune hepatitis. Which of the steps in the chemical reactions that occur during cross-bridge cycling in smooth muscle shown below is responsible for relaxation of contracted smooth muscle and the formation of latch bridges?
a. Step 1
b. Step 2
c. Step 3
d. Step 4
e. Step 5
12. A 23-year-old man is brought to the emergency department after collapsing during basketball practice. On admission, he is lethargic and appears confused. His coach reports that it was hot in the gym and he was drinking a lot of water during practice. An increase in which of the following is the most likely cause of his symptoms?
a. Intracellular tonicity
b. Extracellular tonicity
c. Intracellular volume
d. Extracellular volume
e. Plasma volume
13. A 14-year-old adolescent girl reports blood in her urine 2 weeks after she had a sore throat. She has uremia and a blood pressure of 160/90 mm Hg with peripheral edema, suggestive of volume expansion secondary to salt and water retention. Which of the following is the approximate extracellular fluid volume of a normal individual?
a. 5% of body mass
b. 10% of body mass
c. 20% of body mass
d. 40% of body mass
e. 60% of body mass
14. A previously well 18-year-old woman is admitted to the ICU because of altered mental status. She does not respond to instructions and her arms are postured in a flexor position. Laboratory data reveal a serum sodium concentration of 125 mmol/L. Her friends indicate that the patient had taken ecstasy at a party the night before, and because she was extremely thirsty the next morning, she had consumed a lot of water in a short period of time. Assuming that the reduction in osmolarity is entirely due to water consumption, that her initial weight was 60 kg, and that her initial osmolarity was 300 mOsm/L, which of the following is approximately the quantity of water she would have drunk to produce the observed hyponatremia?
a. 2.5 L
b. 3.5 L
c. 5 L
d. 6 L
e. 7 L
15. A 49-year-old man in end-stage renal failure is able to perform peritoneal dialysis at home. The osmolality of the solution chosen for peritoneal dialysis will determine the rate of ultrafiltration. Which of the following statements best characterizes a molecule whose osmolality is zero?
a. It will not permeate the membrane.
b. It can only cross the membrane through the lipid bilayer.
c. It causes water to flow across the membrane.
d. It is as diffusible through the membrane as water.
e. It is transported across the membrane by a carrier.
16. A 76-year-old woman with a history of uncontrolled hypertension presents in the emergency department with hypotension and shock-like symptoms. Her daughter reports systolic blood pressure near 200 mm Hg earlier in the day and suspects a dissecting aneurysm, which is confirmed with a computed tomography (CT) of the chest. Biopsy of the repaired aorta shows giant cell arteritis, and the woman is placed on a regimen of high-dose prednisone. The anti-inflammatory effect of exogenous glucocorticoids is thought to be due to which of the following?
a. Activation of phospholipase A2
b. Increased capillary membrane permeability
c. Increased formation of leukotrienes
d. Increased release of interleukin-1 (pyrogen) from granulocytes
e. Inhibition of the activation of nuclear factor-κB (NF-κB)
17. A 62-year-old man presents to the emergency room with an acute onset of aphasia and hemiparesis. A CT scan reveals an increase in intracranial fluid. Which of the following solutions will be most effective in reducing intracranial pressure (ICP) following a large hemispheric stroke?
a. 150 mmol sodium chloride
b. 250 mmol glycerol
c. 250 mmol glucose
d. 350 mmol urea
e. 350 mmol mannitol
General Principles: Cellular Physiology
Answers
1. The answer is a. (Barrett, pp 62-63, 116, 151, 422-423, 596-597. Longo, pp 374-378.) Erection is initiated by dilation of the arterioles of the penis, which increases blood flow into the erectile tissue of the organ. The increased turgor of the penis also results from compression of the veins, blocking the outflow of blood from the organ. Erections are produced by the release of nitric oxide (NO), which inhibits the smooth muscle of the corpora cavernosa, allowing blood to fill the penis. NO is a potent vasodilator that acts by activating guanylyl cyclase, resulting in increased production of the second messenger, cGMP. Sildenafil citrate (Viagra®) is an effective and selective inhibitor of cGMP PDE. By blocking the breakdown of cGMP, sildenafil prolongs the action of NO and erections. Sildenafil is most active against PDE5, the type of PDE found in the corpora cavernosa. Other cGMP PDE5 inhibitors used in the treatment of erectile dysfunction include tadalafil (Cialis®; Eli Lilly and Company, Indianapolis, IN, USA) and vardenafil (Levitra®; Bayer Pharmaceuticals Corporation, Leverkusen, North Rhine-Westphalia, Germany and GlaxoSmithKline, Brentford, Middlesex, United Kingdom). Sildenafil is also a potent inhibitor of PDE6 found in the retina, which accounts for the transient blue-green color weakness, one of the side effects of sildenafil. G proteins are coupling molecules that link various receptors to nearby effector molecules, which, in turn, generate second messengers that mediate the hormone’s actions. Inositol triphosphate (IP3) is associated with the membrane phospholipid system for hormonal signal transduction. G-protein activation of the membrane-bound enzyme phospholipase C breaks down membrane phospholipids into diacylglycerol (DAG) and inositol triphosphate. DAG is a potent activator of protein kinase C.
2. The answer is c. (Widmaier, pp 97-100.) Materials that are not soluble in water can only diffuse across the membrane through the lipid bilayer. The most important factor determining how well a substance can diffuse across the lipid bilayer is the substance’s lipid solubility. If two materials have the same lipid solubility, then the permeability of the smaller particle will be greater. Signal transduction pathways differ between water-soluble and lipid-soluble messengers (hormones). Lipid-soluble messengers, including steroid hormones, thyroid hormones, and vitamin derivatives such as retinoids (vitamin A) and vitamin D, interact with intracellular nuclear receptors, in contrast to water-soluble amino acid derivatives and peptide hormones, which interact with cell-surface membrane receptors. In promyelocytic leukemia, fusion of retinoic acid receptor alpha to other nuclear proteins causes aberrant gene silencing and prevents normal cellular differentiation. Treatment with the hormone retinoic acid reverses this repression and allows cellular differentiation and apoptosis to occur.
3. The answer is a. (Barrett, p 7. Longo, pp 2322-2324. Widmaier, pp 96-100.) The rate of diffusion is described by the Fick equation, as follows:
where A is the area available for diffusion, [S1] − [S2
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