QUESTION: 165

A 14-year-old boy presents with weight loss and diarrhea. His tongue becomes sore and blistery after eating oatmeal or rye bread, which leads to the diagnosis of celiac disease. The boy and his parents are advised to be sensitive to symptoms of tetany and paresthesias, since they can occur as a consequence of malabsorption of which of the following?

calcium
carbohydrates
fat
iron
water

Answer(s): A

Explanation:

In patients with celiac disease the protein gluten, which is found in bread, oats, and many other foods containing wheat, barley, or rye, triggers an autoimmune response that causes damage to the small intestine leading to widespread manifestations of malabsorption. Calcium is difficult to absorb, so patients frequently experience symptoms of hypocalcemia such as muscle cramping, titanic contractions, numbness, and tingling sensations. For sensory and motor nerves, calcium is a critical second messenger involved in normal cell function, neural transmission, and cell membrane stability. The nerves respond to a lack of calcium with hyperexcitability. The inability to absorb nutrients such as carbohydrates (choice B) leads to weight loss as experienced by the boy. Fat malabsorption (choice C) is not uncommon in patients with celiac disease as a consequence of greatly diminished absorptive surface. It would manifest in steatorrhea. Iron (choice D), like calcium, is difficult to absorb and may lead to anemia. The general decrease in electrolyte absorption leads to decreased water absorption (choice E). The increased osmotic load in the GI lumen accounts for the boy's diarrhea.

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QUESTION: 166

An adult male becomes hypotensive during surgery because of blood loss. Intravenous administration of 500 ml of which of the following solutions will have the greatest effect in restoring blood volume, and thus blood pressure to normal?

blood plasma
distilled water
hypoosmotic NaCl
isotonic dextrose solution
isotonic saline solution

Answer(s): A

Explanation:

Intravenous solutions are distributed in the various body fluid compartments based on osmolality and their ability to penetrate the vascular wall and the cell membrane. The proteins in blood plasma will remain within the vascular compartment because of their low permeability across the vessel wall. Thus, 500 mL of blood plasma will remain in the vascular compartment. Water (choice B) passes across the cell membrane and the vascular wall easily. Hence distilled water will distribute itself between cellular and extracellular spaces, meaning only a small portion will actually contribute to blood volume, the other choices (C, D, and E) cross the vascular barrier and distribute partially to the extravascular space and thus are less effective intravascular volume expanders.

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QUESTION: 167

Using laboratory micropuncture technique, blood plasma is collected from both the afferent arteriole and efferent arteriole of a renal cortical glomerulus. Which of the following has the lowest afferent/efferent arteriole concentration ratio?

albumin
chloride
glucose
potassium
sodium

Answer(s): A

Explanation:

The process of glomerular ultrafiltration creates a tubular fluid that is essentially protein free. Hence, as plasma passes from the afferent arteriole, through the glomerular capillaries to the efferent arteriole, the protein albumin concentration rises as approximately 20% of the fluid is filtered out, leaving the albumin behind, giving an afferent/efferent arteriole concentration ratio of approximately 0.8. By contrast, the glomerular capillary membrane is freely permeable to water and other small particles such as glucose (choice A), chloride (choice B), potassium (choice D), and sodium (choice E), so their concentrations do not change as approximately 20% of water and solute are filtered into Bowman's capsule, giving afferent/ efferent arteriole concentration ratios of 1.0.

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QUESTION: 168

It is known that stretch receptors contained in the walls of the atria convey nerve impulses to the brainstem via the vagus nerve. Under normal conditions, these nerve impulses are most likely to occur during ventricular systole. What information is communicated to the brain by these nerve impulses?

arterial muscle contraction
diastolic arterial pressure
filling of the atrium by venous pressure
filling of the ventricle
systolic arterial pressure

Answer(s): C

Explanation:

The atrial stretch receptors are depolarized by stretch of the atria proportional to the magnitude of venous- filling pressure. The frequency of action potentials rises to a maximum at the peak of the atrial "v" wave, which signals maximum atrial filling during ventricular contraction. Although the remaining choices (A, B, D, and E) may be influenced by the filling of the heart by venous pressure, the information conveyed to the brain via the atrial stretch receptors relates directly to the filling pressure of the atria themselves.

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