QUESTION: 173

Lack of oxygen (hypoxia) will cause reflex vasoconstriction in the circulation supplying which of the following organs?

brain
heart muscle
kidney
lungs
skeletal muscle

Answer(s): D

Explanation:

Local hypoxia causes vasoconstriction in vessels of the pulmonary circulation. This is an adaptive response, since it will shunt blood away from poorly ventilated alveoli. This response differentiates the pulmonary circulation from the vasculature of other organs. In heart muscle, skeletal muscle, kidney, and brain (choices A, B, C, and E) vasodilation occurs in response to local hypoxia.

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QUESTION: 174

Lipoxygenase converts arachidonic acid to biologically active compounds called leukotrienes. Leukotrienes have been implicated in several disease entities, including allergic asthma, where they are presumed to mediate bronchoconstriction. Introducing leukotrienes into an airway would be expected to cause which of the following responses?

decreased airway resistance
decreased dead space volume
increased functional residual capacity (FRC)
increased lung compliance
increased total lung capacity

Answer(s): B

Explanation:

Bronchiole volume contributes to dead space volume, so increasing bronchoconstriction would decrease bronchiolar volume and thus decrease dead space volume. Bronchoconstriction is a major determinant of airway resistance to air flow. Leukotrienes, by increasing airway constriction, would increase resistance to air flow (choice A). Lung elastic tissue and alveolar surface tension determine lung compliance (choice D), which should not be affected by airway leukotrienes exposure. FRC (choice C), the point of mechanical balance between chest wall and lung, is dependent on lung compliance and, similarly, would not be affected by leukotrienes exposure. Any bronchoconstriction would slightly decrease total lung capacity (choice E).

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QUESTION: 175

Below figure shows the amounts of water ingested and secreted daily into the GI tract by a healthy individual. Since about 100 mL of water is excreted daily in the stool, which of the following volumes (in milliliter) best reflects the daily absorbed water in the indicated areas x, y, and z of the GI tract?

Option A
Option B
Option C
Option D
Option E

Answer(s): B

Explanation:

The small intestine absorbs massive quantities of water. Anormal person takes in about 2 L of fluid every day. Another 7 L of fluid are received by the small intestine daily as secretions from salivary glands (1.5 L), stomach (2 L), pancreas (1.5 L), liver (0.5 L), and the small intestine itself (1.5 L). That results in a total of about 9 L of fluid entering the GI tract daily. In a healthy person the duodenum, jejunum, and ileum absorb the bulk of the water that enters the GI tract, here 8500 mL. The colon absorbs most of the remaining fluid (400 mL), not the bulk of it (choice A) and excretes about 100 mL daily. There is generally no water absorption in the esophagus and stomach. Therefore, choices C, D, and E are incorrect.

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QUESTION: 176

Exhibit:

The action potentials shown in below figure represent those of which kind of cells?

cardiac nodal cells
myelinated motor axons
sensory neurons
skeletal muscle cells
ventricular Purkinje cells

Answer(s): A

Explanation:

The action potentials illustrated must be those of cardiac nodal cells (SA node or AV node). The duration of these action potentials is too long for motor axons, (choice B), sensory neurons (choice C), or skeletal muscle fibers (choice D). Also, the configuration is different and a pacemaker potential is clearly present.
They cannot be ventricular Purkinje action potentials (choice E) because these have a more negative diastolic component that does not gradually depolarize, a longer duration (200 msec) and a plateau region.

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QUESTION: 173

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QUESTION: 175

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QUESTION: 176

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