Physiology Test

Question 1

A hormone is known to activate phospholipase C with subsequent release of calcium from internal stores. The release of calcium most likely occurs as a result of an increase in the concentration of which of the following intracellular second messengers?

Accepted Answer

Inositol 1,4,5-trisphosphate

Answer

When a hormone activates phospholipase C, this enzyme cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) into two second messengers: diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). IP3 then binds to receptors on the endoplasmic reticulum, triggering the release of calcium from these internal stores into the cytoplasm. This increase in intracellular calcium mediates various cellular responses.

Question 2

A 28-year-old man with a history of intravenous drug use comes to the physician because of a 6-week history of fever, nonproductive cough, chills, and progressive shortness of breath. His temperature is 39°C (102.2°F), pulse is 110/min, respirations are 32/min and regular, and blood pressure is 120/80 mm Hg. Physical examination shows a white, patchy, loosely adherent exudate on the buccal mucosa bilaterally. A chest x-ray shows bilateral interstitial infiltrates. After receiving treatment for pneumonia, he agrees to participate in a clinical study of the effects of interleukin-2 (IL-2). After administration of IL-2, which of the following hematologic changes is most likely in this patient?

Accepted Answer

Increased CD4+ T lymphocytes

Answer

The patient's history of HIV and opportunistic infections (Pneumocystis pneumonia, oral candidiasis) indicates significant immunosuppression, typically associated with low CD4+ T lymphocyte counts. Interleukin-2 (IL-2) is a cytokine that stimulates the proliferation, differentiation, and activation of T lymphocytes, particularly CD4+ and CD8+ T cells. Therefore, administration of IL-2 is most likely to lead to an increase in CD4+ T lymphocytes, aiming to bolster the immune response.

Question 3

A 5-year-old girl falls through the ice while skating on an outdoor pond. She is removed from the water within 1 minute, but dry clothing is not available, and she is still cold and wet 20 minutes later. Which of the following mechanisms helps maintain the patient’s core temperature during the period following her rescue?

Accepted Answer

Shivering

Answer

When the body is exposed to cold, shivering is a primary physiological mechanism to generate heat and maintain core temperature. Shivering involves involuntary, rapid contractions of skeletal muscles, which significantly increases metabolic heat production. This process helps to counteract heat loss and prevent hypothermia in cold environments, as seen in the child after falling into icy water.

Question 4

A 39-year-old woman comes to the physician for a follow-up examination because she recently was diagnosed with hypertension. Her blood pressure is 156/100 mm Hg. Physical examination shows no other abnormalities. Serum studies show normal findings. A 24-hour urine collection shows three times the normal excretion of epinephrine and metanephrine. The excessive epinephrine production in this patient is most likely caused by which of the following cell types?

Accepted Answer

Chromaffin

Answer

The elevated urinary excretion of epinephrine and metanephrine is highly suggestive of a pheochromocytoma, a tumor of the adrenal medulla. Chromaffin cells, located in the adrenal medulla, are specialized neuroendocrine cells that synthesize and secrete catecholamines, including epinephrine and norepinephrine. These cells are the source of excessive catecholamine production in pheochromocytoma, leading to hypertension.

Question 5

The blood flow through an organ is measured while the perfusion pressure is varied experimentally. An abrupt, sustained increase in perfusion pressure increases flow initially, but over the course of 1 minute, the flow returns nearly to the baseline level despite continued elevation of the perfusion pressure. The organ under study is exhibiting which of the following?

Accepted Answer

Autoregulation

Answer

This phenomenon describes autoregulation, the intrinsic ability of an organ or tissue to maintain a relatively constant blood flow despite changes in perfusion pressure. When perfusion pressure increases, the blood vessels in an autoregulating organ constrict (myogenic response) or release vasoconstrictors. This increases resistance and returns blood flow towards its baseline level, ensuring stable nutrient and oxygen delivery.

NBME Practice Test

NBME Practice Test

Physiology Test