MCAT Biology Question 142: Answer and Explanation

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Question: 142

7. On a very cold day, a man waits for over an hour at the bus stop. Which of the following structures helps his body set and maintain a normal temperature?

  • A. Hypothalamus
  • B. Kidneys
  • C. Posterior pituitary
  • D. Brain stem

Correct Answer: A

Explanation:

The hypothalamus functions as a thermostat that regulates body temperature. When it's cold outside, nervous stimulation to the blood vessels in the skin is increased, causing the vessels to constrict. This constriction diminishes blood flow to the skin surface and prevents heat loss. Sweat glands are turned off to prevent heat loss through evaporation. Skeletal muscles are stimulated to shiver (rapidly contract), which increases the metabolic rate and produces heat. The hypothalamus is also involved in other processes, including the release of endocrine hormones, regulation of appetite, and circadian rhythms.

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