[Campbell Biology P.938] Suppose after a hard run on a hot day, you dunk your head into a co... | Practice Question

Suppose after a hard run on a hot day, you dunk your head into a cooler filled with ice-cold water. Based on Figure 40.17, which illustrates the thermostatic function of the hypothalamus in human thermoregulation, how might this action primarily help to return your body temperature to normal?

  • A: It triggers widespread vasodilation, increasing blood flow to the skin for heat radiation.
  • B: The cold water activates shivering mechanisms in the head, generating heat to balance the external cold.
  • C: It causes local vasoconstriction, diverting blood away from the skin surface of the head, and allows for efficient heat transfer by conduction from the head to the ice-cold water.
  • D: The cold directly stimulates sweat glands in the head to produce more sweat, which then cools the body through evaporation.

Explanation

Dunking the head in ice-cold water causes local vasoconstriction in the skin of the head, reducing blood flow to the surface and minimizing heat loss through convection to the air. More importantly, it directly transfers a significant amount of heat from the head to the ice-cold water via conduction, rapidly cooling the blood in those vessels and contributing to overall body temperature reduction. The hypothalamus then activates cooling mechanisms.