Final answer:
The hypothalamus causes the body temperature to rise during illness to destroy invading pathogens through the action of pyrogens, which reset the body's thermostat, inducing a fever that inhibits microbial growth and boosts immune function.
Step-by-step explanation:
When the hypothalamus causes a rise in body temperature during an illness, it is purposely trying to destroy the invading pathogens.
The hypothalamus plays a crucial role in thermoregulation. It responds to pyrogens, which are chemicals released when leukocytes destroy bacteria. These pyrogens circulate to the hypothalamus, prompting it to reset the body's thermostat to a higher temperature, causing what is known as a fever.
This fever enhances the activities of the body's protective enzymes and cells while inhibiting those of the invading microbes. A fever also conserves iron, depriving bacteria of this essential nutrient, and the heat generated may also directly kill pathogens. The rise in body temperature is a strategic response to create an unfavorable environment for the pathogens, be they bacteria, viruses, or other microorganisms, and to increase the efficiency of the body's immune response.