Final answer:
The hypothalamus produces a) PGE2 in response to cytokines, leading to an increase in body temperature and inducing fever as a defense mechanism.
Step-by-step explanation:
The hypothalamus responds to a) cytokines released by bacteria or the body itself, by producing PGE2 (Prostaglandin E2), which increases body temperature in the periphery through mechanisms like shivering and vasoconstriction.
When bacteria are destroyed by leukocytes, substances called endogenous pyrogens are created.
These pyrogens circulate to the hypothalamus and cause it to reset the body's temperature set point, creating a fever.
This elevation in temperature is a defensive response of the body that inhibits the growth and replication of pathogens, helps the immune system function more effectively, and can directly destroy certain pathogens.