Final answer:
A fever is produced when endogenous pyrogens released by phagocytic leukocytes after destroying bacteria circulate to the hypothalamus and reset the body's thermostat, leading to an increase in body temperature.
Step-by-step explanation:
Considering the hypothalamus, a fever is produced by endogenous pyrogens acting directly on the hypothalamus. When a bacterium is destroyed by phagocytic leukocytes, chemicals called endogenous pyrogens are released into the blood. These pyrogens circulate to the hypothalamus and reset the thermostat, allowing the body's temperature to increase, which is commonly referred to as a fever. This is a defense mechanism where the increase in body temperature helps to conserve iron, thus reducing nutrients available for bacteria, increases the activity of the body's enzymes and protective cells, while inhibiting those of the invading microorganisms, and may ultimately kill the pathogen.