Blood pH holds near 7.4. Body temperature averages near 37oC. Internal environment is maintained by the tissue fluid, which bathes all the tissues of the body. Tissue fluid is refreshed when oxygen and nutrients exit the blood and wastes enter the blood. The kidneys excrete nitrogenous wastes formed by liver and regulate blood volume, salt balance, and pH of blood. Feedback systems are similar to the thermostat that maintains an even house temperature.
Effectors bring about a response that negates the original conditions that stimulated the receptor.
Ultimately the nervous and endocrine systems control homeostasis. Controlling Body Temperature a. A receptor in hypothalamus senses when temperature of blood falls below normal. A regulatory center in hypothalamus sends nerve impulses to blood vessels of skin causing them to contract and arrector pili muscles to become erect. If temperature continues to fall, the regulator center sends impulses to skeletal muscles to initiate shivering to generate heat.