Studying Organ Systems Organ systems studied in this text are listed in Table 11.2. Nervous system is brain located in dorsal cavity and spine in vertebral canal. Homeostasis holds the internal environment relatively constant, regardless of the conditions in the external environment. 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.