Homeostasis

• Homeostasis operates on many different organ systems, and on different timescales
• Requires detectors to sense the physiological variable, a controller in the hypothalamus or brainstem, and effectors to cause a change
• Operates through negative feedback: a detected signal is compared to the expected signal at set point and corrected accordingly
• set-points can be changed to accommodate different physiological requirements
• the respiratory system, operating in association with the nervous system, regulates the concentration of carbon dioxide in the extracellular fluid. The liver and pancreas control glucose concentration in the extracellular fluid, and the kidneys regulate concentrations of hydrogen, sodium, potassium, phosphate, and other ions in the extracellular fluid.
•  Hemoglobin combines with oxygen as the blood passes through the lungs. Then, as the blood passes through the tissue capillaries, hemoglobin, because of its own strong chemical affinity for oxygen, does not release oxygen into the tissue fluid if too much oxygen is already there. However, if oxygen concentration in the tissue fluid is too low, sufficient oxygen is released to re-establish an adequate concentration. This is the oxygen-buffering function of haemoglobin.
• a higher than normal carbon dioxide concentration in the blood excites the respiratory center, causing a person to breathe rapidly and deeply. This deep rapid breathing increases expiration of carbon dioxide and, therefore, removes excess carbon dioxide from the blood and tissue fluids. This process continues until the concentration returns to normal.