Homeostasis and the Interrelationship of Body Systems
Homeostasis tests how the body maintains stable internal conditions through feedback, transport, nervous and endocrine control, and coordinated organ function. Questions often present a disturbance and ask you to predict the receptor, control center, effector and compensating response.
Core rules and concepts
- Homeostasis maintains variables such as temperature, pH, blood glucose, blood pressure, osmolarity and oxygen near a set point. A regulated variable needs sensors, an integration center and effectors.
- Negative feedback reverses a deviation. Positive feedback amplifies a change and must end with a discrete event, such as childbirth or blood clotting.
- Nervous control is fast and brief; endocrine control is slower and longer-lasting. Many responses combine both, such as blood pressure regulation through baroreceptors and adrenal hormones.
- Organ systems are interdependent: the respiratory system supplies oxygen and removes carbon dioxide; the cardiovascular system transports gases, nutrients and hormones; the kidneys adjust fluid, electrolytes and pH; the digestive system supplies fuel; the integumentary system protects and thermoregulates.
- Compensation can restore a variable toward normal but may burden another system. For example, hyperventilation lowers carbon dioxide and raises blood pH.
Worked example
A person stands quickly and blood pressure falls. Baroreceptors in the carotid sinus and aortic arch detect reduced stretch and send fewer impulses to the medulla. Sympathetic output increases, causing vasoconstriction and faster heart rate, while parasympathetic output falls. Blood pressure rises toward the set point. The response is negative feedback because the initial deviation is opposed, not amplified.
Traps that cost marks
Do not label every feedback loop negative; positive feedback is real but less common. Do not confuse compensation with cure: a compensatory response may normalize one variable while revealing the underlying problem. Do not separate nervous and endocrine effects when a question asks for integrated regulation. Remember that set points can change, as in fever, without the feedback system being broken.
Worked example
In fever, the hypothalamic set point rises, so the body feels cold and shivers until temperature reaches the new set point.