14 Homeostasis and Interactions Between Organ Systems
Learn how feedback and communication among organ systems maintain functional internal conditions during exercise, stress, and infection.
and feedback
The body regulates its internal environment within ranges that support normal cell function. This regulation, called , is dynamic: variables such as temperature, blood pressure, blood glucose, and blood gases can shift as conditions change, while organ systems work together to keep them within workable limits.
Many homeostatic processes use . A receptor detects a change, a control center evaluates it, and effectors respond in a way that opposes the change. For example, when body temperature rises, the nervous system can activate sweat glands and widen skin blood vessels, helping transfer heat to the surroundings. As temperature returns toward its usual range, these responses lessen.
Coordinated responses during exercise
During exercise, working skeletal muscles use more oxygen and nutrients and produce more carbon dioxide, heat, and metabolic by-products. Coordinated responses across several systems help match supply to demand.
The nervous system adjusts heart rate, breathing, and blood-vessel activity.
The respiratory system increases ventilation, bringing more oxygen into the lungs and removing more carbon dioxide.
The cardiovascular system raises cardiac output and directs more blood toward active muscles. This carries oxygen and fuel to the muscles and transports carbon dioxide away.
The muscular system uses the delivered oxygen and fuel to contract, and its activity produces heat.
The integumentary system helps release excess heat through sweating and increased blood flow near the skin.
The urinary system helps regulate water and electrolyte balance as fluid is lost in sweat.
Together, these adjustments help match supply to demand while limiting changes in blood gases, temperature, and fluid balance. Exercise physiology depends on coordinated cardiovascular, respiratory, muscular, and regulatory responses, not on any single system acting alone.
Responses to stress
When the brain perceives a threat, the nervous system rapidly activates the . Signals to the adrenal medulla promote the release of epinephrine and norepinephrine. The heart beats faster and more forcefully, airways widen, and blood flow and available fuel are adjusted to support immediate action.
At the same time, the endocrine system can activate the slower hypothalamic–pituitary–adrenal (HPA) axis. The hypothalamus signals the pituitary, which signals the adrenal cortex to release cortisol. Cortisol helps coordinate longer-lasting changes in energy use and other body functions.
When the stressor passes, sympathetic activity decreases and parasympathetic activity supports a return toward resting conditions. The response is useful in the short term, but prolonged stress can keep multiple systems under sustained demand.
Temperature regulation during illness
During some infections, immune signals cause the hypothalamus to raise the body's temperature set point. This change produces a : the body responds as if it were too cold, with skin blood vessels constricting to reduce heat loss and shivering potentially increasing heat production. As temperature approaches the raised set point, these responses ease.
When the set point later returns toward its previous level, sweating and widening of skin blood vessels help release heat. This process brings together the immune system, which produces signals during infection; the nervous system, which regulates the temperature set point; the muscular system, which produces shivering; and the integumentary and cardiovascular systems, which change heat loss through the skin.
is distinct from . In , the hypothalamic set point rises; in , body temperature rises without that set-point change.