Homeostasis is the body's ability to keep its internal conditions stable while the outside world changes. Most of this control works through feedback loops.
Parts of a feedback loop
A sensor detects a change, a control center compares it with a set point, and an effector acts to correct it. The brain, especially the hypothalamus, and the endocrine glands are the main control centers.
Negative feedback
Most loops are negative: the response reverses the change. When blood sugar rises, insulin brings it down; when the body is hot, sweating and wider skin vessels cool it.
Positive feedback
A few loops amplify the change until an event is complete. Examples are uterine contractions in labor and the clotting cascade.
When control fails
Disease often means a loop is overwhelmed or broken. Fever, diabetes, shock and dehydration are all failures of homeostasis.
| Value | Sensor or control center | Correction |
|---|---|---|
| Body temperature | Hypothalamus | Sweating or shivering, skin vessels open or close |
| Blood glucose | Pancreas | Insulin lowers it, glucagon raises it |
| Blood pressure | Baroreceptors in the carotid and aorta | Heart rate and vessel tone change |
| Blood CO2 and pH | Chemoreceptors in the brainstem | Breathing rate and depth change |
At the bedside
Vital signs are a window into homeostasis: a fast heart rate is often the body compensating for blood loss, fever or pain. Treat the cause, not just the number.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).