Homeostasis is the process by which living organisms keep internal conditions within a healthy range. Your body must regulate temperature, blood glucose, water level, pH, oxygen, and many other variables even when the outside environment changes. This matters because cells can only work properly when their surroundings stay close to the conditions enzymes and membranes need.
Without homeostasis, small changes can grow into dangerous stress on organs and tissues.
A feedback loop is the control system that helps the body detect change and respond to it. Receptors sense a variable, a control center compares the value to a set point, and effectors create a response that changes the variable. Negative feedback reverses the original change and is the main way homeostasis is maintained.
Positive feedback amplifies a change until a specific endpoint is reached, such as during childbirth or blood clotting.
Key Facts
- Homeostasis keeps internal conditions stable within a range, not at one exact unchanging value.
- A basic feedback loop follows: stimulus, receptor, control center, effector, response.
- Negative feedback reduces change: response opposes stimulus.
- Positive feedback increases change: response strengthens stimulus until an endpoint stops the loop.
- Body temperature is regulated near 37°C by sweating, shivering, and changes in blood flow to the skin.
- Blood glucose regulation uses hormones: insulin lowers blood glucose and glucagon raises blood glucose.
Vocabulary
- Homeostasis
- Homeostasis is the maintenance of stable internal conditions within a living organism.
- Set point
- A set point is the target value or range that a body variable is regulated around.
- Receptor
- A receptor is a sensor that detects a change in a body condition and sends information to a control center.
- Effector
- An effector is a muscle, gland, or organ that carries out a response to change a body variable.
- Negative feedback
- Negative feedback is a control process in which the response reduces or reverses the original change.
Common Mistakes to Avoid
- Thinking homeostasis means conditions never change is wrong because body variables naturally fluctuate within a healthy range.
- Confusing negative feedback with something harmful is wrong because negative means the response opposes the change, not that the effect is bad.
- Calling all feedback loops negative feedback is wrong because positive feedback amplifies change and is used in special processes with clear endpoints.
- Forgetting the control center is wrong because receptors only detect change, while the control center compares the condition to the set point and coordinates the response.
Practice Questions
- 1 A person's body temperature rises from 37°C to 38.5°C during exercise. Name the stimulus, one receptor type or location, the control center, and two effectors that help return temperature toward the set point.
- 2 A student has a blood glucose level of 150 mg/dL after a meal, and the normal fasting range is about 70 to 100 mg/dL. Which hormone should increase, and how does it help lower blood glucose?
- 3 Explain why blood clotting is considered positive feedback but body temperature regulation is considered negative feedback.