Overview
This lecture explains how the body maintains a stable internal environment, known as homeostasis, using feedback loops and highlights examples of these mechanisms.
What is Homeostasis?
- Homeostasis is the process by which living organisms maintain a stable and optimal internal environment.
- Factors regulated include pH, temperature, electrolyte balance, and glucose levels.
- All life must maintain homeostasis for biomolecules to function properly.
Key Systems in Homeostasis
- The nervous system detects changes and sends signals through neurons.
- The endocrine system releases hormones to restore balance.
- The kidneys help regulate water and electrolyte balance by filtering blood.
Negative Feedback Loops
- Negative feedback counteracts changes to return the body to its optimum state.
- The sensor detects change, informs a control center, which triggers a response to reverse the change.
- Example: When blood glucose rises after eating, the pancreas releases insulin to lower glucose levels by promoting cellular uptake.
- Body temperature is regulated by the hypothalamus: it initiates cooling (vasodilation, sweating) or warming (vasoconstriction, shivering, goosebumps) responses.
- Negative feedback also maintains blood pH, blood pressure, and hormone levels.
Positive Feedback Loops
- Positive feedback amplifies a response, pushing conditions further from the starting point, and usually operates briefly.
- Example: In childbirth, oxytocin levels increase to intensify uterine contractions until delivery.
- Example: Blood clotting involves a rapid cascade of chemicals and platelets to quickly seal injuries.
Consequences of Homeostatic Imbalance
- Failure to maintain homeostasis leads to diseases like diabetes mellitus, caused by chronic high blood glucose.
Key Terms & Definitions
- Homeostasis — maintenance of a constant internal environment.
- Negative Feedback — a mechanism that counteracts deviations from a set point.
- Positive Feedback — a mechanism that amplifies changes, driving processes to completion.
- Insulin — a hormone from the pancreas that lowers blood glucose.
- Hypothalamus — a brain region that regulates temperature and other homeostatic functions.
- Oxytocin — a hormone that promotes labor contractions.
- Vasodilation — widening of blood vessels to release heat.
- Vasoconstriction — narrowing of blood vessels to retain heat.
Action Items / Next Steps
- Review examples of negative and positive feedback in the body.
- Prepare for questions on feedback loops and their physiological roles.