Homeostasis
This lesson covers:
- The role of receptors and effectors in maintaining homeostasis
- What negative feedback systems are
- What positive feedback systems are
What is homeostasis?
Homeostasis is the maintenance of a stable internal environment within restricted limits in organisms.
This ensures that cells function normally despite changes in the external environment.
Why homeostasis is important:
- It keeps the internal environment constant for metabolic reactions.
- It ensures cells function properly and avoid damage.
- It helps organisms respond and adapt to external changes.
Control mechanisms in homeostasis
Homeostasis is coordinated by several different control mechanisms, consisting of receptors, coordinators, and effectors throughout the body.
The roles of receptors, coordinators, and effectors in homeostasis:
- Receptors - These sensory receptors detect stimuli and send signals to the brain about changes in the internal environment, like changes in blood pH and temperature.
- Coordinator - This receives and interprets information from receptors and sends instructions to an appropriate effector.
- Effectors - These are muscles or glands that act on signals from the brain and cause responses to reverse changes and regain equilibrium, such as sweating to reduce high temperature.
These control mechanisms aim to maintain conditions around an optimum point: the point at which the system operates best.
Negative feedback systems
Negative feedback systems involve coordination between receptors and effectors to control conditions around set optimum points, where the system works best. A derivation from the optimum point leads to changes that bring the system back to the optimum point.
Negative feedback works as follows:
- Receptors detect a change in one direction, like rising blood glucose.
- Signals trigger effectors to produce responses that reverse the initial change, like releasing insulin to lower blood glucose.
- Conditions return to their set range.
Examples of negative feedback mechanisms
There are many examples of negative feedback mechanisms in the body, but there are a few that you need to know about.
- Maintaining blood glucose concentration
- Why it is important - Glucose is needed for respiration, but too much glucose can affect water potential in blood and cells.
- How it is achieved - Insulin and glucagon adjust blood glucose concentration to maintain a healthy supply of glucose.
- Maintaining blood pH
- Why it is important - Changes in pH can impair enzyme action.
- How it is achieved - Adjustments are made to the acid-base balance in the blood to maintain the optimum pH.
- Maintaining temperature
- Why it is important - Changes in temperature can impair enzyme action.
- How it is achieved - Adjustments are made, for instance by sweating or shivering, to maintain the optimum temperature.
- Water regulation
- Why it is important - Too much or too little water in the blood and cells can cause cells to burst or shrink due to osmosis.
- How it is achieved - Water is removed or reabsorbed from blood or tissue fluid to maintain the optimum water potential.
Positive feedback systems
Positive feedback, in contrast to negative feedback, amplifies changes rather than reversing them. In other words, a deviation from an optimum causes changes that result in an even greater deviation from the optimum point.
Positive feedback works as follows:
- An initial change occurs, like the release of clotting factors after a blood vessel injury.
- Effectors are stimulated and enhance the change, like more clotting factors being released.
- The change continues until an endpoint is met, like a clot being fully formed.
Examples of positive feedback mechanisms
Positive feedback is less common than negative feedback in homeostasis, as uncontrolled responses can disrupt the body's equilibrium. Tight regulation is essential to prevent harm when changes intensify in these systems.
But, there are some examples of positive feedback mechanisms in the body that are useful to know.
Examples of positive feedback:
- Blood clotting - Clotting factors activate further clotting.
- Childbirth - Oxytocin stimulates more uterine contractions.