Homeostasis

Homeostasis (Homoios = Similar; Stasis = Standing)

The ability of an organism to maintain a consistent internal environment in response to changing internal or external conditions.

The Three Components of Homeostasis

1. Receptor

2. Control Center

3. Effector

Receptor

Detects change in a variable (typically a sensory neuron).

Control Center

Interprets input from receptor & initiates changes through effector “go between”.

Effector

Structure that brings about changes to alter the stimulus

Stimulus

Changes in variable that is regulated. (e.g., hange in temperature sensed by skin).

Negative Feedback

• Controls most processes in the body

• Variable fluctuates within a normal range around a set point

• Resulting action is in the opposite direction of the stimulus

e.g., temperature regulation, HR/BP with exercise, breathing rate in response to CO2 levels.

Positive Feedback

• Occurs much less frequently than negative feedback

• Stimulus reinforced to continue moving/amplify variable in same direction until a climactic event occurs, then body returns to homeostasis

e.g., breastfeeding, blood clotting, labor