Homeostasis refers to the maintenance of a stable internal environment in the body. The body achieves homeostasis through negative feedback mechanisms that regulate physiological variables like core temperature, pH, blood glucose, and blood pressure when they deviate from their set points. A homeostatic control system consists of receptors that monitor the variable, a control center that establishes the set point, and effectors that adjust the variable back toward the set point through negative feedback. Examples provided demonstrate how negative feedback regulates body temperature through sweat glands and antidiuretic hormone secretion, while positive feedback increases oxytocin secretion during childbirth.

1. Homeostasis
• Homeostasis (ho. -me.-o-STA. –sis) Greek
• Homeo means similar
• Stasis means state of standing
• Refers to the existence of a stable internal environment

2. Homeostasis
• Homeostasis is the existence and maintenance of a relatively constant
environment within the body
• To achieve homeostasis, the body must actively regulate conditions
that are constantly changing
• We are continuously exposed to new conditions
• These conditions are called variables because their values can change

3. Examples of physiological variables
• Core temperature
• Water and electrolyte concentrations
• pH (acidity or alkalinity) of body fluids
• Blood glucose levels
• Blood and tissue oxygen and carbon dioxide levels
• Blood pressure

4. Variable - body temperature
 Body temperature is a variable that can increase in a hot environment or
decrease in a cold one
 Homeostatic mechanisms, such as sweating or shivering, normally maintain
body temperature near an ideal normal value, or set point
Homeostasis

5. Homeostasis
Components of homeostasis control system
1. Receptor
2. Control center
3. Effector

6. The elements of a homeostatic control system

7. Homeostasis
• Negative feedback – reducing the amount of change (whole
mechanism is shut off)
• All are controlled by negative feedback mechanism
• Positive feedback – increasing the amount of change (reaction
continues at an even faster rate)
• Positive feedback is less common but important

8. Negative Feedback
• Most systems of the body are regulated by negative-feedback mechanisms,
which maintain homeostasis
• Negative means that any deviation from the set point is made smaller or is
resisted
• In a negative-feedback mechanism, the response to the original stimulus results
in deviation from the set point, becoming smaller
• Example of important negative-feedback mechanisms
• Maintaining normal body temperature

9. Negative feedback mechanisms
Three components
1. A receptor, which monitors the value of a variable such as body
temperature
2. A control center, such as part of the brain, which establishes the
set point around which the variable is maintained through
communication with the receptors and effectors
3. An effector, such as sweat glands, which can adjust the value of
the variable, usually back toward the set point

10. Negative-Feedback Mechanism: Body Temperature

11. Example of a physiological negative feedback mechanism: control of body temperature.

13. Negative feedback regulation of secretion of antidiuretic hormone (ADH)

14. Regulation of secretion of oxytocin through a positive feedback mechanism