1. Homeostasis NOTES

2. What is Homeostasis?
Homeostasis - maintenance of a stable internal environment
Body is in a state of dynamic equilibrium
changing
normal balance

3. FEEDBACK CONTROL LOOP Consists of THREE parts:
Receptor - provides information about environment
Integrator – control center that makes sure body is at set point or ideal level
Effector – action that moves level closer to set point

5. Negative Feedback Mechanisms
Most control mechanisms in the human body are negative feedback mechanisms
A negative feedback mechanism DECREASES the intensity of the stimulus or eliminates it
When a variable is above or below set point, integrator triggers a move in the OPPOSITE DIRECTION to reach the set value
Ex: body temperature, blood pressure, pH & CO2 levels, blood glucose levels

8. Pituitary gland releases vasopressin (ADH)  kidneys store more water as it makes urine
*Alcohol + coffee block ADH  more urination and loss of water

9. Positive Feedback Mechanisms
A positive feedback mechanism ENHANCES the original stimulus to ACCELERATE activity
Integrator triggers a move in the SAME DIRECTION triggering an “explosive” response
Positive feedback mechanisms are less common
Examples: blood clotting, childbirth (oxytocin)
Labor Contractions

10. Positive Feedback Mechanism Example
Break or tear in blood vessel wall
Clotting occurs as platelets adhere to site and release chemicals
Released chemical attract more platelets, which release more chemicals
Clotting proceeds until break is sealed by newly formed clot

11. Homeostatic Imbalances
Most diseases cause homeostatic imbalances: chills, fevers, elevated white blood cell counts etc.
Aging reduces our ability to maintain homeostasis