1. HOMEOSTASIS
Homeostatic regulation is the adjustment of physiological systems to preserve homeostasis.
Two general mechanisms are involved in homeostatic regulation: autoregulation and extrinsic regulation:
1. Autoregulation, (intrinsic regulation)a cell, a tissue, an organ, or an organ system adjusts automatically in response to some environmental change.
Example: oxygen decrease- cells release chemicals- dilate bl.vessels.
2. Extrinsic regulation nervous system or endocrine system control or adjust the activities of many systems .
For example: exercise-n.s. increases heart rate & n.s. reduces blood flow to less active organs(digestive)

2. nervous system directs rapid, short-term, and very specific responses
nervous system directs rapid, short-term, and very specific responses. (hot stove)
endocrine system releases chemical messengers, called hormones, that affect tissues and organs throughout the body.
The responses may not be immediately apparent, but they may persist for days or weeks.
Ex:regulation of blood volume and composition (starvation).
The endocrine system also plays a major role in growth and development

3. homeostatic regulatory mechanism consists of three parts:
(1) a receptor, a sensor that is sensitive to a particular environmental change, or stimulus;
(2) a control center, or integration center, which receives and processes the information supplied by the receptor; and
(3) an effector, a cell or organ that responds to the commands of the control center and whose activity either opposes or enhances the stimulus.

4. NEGATIVE FEEDBACK
an effector activated by the control center opposes, or negates, the original stimulus. Negative feedback thus tends to minimize change,
Most homeostatic regulatory mechanisms involve negative feedback. (body temperature)hypothalamus,

5. Negative feedback

6. POSITIVE FEEDBACK
In positive feedback, an initial stimulus produces a response that exaggerates or enhances the change in the original conditions rather than opposing it.
positive feedback loops are often incorporated into control mechanisms in which a potentially dangerous or stressful process must be completed quickly.
For example, the immediate danger from a severe cut is the loss of blood, which can lower blood pressure and reduce the efficiency of the heart
----clotting gets under way, each step releases chemicals that accelerate the process. formation of a blood clot, patches the vessel wall and stops the bleeding. Also labor and delivery,

7. Positive feedback