HOMEOSTASIS

The homeostatic mechanism in the body is responsible for maintaining the normalcy of various body systems.
This is achieved by:
(a) Feedback
(b) Feed forward

FEEDBACK MECHANISM

• Any change in pattern of any system activates
sensors
• These signals reach a control centre.
• The effectors bring about the necessary change by causing the required action.

Two types of feed back mechanisms operate to maintain normalcy of a system.
These are :-
A. Negative feedback
B. Postive feedback

A. Negative Feedback Mechanism
• A change in homeostasis causes to inhibit the natural activity to bring the change under control

• Example: Thyroid hormone regulation

Increase in serum thyroxine levels (hyperthyroid state
                  ↓
Detected by the pituitary gland
                  ↓
Negative feedback on TSH secretion
                  ↓
Decrease in TSH secretion
                  ↓
Decrease in thyroid levels

Other examples
1. Adrenocorticotrophin hormone (ACTH) and cortisol secretion
2. Regulation of extracellular fluid volume
3. Regulation of blood calcium
4. Regulation of body temperature
5. Regulation of blood pH
6. Regulation of blood pressure and blood

B.Positive Feedback Mechanism
• In this type of feedback, there is increase in the activity in the same direction.
Positive feedback systems are less common n both physiological and pathological states.
• Physiological positive feedback: This is very useful in life processes.
• Example- Milk ejection reflex

Baby suckles at the breast
                     ↓
Afferents reach the pituatary
                    ↓
Oxytocin release
                    ↓
Milk ejection from the breast
                    ↓
Baby suckles more

Other examples
1. Ovulation
2. Parturition
3. Blood clotting
4. Depolarization and repolarization of nerve cell

• Pathological positive feedback
A pathological positive feedback can cause death of the organism when there is severe haemorrage, e.g., shock or death due to haemorrage.

Thus negative feedback is always concerned with maintenance of homeostasis. Some positive feedback mechanisms disturb homeostasis and cause disease or death.

FEED FORWARD REGULATION

This is another type of regulatory process used along with negative feedback systems. These initiate responses in anticipation of a change, e.g., regulation of body temperature.
in response to change in environmental temperature.

SIGNIFICANCE

When the body homeostasis is disturbed due to failure of the homeostatic regulating mechanisms, disease develops.