Negative & Positive Feedback Mechanism | CHAPTER 5 | Basic Science

Negative & Positive Feedback Mechanism – Introduction to fundamental concepts of Biological Science including the organization and common characteristics of living matters, cell structures and functions, food production by photosynthesis, harvesting energy, mechanism of cells reproduction, genetics, evolutions, and Human Biology. Introduction to general chemistry including basic concepts about matter, atomic structure, chemical bonds, gases, liquid, and solids, solutions, chemical reactions, acid, bases, and salt;

organic and biochemistry including hydrocarbons and their derivatives, carbohydrates, lipids, proteins, enzymes, vitamins, and minerals, nucleic acids; principles of physics and applications to nursing including gravity and mechanics, pressure, heat and electricity; nuclear chemistry and nuclear physics, effects of radiation on human beings, and protection and disposal. The aim of the course is to acquire knowledge and skills in general biological science, general chemistry and physics.

Negative & Positive Feedback Mechanism

Negative Feedback Control Mechanism

If some factor becomes excessive or deficient, a control system that returns the factor toward a certain mean value and thus maintaining homeostasis. Most control systems of the body act by this process. For example,

1. Blood pressure control system: In high blood pressure, baroreceptor feedback mechanism comes into action and decrease blood pressure. In low blood pressure, chemoreceptor feedback mechanism comes into action and increase blood pressure.
In both case, these effects are negative to the initiating stimulus.

2. Regulation of blood CO2 concentration:
a. ↑ PCO2 in blood → Respiratory center →↑ Pulmonary ventilation→PCO2 in blood.
b. PCO₂ in blood → Respiratory center →→ Pulmonary ventilation→↑PCO2 in blood.
In both case, these effects are negative to the initiating stimulus

3. Regulation of acid base balance.
4. Regulation of water balance.
5. Regulation of electrolyte balance.

Positive Feedback Mechanism

the initiating stimulus causes more of the same, it is called positive feedback mechanism.

Examples:

A. Positive feedback mechanism sometime causes vicious circle and thereby death: Positive feedback mechanism does not lead to stability but to instability of the body and often death.

• For example: If a person suddenly bled 2 liters of blood by any means →→ Cardiac pump → Blood pressure Blood flow to heart muscle Heart becomes weak → Further cardiac pump Further blood pressure →→ Further in blood flow to heart →Heart becomes more weak → This cycle repeats→ Death.

B. Positive feedback mechanism can sometimes be useful.
For example:

• Blood clotting: When a blood vessel is ruptured, Clotting factors are activated. Some factors act on other inactive factors and activate them. This process continues until a clot is formed and bleeding is stopped.
• Child birth: When the gravid uterus contracts, the baby’s head pushes through the cervix and stretch of the cervix sends signals to the uterine muscles, back to the body of the uterus, causing more powerful contractions. Thus, uterine contraction stretches the cervix and the cervical stretch causes more uterine contraction. This process continues until uterine contraction is strong enough to deliver the baby.
• Generation of nerve signals: When a nerve fiber is stimulated by any stimulus → Slight leakage of Na through Na channels into the nerve fibers→ Change in membrane potential→ This change causes opening of more & more Na channels → Explosion of Na leakage into the nerve fiber Generation of action potential.

Difference Between Positive & Negative Feedback Mechanism:

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