Negative Feedback Mechanism

Two type of feedback mechanism-

 

1. Positive feedback mechanism
2. Negative feedback mechanism

Here we discuss Negative feedback mechanism-

Inn a feedback system, the hormone secreting tissue continuously receives information (feedback) in the form of chemical signals concerning the cellular process it controls. If condition change, the tissue can act upon the information and adjust its rate of secretion. 

Commonly the control of hormonal secretions involves a negative feedback mechanism.

In such system, an endocrine gland is sensitive to the concentration of a substance it regulates or to the concentration of a product of a process it regulates. whenever this concentration reaches a certain level, the endocrine gland is inhibited (a negative effect), and its secretory activity decreases. 

Then, as the concentration of its hormone drops, the concentration of the regulated substance drops too, and the inhibition on the gland is released. When the gland is no longer inhibited, it begins to secrete its hormone again.

As a result of such negative feed back systems, the concentrations of some hormones remain relatively stable, although they may fluctuate within normal range.   

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Positive Feedback Mechanism

Positive Feedback Mechanism

Two type of feedback mechanism 

1. Positive feedback mechanism
2. Negative feedback mechanism

Here we discuss positive feedback mechanism

 

A positive feedback system is operating when an endocrine gland is stimulated to increase its rate of hormonal secretion (a positive effect) by a substance it caused to be produced. consequently, still more product forms and then more hormone is secreted.

Such a system is unstable in that it tends to produce extreme changes in conditions. Positive feedback system occur rarely in organism, however, one example of this type of system involves the sex hormone estrogen. This steroid is secreted by cells in the ovary in response to an anterior pituitary hormone (FSH). 

When estrogen is present in a certain blood concentration, it causes an increase in the secretion of some anterior pituitary hormones (including FSH), so that positive feedback exists for a short time

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Physiology of respiration in human

The following steps are involved in mechanism of respiration:

1. Breathing
2. Exchanges of gases on the alveolar surface
3. Cellular or internal respiration

Breathing 

Inhale fresh air into lung and expel out air from lung, called breathing. 

it completed in two steps:

• Inspiration
• Expiration

Inspiration 

Inhalation of fresh air into lung. It is an active process.

Physiology of respiration in human Flow Chart

Expiration 

Air expelling out air from lungs. It is a passive process.

Physiology of respiration in Human Exhalation Flow Chart

Exchange of gases

• Exchange of gases at the level of lungs between the alveoli and capillaries.
• Exchange of gases at the level of tissue between the capillaries and various body cells.
• Exchange of gases occurs due to different partial pressure of gases.
• Release of carbon dioxide, which occurs at alveolar level.

Transport of oxygen

• Transport of oxygen by RBCs respiratory pigment, called Hemoglobin.
• Hemoglobin has 4 iron atoms; each iron atom attaches one oxygen atom.

1 gram of hemoglobin transports 1.34 ml oxygen.

Physiology of respiration in human reaction

In alveoli, the partial pressure of carbon dioxide (PCO2) is low as compared to partial pressure of in de-oxygenated blood. 

PCO2 in alveoli is ↓ and ↑ PCO2 in deoxygenated blood.

The CO2 present in carbonic acid and carbamino hemoglobin would split because of low PCO2 in alveolar air and dissociation of CO2 into the alveolar (from the capillary) would occur.

Transport of carbon dioxide (CO2)

CO2 is carried in blood in 3 major forms:-

• Carbonic acid: around 5-10% of the total of CO2 is transported in this form.
• Carbamino haemoglobin: around 10% of the total of CO2 is transported in this way.
• Hydrogencarbonate ions: around 85% of the total of CO2 is transported in the blood as this form.

Cellular or internal respiration

It is a very complex process. Internal respiration involves in various process by which food elements are oxidized in cells.

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