Physiology of Respiration | HSEB Notes of Biology Class 12

Biology | Zoology
HSEB Notes on Physiology of respiration
Lesson :  Respiration
Class : 12

Physiology of respiration can be studied under following headings.

1. external respiration

2. transportation of O2 by blood

3. internal respiration

4. transportation of CO2 by blood.

External respiration - it is uptake of O2 and release of CO2. It takes place in the lungs called breathing. 

Transport of O2 by blood - RBC of blood contain haemoglobin as respiratory pigment. Human blood contains nearly 150 gram of Hb per 100 ml. haemoglobin readily combines with and dissociates to form free Oxygen. => Hb + O2 == HbO2

Oxyhaemoglobin is unstable compound and thus can dissociate quickly. The quantity of O2 combining with Hb depends upon pressure of Oxygen. The graph in which percentage of saturation of blood is plotted against PO2 is called Oxygen dissociaton curve. It is S shaped. It indicates that blood has high affinity for O2. In man, arterial blood has PO2 of about 95 mm Hg and Hb is about 95 % saturated. In venous blood, PO2 is about 40 mm Hg and about 70 % haemoglobin is saturated with O2. The Oxygen and CO2 transport is closely associated. Increase in conc. of CO2 decreases the amount of O2 that can be carried in the blood at a given partial pressure of O2. This is known as Bohr’s effect. The graph shows that the increase in the PCO2 lowers the curve.

Internal respiration - it is tissue respiration. Digested food is oxidized to liberate energy.
Transport of CO2 - CO2 is product of respiration. CO2 is poisonous. It should be removed quickly. It takes place by following way. 

1. By plasma in the form of carbonic acid - CO2 dissolve in water of blood plasma to form carbonic acid, about 7 % of total CO2 s carried in this way. 
2. In the form of bicarbonates of Na and K - CO2 enters into the RBC to dissolve into water. It is catalysed by carbonic anhydrase enzyme. H2CO3 ionises to form bicarbonate and hydrogen. The bicarbonate ions combine with Potassium ion to form Potassium bicarbonate. Upon saturation, Potassium bicarbonate ionizes into Potassium and bicarbonate ion, These ions being at higher conc. within red cells, come out into plasma and combine with available Na ion to form Sodium bicarbonates. The loss of bicarbonate ions is balanced by chloride ions diffusing into RBC from plasma . the exchange of Cl and HCO3 between plasma and RBC is known as Chloride shift or Hamberger’s phenomenon. In the lungs, these reactions are reversed. The exchange of Cl and HCO3 is reversed. H2CO3 is formed again which break down into water and CO2. CO2 in exhaled. In this way about 70 % of CO2 is transported.
3. By RBC in the form of carbamino compounds - amino acid present in RBC get oxidized to release amino group and carboxyl group. Carbon dioxide combines with amino group to form carbamino compounds. About 23 % is transported in this form.

Don't forget to LIKE, SHARE and COMMENT and also Join with us on FACEBOOK and GOOGLE+