Regulation of Respiration

Respiration may be defined as the process in which oxygen is taken inside the body from the environment for the oxidation of food to release energy and the carbon dioxide so produced during oxidation is expelled out of the body.

The process of oxidation of food is very complex.

It involves a series of complex biochemical reactions and the released energy is stored in the form of ATP molecules.

However, for simplicity sake, the multistep reaction can be briefly expressed as follows:

Types of Respiration

1. Direct and Indirect Respiration

(a) Direct Respiration:

There is direct exchange of gases between the carbon dioxide of the body cells and oxygen of water and there is no blood for the transport of gases.

Exchange of gases occurs on the principle of diffusion.

It is found in unicellular organisms like aerobic bacteria and protists (e.g. Amoeba) and metazoans like sponges, coelenterates (e.g. Hydra), flatworms, roundworms and insects.

(b) Indirect Respiration:

There is no direct contact between the body cells and the surrounding air or water the source of oxygen is called respiratory medium.

It is found in larger and complex forms of animals.

These organisms have some specialised organs; gills (most of crustaceans, molluscs, insect larvae, all fishes and amphibians); lungs (snails, amphibians, all reptiles, birds and mammals).

In this the transportation of oxygen and carbondioxide between the respiratory organs and the body cells is brought about by the blood of the Circulatory system.

2. All physical and chemical reactions in which atmospheric air oxidises food in the body cells resulting in production of energy and liberation of CO2 are included in respiration.

It is of following types:

(a) Anaerobic respiration:

It occurs when nutrients are oxidised without using O2 (also called fermentation).

In yeast, glucose forms ethyl alcohol and CO2, In bacteria and muscles, glucose is converted into lactic acid.

Endoparasites also respire anaerobically.

Anaerobic respiration is low energy yielding process.

In mature RBCs also anaerobic respiration occurs due to loss of mitochondria along with other cell organelles.

(b) Aerobic respiration:

Cells utilize O2 for oxidising nutrients.

O2 is used either from atmospheric air or from water.

It involves:

(i) External respiration: gaseous exchange between blood and air (or water) of O2 and CO2,

(ii) Transport of gases to the tissues.

(iii) Internal respiration : gas.eous exchange between blood and tissues.

(iv) Cellular respiration : oxidation of nutrients in the cells and liberation of energy.

Phases of Aerobic Respiration.

(i) External Respiration (Breathing or ventilation).

It is the exchange of oxygen of surrounding gaseous or liquid medium and carbon dioxide of blood through a liquid medium by diffusion across the body surface or the respiratory surface. It is purely a physical process which depends upon the principle of diffusion and no energy is produced.

(ii) Internal Respiration.

It is the exchange of oxygen of blood and carbon dioxide of the body cells through tissue fluid at the cellular level. Internal respiration involves the energy production and is a physico-chemical process.

(iii) Cellular Respiration:

It is utilisation of O2 by cells for energy production and resultant release of CO2,