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Unit 8 BREATHING AND EXCHANGE OF GASES

BREATHING AND EXCHANGE OF GASES




 RESPIRATORY SYSTEM

INTRODUCTION
Definition
Respiration is the physiological catabolic process in which gaseous exchange occurs to oxidise food. The energy generated is utilized and by products, CO2 and H2O are given out.
So, respiration is a physio-chemical process. The surface at which exchange of gases occurs is called
respiratory surface, and the compounds oxidised in respiration are called respiratory substrate.

TYPES OF RESPIRATION
Following are the types of respiration.
Direct and Indirect respiration
Aerobic and Anaerobic respiration
Direct and Indirect respiration

Direct respiration
(i) In this type of respiration, there is direct exchange of gases in between body cells and respiratory
medium.
(ii) Exchange of gases occurs on the principle of diffusion, through moist body surface.
(iii) Direct respiration is found in unicellular organisms like, aerobic bacteria, amoeba, ssponges, hydra, flatworm, roundworm etc.

Indirect respiration
(i) In this type of respiration, their is no direct contact in between the body cells and respiratory medium.
(ii) Indirect respiration is found in complex and higher form of organism.
(iii) Higher organism have some specialized, structure for gaseous exchange which are called respiratory organs.

e.g.
(a) Skin - Skin is respiratory organ in annelida and amphibians.
(b) Gills - Most of crustaceans, mollusca, all fishes and some amphibians the exchange of gases in gills is called branchial respiration.
(c) Lungs - Lungs is respiratory organ in snails, some amphibians, all reptiles, birds and mammals.
(d) Trachea - Trachea is respiratory organ in insects.

AEROBIC AND ANAEROBIC RESPIRATION
Aerobic respiration
(i) Respiration which occurs in presence of oxygen is called aerobic respiration.
(ii) The oxygen completely oxidises the food to CO2 and H2O releasing large amount of energy. This process can be shown by following way.

C6H12O6 + 6O2  6CO2 + 6H2O + 2880 KJ Energy

(iii) Such type of respiration (aerobic respiration) found in most animals and plants.
Phases of aerobic respiration


There are two phases of aerobic respiration.
A- External respiration
B- Internal respiration
The process of exchange of O2 from the atmosphere with CO2 produced by the cells is called breathing, commonly known as respiration.





 Pharynx is the common passage for food and air.
 In human, path of air is :


Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure. Inspiration is initiated by the contraction of diaphragm and external inter costal muscles (EICM). Expiration takes place when the intrapulmonary pressure more than the atmospheric puressure. In this diaphragm and EICM are relaxed.

 Alveoli are the primary sites of exchange of gases. Exchange of gases also occur between blood and tissues.
 O2 and CO2 are exchanged in these sites by simple diffusion mainly based on pressure/concentration gradient.
 Partial pressures (in mm Hg) of oxygen and carbon dioxide.

 Blood transport O2 in the form of oxyhaemoglobin. O2 can bind with heamoglobin in a reversible manner to form oxyhaemoglobin. Each haemoglobin molecule can carry a maximum of four molecules of O2. Binding of oxygen with haemoglobin is primarily related to partial pressure of O2.

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