The respiratory passage in mammals includes external mares, nasal chamber, respiratory chamber, nasopharynx, larynx, trachea, bronchi and two lungs. Inside the lungs the bronchus capillaries ending in alveoli.
Mechanism of Breathing:
The expansion and contraction of the chest occurs by the action of some voluntary and involuntary muscles. The expansion and contraction of thoracic cavity bring about the expansion and contraction of the ribs. Two types of muscles help in breathing.
External intercostals muscles
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Internal inter costal muscles.
Diaphragum is a dome shaped musculo-fibrous structure attached with radiating muscles fibres.
Process of breathing occurs in two phages like inspiration and expiration. Inspirations enlarge the thoracic cavity and allow the entry of fresh air. Expiration is a passive process reduces the volume of thoracic cavity and the air comes out.
Exchange of gases:
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During breathing alveoli gets filled with air.
Diffusion of O2 occurs from alveolar air into the blood and CO2 out of blood into the alveoli.
Transportation of gases: Oxygen is carried out as a physical solution and as oxyhaemoglobin. About 0.3ml of oxygen is transported in 100ml of blood. Most of the 02 is transported in the form of oxyhaemoglobin. Haemoglobin forms a loose chemical combination with 02, at high 02 tensions to form oxyhaemoglobinb.
Hb4 + 4O2 -à ß Hb4 O8 (()xyhaemoglobin)
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Oxyhaemoglobin dissociates releasing oxygen at the cellular level.
Carbon dioxide evolves due to oxidation in the tissues reaches the respiratory surface through venous blood circulation. CO2 is transported to the lungs as carbamino compounds, bicarbonates and carbonic anhydrase.
The ultimate function of respiratory activity is cellular oxidation of digested food materials to release energy. The break down of glucose occurs under two major steps like glycolysis and kreb cycle.