Q. 275.0( 1 Vote )
Why does gaseous
• The more oxygen is released from Oxyhaemoglobin in a more active tissue because its partial oxygen pressure is lower than the least active tissue. The lower PO in the active tissue causes the dissociation of Oxyhaemoglobin to release sufficient oxygen required by the tissues.
• The CO from the tissue is carried in the blood in three different forms, bicarbonate in plasma and erythrocytes, carbamino-haemoglobin in erythrocytes and small amounts of dissolved carbon dioxide in plasma. On reaching the lungs blood is oxygenated. It donates H which joins bicarbonate to form carbonic acid. This carbonic acid cleaves into water and carbon dioxide by carbonic anhydrase. In this way, the carbon dioxide is released from the carbamino-haemoglobin. The oxygen affinity of haemoglobin also gets enhanced with the fall in the blood PCO resulting from the elimination of carbon dioxide from the blood in the lungs.
• The blood in the tissue capillaries contains higher PO than the tissue fluid. So, oxygen is released from Oxyhaemoglobin diffuses from the capillary blood to the tissue fluid and finally to the cells of the tissues. The CO diffuses from the cells to the tissue fluid to raise its PCO than the capillary blood. This enables carbon dioxide to diffuse from the tissue fluid to the capillary blood.
• Erythrocytes lack mitochondria and respiratory enzymes to perform the process of aerobic respiration. Therefore, they undergo aerobic respiration to carry out anaerobic metabolism only.
• Gaseous exchange continues in the lungs continuously because some air remains inside the lungs even after deepest exhalation. This air is called as residual volume, which is never driven out, and this is sufficient to precede gaseous exchange without any interruption.
• The contraction of the external intercostals muscles and diaphragm increases the volume of the thoracic cavity and lowers the pressure in the lungs. To fill up this gap fresh air rushes to the lungs resulting in the inspiration.
The relaxation of the aspiratory muscles decreases the volume of the thoracic cavity and subsequently, pressure in the lungs increase. To equalize this pressure, the air from the lungs rushes out through the respiratory passage to bring about expiration.
• The pulmonary artery contains deoxygenated blood and this has PO much lower than that of alveolar PO. So, oxygen from the alveolar air diffuses into the blood
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