Breathing and Exchange of Gasses

Mechanism of breathing,exchange of gases,regulation

  1. During inspiration, diaphragm and external intercostal muscles contract, so that diaphragm becomes flat to increase the thoracic cavity’s volume.
  2. Abdominal muscles relaxes and so it plays passive role in inspiration.
  3. Diaphragm comes back its original dome shaped position as it relaxes along with external intercostal muscles.
  4. Internal intercostal muscles and abdominal muscles contracts during inspiration and so are termed as active muscles of expiration.
  5. Breathing in higher animals is termed as negative pressure breathing as the increased thoracic volume decreases the pressure inside, so that the oxygen from the atmosphere moves inside the lungs with high pressure.
  6. Normal breathing rate is humans is about 12-16 times/min.
  7. To breath, thorax contributes 25% movement and abdomen -75%. But in pregnant women entire breathing is due to lateral movements of thorax.
  8. Respiration is of 2 types. (i) External and (ii) Internal
  9. Exchange of gases between alveoli and blood is external respiration; Utilisation of oxygen by cells from the alveoli constitutes internal respiration that happens for the process of oxidation.
  10. Alveolar wall has a rich network of blood capillaries, by possessing a respiratory membrane with (0.2 mm thickness) a diffusion capacity.
  11. Gases always move from higher partial pressure to lower partial pressure. Partial pressure is the pressure exerted by an individual gas in a total composition.
  12. Respirator gas Atmospheric air Alveoli deoxygenated blood oxygenated blood Tissue
    O2 159 104 40 95 40
    CO2 0.3 40 45 40 45

Transportation of Gases:

  1. 3% of O2 is carried by plasma and rest 97% of O2 combines with Haemoglobin (Hb) to form oxyhaemoglobin.
  2. 1g of Haemoglobin carries 1.34 ml of O2.
  3. Under normal conditions 5 ml of O2 is transported to tissues by 100 ml of blood.
  4. Oxygen competing with CO2 to form oxyHaemoglobin is termed as Haldane effect.
  5. Factors promoting O2 association with Haemoglobin are low CO2, low H+ ions and low temperature, where temperature plays a passive role.
  6. 7% CO2 of is transported through plasma; 23% through Haemoglobin as carbamino Haemoglobin and rest 70% is carried to lungs as bicarbonate ions.
  7. Carbonic anhydrase is an enzyme that converts H2O and CO2 into H2CO2 inside RBC and it rapidly dissociates to form H+ ions and \tt HCO_3^{^-} ions.
  8. \tt HCO_3^{^-}; ions diffuses out from RBC and hence chloride ions move inside to compensate the loss and is termed as Hamburger phenomenon (or) Chloride shift.
  9. CO2 Competing with O2 to form carbamino Hb is termed as Bohr effect.
  10. Factors promoting O2 dissociation are high CO2, H+ ions and temperature.
  11. O2 association curve is always sigmoidal and if it dissociates with Hb, the curve shifts to right; If the O2 associates with Hb, it shifts towards left.
  12. Foetal Hb and myoglobin saturates with O2 with very less partial pressure of oxygen.

Regulation of Heart Beat:

  1. A group of neurons placed is pons vavoli and medulla oblongata act as breathing centre for human.
  2. Medulla oblongata contains Dorsal (inspiration) and Ventral respiratory group (inspiration and expiration).
  3. Pons possess pneumotaxic and apneustic centre.
  4. Chemically respiration is controlled by carotid bodies and Aortic bodies.

Watch this video for the topic Mechanism of breathing,exchange of gases,regulation Part-1 from 0:27 to 12:13

Watch this video for the topic Mechanism of breathing,exchange of gases,regulation Part-2 from 25:08 to 44:12

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