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.