Breathing And Exchange Of Gases Notes For NEET
Cells utilise oxygen for metabolism and produce energy along with substances like carbon dioxide which is harmful. Animals have evolved different mechanisms
for the transport of oxygen to the cells and for the removal of carbon dioxide from there. We have a well developed respiratory system comprising two lungs and associated air passages to perform this function. The first step in respiration is breathing by which atmospheric air is taken in (inspiration) and the alveolar air is released out (expiration). Exchange of O2 and CO2 between deoxygenated blood and alveoli, transport of these gases throughout the body by blood, exchange of O2 and CO2 between the oxygenated blood and tissues and utilisation of O2 by the cells (cellular respiration) are the other steps
involved. Inspiration and expiration are carried out by creating pressure gradients between the atmosphere and the alveoli with the help of specialised muscles –
intercostals and diaphragm. Volumes of air involved in these activities can be estimated with the help of spirometer and are of clinical significance. Exchange of O2 and CO2 at the alveoli and tissues occur by diffusion. Rate of diffusion is dependent on the partial pressure gradients of O2 (pO2) and CO2 (pCO2), their solubility as well as the thickness of the diffusion surface. These factors in
our body facilitate diffusion of O2 from the alveoli to the deoxygenated blood as well as from the oxygenated blood to the tissues. The factors are favourable for the diffusion of CO2 in the opposite direction, i.e., from tissues to alveoli.
Oxygen is transported mainly as oxyhaemoglobin. In the alveoli where pO2 is higher, O2 gets bound to haemoglobin which is easily dissociated at the tissues where pO2 is low and pCO2 and H+ concentration are high. Nearly 70 per cent of carbon dioxide is transported as bicarbonate (HCO3
–) with the help of the enzyme carbonic anhydrase. 20-25 per cent of carbon dioxide is carried by haemoglobin
as carbamino-haemoglobin. In the tissues where pCO2 is high, it gets bound to blood whereas in the alveoli where pCO2 is low and pO2 is high, it gets removed from the blood. Respiratory rhythm is maintained by the respiratory centre in the medulla region of brain. A pneumotaxic centre in the pons region of the brain and a chemosensitive area in the medulla can alter respiratory mechanism.
17.1 Human Respiratory System
17.2 Mechanism Of Breathing
17.3 Respiratory Volumes And Capacities
17.4 Exchanges Of Gases
17.5 Transort Of Gases
17.6 Regulation Of Respiration
17.7 Disorder Of Respiratory System