Q.Write the mechanism of transport of CO2 in blood. OR What is digestion? Write two functions of HCl in the digestion of food.

Transport Of Carbon Dioxide

The Problem CO₂ Poses

Active tissues, such as muscles during exercise, constantly produce carbon dioxide as a waste product of burning fuel, and it must be carried away — a build-up is toxic. Unlike sugar dissolving in tea, carbon dioxide does not simply dissolve in blood in bulk; it travels using three different methods, the most important of which converts it into an entirely different chemical form.

The Three Forms of Transport

At rest, blood carries carbon dioxide from the tissues to the lungs roughly as follows:

Bicarbonate — the main route

Inside red blood cells, an enzyme called carbonic anhydrase speeds up the otherwise slow reaction of carbon dioxide with water to form carbonic acid, which instantly splits into a hydrogen ion and a bicarbonate ion. The bicarbonate diffuses out into the plasma, while the hydrogen ion stays inside the cell.

Carbamino compounds

Carbon dioxide can also bind directly to the amino groups on the globin part of haemoglobin, at a site different from where oxygen binds, forming a carbamino compound. This reaction is reversible: favoured when oxygen levels are low, as in the tissues, and reversed when oxygen levels are high, as in the lungs.

Dissolved CO₂

A small amount simply dissolves in plasma and travels as gas. It is the least significant by quantity but is the form that directly sets the partial pressure of carbon dioxide in blood.

From Tissues to Lungs …