Question

Explain how oxygen and carbon dioxide are transported from lungs to tissues and from tissues to lungs in the Respiratory System.

Answer 1

The transpoprt of O2 and CO2 by the blood is often referred as gas transport.

• Oxygen transported from lungs to the tissues in two forms : in combination with haemoglobin in the red cell or physically dissolved in the plasma.

In physically dissolved form

• In physically dissolved form in plasma,only about 2% of oxygen is transported.The amount of physically dissolved oxygen in the blood can predicted with Henrys law.
• The law states that the amount of gas that dissolves in a liquid at a given temperature is proportional to the partial pressure of the gas.

In combination with hemoglobin

• more than 90% of O2 is transported in combination with Hb.
• This becomes possible due to the binding affinity of hemoglobin for oxygen.
• Hemoglobin that binds with oxygen is called oxyhemoglobin (HbO2) and the hemoglobin that doesnot bind with O2 is called deoxyhemoglobin or reduced hemoglobin.

​​​​​​​Carbon dioxide transport

• Carbon dioxide is produced mainly during aerobic cellular metabolism of glucose and during conversion of carbohydrates to fat.From tissues,CO2 is transported to the lungs in the venous blood and then exhaled in the expired air.
• CO2 is transported in blood in three forms

1. ​​​​​​​Physically dissolved in the plasma
2. As bicarbonate ions in plasma and in red cells
3. As carbamino protein complexes.