QS Study

Oxygen is one of the substances transported with the support of red blood cells. The red blood cells restrain a pigment called hemoglobin, each molecule of which binds four oxygen molecules. The protein inside red blood cells that carries oxygen to cells and carbon dioxide to the lungs is hemoglobin.

Oxygen is transported in the blood in two form –

  • In chemical combination with Hb of RBC O2 – Hb (97%).
  • In dissolve state: In plasma (3%).

Transported of Oxygen from alveolar air to tissue cells occurs in four steps.

(1) Diffusion of Oxygen from the alveolar air

  • Po2 in the alveolus = 104 mmHg
  • Po2 in the pulmonary capillaries at the arterial end = 40 mmHg.
  • The pressure difference of Oxygen between alveolar air and pulmonary blood is = 104 – 40 = 64 mmHg.
  • This 64 mmHg pressure difference causes diffusion of Oxygen from alveolus to pulmonary blood.

Fig: Oxygen transport process in Blood

(2) Transport of Oxygen in the blood:

Oxygen is transported in the blood in 2 ways.

By forming O2-Hb, about 97% of Oxygen is carried in this form. Oxygen combines with Hb by the process of oxygenation.

As dissolved state: Remaining 3% of Oxygen is transported in the dissolved state in the water of the plasma and cells. It is responsible for the partial pressure of Oxygen (Po2) in blood for saturation of Hb.

(3) Diffusion of Oxygen from blood to the tissue space:

Oxygen diffuses from blood to the tissue space –

  • Blood (arterial end) Po2 = 95 mmHg
  • Po2 in the interstitial space = 40 mmHg
  • Pressure difference = (95 – 40) mmHg = 55 mmHg.

This 55 mmHg pressure difference causes diffusion of Oxygen from blood to tame space.

(4) Diffusion of Oxygen from interstitial fluid to cells.

  • Po2 of intestinal space = 40 mmHg.
  • Po2 inside the cells (5-40 mmHg) average 23 mmHg.
  • Pressure difference (40 – 23) mmHg = 17 mm of Hg.
  • This 17 mm of Hg pressure difference causes diffusion of Oxygen from tissue space to cells.

In this way, Oxygen is transported from lungs to cells.

Name of the factors that influence the oxygen-carrying capacity of blood –

  • Hb Conc.: The Oxygen carrying capacity of blood is proportional to the Hb cone.
  • Amount of dissolved Oxygen.
  • The affinity of the Hb of Oxygen.