Oxygen Transport In Blood: From Lungs To Tissues

Oxygen Transport In Blood: From Lungs To Tissues

Describe transport of oxygen in blood. (or) Oxygen-haemoglobin dissociation curve.
Answer:

Transport of oxygen:

• Oxygen is transported by the blood from alveoli to the tissue.
• Oxygen is transported in blood in 2 forms.

1. Dissolved form:

• Oxygen dissolves in water of plasma and is transported.
• Oxygen transported in this form is 0.3 ml per 100 ml of blood per 100 mm Hg pO₂

Oxygen in Blood Significance:

• About 3% of total oxygen in blood is transported in this form.
• Oxygen is transported in this form in stress full conditions like exercise.
• It occurs due to excess demand of oxygen by the tissues.

Amount of oxygen transported:

• Arterial – 0.3 ml per 100 ml of blood.
• Venous – 0.12 ml per 100 ml of blood.

2. In combination with haemoglobin:

• Oxygen combines with haemoglobin in blood and is transported as oxyhaemoglobin.
• Each haemoglobin molecule has 4 heme groups which have an iron in ferrous form.
• Sixth valency bond of each Fe²⁺ combines with 2 atoms of oxygem.
• Therefore, S atoms of oxygen combines with one mole of haemoglobin.
• No oxidation reaction takes place during this combination.

Oxygen in Blood Significance:

• Maximum amount of oxygen, about 97% is transported in this form.
• Oxygen can be released from haemoglobin easily when needed.
• Haemoglobin also accepts oxygen readily when the pO₂ is more and gives out oxygen when the pressure is less.

Oxygen carrying capacity of haemoglobin:

• One gram of haemoglobin carried 1.34 ml of oxygen.
• This is called oxygen carrying capacity of haemoglobin.
• 1 gram of Hb = 1.34 ml of oxygen.
• Now, normal haemoglobin content – 15 gram%.
• So, oxygen carried in this form (15 x 1.34) ml = 20.1 ml of oxygen in 100 ml of blood.
• But the 15% of haemoglobin carries only 19 ml% of oxygen.
• It is due to absence of full saturation of haemoglobin with oxygen.
• It is saturated only for about 95%.
• The oxygen carrying capacity of haemoglobin is given by oxygen haemoglobin dissociation curve.

Oxygen haemoglobin dissociation curve:

• The relationship between the partial pressure of oxygen and the percentage saturation of haemoglobin with oxygen is explained graphically by the oxygen haemoglobin dissociation curve.
• It is sigmoid shaped.
  1. Lower part of curve.
     • Indicates dissociation of oxygen from haemoglobin.
  2. Upper part of curve.
     • Indicates acceptance of oxygen by haemoglobin depending upon the partial pressure of oxygen.

Amount of oxygen transported in this form:

• Arterial blood = 19 ml per 100 ml of blood.
• Venous blood 13.88 ml per 100 ml of blood.