Question

Each 100 ml of human arterial blood carries P ml of $O_2$ and Q ml of $C{O}_2$ whereas each 100 ml of venous blood carries R ml of $O_2$ and S ml of $C{O}_2$ . Choose the CORRECT values of P, Q, R and S.

• A. P = 48 ml, Q = 19-20 ml, R = 52 ml, S = 14-15 ml
• B. P = 19-20 ml, Q = 48 ml, R = 14-15 ml, S = 52 ml
• C. P = 14-15 ml, Q = 52 ml, R = 19-20 ml, S = 48 ml
• D. P = 52 ml, Q = 14-15 ml, R = 48 ml, S = 19-20 ml

Answer 1

The correct option is B P = 19-20 ml, Q = 48 ml, R = 14-15 ml, S = 52 ml

Oxygen is carried in blood in two forms:

1. Dissolved

2. Bound to Haemoglobin

Dissolved oxygen follows Henry’s law -> amount dissolved is proportional to partial pressure.

For each mm of Hg of PAO2, dissolved O2 = 0.003 ml of O2 per100 ml of blood.

Total HB include HbO2, DeoxyHb, MetHb, COHb.

1 GMC of Hb can bind with 1.34ml of O2

Total O2 content per 100 ml :

In arterial blood = 1.34x Hb xsaturation +0.003 x pO2

= 1.34 x 15 x 0.957 + 0.003 x100

= approximately 20 ml / 100 ml of blood.

In venous blood = 1.34x 15 x0.75. + 0.003 x 40

= approximately 15 ml / 100 ml of blood.

Carbon dioxide is transported in the blood in three ways :

1) Dissolved in blood

2) Buffered with water as carbonic acid

3) Bound to hemoglobin.

At a Hb concentration of 15 gm / 100ml of blood, venous blood contains approximately 52 ml of CO2 / 100ml of blood and arterial blood contains approximately 48 ml of CO2 / 100 ml of blood.

Option B is correct.