Gas Transport In The Blood Part 1

Question 1

Explain the effect of partial pressure in gas solubility with Henry’s law

Answer 1

The amount of a given gas dissolved in a given type and volume of liquid at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid

The partial pressure of a gas in solution is the partial pressure in the gas mixture with which the solution is in equilibrium

Question 2

Describe and explain the means of O2 carriage in the blood

Answer 2

Most O2 in the blood is transported bound to haemoglobin in the red blood cells

O2 is present in blood in two forms:
1 bound to haemoglobin 98.5%
2 physically dissolved 1.5%

Question 3

Explain oxygen binding to haemoglobin

Answer 3

Haemoglobin can form a reversible combination with O2
Each Hb molecule contains 4 haem groups
Each haem group reversible binds to one O2 molecule
Haemoglobin is considered fully saturated when all Hb present is carrying its maximum O2 load
The PO2 is the primary factor which determine the percent saturation of haemoglobin with O2

Question 4

Explain the oxygen delivery index (DO2I)

Answer 4

Oxygen delivery to the tissues is a function of oxygen content of arterial blood and the cardiac output
DO2I = CaO2 x CI

Question 5

Explain oxygen content of arterial blood (CaO2)

Answer 5

The O2 content of arterial blood is determined by the haemoglobin concentration and the saturation of Hb with O2
CaO2 = 1.34 x (Hb) x SaO2

Question 6

How can oxygen delivery to tissues be impaired

Answer 6

Decreased partial pressure of inspired oxygen

Respiratory disease - these can decrease arterial PO2 and hence decrease Hb saturation with O2 and O2 content of the blood

Heart failure - decreases cardiac output

Anaemia - decreases Hb concentration and hence decreases O2 content

Question 7

Explain co-operativity

Answer 7

Binding of one O2 to Hb increases the affinity of Hb for O2

Question 8

Explain the significance of the sigmoid curve

Answer 8

Flattens where all sites become occupied

Flat upper portion means that moderate fall in alveolar PO2 will not much affect oxygen loading

Steep lower part means peripheral tissues get a lot of oxygen for a small drop in capillary PO2

Question 9

Explain the Bohr effect

Answer 9

A shift of the curve to the right which increases release of O2 by conditions at the tissues

Question 10

Explain foetal haemoglobin (HbF)

Answer 10

HbF differs from adult in structure as has 2 alpha and 2 gamma subunits
It interacts less with 2,3-Biphosphoglycerate in red blood cells and so has higher affinity for O2
Dissociation curve is shifted to the left

Question 11

Explain Myoglobin

Answer 11

Myoglobin is present in skeletal and cardiac muscles
One haem group per myoglobin molecule
No cooperative binding of O2
Dissociation curve is hyperbolic and O2 is released at very low PO2

Presence of myoglobin in blood indicates muscle damage