Oxygen Transport

Question 1

describe mechanism of oxygen transport

Answer 1

transported in two forms :

• physically dissolved in plasma 3%
• in combination with hb in red cell 97%

dissolved form:

• in a normal healthy adult, 0.3 ml of o2 is transported in dissolved form in 100 ml of blood
• as cardiac output is 5 L/min- oxygen transported at rest - 15 ml/min

in combination with hb
- about 97%
- possible due to the binding affinity of hb for oxygen
- hb that binds with oxygen - oxyhaemoglobin and hb that does - deoxyhaemoglobin or reduced-haemoglobin.
- process of o2 molecules combining loosely and reversibly with heme portion of hb - oxygenation
- single hb molecule can bind to 4 other oxygen molecules.
- only when iron is in ferrous state (fe2+)
- the fe2+ when oxidised to fe3+ iron forms methemoglobin,, which cannot bind to oxygen.
- each gran of hb binds with 1.34 ml of oxygen.
- in a healthy individual the Oxygen carrying capacity (the max amount of oxygen that can be carried by) of arterial blood is about 20ml/100 ml blood.
- Hb is 97% saturated with O2. Hence 100 ml of arterial blood containing 15 gm of Hb contains 19.4 ml of O2.
- As pO2 at tissues is 40mmHg, at which Hb is 75% saturated with O2 and has an O2 content of 14.4 ml per 100 ml blood,
thus each 100 ml of arterial blood delivers 5 ml of O2 to tissues

Question 2

oxygen haemoglobin dissociation curve

Answer 2

explains the relationship between pp of o2 in blood with oxygen saturation of hb.

• s shaped curve (sigmoid)
• as po2 rises the hb saturation progressively increases
• however saturation is not linear with inc in po2 for which the curve becomes sigmoid shaped.

divided into two major phases :

steep phase: steep slope between po2 of 10-60 mm hg
hb 89% saturated at 60 mm hg
- less inc in po2 leads to greater percentage saturation of hb and therefore, facilitates oxygen loading.
- change in slope in reverse direction (from 60 to 10) causes unloading
- a small dec in po2 in the tissue results in unloading of large amounts of oxygen to the tissues

plateau phase:

• inc in po2 above 60 produces only a small inc in oxygen binding
• inc in po2 from 60 to 100 in the plateau region of the curve illustrates that oxygen saturation and content remain apparently constant over a wide alteration in alveolar po2.

Increase in Pco2 reduces the affinity of Hb for O2 and shifts O2- Hb curve to right

• This is called Bohr Effect which helps O2 uptakes in lungs and O2 release to the tissues.
• Increase in H ion conc., rise in 2,3 DPG and rise in temp reduce the affinity and promote O2 delivery to tissues.