Question

Describe how O2 and CO2 are transported in the blood and the effect of exercise on transport of each. Include in your discussion pH and temperature.

Answer 1

TRANSPORT OF CARBON DIOXIDE

The blood transports carbon dioxide comparatively easily because of its higher solubility

There are three ways of transport of carbon dioxide

a) In dissolved state : Approximately 5-7 per cent of carbon dioxide is transported, being dissolved in the plasma of blood.

b) as Carbamino haemoglobin : About 20-25% CO2 react with the amine group of Haemoglobin and form carbamino-haemoglobin.

C) in the form of bicarbonate : Bulk of CO2 is transported by plasma as bicarbonate

Carbon dioxide produced by the tissues, diffuses into the RBCs, where it reacts with water to form carbonic acid (H2CO3). This reaction is catalysed by the enzyme, Carbonic anhydrase. RBCs contain a very high concentration of this enzyme.

Now carbonic acid dissociates into Hydrogen and bicarbonate ions.

The hydrogen ions released from carbonic acid combine with haemoglobin and form haemoglobinic acid (H.Hb)

The majority of bicarbonate ions formed within the erythrocytes diffuse out into the plasma along a concentration gradient. In the plasma bicarbonate ions, combine with sodium and form Sodium bicarbonate (NaHCO3).

Nearly 70% CO2 transported by plasma as NaHCO, form.

In response of HCO3, chloride ions diffuse from plasma into the erythrocytes to maintain the ionic balance. Thus, electrochemical neutrality is maintained. This is called Chloride shift or Hamburger Phenomenon.

TRANSPORT OF OXYGEN

As much oxygen comes in the blood from air, it is approximately 3% dissolves in the blood plasma. Remaining 97% oxygen combines with haemoglobin to form oxyhaemoglobin. Oxygen can bind with Hb in a reversible manner to form oxyhaemoglobin.

Haemoglobin is a red coloured iron containing pigment present in the RBC.

Haemoglobin is made up of 4 units. Each unit has 1 Fe in +2 state. Each haemoglobin molecule can carry a maximum of four molecules of O,

1 gm of haemoglobin transports 1.34 ml of oxygen. 100 ml (1 dL) of blood contains normally 15 gm of haemoglobin, so 100 ml blood transports approximately 20 ml of oxygen.

In a conducting cycle blood gives its 25% Oxygen to tissues. So every 100 ml of oxygenated blood can deliver around 5 ml of Oxygen to tissue under physiological condition.

Binding of oxygen with haemoglobin is primarily related to partial pressure of Oxygen But PCO2, hydrogen ion concentration and temperature are the other factors which can interfere with this binding.

Oxygen does not oxidise haemoglobin. Formation of oxyhaemoglobin is a process of oxygenation.The valency of iron is 2 in oxyhaemoglobin. Some gases (e.g. Ozone) oxidise haemoglobin.

At the time, oxyhaemoglobin reaches upto the tissues it dissociates. O2 freed from it goes into the tissue fluid from blood. In place of it, CO, from tissue fluid comes into blood. Gaseous exchange between blood and tissue is called internal respiration or tissue respiration. It is also done by simple diffusion.

EFFECT OF EXCERSICE

First of all here are the some factors which increases efficiency of oxygen delivery.

a) increase in acidity or decrease in pH

b) increase in intermediate metabolites such as 2,3DPG)

c) increase in the temp

d) increase in pCO2

Exercise causes an INCREASE IN ACIDITY, TEMPERATURE AND INCREASE IN METABOLISM INTERMEDIATES (2,3DPG) and a decrease in oxygen in your muscle tissues. This causes an increased dissociation of oxygen from your blood flowing through your muscles, supplying them with much needed oxygen.

THUS, EXERCISE CAUSES OXYGEN-HAEMOGLOBIN DISSOCIATION CURVE TO SHIFT RIGHT DUE TO DECREASED AFFINITY OF HAEMOGLOBIN TO OXYGEN. THIS DECREASED AFFINITY TO OXYGEN PROMPTS RELEASE OF OXYGEN FROM HAEMOGLOBIN TO TISSUES MORE EFFICIENTLY.

(The Bohr effect describes how the affinity of hemoglobin for oxygen changes depending on the local biochemical conditions. An increase in acidity, temperature and the concentration of intermediate chemicals in the conversion of sugar to energy—specifically 2,3-diphosphoglycerate—decreases hemoglobin's affinity for oxygen, causing oxygen to diffuse into the tissues.)

(Haldane effect- Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin which increases the removal of carbon dioxide. This property is the Haldane effect. Consequently, oxygenated blood has a reduced affinity for carbon dioxide. Thus, the Haldane effect describes the ability of hemoglobin to carry increased amounts of carbon dioxide (CO2) in the deoxygenated state as opposed to the oxygenated state. A high concentration of CO2 facilitates dissociation of oxyhaemoglobin.)