the role of haemoglobin

Components of blood

Plasma - fluid part of mass transport system

Erythrocytes (RBCs) - contain haemoglobin that carries oxygen from lungs to all cells

Leucocytes (WBCs) - defend the body against infections

Platelets - tiny fragments of cells involved in blood clotting

Erythrocytes

Transport oxygen from the lungs to all the cells

They have a large surface area to volume ratio due to the bioconcave disc shape of the cell

No nucleus thus more space inside the cell for haemoglobin to carry more oxygen

Haemoglobin

A globular protein composed of four polypeptide chains - two alpha chains and two beta chains each with a ring like heme group containing an iron atom. Oxygen binds reversibly to these iron atoms and is transported through blood

At the lungs

Concentration of oxygen is low in RBCs, oxygen diffuses into RBCs, oxygen binds with haemoglobin to form oxyhaemoglobin

In the body tissues

Concentration of oxygen is higher in cytoplasm of RBCs, oxygen diffuses out of the RBCs into the cells, haemoglobin releases oxygen into the tissue

Binding of oxygen to haemoglobin

The binding of the first oxygen molecule induces change in the shape of the haemoglobin that increases its ability to bind to the other three oxygen molecules

As each oxygen molecule binds, it alters the conformation of haemoglobin, making subsequent binding easier

This means haemoglobin will have a higher affinity for oxygen in oxygen rich areas (lungs), promoting oxygen loading

Conversely, haemoglobin will have a lower affinity for oxygen in oxygen starved areas (muscles) promoting oxygen unloading

Oxygen affinity

the degree to which oxygen tends to combine with the haemoglobin molecule

Oxygen saturation

a measure of the amount of oxygen take up by haemoglobin at a particular time to form oxyghaemoglobin

Partial pressure of oxygen

a measure of dissolved oxygen in the blood

Oxygen dissociation curve

describes the relation between the partial pressure of oxygen and oxygen saturation percentage

The Bohr Effect

changes in the oxygen dissociation curve of haemoglobin that occur due to a rise in carbon dioxide lebels and a reduction of the affinity of haemoglobin for oxygen starved areas

Effect of carbon dioxide on oxygen dissociation curve

An increase in concentration of carbon dioxide decreases the amount of oxyhaemoglobin formation

according to Bohr affect, for any particular partial pressure of oxygen, the affinity of haemoglobin towards oxygen decreases and favours dissociation of oxyhaemoglobin when the partial pressure of carbon dioxide increases

It means higher concentration of carbon dioxide causes the dissociation of oxyhaemoglobin releasing free oxygen

increase in PCO2 shifts the oxygen dissociation curve to the right

higher PCO2 lowers the affinity of haemoglobin for oxygen

Fetal Haemoglobin

main oxygen carrying pigment in the human fetus found in fetal red blood cells and is involved in transporting oxygen from the mother's blood stream to organs and tissues in the fetus

Myoglobin

oxygen binding molecule found in skeletal muscle tissue. it has a higher affinity for oxygen than haemoglobin or fetal haemoglobin and becomes saturated at lower partial pressures of oxygen and serves as an oxygen store