haemoglobin and oxygen transport

• the ability of haemoglobin to associate with and release oxygen is dependent on the concentration of oxygen in the surrounding tissues.
• The concentration of oxygen is meausred by the relative pressure that it contributes to in a mixture of gases. this is called partial pressure of oxygen- it is also called the oxygen tension and is measured in kilo pascals.
• haemoglobin can associate with oxygen in a way that produces an s shaped curve, also known as the haemoglobin association curve. at low oxygen tensions, the haemoglobin doesn't readily associate with oxygen molecules. this is because the haem groups that attract oxygen are at the centre of a haemoglobin molecule, making it difficult for oxygen to reach the haem group to associate with it. this difficulty in combining with the first oxygen molecule accounts for the low saturation levels of haemoglobin in low oxygen tensions.
• as oxygen tension rises, the diffusion gradient into the haemoglobin molecule increases. eventually, one oxygen molecule enters the haemoglobin molecule and associates with one of the haem groups. this causes a slight change in the shape of the haemoglobin molecule, known as a conformational change to allow more oxygen molecules to enter the molecule to associate with the other haem groups relatively easily. this accounts for the steepness of the curve as the oxygen tension rises.
• As t he haemoglobin reaches 100 % Saturation, the curve begins to level off to create the S shape. mammalian haemoglobin is well adapted to transporting hemoglobin to the tissues of its body. the oxygen tension found in the lungs is sufficient to produce close to 100 % saturation. The oxygen tension in respiring body tissues is sufficiently low enough to cause oxygen to dissociate readily from nearby oxyhameoglobin.