Oxyhaemoglobin Dissociation Curve or Oxygen Dissociation Curve:

The oxyhaemoglobin dissociation curve, also known as the oxygen dissociation curve, is a graphical representation of the relationship between the partial pressure of oxygen (PO2) and the percentage saturation of haemoglobin with oxygen (%O2 saturation). This curve demonstrates how haemoglobin's affinity for oxygen changes with varying oxygen pressures in the blood. It plays a crucial role in understanding the transport and release of oxygen by haemoglobin in the body.

Graphical Representation:
The oxyhaemoglobin dissociation curve is typically represented as an S-shaped curve on a graph. The x-axis represents the partial pressure of oxygen (PO2) in mmHg, while the y-axis represents the percentage saturation of haemoglobin with oxygen (%O2 saturation). The curve starts at the bottom-left corner, indicating low oxygen saturation in the blood at low oxygen pressures. As the oxygen pressure increases, the curve rises steeply until it reaches a plateau, indicating high oxygen saturation.

Explanation:
The oxyhaemoglobin dissociation curve illustrates the relationship between oxygen pressure and haemoglobin's affinity for oxygen. At lower oxygen pressures, such as in the tissues, the curve demonstrates that haemoglobin has a lower affinity for oxygen. As a result, oxygen is more readily released from haemoglobin, facilitating oxygen delivery to the tissues.

As the partial pressure of oxygen increases, such as in the lungs, the curve shows that haemoglobin's affinity for oxygen increases. This allows haemoglobin to bind to oxygen more readily, enhancing the uptake of oxygen from the lungs into the blood.

The steep portion of the curve, known as the steep region, represents the transition phase where haemoglobin rapidly binds to oxygen in the lungs. This ensures efficient oxygen uptake in the lungs where oxygen pressures are high.

The plateau portion of the curve, known as the flat region, indicates that even a slight increase in oxygen pressure results in a significant increase in oxygen saturation. This indicates that haemoglobin is almost saturated with oxygen at high oxygen pressures, ensuring efficient oxygen transport to the tissues.

The oxyhaemoglobin dissociation curve is influenced by various factors such as pH, temperature, carbon dioxide levels, and the concentration of 2,3-BPG (2,3-bisphosphoglycerate). These factors can shift the curve to the right or left, affecting haemoglobin's affinity for oxygen.

Understanding the oxyhaemoglobin dissociation curve is vital in comprehending how oxygen is transported and released in the body. It helps explain the efficiency of oxygen delivery to the tissues and the role of haemoglobin in oxygen transport.