![]() Inactive tissues such as skeletal muscles, pO₂ is much below 40 mmHg. Hence, oxyhemoglobin ensures oxygen transport for survival for 4-5 minutes after stopping the heart or when breathing is interrupted. The remaining is in the form of ‘reserve’ in the blood itself. It means that oxygen transport by oxyhemoglobin to resting tissues is about 22%. Haemoglobin is 75% saturated when pO₂ is 40mmHg, the pO₂ of tissue cells at rest. It is said to be 50% saturated when each haemoglobin, on average, carries two oxygen molecules.Ībout 97% of haemoglobin is saturated in systemic arteries, where pO₂ is about 95mmHg. Haemoglobin is 100% saturated when each haemoglobin molecule carries four oxygen molecules. This is known as the oxygen dissociation curve. A sigmoid curve is formed when the % saturation of haemoglobin with O2 is plotted (on the y-axis) against the pO2 (on the x-axis). The attachment of oxygen to haemoglobin is predominantly determined by O2 partial pressure. The Relationship between haemoglobin and Oxygen Partial Pressure This process is termed oxygenation of haemoglobin.Īnd at tissues (or other organs) where the oxygen tension is low, oxyhemoglobin splits into oxygen and haemoglobin, thereby transporting oxygen from the above-dissociated oxygen. Oxygen binds with the haemoglobin to form the oxyhemoglobin, bright red-coloured. In the lungs, where the oxygen tension is high, oxygen transport will occur by binding to haemoglobin (dark red). Each haemoglobin molecule carries four molecules. One O2 can bind to the ferrous ion (Fe) at the centre of the haem group. Haemoglobin consists of four polypeptides, and each polypeptide is attached to one heme group. Haemoglobin is an iron-containing pigment present in red blood cells, and this is responsible for the red colour of RBC. The transport of O2 through plasma occurs because some O2 is dissolved in plasma, which comprises about 3% of the total O2 transport.Ī significant amount of oxygen, about 97%, is transported by binding to haemoglobin in RBC. Transport of oxygen to the organs or tissues occurs via blood and plasma: Two ways for the Transport Oxygen to Tissues Typically, 100ml of oxygenated blood carries 5ml of oxygen. Each molecule of haemoglobin carries about four molecules of oxygen. Haemoglobin is an iron-containing molecule that becomes oxyhemoglobin when it binds to oxygen. Conversely, carbon dioxide diffuses out of the bloodstream and into the alveoli, expelled out from the body. Oxygen enters the bloodstream through capillaries by diffusion, where oxygen transport takes place to the tissues via plasma and red blood cells (RBCs). Oxygen and carbon dioxide play a vital role in the exchange of gases. Generally, the gaseous exchange occurs in the alveoli of the lungs.
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