BIOCHEMISTRY - Main Regulators and Biological Fluids of the Human Body - 2016

5. BLOOD BIOCHEMISTRY

5.4. Main Functions of Blood

The main Functions OF Blood include Respiration, Carbon dioxide transport, nutrient and metabolite transport, and blood clotting.

Respiratory function. This is performed by erythrocyte Hemoglobin. Hemoglobin absorbs oxygen from the atmosphere; blood is oxygenated in the lung capillaries, resulting in The formation of oxyhemoglobin (Process 1):

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Tissue capillaries have a lower pressure, which triggers the dissociation of oxyhemoglobin (Process 2) and the release of oxygen.

The oxygen capacity of blood (the maximum amount of oxygen bound by the blood) depends on the blood hemoglobin concentration.

Blood loss, anemia (a deficiency of red Blood Cells or hemoglobin), impaired respiratory and circulatory functions, as well as high-altitude ascent, lead to reduced blood oxygen saturation (known as hypoxemia) and The Development of Hypoxia (inadequate oxygen supply to Tissues). Physical exertion dramatically increases the body's demand for oxygen, resulting in functional hypoxia.

Carbon dioxide transport. Carbon dioxide is transported as sodium bicarbonate (in plasma) and potassium bicarbonate (in erythrocytes).

The following processes take place in the pulmonary capillaries:

where E is the enzyme Carbonic anhydrase.

Carbon dioxide is eliminated through exhaled air. The lower the atmospheric partial pressure, the greater the removal of CO₂. For instance, blood carbon dioxide levels drop in high-altitude environments (leading to hypocapnia).

Transport of nutrients and metabolites. During Digestion, as well as from Endocrine glands and other tissues and Organs, various substances enter the bloodstream. The blood distributes them throughout the body, ensuring tissue nourishment and METABOLISM.

Blood clotting (coagulation). This is a protective physiological response to blood loss caused by vascular trauma. A blood clot seals the vessel, stopping the bleeding. However, blood clotting can also occur inside a blood vessel due to pathological changes in its endothelial lining (a condition known as thrombosis).

The following biochemical processes occur during bleeding from an injured vessel:

1) platelets disintegrate, and damaged cells release inactive thromboplastin;

2) thromboplastin acts upon the enzyme thrombokinase via activation factors;

3) thrombokinase triggers The conversion of prothrombin (a plasma protein) into Thrombin (an enzyme);

4) thrombin acts on the blood protein fibrinogen;

5) fibrinogen is converted into the readily polymerizing protein fibrin (a thread-like substance), forming a gel-like blood clot (thrombus);

6) the thrombus dissolves once the blood vessel has healed.