Plasma constitutes 55% of total blood volume. Composed of 90% water, salts, lipids and hormones, it is especially rich in proteins (including its main protein albumin), immunoglobulins, clotting factors and fibrinogen.
Plasma performs several functions: transporting blood cells and nutrients; regulating the body’s water and mineral salts; irrigating tissues; providing a defence against infections; and coagulating blood.
The albumin contained in plasma prevents the blood from losing too much water and consistency as it travels through the narrow, water-permeable blood vessels (capillaries). Albumin transports various blood components and nutrients. The immunoglobulins also contained in plasma are antibodies that, along with white blood cells, play an important role in fighting against pathogens. Clotting factors, in combination with platelets, control hemorrhaging.
A deficiency in these proteins can cause various health problems. For example, the lack of albumin can lead to the inability to retain water in the vessels, the lack of immunoglobulins can lead to a decline in the body’s immune defences and a lack of clotting factors can lead to blood clotting anomalies.
Red blood cells, white blood cells and platelets are suspended in plasma.
White Blood Cells
There are between 6,000 and 8,000 white cells per cubic millimetre of blood. White cells, slightly larger than red cells, are also called leukocytes. They purify and protect the body from infections. Once an infection is detected in any part of the body, the while cells move in to fight it.
Platelets, or thrombocytes, are smaller than the red and white blood cells. Platelets play a role in blood coagulation and wound healing. When a blood vessel ruptures, platelets combine with fibrin, derived from fibrinogen, to form a clot.
Red Blood Cells
A drop of blood the size of a pinhead contains approximately 5 million red blood cells (erythrocytes). They are small biconcave disks without a nucleus and get their red colour from an iron-containing protein called hemoglobin. Red cells make up between 37% and 43% of blood volume in women and between 43% to 49% in men. Red blood cells carry oxygen throughout the body.