Biology Made Easy - Composition of the Blood

Blood is composed of 55% plasma and 45% formed elements.

Plasma is 90% water, 8% proteins and 2% other dissolved solutes. There are multiple types of proteins in the plasma. Albumin is the most common protein in plasma, making up 60% of the plasma proteins. Albumin is made by the liver, as are most of the plasma proteins. Liver diseases can disrupt the production of these vital proteins. Albumin contributes to blood viscosity and also transports and carries lipids, hormones, and calcium. It also helps in maintaining blood pH.

Another group of plasma proteins are the globulins. The alpha globulins transport lipids, fat-soluble vitamins, and copper. They are also involved in blood clotting. The beta globulins transport iron and lipids in the blood. They also form Complement proteins that are involved in protection by the immune system. Gamma globulins also function in the immune system. They are immunoglobulins, or antibodies. Antibodies are highly specific for certain chemical antigens, and they are the reason our immune system has memory for antigens that can last for years and result in a strong attack at second exposure.

Another plasma protein is fibrinogen. This is a protein involved in clotting, but fibrinogen is the inactive form of the protein. When a clot needs to be formed, it is converted into the active protein fibrin. Fibrin forms long strands which turn into a meshwork, allowing a clot to form.

The other dissolved solutes in the plasma include electrolytes, wastes, respiratory gases, hormones, nutrients, and enzymes. Most of these are not performing functions for the blood, they are merely being transported by the blood to different areas of the body.

The composition of the blood would be incomplete without the formed elements. The formed elements are made up almost entirely of red blood cells. These carry oxygen throughout the blood using the protein hemoglobin. The scientific term for red blood cells is erythrocytes.

Leukocytes are white blood cells. There are five different types of white blood cells and they are separated into two categories. Granulocytes are named because they have dark staining granules that can be seen under a microscope. The granulocytes include the neutrophils, eosinophils, and basophils. The agranulocytes do not have the dark staining granules. The agranulocytes include the lymphocytes and the monocytes.

Platelets are also a formed element, and vital in the composition of blood. They make up a tiny percentage of the formed elements, but they are necessary in the clotting process.