Blood has three main functions: transport, protection and regulation.
Blood transports the following substances:
Gases, namely oxygen (O2) and carbon dioxide (CO2), between the lungs and rest of the body
Nutrients from the digestive tract and storage sites to the rest of the body
Waste products to be detoxified or removed by the liver and kidneys
Hormones from the glands in which they are produced to their target cells
Heat to the skin so as to help regulate body temperature
Blood has several roles in inflammation:
Leukocytes, or white blood cells, destroy invading microorganisms and cancer cells
Antibodies and other proteins destroy pathogenic substances
Platelet factors initiate blood clotting and help minimise blood loss
Blood helps regulate:
pH by interacting with acids and bases
Water balance by transferring water to and from tissue
Composition of blood
Blood is classified as a connective tissue and consists of two main components:
1. Plasma, which is a clear extracellular fluid, Blood plasma is a mixture of proteins, enzymes, nutrients, wastes, hormones and gases.
2. Formed elements, which are made up of the blood cells and platelets
The formed elements are so named because they are enclosed in a plasma membrane and have a definite structure and shape. All formed elements are cells except for the platelets, which tiny fragments of bone marrow cells.
Formed elements are:
Erythrocytes, also known as red blood cells (RBCs)
Red blood cells (RBCs), also known as erythrocytes, have two main functions:
To pick up oxygen from the lungs and deliver it to tissues elsewhere
To pick up carbon dioxide from other tissues and unload it in the lungs
Whenever a germ or infection enters the body, the white blood cells snap to attention and race toward the scene of the crime. The white blood cells are continually on the lookout for signs of disease. When a germ does appear, the white blood cells have a variety of ways by which they can attack. Some will produce protective antibodies that will overpower the germ. Others will surround and devour the bacteria.
The human body does not handle excessive blood loss well. Therefore, the body has ways of protecting itself. When, for some unexpected reason, sudden blood loss occurs, the blood platelets kick into action.
Platelets are irregularly-shaped, colorless bodies that are present in blood. Their sticky surface lets them, along with other substances, form clots to stop bleeding.
When bleeding from a wound suddenly occurs, the platelets gather at the wound and attempt to block the blood flow. The mineral calcium, vitamin K, and a protein called fibrinogen help the platelets form a clot.