Blood is made up of minute elements called cells suspended in a pale yellow fluid known as plasma. Each drop of blood contains primarily three types of cells - about 250 million red corpuscles, 400, 000 white corpuscles and 15 million platelets. Each of them plays a part in keeping the body healthy.
Blood is red in colour. This red colour comes from red blood cells. These cells contain a substance called haemoglobin, a combination of iron and other materials that give them the red colour. Haemoglobin makes it possible for red cells to pick up oxygen from the lungs and to carry the oxygen to all parts of the body. The trillions of cells that make up the body need oxygen to survive. As such, the red blood cell distributes its load of oxygen, it picks up carbon dioxide waste from the body cells and takes it to the lungs to be breathed out. Red blood cells have no power to move on their own. They must be pumped throughout the body in the blood stream. The red cells are manufactured in the bone marrow of the larger bones of the body. The red cells are continuously at work and they have an average life span of 120 days. New ones are made constantly at a rate of millions per second.
Old blood cells are sent to an organ called spleen, where they are taken apart. The wastes are disposed of and iron is recycled to go into new red blood cells. Certain food such as red meat, cereals and green vegetables provide the body with iron. For donating blood one must have at least 12. 5 gm. of haemoglobin per 100 ml of blood.
There are several types of white blood cells. Together these cells provide an active defence to protect the body when it is invaded by bacteria, viruses or other harmful substances. 60 to 70 percent of the white cells have a very simple mission. Their job is to attack and literally eat up bacteria and other harmful substances. They are the body’s first line of defence against infection and many illnesses.
Another very important group of white blood cells protect the body against catching the same disease over and over again. These cells are especially effective against many diseases that are caused by bacteria and viruses.
Many common diseases, such as chickenpox, are caused by viruses.The first time one of these diseases is caught, it triggers an immediate reaction from these special white blood cells. They begin to produce a substance called antibody meant to fight the virus. The antibodies are produced too late to prevent the first occurrence of the disease. However, the antibodies are stored away available to prevent the disease from occurring a second time. A different type of specific antibody is produced for each type of virus that causes disease.
Platelets are tiny irregular shaped cells and. like red blood cells, are made in the bone marrow. Platelets are sticky. They can and do stick to each other and to the inner surfaces of blood vessels. When a blood vessel cut or punctured, platelets begin to gather at the site of the injury. The platelets stick to each other and to the edges of the injury, forming a plug that reduces the loss of blood. As the plug gets bigger, it becomes more solid and firm. It becomes a clot or scab, stopping the flow of blood and providing a foundation upon which the healing process can take place.
The fluid part of blood called plasma carries all cells. 55% of blood consists of plasma while cells constitutes 45% of the blood. Out of the 55% of plasma, 92% is water. The balance 8% of plasma consists of proteins,sugar, fats, vitamins and minerals that are needed by the body cells. In addition, plasma contains antibodies and hormones. Hormones are chemical messengers that regulate growth, physical responses to emotions and other body functions.
Circulation of Blood