Blood is a fluid made up of cells and a watery part. It supplies all parts of your body with the oxygen and nutrients you need to stay alive. Blood carries away your body's wastes such as carbon dioxide. Blood protects you from germs that can cause disease. Blood can warm you up or cool you down and help heal wounds.
Your body has a network of tubes, called blood vessels, through which blood flows. The names of these blood vessels are: arteries, veins, and capillaries. Blood constantly flows from your heart, around your body and back to your heart through these vessels. The heart has a very important job!
The heart is a big muscle about the size of your fist. Its job is to pump blood to all parts of the body. The heart beats 70-80 times a minute and it beats more than thirty million times a year! It never stops! The heart has four chambers (like rooms); two atria, and two ventricles. Your heart, blood, and blood vessels all work together. This is called the circulatory system.
Your arteries expand and contract when the lower chambers of the heart, the ventricles, contract. You can feel this throbbing at a few places on your body where the arteries are close to the skin. This is called your pulse.
Red blood cells perform the most important blood duty. A single drop of blood contains millions of red blood cells which are constantly traveling through your body delivering oxygen and removing waste. If they weren't, your body would slowly die.
Red blood cells are red only because they contain a protein chemical called hemoglobin which is bright red in color. Hemoglobin contains the element Iron, making it an excellent vehicle for transporting oxygen and carbon dioxide. As blood passes through the lungs, oxygen molecules attach to the hemoglobin. As the blood passes through the body's tissue, the hemoglobin releases the oxygen to the cells. The empty hemoglobin molecules then bond with the tissue's carbon dioxide or other waste gases, transporting it away.
Over time, the red blood cells get worn out and eventually die. The average life cycle of a red blood cell is 120 days. Your bones are continually producing new blood cells, replenishing your supply. The blood itself, however, is re-circulated throughout your body, not being remade all of the time.
Since the human body is continually making more blood, it is safe for healthy adults to donate blood. The blood is then stored for use in emergency situations. Initially after giving blood, the donor may feel some momentary lightheadedness due to the loss of oxygen-rich red blood cells and blood sugar. The body quickly stabilizes itself.
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 white blood cells have a rather short life cycle, living from a few days to a few weeks. A drop of blood can contain anywhere from 7,000 to 25,000 white blood cells at a time. If an invading infection fights back and persists, that number will significantly increase.
A consistently high number of white blood cells is a symptom of Leukemia, a cancer of the blood. A Leukemia patient may have as many as 50,000 white blood cells in a single drop of blood.
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.
A clot begins to form when the blood is exposed to air. The platelets sense the presence of air and begin to break apart. They react with the fibrinogen to begin forming fibrin, which resembles tiny threads. The fibrin threads then begin to form a web-like mesh that traps the blood cells within it. This mesh of blood cells hardens as it dries, forming a clot, or "scab."
Calcium and vitamin K must be present in blood to support the formation of clots. If your blood is lacking these nutrients, it will take longer than normal for your blood to clot. If these nutrients are missing, you could bleed to death. A healthy diet provides most people with enough vitamins and minerals, but vitamin supplements are sometimes needed.
A scab is an external blood clot that we can easily see, but there are also internal blood clots. A bruise, or black-and-blue mark, is the result of a blood clot. Both scabs and bruises are clots that lead to healing. Some clots can be extremely dangerous. A blood clot that forms inside of a blood vessel can be deadly because it blocks the flow of blood, cutting off the supply of oxygen. A stroke is the result of a clot in an artery of the brain. Without a steady supply of oxygen, the brain cannot function normally. If the oxygen flow is broken, paralysis, brain damage, loss of sensory perceptions, or even death may occur.
It's a straw-colored, clear liquid that is 90 percent water, and it is an essential ingredient for human survival. It might seem like plasma is less important than the blood cells it carries. But you can't have one without the other. Besides water, plasma also contains dissolved salts and minerals like calcium, sodium, magnesium, and potassium. Microbe-fighting antibodies travel to the battlefields of disease by hitching a ride in the plasma. Without plasma, the life-giving blood cells would be left floundering without transportation.
Blood plasma that escapes from the blood vessels is absorbed into the surrounding tissue. This tissue fluid collects in tubes throughout the body and is known as lymph. From the lymph tubes, it returns to the blood after passing through a lymph node. If you've ever broken a blister, you've seen lymph. It's a colorless, slightly sticky liquid.
Lymph is an important part of the circulatory system. It aids the body's absorption of nutrients and helps to remove waste from the tissue. The lymph collects the body's waste and then deposits it in a lymph node as it passes through. Lymph nodes are clumps of tissue that collect the waste deposits. Your tonsils and adenoids are two examples of lymph nodes. The lymph nodes also assist the spleen and the bones in producing new white blood cells.