Personal tools
You are here: Home > Explore Elementary Hematology > Red Blood Cells

Learn About Red Blood Cells and Platelets

Red blood cell - or erythrocytes (e-rith'ro-sites) - make up about 45 percent of the solid part of the blood. In a healthy person, there are approximately 5.5 million red blood cells per cubic inch of blood. This means red blood cells out number white blood cells 1,000 to 1. Erythrocytes are disc-shaped cells that have no nucleus. They are made mostly of hemoglobin, a protein that contains iron and a pigment that causes blood to have its red color.

The function of erythrocytes is to pick up oxygen at the lungs and carry it to the tissues. Red blood cells are the "distributors" of the blood, carrying oxygen to the tissues and taking carbon dioxide (a waste product) from the tissues to the lungs where it is exhaled. The hemoglobin is the part of the erythrocyte that actually carries the oxygen and carbon dioxide.

Red blood cells are made in the red marrow of bones, and live about 120 days. Because they wear out so quickly, an entire supply of red blood cells is renewed every four months. As red blood cells wear out in the bloodstream, they are taken in by the spleen, an organ on the left side of the abdomen below the stomach, and destroyed. Parts of the old cells are salvaged to make new red blood cells.

The picture below shows what a blood smear looks like under a microscope. The many red disks are red blood cells. The purple cell in the center is a white blood cell.


Red Blood Cell 1Medical technologists are often asked to count the number of red blood cells in a patient's blood and evaluate their shape and color. Instruments are available that will automatically count the number of cells. The technologist looks at a blood smear under a microscope to evaluate the shape and color of the cells.

A common disorder of red blood cells is anemia. Anemia is a broad term used to describe all diseases where a person has decreased amounts of hemoglobin, and usually not enough red blood cells. The color and shape of the person's red blood cells can tell a technologist or doctor what type of anemia the person has.

There are many different types of anemia. Some anemia may not cause problems unless people exert themselves. These people may have trouble breathing during exercise, and usually appear pale. Other, more severe, anemia can cause muscle cramping, dizziness, fatigue, and insomnia. The most severe anemia may cause coma and death. Such severe symptoms occur because oxygen is not getting to tissues and waste products are building up in the tissues. Think of it as a restaurant that didn't hire enough wait staff: a few waiters (i.e.- red blood cells) are running around like crazy trying to get the food (i.e.- oxygen) out to the customers (i.e.- tissue cells) and clear tables (i.e.- remove wastes). The dirty dishes pile up on tables and food sits back in the kitchen (i.e.- the lungs).... Of course, the customers are not happy!

 

Red Blood Cell 2Anemia can be caused because someone is not making enough red blood cells, because they are destroying red blood cells before they are actually worn out, because they are making defective hemoglobin or red blood cells, or because they have experienced a great blood loss. Many people are mildly anemic just because they don't get enough iron in their diet. Remember, iron is needed to make the hemoglobin!

Platelet - or thrombocytes (throm'-bo-sites) - are the smallest cells in the blood. They are fewer in number than red blood cells, but greater in number than white blood cells. Normally, there are approximately 300,000 platelets in every cubic inch of human blood. Platelets are made in the red marrow of bone and lymph nodes and live for about five to ten days.

Platelets are the "maintenance workers" of the blood. When thrombocytes touch the rough surface of a torn blood vessel, they stick to it and each other. Platelets release factors that form a thread-like substance (fibrin) which forms a clot. The clot hardens into a scab, which covers the breakage until the vessel heals. Then, the clot breaks off and dissolves in the blood. Clotting is very important because without it, blood would continue to flow from the vessel like a leaky hose! Some people are missing some of the factors that produce the clot. They are known as hemophiliacs. When they get cut, they may not be able to stop bleeding.

 

Red Blood Cell 3

The small purple cells (pictured at left) are platelets. Notice that they are smaller than the red blood cells around them.

Medical technologists may be asked by doctors to count the number of platelets a patient has in their blood. The same instrument that counts the red blood cells can also count platelets. When someone does not have enough platelets, this is known as thrombocytopenia. This can cause a person to bleed excessively after an injury or surgery, because there aren't enough cells to do the job. There are many different diseases that cause thrombocytopenia.

When someone has too many platelets, this is known as thrombocytosis. It is often a temporary reaction to major trauma (like surgery), and will go away on its own. A small percentage of people with thrombocytosis may make unnecessary clots, which can be very dangerous if they block important blood vessels. If they block heart vessels, they can cause a heart attack.

There are also some inherited diseases that affect platelet quality. Thrombocytopathy is the name for diseases that cause poor platelet quality.

Platelets are very fragile cells and can be greatly affected by drugs. Aspirin, alcohol, and some antibiotics can "hurt" platelets, so they don't work properly. This means that even though a person may have a normal number of platelets in their blood, they will bleed excessively after an injury because their platelets aren't doing their job. Even some foods like fish, garlic, and onion, in addition to making your breath stinky, can affect the quality of your platelets if you eat too much of them.

by Clark, Leslie A. last modified Feb 23, 2012 10:41 AM