The Circulatory System

Blood vessels, arteries and veins, circulate blood to our entire body. In the figure to the left, arteries are colored red, indicating they carry oxygenated blood. Veins are colored blue to showing that the cells they carry are oxygen poor.

The heart pumps blood to the lungs where oxygen is absorbed. This turns the blood from blue to bright red.


The blood then returns to the heart where it is distributed to the rest of the body via the arteries. Used blood returns to the heart via the veins.

As the arteries go out from the heart towards our arms, legs, internal organs and skin, they branch into finer and finer tubes. By the time the arteries reach the fingers they have become so small that they are called arterioles. In the finger tips and tissues these branch further into very tiny blood vessels called capillaries.

Millions of tiny red cells are busy carrying oxygen to all the tissues of the body. These red cells are so small that you could line up 350 of them on the head of a pin!

When you accidentally cut your finger, you are actually cutting thousands of capillaries. The capillaries are so small that the red blood cells have to line up one by one in a traffic jam just to get through!



Normal red cells are rubbery, and must distort to get through the capillaries. If the tissues that the red cells are near are starved for oxygen, they absorb more oxygen from the red cell. If the tissues aren't "hungry" for oxygen, then they don't use all the oxygen that the red cell is carrying.

Sickle cell anemia is a painful disease caused by red blood cells that become malformed into bent and distorted shapes. These "sickled" cells don't have the ability to flex like the normal cells as they travel through the capillaries.

When the red cells sickle, the tissues can't get oxygen and get even hungrier, This actually causes more sickling to happen and things gets worse and worse.

A person in a sickle cell crisis may have a fever, they can even have a stroke if they are not treated promptly. They should see a doctor immediately, but should be taken by someone else since exercise makes a sickle cell crisis worse. The doctor will give them oxygen and medication and make them lie down until the crisis is over. There is a test you can do to see if you or someone you know has the tendency to have a sickle cell crisis. This web site was designed to help understand sickle cell disease.