Wikijunior:Human Body/CirculatorySystem

The job of the circulatory system is to provide oxygen and nutrients to all the parts of the body. Waste products like carbon dioxide are carried away so they can leave the body.

What does the circulatory system look like?
The heart is about the size of a fist. The blood vessels are long, thin tubes that carry blood. There are thousands of blood vessels. If you stretched them all out, one person's blood vessels would cover over 60,000 miles (96,560 kilometers)!

What are the parts of the circulatory system?
The circulatory system includes the heart, blood, and blood vessels. Blood vessels are the tubes that carry blood all over the body. Arteries, veins, and capillaries are all different kinds of blood vessels. It also includes the lymphatic system, which comprises a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally towards the heart.

What is the function of the circulatory system?
The circulatory system has four main functions:


 * 1) Transport of nutrients, oxygen, and hormones to cells throughout the body and removal of metabolic wastes (carbon dioxide, nitrogenous wastes).
 * 2) Protection of the body by white blood cells, antibodies, and complement proteins that circulate in the blood and defend the body against foreign microbes and toxins.
 * 3) Clotting mechanisms are also present that protect the body from blood loss after injuries.
 * 4) Regulation of body temperature, fluid pH, and water content of cells.

How does the circulatory system interact with other parts of the body?
All the parts of your body need a supply of blood. This red sticky liquid carries food and oxygen to every part of your body. The heart and its network of blood vessels are called the circulatory system. The artery that carries oxygen-rich blood cells away from your heart is called the aorta and the vein that takes it back again is called the vena cava.

Your heart is made of two pumps. The left pump or left ventricle receives blood filled with oxygen from your lungs and sends it around your body. The right pump or right ventricle gets blood from the body and sends it to the lungs to pick up some more oxygen. The inside walls of your heart squeeze regularly to pump the blood around your body. This is called the heart beat.

In your body you have one way valves in your main veins and in your heart. They make your blood flow the right way around your body. If your blood tries to go the other way the valve will snap shut so your blood can’t get through.

Your arteries have thick walls to cope with the high pressure of the blood from your heart. They branch out to make a network of very small blood vessels called capillaries. Many substances can pass through the walls. Not only oxygen passes from blood to nearby cells but carbon dioxide and other waste matter passes into the capillary to be carried away.

Your blood is made up of four things. About half of your blood is made up of plasma, about 40% is made of red blood cells which carry oxygen and a very little bit is made of white blood cells and platelets. Plasma is a pale yellow liquid. It is made up of sugars, salts and other body chemicals.

Red blood cells are donut shaped which carries oxygen around the body. The blood gets its red colour from these cells. Hemoglobin I your red blood cells are the red I it. The amount of oxygen in the blood cell determines how red the cell is. White blood cells go around the body looking for germs to eat.

They are like jelly filled bags and can change their shape to get out of the blood stream and go into other body parts. Platelets help you clot your blood if you prick yourself or get a bruise. They are made in bone marrow and are round or oval in shape.

In models or diagrams oxygen rich blood is shown red and veins carrying old blood are shown in blue when it is actually a darker red.

How can you keep your circulatory system healthy?
Regular exercise and eating healthy food helps keep the heart healthy. Sometimes, the circulatory system has problems like high blood pressure or high cholesterol. Diet, exercise, and sometimes medication can help those problems.