There are four parts of blood, red and white blood cells, plasma, and platelets.
Red Blood Cells
Red blood cells carry oxygen throughout the body. Red blood cells are the most numerous blood cells in the body. They are always being produced in bone marrow. Red blood cells look like disks or donuts. Red blood cells live about 120 days.
White Blood Cells
White blood cells fight infections in the body. Some cells carry antibodies that destroy foreign cells and diseases. Others hurt invaders and germs. If a infection fights back the white blood cell's numbers will increase. White blood cells do not live long, they live only a few days to a few weeks.
(white blood cells are shown in the box.)
Platelets
Platelets help blood clot or heal at the sight of a wound. The clot begins to form when the blood is exposed to air. White blood cells and platelets make up less than 1% of your blood. Platelets are cell fragments (shown in yellow).
Plasma
Plasma is a yellow/clear liquid that is 90% water. The major function of plasma is to transport blood cells and platelets through veins and arteries. It carries nutrients to cells and removes their waste. It also carries minerals such as calcium, sodium, and potassium, throughout the body.
(Plasma is the yellow liquid.)
Types of Blood Vessels
Your body contains over 100,000 miles of blood vessels. There are three types of blood vessels: arteries, capillaries, and veins. Arteries are the blood vessels that carry blood away from the heart to all parts of the body. They are tough on the outside, but smooth on the inside. Capillaries are the smallest blood vessels which provide body cells with blood and connect arteries with veins. Capillaries are very thin. They are so thin that when blood passes through the cells have to go through single file. Capillaries help release excess heat. The heat is delivered to the capillaries, which is then rapidly release into the tissue. A result of this is that your skin takes on a red appearance. Arteries pass the blood to capillaries and capillaries pass it onto veins. Veins are blood vessels that carry blood from all parts of the body back to the heart.