Zanzibar Education Panel

Blood is a fluid comprising red blood cells, several types of white blood cells and small fragments of blood cells called platelets, which are involved in the blood clotting process. These cells are all suspended in yellowish or straw-coloured liquid called plasma. The red blood cells contain a protein called haemoglobin, which is red in colour and contains a lot of iron. The haemoglobin picks up oxygen as the blood passes through the lungs and distributes it around the body. There are five types of blood vessels:

1       Artery (plural arteries) is subjected to higher blood pressure than any other vessels and the blood flow in them ‘pulses’, meaning that the blood pressure and the rate of blood flow vary with the pumping action of the heart. Arteries have layers of muscular and elastic tissue in their walls, which allows the vessels to expand with the contraction of the heart, and contract again as the heart refills with blood.

2       Arterioles are smaller vessels that distribute the blood into the network of capillaries (capillary beds). They too have layers of muscle in their walls; this is very important, because it controls how much blood goes into the capillaries.

3       Capillaries are the smallest blood vessels in the body, having an internal diameter hardly larger than the diameter of a single red blood cell.

4       Venules collect blood from the capillary networks. The blood pressure in these vessels is low, and they do not pulse.