What are the three types of capillaries?
Capillaries are used to transport gases, nutrients and waste products into the blood. They are normally about 1 mm long and 3-10 micrometers in diameter. There is not one cell in the entire body that is more than three or four cells away from a capillary. This is very important because every cell needs to be able to absorb oxygen and nutrients and get rid of metabolic wastes. In a mammal there are three types of capillaries: continuous, fenestrated and sinusoidal. Continuous capillaries are made up of an endothelium that is 0.2-0.4 micrometers thick that has a basement membrane. The endothelium cells are separated by clefts. Each cell has many vesicles that can be used for transporting substances in and out of the capillary. The transfer of products through the membrane is done either through or between the endothelium cells. Lipid soluble substances can be transferred through the cells while water and ions have to be transported in between cells in the clefts. The vesicles are still b
