2.5 - Structure and Functions of Arteries, Capillaries and Veins


The Structure and Function of Arteries, Capillaries and Veins

Higher Human BIology 2.5


Blood circulates from the heart through the arteries, to the capillaries, then the veins and back to the heart. 

There is a decrease in pressure as blood moves away from the heart.

Blood Vessels

The lumen of each blood vessel has a thin layer of epithelial cells (endothelium). The blood vessel wall around the endothelium differs between vessels. 


    • carry blood away from the heart at high pressures
    • have thick walls and a narrow lumen 
    • have an outer layer of connective tissue
    • have a middle layer containing smooth muscle

The elastic fibres allow the artery wall to pulsate. The smooth muscle in the walls of arterioles can contract (vasoconstriction) and relax (vasodilation), depending on what the body needs.

Vasoconstriction is the contraction of the smooth muscle in the artery and decreases the diameter of the lumen. It decreases the blood flow into capillaries.

Vasodilation is the relaxation of smooth muscle in the artery and increases the diameter of the…


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