(i) Arteries :

These are blood vessels which carry blood away from the heart to different parts of the body. Wall of the arteries The wall of the arteries is made up of three layers,

 outer, (made of connective tissue and elastic fibres),

 middle (made of thick muscular tissue and elastic fibres) and

 Inner, endothelium. Vasoconstriction The contraction of the circular (smooth muscles) of arteries and arterioles is under the control of nervous and endocrine systems.

When stimulated the muscle contracts, constricting the arterioles (vasoconstriction) and thus reducing the flow of blood in them. Vasodilation When the muscles are relaxed the arterioles are dilated (vasodilation) more blood flows in them. Arterioles The arterioles themselves divide repeatedly until they form a dense network of microscopic vessels, called capillaries.

Atherosclerosis.

(G. athere = porridge; skeleoris = hardening): It is coexisting atheroma and arteriosclerosis; Atheroma is deposition of hard yellow plaque of lipoid material in the inner most layer of the arteries, which may be due to high level of cholesterol in the blood. Arteriosclerosis is a degenerative arterial change associated with advancing age. Primarily a thickening of middle layer of arteries, and usually associated with some degree of atheroma. Effects. Atherosclerosis causes narrowing and hardening of arteries. This increases the risk of formation of thrombus,and if thrombus is formed in the brain or heart it is fatal. (Atherosclerosis is a major condition leading to heart attack.)