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Cholesterol circulates in the bloodstream contained in molecules called lipoproteins. The two most common forms are high-density lipoproteins ("good cholesterol", which reduces atherosclerosis) and low-density lipoproteins ("bad cholesterol", which increases atherosclerosis).
Cholesterol circulates in the bloodstream contained in molecules called lipoproteins. The two most common forms are high-density lipoproteins ("good cholesterol", which reduces atherosclerosis) and low-density lipoproteins ("bad cholesterol", which increases atherosclerosis).
The wall of an artery is made of up three layers - the innermost ''tunica intima'', the muscular ''tunica media'', and the outer ''tunica adventitia''. Atherosclerosis affects the middle of these layers. It is initiated by injury to the wall of an artery. In most cases, this is due to [[hypertension|high blood pressure]]. This increases the permeability of the tunica intima, allowing the passage of lipoproteins and white blood cells called [[macrophage|macrophages]] into the tunica media. Macrophages are responsible for engulfing debris through the process of phagocytosis, which allows its removal from the body. When they phagocytose lipoproteins, they trap the cholesterol in the tunica media, and become ''foam cells''.
The wall of an artery is made of up three layers - the innermost ''tunica intima'', the muscular ''tunica media'', and the outer ''tunica adventitia''. Atherosclerosis affects the inner two layers. It is initiated by injury to the wall of an artery. In most cases, this is due to [[hypertension|high blood pressure]]. This increases the permeability of the tunica intima, allowing the passage of lipoproteins and white blood cells called [[macrophage|macrophages]] to the space between the tunica intima and media. Macrophages are responsible for engulfing debris through the process of phagocytosis, which allows its removal from the body. When they phagocytose lipoproteins, they trap the cholesterol in the artery wall, and become ''foam cells''.
The macrophages release chemicals known as cytokines, which cause an inflammatory response. This results in the migration of smooth muscle cells, or myofibroblast, which lays a fibrous outer shell around the foam cells. The foams cells eventually die, resulting in the trapping of cholesterol and cellular debris inside the shell. The shell and its lipid core is known as a plaque, or atheroma. Occasionally cholesterol may crystallise within the plaque, forming cholesterol clefts.
==References==
==References==
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