Types of blood vessels: Veins Arteries Common structures Tunica adventitia Tunica media Tunica intima Lumen

 Atherosclerosis is a type of arteriosclerosis or hardening of the arteries.  denotes the formation of fibrofatty lesions in the intimal lining of the large and medium-sized arteries, such as the aorta and its branches evident for 20 to 40 years or longer.

 Nonmodefiable risk factors :- 1. increasing age, 2. family history of premature CHD. 3. male sex.  Modefiable risk factors :- 1. cigarette smoking. 2. Obesity. 3. Hypertension. 4. high blood cholesterol levels. 5. Diabetes mellitus.

 Other risk factors :- 1. C-reactive protein (CRP). 2. serum homocysteine. 3. serum lipoprotein (a). 4. infectious agents. 5. endothelial dysfunction.

 The lesions associated with atherosclerosis are of three types: 1. the fatty streak. 2. the fibrous atheromatous plaque. 3. the complicated lesion.  The latter two are responsible for the clinically significant manifestations of the disease.

 Fatty streaks are thin, flat, yellow intimal discolorations that progressively enlarge by becoming thicker and slightly elevated as they grow in length.  Histologically, they consist of macrophages and smooth muscle cells that have become distended with lipid to form foam cells.

 The fibrous atheromatous plaque is the basic lesion of clinical atherosclerosis. It is characterized by the accumulation of intracellular and extracellular lipids, proliferation of vascular smooth muscle cells, and formation of scar tissue.  The lesions begin as a gray to pearly white elevated thickening of the vessel intima with a core of extracellular lipid (mainly cholesterol) covered by a fibrous cap of connective tissue and smooth muscle.  As the lesions increase in size, they bulg on the lumen of the artery and eventually may occlude the vessel or predispose to thrombus formation, causing a reduction of blood flow.

1. Thrombosis is the most important complication of atherosclerosis. 2. Hemorrhage. 3. Ulceration. 4. scar tissue deposits. 5. Aneurysms. 6. Infarction.

 Hyperlipidemia, particularly LDL is the main cause of atherosclerosis.