HISTOLOGY OF BLOOD VESSELS DR. ABDUL WAHEED ANSARI CHAIRPERSON & PROF. ANATOMY RAK COLLEGE OF MEDICAL SCIENCES RAK MEDICAL &HEALTH SCIENCES UNIVERSITY. U.A.E

Dissection of aorta in Marfan’s syndrome This aortic dissection occurred just above the aortic root in a patient with Marfan's syndrome. The tear extends across the aorta. Hemopericardium with tamponade occurred within minutes of this event. .

Coronary atherosclerosis. The coronary at the left is narrowed by 60 to 70%. The coronary at the right is even worse with evidence for previous thrombosis with organization of the thrombus and recanalization such that there are three small lumens remaining, one of which contains additional recent thrombus

A normal coronary artery cross section This is a normal coronary artery. The lumen is large, without any narrowing by atheromatous plaque. The muscular arterial wall is of normal proportion.

This is an example of an atherosclerotic aneurysm of the aorta in which a large "bulge" appears just above the aortic bifurcation. Such aneurysms are prone to rupture when they reach about 6 to 7 cm in size. They may be felt on physical examination as a pulsatile mass in the abdomen. Most such aneurysms are conveniently located below the renal arteries.

Blood vessels are usually composed of three layers The tunica intima, tunica media, and tunica adventitia. The tunica intima consists of a layer of endothelial cells lining the lumen of the vessel, as well as a subendothelial layer made up of mostly loose connective tissue. Often, the internal elastic lamina separates the tunica intima from the tunica media. The tunica media is composed chiefly of circumferentially arranged smooth muscle cells. Again, the external elastic lamina often separates the tunica media from the tunica adventitia. Finally, the tunica adventitia is primarily composed of loose connective tissue made up of fibroblasts and associated collagen fibers.

The internal and external elastic laminae separates the tunica media from intima and adventitia

Elastic lamellae are seen in tunica media in aorta ( elastic artery)

Muscular arteries Smooth muscle becomes the predominant constituent of the tunica media. Internal and external elastic laminae are prominent. The tunica intima is thinner than the intima of elastic arteries.

ARTERIOLES The tunica intima consists of a continuous endothelium and a very thin subendothelial layer. In addition, a thin, fenestrated internal elastic lamina is present in larger arterioles but absent in terminal arterioles. Generally, the tunica media consists of 2 layers of smooth muscle cells. But in the smallest arterioles there is a single layer. The tunica adventitia is a thin sheath of connective tissue.

Capillaries average from 9 to 12 µ m in diameter The wall consists of extremely attenuated endothelial cells. In cross section, the lumen of small capillaries may be encircled by a single endothelial cell, while larger capillaries may be made up of portions of 2 or 3 cells. No smooth muscle is present. There are 3 types of capillaries: continuous, fenestrated, and discontinuous. Capillaries and venules are the principal vessels where exchange between the blood vascular space and the interstitium takes place.

Continuous capillaries Those with numerous transport vesicles that are primarily found in skeletal muscles, finger, gonads, and skin. Those with few vesicles that are primarily found in the central nervous system. These capillaries are a constituent of the blood brain barrier. Continuous capillaries are seen here in skeletal muscles.

Fenestrated capillaries In an EM picture of a fenestrated capillary, the fenestrations are visible and allows the blood to leave in to the interstitium. Such capillaries are found in kidney glomeruli, and endocrine glands.

Sinusoidal capillaries or discontinuous capillaries Such type of capillaries have wide diameter. These are found in the liver, spleen, lymph nodes, bone marrow and some endocrine glands.

Veins Have the same 3 layers as arteries, but boundaries are indistinct and elastic components are not as well developed in veins. Histologically, veins are usually collapsed because of the thinner, less elastic walls.

Compare and contrast between an artery and a vein This image shows a cross section of an artery and a vein. Arteries are blood vessels that carry blood from the heart to tissues. Veins are blood vessels that return blood from the tissues to the heart Both arteries and veins are composed of three layers of tissue called tunics. The innermost layer (called the tunica intima, or interna) consists of a single layer of squamous, endothelial cells on top of a thin, elastic basement membrane called the internal elastic lamina. These endothelial cells form a smooth inner surface on the healthy lumen. The middle (usually much thicker) layer is the tunica media, which consists of layered smooth muscle cells along with elastic connective tissue fibers. These smooth muscle cells, which are under the control of the sympathetic nervous system, function to adjust the diameter of the lumen, thereby regulating the flow of blood through the vessel. The third, outermost layer is the tunica adventitia (externa), which is composed primarily of elastin and collagen connective tissue fibers, functions to support and protect blood vessels. Note that the wall of the artery is much thicker than that of the vein, reflecting the need to withstand the higher arterial pressures. Arteries have a thicker tunica media. In histological preparations they more often retain their round profiles when cut in cross section. Veins tend often to look "collapsed" or flattened under the same circumstances. In addition, the tunica media of veins is much thinner than in arteries, and the adventitia is the thickest layer. Blood clot in the lumen Tunica media Lumen Tunica adventitia Tunica intima Blood Wall of the vein

References http://faculty.une.edu/com/abel l/histo/histolab3a.htm http://quizlet.com/8396978/art ery-vein-and-nerve-slide-flash- cards/ http://www.vetmed.vt.edu/educ ation/curriculum/vm8054/Labs/ Lab20/LAB20.HTM http://www.histology.leeds.ac.u k/circulatory/capillaries.php http://www.udel.edu/biology/W ags/histopage/vascularmodeling page/circsystempage/capillaries/ capillaries.html Text book of Human Histology- Inderbir Singh-6th edition ( pages 178-186)