(BQ) Part 2 book "Textbook of pathology" presentation of content: The blood vessels and lymphatics, the heart, the respiratory system, the oral cavity and salivary glands, the gastrointestinal tract, the kidney and lower urinary tract, the male reproductive system and prostate, the female genital tract, the endocrine system, the musculoskeletal system,.and other contents. | 390 Section III SYSTEMIC PATHOLOGY The Blood Vessels and Lymphatics Chapter 15 The blood vessels are closed circuits for the transport of blood from the left heart to the metabolising cells, and then back to the right heart. The blood containing oxygen, nutrients and metabolites is routed through arteries, arterioles, capillaries, venules and veins. These blood vessels differ from each other in their structure and function. SECTION III ARTERIES NORMAL STRUCTURE Depending upon the calibre and certain histologic features, arteries are divided into 3 types: large (elastic) arteries, medium-sized (muscular) arteries and the smallest arterioles. Systemic Pathology Histologically, all the arteries of the body have 3 layers in their walls: the tunica intima, the tunica media and the tunica adventitia. These layers progressively decrease with diminution in the size of the vessels. 1. Tunica intima. This is the inner coat of the artery. It is composed of the lining endothelium, subendothelial connective tissue and bounded externally by internal elastic lamina. Endothelium is a layer of flattened cells adjacent to the flowing blood. Narrow junctions exist between the adjoining endothelial cells through which certain materials pass. The integrity of the endothelial layer is of paramount importance in maintenance of vascular functions since damage to it is the most important event in the initiation of thrombus formation at the site. Subendothelial tissue consists of loose meshwork of connective tissue that includes myointimal cells, collagen, proteoglycans, elastin and matrix glycoproteins. Internal elastic lamina is a layer of elastic fibres having minute fenestrations. 2. Tunica media. Tunica media is the middle coat of the arterial wall, bounded internally by internal elastic lamina and externally by external elastic lamina. This layer is the thickest and consists mainly of smooth muscle cells and elastic fibres. The external elastic lamina consisting of condensed .
