Arteries

Arteries 1 Blood Pressure indicates the structure of blood vessels High pressure low pressure 2 Classification of Arteries Large, elastic (conducting) arteries: Aorta, Brachiocephalic, Common carotid, Subclavian, Common iliac and pulmonary trunk. Medium sized, muscular arteries : femoral, brachial, radial…… Small sized, arterioles 3 Elastic Arteries 4 Tunica intima  Simple squamous epithelium, made of one layer of endothelial cells. The endothelium rests on a basal lamina  The subendothelial layer of connective tissue consists of a delicate, interlacing network of collagen and elastic fibers.  The internal elastic lamina is indistinct because the innermost elastic lamina of the media blends with adjacent laminae, without clear distinction between them 5 Elastic Arteries …Tunica media Tunica media consists of many fenestrated lamella of elastin. The number of elastic lamella increase with age (35-70). The extracellular matrix is secreted by smooth muscles. A fenestrated external elastic lamina is present; it allow diffusion of nutrient from the adventitia to the media. 6 Elastic Arteries Tunica adventitia It is relatively thin. Composed of loose connective tissue. Contains few scattered smooth muscles. Vasa vasorum are abundant and may extend to the media. 7 H&E Elastic laminae are not easily seen with this stain (H&E) and need special preparative and staining methods for elucidation LM of part of the aortic wall. The intima (TI) abuts the lumen (Left). A thick media (TM) and an outer adventitia (TA) are also shown. Nuclei in the media at this magnification are mostly those of smooth muscle cells. 60×. H&E 8 Look at the next slide where, Gomori aldehyde fuchsin a special preparative and staining methods have been used for elucidation of Elastic fibers 9 60×. Gomori aldehyde fuchsin. special preparative and staining methods for elucidation of elastic fibers 25-year-old tunica media (TM). LM ll of the aorta 10 Another special stain, Verhoff stain A.sh I M A.sh A.sh A A.sh A.sh Transverse section of rat thoracic aorta stained with Verhoff stain. The darker elastic fibers are prominent tunica intima(I), tunica media (M), and tunica adventitia(A). X 400Dr. Shatarat 2019 11 M A.sh A.sh A.sh A.sh A I Perivascular fat A.sh A.sh A.sh A.sh transverse section of the wall of thoracic aorta of rat, stained with orcein stain (×400) showing dark stained elastic fibers and normal tunical layers (tunica intima (I), tunica media (M) and tuica adventitia (A)). scale bar =50 μm. 12 In the next slide you would see a comparison between a section of the aorta taken from a newborn and 25 -year-old You can see that The number of elastic laminae —the dark, wavy bands—increases with age 13 LMs of the wall of the aorta of a newborn 25-year-old A.sh Comparative LMs of the wall of the aorta of a newborn (Left) and 25-year-old (Right). In both vessels, a relatively thin tunica intima (TI) merges with a prominent tunica media (TM). This stain specifically demonstrates elastic tissue, a prominent feature of these arteries. The number of elastic laminae —the dark, wavy bands—increases with age. Vasa vasorum (arrows) occupy loose connective tissue of theDr.adventitia (TA). 60×. Gomori aldehyde fuchsin.14 Shatarat 2019 Clinical correlations The FBN1 gene Responsible for making a protein called fibrillin-1 This protein is transported out of cells into the extracellular matrix In this matrix, molecules of fibrillin-1 attach (bind) to each other and to other proteins to form threadlike filaments called microfibrils. Microfibrils form ELASTIC FIBERS which enable the skin, ligaments, and blood vessels to stretch. Microfibrils also provide support to more rigid tissues such as bones and the tissues that support the nerves, muscles, and lenses of the eyes. 15 16 An aneurysm  is an abnormal localized dilation in the weakened wall of an artery.  An aortic aneurysm occurs when the diameter of part of the aorta increases by 50% or more.  A true aneurysm is a large bulge in the wall that consists of all three tunics.  Rupture may lead to fatal bleeding in only a few minutes.  Atherosclerosis is a major cause of most aortic aneurysms. Read only Infection, inflammation, syphilis, and the genetic connective tissue disorder Marfan syndrome also weaken arterial walls, and chronic hypertension induces susceptibility to aneurysms because elevated arterial pressures place undue stress on vessel walls 17 From a functional stand point, elastic arteries serve primarily as conduction tubes; however, they also facilitate the continuous and uniform movement of blood along the tube Blood flow occurs as follows: The ventricles of the heart pump blood into the elastic arteries during systole (the contraction phase of the cardiac cycle). The pressure generated by contraction of the ventricles moves the blood through the elastic arteries and along the arterial tree. Simultaneously, it also causes the wall of the large elastic arteries to distend The distension is limited by the network of collagenous fibers in the tunica media and tunica adventitia During diastole(there laxation phase of the cardiac cycle when no pressure is generated by the heart ,the recoil of the distended elastic arteries serves to maintain arterial blood pressure and the flow of blood within the vessels Initial elastic recoil forces bloodbothawayfromandbacktowardthehear 18 Muscular Arteries Distributing arteries 19 Muscular Arteries , Tunica intima thinner than in elastic arteries. Sub endothelial CT contains few smooth muscles. Prominent internal elastic lamina, which might be duplicated. Processes from endothelium pass through fenestrae in IEL and form gap junction with smooth muscles in the media. 20 Muscular Arteries Tunica media Tunica media is composed mostly of smooth muscles. Smooth muscles are circularly arranged. The number of layers of smooth muscles is 4-40. Each smooth muscle has a basal lamina. Other components: type III collagen and chondroitin sulfate. External elastic lamina is seen in large muscular arteries. 21 Muscular Arteries, Tunica adventitia Tunica adventitia contains elastic and collagen fibres. Ground substance contains dermatan sulfate and heparan sulfate. Occasional longitudinal smooth muscles are seen. Contains vasa vasorum and unmyelinated nerve fibres. 22 muscular artery media adventitia INTIMA H& E 23 LM of the wall of a muscular artery. In this partly constricted artery, the lumen (*) caliber is small relative to the muscular wall thickness. A prominent internal elastic lamina (IEL) looks corrugated. Several layers of circular smooth muscle occupy the media (TM); loose connective tissue, the adventitia (TA). 240×. H&E. 24 Prominent internal elastic lamina LMs of the wall of a muscular artery 320×. Gomori aldehyde fuchsin 25 Arterioles 26 Arterioles Their diameter is < 0.1 mm. They control the peripheral resistance and regulate flow to capillaries. IEL may be present. Tunica media is 1-3 layers of smooth muscles. No EEL. Tunica adventitia is small. 27 As noted earlier, vascular resistance is the opposition to blood flow due to friction between blood and the walls of blood vessels. Vascular resistance depends on (1) Size of the blood vessel lumen (2) Blood viscosity (3) Total blood vessel length.  Size of the lumen. The smaller the lumen of a blood vessel, the greater its resistance to blood flow. The smaller the diameter of the blood vessel, the greater the resistance it offers to blood flow. For example, if the diameter of a blood vessel decreases by one-half, its resistance to blood flow increases 16 times. Vasoconstriction narrows the lumen, and vasodilation widens it. Normally, moment-to-moment fluctuations in blood flow through a given tissue are due to vasoconstriction and vasodilation of the tissue’s arterioles. As arterioles dilate, resistance decreases, and blood pressure falls. As arterioles constrict, resistance increases, and blood pressure rises. 28 LM of an arteriole in transverse section. Tightly arranged smooth muscle cells (SM) are oriented more or less circularly relative to the lumen (*). Their contraction causes the internal elastic lamina (IEL) to appear corrugated and endothelial cell (En) nuclei to bulge into the lumen. The adventitia (TA) contains connective tissue cells (mostly fibroblasts) and collagen fibers. 720×. H&E. 29 Metarterioles They directly supply capillary beds. The smooth muscle layer in the media is incomplete. Each smooth muscle encircles the endothelium. They act as sphincters. 30