Anatomy of Circulation II: Conduction System and Peripheral Vessels Part 4 PDF

13/03/24 Anatomy of circulation II: conduction system and peripheral vessels: part 4 Learning objective: de ne and explain the histology of the peripheral vascular vessels. The difference bet ween arteries, arterioles and veins. Arteries vs Veins: Arteries are efferent vessels that operate in a high...

13/03/24 Anatomy of circulation II: conduction system and peripheral vessels: part 4 Learning objective: de ne and explain the histology of the peripheral vascular vessels. The difference bet ween arteries, arterioles and veins. Arteries vs Veins: Arteries are efferent vessels that operate in a high-pressure system. Veins are afferent vessels that operate in a low-pressure system. Arteries usually have thicker walls than veins. Walls of blood vessels are composed of 3 layers: 1. Tunica intima ( inner ). 2. Tunica media ( middle ). 3. Tunica adventitia ( outer ). Arteries: There are 3 types of arteries: 1. Elastic. 2. Muscular. 3. Arteriole. Elastic Arteries: Largest arteries found closest to the heart. Examples include the aorta, pulmonary arteries and common carotid. They have highly elastic walls which are able to expand during ventricular contraction. There is also passive recoil during ventricular relaxation. Large lumen relative to their wall thickness. They conduct blood from the heart to the muscular arteries. The tunica intima is relatively thick and is composed of an endothelium that lines the luminal surface of the vessel. There is a subendothelial layer of connective tissue, which consists mostly of collagen and elastic bres. There is also an internal elastic lamina which often blends with elastic bres of the tunica media. The tunica media is the most prominent of the three layers in elastic arteries. Elastic bres allow for shape change, whereas collagen gives tensile strength to the arterial walls. Contraction of smooth muscle is controlled by the ANS. smoghs muscle collagen fibres Elastic fibres The tunica adventitia is made up of loose, irregular connective tissue with collagen bres and scattered broblasts. The bre is often blended into the surrounding tissues and stabilises the position of the vessel. Vasa vasorum supply oxygen and nutrients to the outer layers. Muscular Arteries: These help regulate blood ow to organs and part of the body by contraction and relaxation of smooth muscle in their walls. Examples include femoral, brachial and superior mesenteric. Very in size and adapt in response to functional demands. The lumen is small in comparison to the arterial wall thickness. Tunica media is the thickest layer. The tunica media is dominated by smooth muscle cells which are arranged into circular layers. There are variable numbers of elastic and collagen bres and the occasional broblast. In this layer there is an external elastic lamina. The tunica intima has a prominent internal elastic lamina. The tunica adventitia is loose collective tissue that contains collagen and elastic bres that blend with the surrounding connective tissue. Arterioles: Smallest arteries. Small resistance vessels that mainly regulate systemic blood pressure. Can undergo vasoconstriction or vasodilation in response to neural and non-neural stimuli. Arterioles walls are thick relative to the lumen. The tunica intima has attened endothelial cells resting on basal lamina. Internal elastic lamina is prominent in larger arterioles but extremely thin or absent in the smaller ones. The tunica media is 1-2 layers of circularly arranged smooth muscle cells. Smooth muscle action controls systemic blood pressure. Capillaries: These are an intermediate complex net work bet ween arteries and veins. There is no tunica media or adventitia. Single layer of endothelium attached to the underlying basement membrane with scattered pericytes. continuous fenestrated sinusoidal Veins: There are 3 types of veins with thin walls relative to their arterial counterparts due to being in a low pressure system. The walls typically have more collagen, which imparts great tensile strength, than elastic bres. Adventitia is quite prominent with connective tissue to help support weaker veins. Low intraluminal pressure means valves are needed to prevent back ow. Valves: Venous system must retain blood to the heart, often against gravity. Valves preventing back ow of blood. Contraction of the thinner smooth muscle in the walls of the veins. Contraction of external skeletal muscle, compressing veins. Venules: Valve lea ets project into the lumen. Endothelium of valve is continuous with the endothelium of the venule. The tunica media is indistinct with 1 or 2 layers of circularly arranged smooth muscle cells. The tunica adventitia is prominent and made of connective tissue. Muscular ( medium ) veins: These are commonly found in the muscular arteries. Many contain valves. The tunica intima is a thin layer consisting of an endothelial layer and supporting tissue. The tunica media contains small bundles of circularly arranged smooth muscle cells and also collagen bres. The tunica adventitia is prominent with large amount of collagen. Large veins: Large capacity vessels that return blood under low pressure to the heart. The tunica intima has an endothelial layer as well as broelastic tissue. The tunica media has a few layers of smooth muscle. The tunica adventitia is the thickest layer, containing collagen and longitudinally arranged smooth muscle bres. Vasa vasorum supplies the outer layers with blood.