Cardiovascular System Histology PDF

cardiovascular system histology Created @November 26, 2024 10:54 AM Tags workshop notes overview general objective: to know and recognise the histological structure of blood vessels and the heart, and then...

cardiovascular system histology Created @November 26, 2024 10:54 AM Tags workshop notes overview general objective: to know and recognise the histological structure of blood vessels and the heart, and then to relate vascular structure to its function generally, and specifically in organs specific objectives: to know the architecture of vascular structures to distinguish the tunica intima, media and adventitia in arteries and veins to describe the types of capillaries and sinusoids and their features the vascular system: the cardiovascular system is comprised of the following structures: heart → pumps blood through the system arteries → vessels that deliver blood to tissues capillaries → networks of small vessels that perfuse tissues veins → vessels that return blood to the heart blood vessels are found in all tissues of the body with very few exceptions, such as epithelia and cartilage cardiovascular system aorta: cardiovascular system histology 1  blood vessels have walls composed of three layers (or tunics): tunica intima → endothelium and loose connective tissue tunica media → concentric layers of varying amounts of elastic fibres, smooth muscle cells, and collagen fibres, as this is typically the thickest layer in arteries tunic adventitia → outer layer of connective tissue, this is typically the thickest layer in veins viewing the wall of the aorta, can see it is an elastic artery; and the tunica media is the thickest layer, containing prominent elastic tissue identify: tunica intima → innermost layer; consists of endothelium, subendothelial connective tissue, and internal elastic lamina tunica media → thick middle layer; contains elastic laminae, smooth muscle cells, and some collagen elastic laminae → sheets of elastin in the tunica media; allow the aorta to stretch and recoil smooth muscle cells → found in the tunica media; synthesize elastin, collagen, and extracellular matrix collagen → provides tensile strength; found in all layers but mainly in the media and adventitia cardiovascular system histology 2  tunica adventitia → outermost layer; composed of connective tissue, collagen, elastic fibres, and cells like fibroblasts vasa vasorum → small blood vessels in the adventitia and outer media; supply nutrients to the vessel wall adipose tissue → found in the adventitia; provides cushioning and energy storage nervi vasorum → nerve fibres in the adventitia; regulate vascular tone lymphatics (i.e. thoracic duct) → present in the adventitia to aid fluid drainage need for abundance of elastic laminae → essential for the aorta's ability to accommodate high-pressure blood flow during systole and recoil during diastole, maintaining continuous blood circulation vena cava: the superior and inferior vena cavae are large veins, as the wall is thinner and has less distinct layers than the aorta identify: tunica intima → thin inner layer with endothelium and sparse connective tissue tunica media → thin middle layer with fewer circularly arranged cardiovascular system histology 3  smooth muscle fibres compared to arteries tunica adventitia → thick outer layer, dominant in the vena cava; contains collagen, elastic fibres, and longitudinal smooth muscle bundles vasa vasorum → present in the adventitia; supplies nutrients to the vessel wall longitudinal smooth muscle → prominent in the adventitia; aids in venous return under low pressure note: the intimal, medial and adventitial layers are present in veins but less clearly demarcated than in arteries compare differences: smooth muscle fibre distribution in aorta → smooth muscle fibres are circularly arranged in the tunica media, mixed with elastic laminae for flexibility and strength smooth muscle fibre distribution in vena cava → fewer circular fibres in the media, with prominent longitudinal smooth muscle fibres in the adventitia for support and venous return function of aorta → conducts oxygenated blood from the heart under high pressure to systemic circulation relation to smooth muscle fibre distribution: circular smooth muscle in the media helps maintain cardiovascular system histology 4  vessel tone and support elastic recoil function of vena cava → returns deoxygenated blood to the heart under low pressure relation to smooth muscle fibre distribution: longitudinal smooth muscle in the adventitia provides structural support and assists in venous blood flow neurovascular bundle: muscular arteries distribute blood to specific organs in response to functional needs → and most of the named arteries in the body are muscular arteries → tunica media is composed of concentric layers of smooth muscle cells → the contraction and relaxation of these muscle cells regulate blood flow by changing the size of the lumen a prominent internal elastic lamina separates the tunica intima from the media; and in larger arteries, an external elastic lamina also separates the tunica media from the adventitia identify: tunica intima → inner layer of vessels with endothelium and subendothelial connective tissue tunica media → middle layer with smooth muscle fibres and elastic components cardiovascular system histology 5  tunica adventitia → outer connective tissue layer with collagen, elastic fibres, and vasa vasorum internal elastic lamina → elastic layer between intima and media; prominent in muscular arteries external elastic lamina (more diffuse) → diffuse elastic layer between media and adventitia; more visible in muscular arteries elastic artery structure → thick tunica media with abundant elastic laminae and smooth muscle; less distinct internal and external elastic laminae muscular artery structure → tunica media dominated by smooth muscle, prominent internal and external elastic laminae compare structural differences: elastic arteries → more elastic fibres in the media for flexibility muscular arteries → more smooth muscle for precise control of blood flow function of elastic artery → dampens pressure changes from the heart to ensure steady blood flow relevance of structural differences: elastic laminae allow stretch and recoil function of muscular artery → regulates blood flow to specific organs cardiovascular system histology 6  relevance of structural differences: smooth muscle allows for vasoconstriction and vasodilation gallbladder: arterioles regulate the flow of blood into capillary beds, and they provide the majority of the resistance to blood flow in the body the tunic media is reduced to one or two concentric layers of smooth muscle cells the contraction of the smooth muscle cells constricts the lumen of the arteriole, reducing the flow of blood, and increasing vascular resistance capillaries are the smallest blood vessels (less than 10 µm in diameter), and the thin wall of capillaries is composed of endothelial cells supported by a basement membrane identify: arteries → large blood vessels supplying oxygenated blood to the gallbladder arteriole → smaller branches of arteries, with a thin layer of smooth muscle for controlling blood flow veins → vessels that carry deoxygenated blood away from the gallbladder venules → small veins that collect blood from capillaries, with thin walls cardiovascular system histology 7  lymphatics → tiny vessels responsible for draining excess interstitial fluid and waste products valves (if present) → found in veins and lymphatics to prevent backflow compare distribution of tunicae in: arteries → thick tunica media with smooth muscle and elastic fibres for high-pressure blood flow arteriole → thin tunica media with smooth muscle for regulation of blood flow veins → thin tunica media, thicker tunica adventitia for lower-pressure blood flow venules → very thin tunica media and adventitia, designed for low- pressure blood return lymphatics → thin walls, often without a clear tunica media; valves prevent fluid backflow valves (if present) → present in veins and lymphatics, consisting of a fold of the tunica intima to ensure unidirectional flow cardiovascular system histology 8