Histology Of Blood Vessels Notes
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Circulatory system Overview
-there are two separate but connected components: cardiovascular system, transports blood around the body lymphatic vascular system , collects excess extracellular fluid and returns it to the cardiovascular system
-cardiovascular system: made of a heart which pumps blood and blood vessels which transport it around the body.
-Heart pumps blood at high pressure- transmitted through large elastic arteries that carry blood away from the heart- smaller muscular arteries- thin walled- capillary beds- drained by venules
-the cardiovascular system is divided into the pulmonary circulationdeoxgynated blood pumped from the right side of the heart to the lungs where it is oxygenated and returned to the left side of the heart. This circulation is low resistance and low pressure Systemic circulation: oxygenated blood pumped by the left side of the heart and returns to the right after completing a circuit- high resitance and high arterial pressure
-portal system: Blood is carried from one site to another without directly involving the heart: hepatic portal system, hypothalamic pituitary portal system Blood vessels Functions:
-O2, co2 delivery
-Delivery of hormonal signals
-control blood flow Structure of vessels
-all arteries are composed on three concentric layers i) Tunica intima:
-continuous sheet of flattened simple squamous endothelial cells that lines the lumen - provides a smooth surface for flow
-Supporting this is sub endothelial connective tissue- loose connective tissue
-lined with internal elastic lamina (thin band of elastic fibres)
d) initiation of coagulation: when endothelial cells are damaged they release von Willebrand factor-these attach to the underlying collagen. Glycoprotein 1b receptors on platelet membrane bind to vWf, other glycoprotein receptors bind to collagen. This leads to platelet adhesion, stimulation of the glycoprotein receptors triggers the platelet activation pathway- coagulation plug Von willebrand's disease: genetic disorder- individual is inacapable of producing a normal amount of Von Willebrand's factor, problems with blood clotting- bruising easily, longer bleeding time, excessive bleeding from tooth extraction/ excessive menstrual bleeding and bloody mucous membranes e) angiogenesis: occurs in response to repair damaged vessels, or form new vessels in repairing injuries or subsequent to menstruation. New vessels arise from existing vessels due to interaction of signalling molecules angiopoietins 1 + 2 with specific receptors on endothelial cells that induce mitotic activity in pre existing endothelial cells and recruit smooth muscle cells to form the tunica media f) synthesis of growth factors: colony stimulating factors- these induce cells of the blood lineage to undergo mitosis and produce various blood cells, growth inhibitors oxidation of lipoproteins: endothelial cells also oxidise high cholesterol containing low density lipoproteins so that the oxidised by product can be phagocytosed by macrophages ii)Tunica media: thickest of three layers, circularly arranged smooth muscle cells, replaced by elastic in elastic arteries
-interspersed within the layers are elastic fibres and type 3 collagen. The collagen provides resistance and if not made properly leads to aneurysm. Ehlers Danlos syndrome 4: autosomal dominant defect in type 3 collagenblood vessels are fragile and prone to rupture
-external elastic lamina iii) Tunica adventitia: outermost layer of the vessel wall- fibroelastic connective tissue arranged longitudinally with adipose tissue. There is mostly fibroblasts, type 1 collagen fibres, elastic fibres, adipose tissues. Larger vessels there is also the vaso vasorum; small blood vessels that supply the tunica adventitia and the tunica media -prevalent in veins as venous blood contains less oxygen and nutrients ARTERIES
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