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Lecture 7

Lecture 7-Blood Vessels.docx

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University of Toronto Scarborough
Biological Sciences
Stefan Rusyniak

Lecture 7-Blood Vessels Circulatory System - A closed circuit (mostly) where you have blood flowing by the heart into arteries, passing through capillaries Blood Vascular System 1. Pulmonary Circulation-capillaries pump blood to lungs 2. Coronary Circulation-pump blood to heart (lots of capillaries in cardiac myocytes) 3. Systemic Circulation-through system; come back through vena cava - Blood vessels is the pathway to which blood, oxygen, nutrients, and waste collect - Helps maintain temperature (muscles generate heat = released into vascular system = blood travels to surface of skin = to remove as much heat as possible = to cool down core = thermoregulation) - Distribution of hormones and immune system - Structure of blood vessels : artery, vein, capillary depends on what it has to deal with Arteries - Deal with higher blood pressure (closer to the heart arteries = has to deal with cardiac output of blood being pumped out; heart contracts and relaxes so doesn’t deal with high pressure all the time); release of pulsitle flow - So need to be able to deal with constant change of pressure; arteries can smooth pressure out because arteries get thinner (so want lower pressure to prevent rupturing; want a constant stream rather than on/off flow) - Not a function of veins - Walls needs more muscle and elasticity because it needs to be able to expand when pressure is high and recoil; allows us to smooth out flow (need to have smooth muscle and elasticity) - One of the ways that smooth muscle can be activated to contract is pressure and pull against it = contracts back Veins - Vessels that return blood to heart (not all is deoxygenated because pulmonary veins are rich in oxygen) - Return blood to heart after passing through capillary beds - Blood is flowing against gravity = need valves that prevents backflow and they themselves will have a pumping action around them controlled by the muscle (e.g. legs) contraction = expands sideways and thickens a little bit = compresses veins which creates pressure pushing blood forward - Structure of veins (walls) is thinner than arteries because they need to be able to collapse and compressed to allow blood flow = goes towards heart due to valves - Blood reservoir because blood flows at slow right about 70% of blood in veins (larger lumen than artery); thinner wall General Organization 1. Tunica intima = innermost layer - Sub endotheilia CT = thin (might not see it); becomes thicker with age- Internal elastic membrane (wavy layer of material; elastin in blood vessels tend to be contained in this continuous sheet of elastin = continuous membrane that lines the interior of blood vessel; has pores in it that will allow diffusion) - Dark line = border b/w T.intima and (smooth muscle; thickened arteries and think veins) - External elastic membrane (not as continuous as IEM); connective tissue underneath it which is relatively dense which will connect blood vessel to other vessels or other organs - Innermost part of is endothelium (squamous cell = fairly inactive = most part is true) - One of the main functions in blood vessel is to act as a boundary b/w components in blood stream and underlying tissue o Endothelium is non-thrombogenic = resists the formation of blood clots; important because platelets activated by contact with collagen; the moment you have damage to endothelium, blood clotting begins = begins process of healing o Epithelia cells have ability to allow transport and diffusion of oxygen and nutrients to feed tissue of endothelium o Pores in IEM to allow diffusion of nutrients to reach muscle cell o Endothelial activation = happens when there is actual damage; changes function completely (pro thrombogenic); release factors that increase clotting; produces adhesive molecules and molecules on surface that allows WBCs to stick to ot; produce cytokins = signalling molecules that will direct WBCs to damaged area; produce signalling molecules hat will cause muscle constriction (muscle in will contract) causes lumen in blood vessels to become smaller so prevent excessive bleeding - Sub-endothelia CT o Fibroblasts; but main cell type is smooth muscle (have divided within and then travel across pores of IEM and into sub-endothelial CT) o Cholesterol accumulates in in SECT. initially, macrophages will internalize cholesterol and store it but macrophage will look; eventually smooth muscle fibres will accumulate foam cells as well; eventually calcium will be deposited as well = streaks within walls of arteries; tend to make it more stiff and rigid preventing arteries to be as expansive and elastic as before = hardening of blood vessels = high blood pressure (lumen size decreases which increase vascular resistance = atherosclerosis) o Over time we accumulate endothelia tissue (more fibres get build up); Tunica intima grows in size = lumen size decreases = increases blood pressure (tends to generate more vascular resistance on surface of endothelium = small damage to it which might cause some blood clots = attached to sides of blood vessels which will then detach to circulate and lodge itself in some blood vessel and so blood stops flowing to that part; easily broken up via enzymes but when we have a larger blood clot that travels to wrong place = heart attack, stroke; tunica intima because CT comes thicker with age and lumen becomes smaller = increases with age (more at risk) - IEM o Boundary line between T.I. and TM o Continuous sheet of thick layer elastic fibre o Pores in it to allow diffusion from Ti to TM o If you see it in a vessel = most likely looking at artery because only LARGE veins show this (all arteries have this even smallest ones); IEM allows blood vessel allows it recoil back to original shape (veins don’t so don’t require as much elastic) o 2. Tunica media = middle- Muscle layer (smooth muscle) especially arteries an
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