2.5 - Blood Vessels

• blood is transported through arteries veins and capillaries
• blood circulates from the heart through the arteries to the capillaries then to the veins back to the heart
• blood pressure decreases as it moves away from the heart
• the lumen is lined with a layer of endothelial cells
• arteries always carry blood away from the heart
• arteries carry oxygenated blood except from the pulmonary artery
• arteries carry blood under high pressure
• arteries and veins have a middle layer containing smooth muscle and elastic fibres
• arteries and veins have an outer layer of connective tissue containing elastic fibres
• the arteries elastic walls stretch to accommodate the surge of blood from the heart
• the arteries smooth muscle contracts causing vasoconstriction
• vasoconstriction decreases the diameter of the lumen and decreases blood flow into the capillaries
• the arteries smooth muscle relaxes causing vasodilation
• vasodilation increases the diameter of the lumen and increases the blood flow to the capillaries
• veins have valves which prevent the backflow of blood
• vasoconstriction and vasodilation controls the blood flow through the arteries
• arteries have a narrow lumen
• veins have a wide lumen
• arteries have thick muscular walls
• veins have thinner muscular walls then arteries
• veins carry blood at low pressure
• capillaries allows the exchange of substances through tissues of the body through their thin walls
• capillaries connect the smallest branches of arteries and veins
• capillary walls are one cell thick
• pressure filtration causes plasma to pass through the thin capillary wall into the tissue fluid surrounding the cells
• tissue fluid can supply cells with glucose, oxygen and other useful substances
• carbon dioxide and other metabolic waste products can diffuse into tissue fluid to be excreted
• most tissue fluid returns to the blood but the excess drains into the lymphatic system and is returned to the circulatory system called lymph
• plasma and tissue fluid are contain similar substances except plasma contains plasma proteins
• lymph circulates around the body through lymph vessels
• veins carry deoxygenated blood except from the pulmonary vein