Mammals have a transport mechanism called circulatory system. The circulatory system is composed of the heart and the associated blood vessels Arteries Carry blood away from the heart. Blood that flows through arteries is pulsing and at a high pressure. Contain elastic fibres and collagen fibres Arteries have narrow lumen maintaining high pressure facilitate faster movement of blood Have thick, elastic walls which can expand and recoil as the blood pulses through. The artery wall contains variable amounts of smooth muscle. It carries oxygenated blood except in pulmonary artery Relate the structure of the artery to its function Arteries transport swiftly and at high pressure to the tissues made up of an inner endothelium this layer is very smooth, minimizing friction with the moving blood. also made up of tunica media Contain smooth muscle and elastic fibres Tunica extern Contain elastic fibres and collagen fibres. Arteries have narrow lumen maintaining high pressure facilitate faster movement of blood. Elastic walls to allow for expansion when pressure increases semilunar valves to prevent backflow of blood Veins Carry low-pressure blood back to the heart the lumen is larger than in arteries, reducing friction which would otherwise slow down blood movement Have thin muscular wall with little elastic tissue Contain valves, to prevent the backflow of blood No pulses and blood flows slowly. Deoxygenated blood except pulmonary vein Capillaries Tiny vessels with just enough space for red blood cells to squeeze through Have no muscles or elastic tissue. Blood flows slowly and no pulses. Large lumen relative to diameter single cell walled and they are permeable and unable to constrict. there are often gaps in the walls through which plasma (the liquid component of blood) can leak out deliver nutrients, hormones and other requirements to body cells, and take away their waste products Small size and thin walls minimize diffusion distance this enables the exchange to take place rapidly between the blood and the body cells. How the structure of arteries and capillaries is related to their function. artery thick elastic layer in artery even outflow/associated with recoil thick muscular layer to allow pausatile flow of blood; endothelium layer for smooth flow of blood; thick collagen layer to allow blood flow under pressure small lumen allow rapid flow of blood capillary capillary wall is thin/only endothelium gaps for the exchange of materials like white blood cells capillary form a branched network to increase surface area for exchange of materials narrow diameter to minimize diffusion distance narrow lumen -more diffusion efficient