blood vessels

ARTERY- tough outer layer tissue- small lumen, smooth lining- elastic fibres and smooth muscle-O2 blood from heart to body at high pressure- peripherical arteries contract and recoil  and change lumen size to control BP (decreases away from heart)- lumen size in arterioles get smaller away from heart- more elastic fibres near heart but less away and more muscle tissue away from heart- deox blood in pulmonary artery from heart to lungs -& in umbilical cord from fetus to placenta during pregnancy

CAPILLARIESarterioles- network of capillary branched for O2 to diffuse between cells due to their small size and low BP- as the capillary wall with epithelial cells is one cell thick rapid diffusion of waste in & O2 out- carries oxygenated blood away from heart

 VEINS-deox blood to heart e.g. inferior/superior vena cava-thin layer muscle+elastic fibres with large lumen and smooth inner surface, tough outer layer of collagen fibres- low BP with semi lunar valves preventing back flow-muscles contract & relax so blood travels one direction

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