we related the structure of blood vessels to the function today.
arteries are large, and have thick elastic walls. they can expand and contract, but are restricted by cologens, and they are thick so taht they can withstand the pressure of pulses. the pulses drive blood through the arteries. small arteries that branch off arteries are called arterioles.
veins are smaller, and have smaller holes than arteries, but bigger in proportion. there is no pump pushing the blood through veins, but they have valves which preevnt blood from going backwards (they close up if blood goes backwards) smaller veins are called venules.
capillaries are the tiny in between ones. they have walls, once cell thick, for easy diffusion, and dont fit much blood in. they are used to deliver blood to and from the cells.
lymph is a white substance found deep within tissue (whereas blood is not found deep in the tissue coz capillaries dont go there). lymph is a white liquid with dissolved substances from the body in it, and goes through lymph vessels to go back to the heart. lymph is also a rich source of white blood cells, so its a way white blood cells get around to fight off infection. lymph vessels meet around the shoulders in lymph nodes, and the tonsils are used to fight infections in the throat (coz white blood cells are abundant in lymph). people whos tonsils cannot fight infection anymore, have them removed.
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