#12 the circulatory system (blood vessels)

lumen

central area of the vessel that contains the blood

tunica intima

innermost layer of the blood vessel

what is in direct contact with the blood flowing in the lumen

tunica intima

what is the tunica intima composed of

simple squamous endothelium that is continuous with the endothelial lining of the heart

tunica media

circularly arranged smooth muscle and sheets of elastin

tunica externa

outermost layer of the vessel

what is the tunica externa composed of

loosely arranged collagen fibres

what does the tunica externa do

• anchors the vessel to surrounding fibres

• protects and reinforces the vessel

arteries

transport blood AWAY from the heart

two types of arteries

1. elastic arteries

2. muscular arteries

what do elastic arteries contain

elastin

where are elastic arteries mainly located in

tunica media (but can be in the other two layers)

what do muscular arteries contain

more smooth muscle than elastin

in muscular arteries, the smooth muscle is mainly concentrated in

the tunica media

example of elastic arteries

aorta

example of muscular arteries

most of the arteries in the body including the coronary artery

arterioles

smallest arteries, very muscular

what do arterioles function in

regulate the flow and pressure of blood

what is the only layer that is present in capillaries

tunica intima → endothelium and basement membrane only

venules

smallest veins

two types of venules

small and large

small venules are only composed of

tunica intima

large venules are composed of

a very thin tunica intimate and a tunica externa

veins function to

return blood back to the heart

what do veins contain to prevent back flow

valves

where are valves especially important in

the legs

• gravity opposes motion

what do veins have

• very large lumen

• thin tunica intima

which blood vessel is prone to collapse

veins