Characteristics of blood vessels

layer of artery

Thick smooth muscle

Thick elastic layer

Narrow lumen

Endothelial layer

Blood at high pressure

what does the artery do

Arteries take blood away from the heart .

elastic tissue

so that they can expand when pressure increases following a beat of the heart (systole) and then recoil while the heart relaxes (diastole). This recoil helps to push the blood further along the vessel. The stretch and recoil of the arteries is what is felt when a pulse is taken.

endothelial

helps reduce friction to ensure the blood flows smoothly

muscles are thicker

d help the vessel withstand the high pressures. They can also contract (vasoconstriction) to restrict blood flow to a particular area or relax (vasodilation) to allow more blood flow to the area

Vein structure

Thin smooth muscle

Thin elastic layer

Semilunar valve

Wide lumen

Blood at low pressure

what do veins do

Veins carry blood that has already been through tiny capillaries

semilunar valves do

To prevent backflow of blood, semilunar valves extend from the endothelial layer.

what does the lumen do

. The lumen of the vein is wider than that of the artery and tends to be more oval in shape. Having a large lumen reduces the resistance on the blood allowing it to flow more easily. Due to the low pressure and the need to return the blood to the heart, the body relies on the contraction of skeletal muscle to squeeze the contents of the vein.

capillaries structure

Wall one cell thick

Very narrow lumen

Squamous endothelium

Blood at very low pressure

function of capillaries

The function of capillaries is to allow exchange of substances between blood and tissues. To allow this exchange it must be easy for the substances to diffuse into or out of the blood.

1 cell thick and squamous

This reduces the diffusion pathway allowing rapid diffusion of substances. Furthermore, small gaps between endothelial cells also aid diffusion.