First 431 words of the document:
Reianna Shakil L6EFBiology19/11/12
Artery Vein Capillary
Elastic tissue Large amount, especially in arteries close to Small amount. Blood in veins is at low None.
the heart. This allows the wall to stretch and pressure, so there is no need for the walls
in wall recoil as high-pressure blood pulses through. to be elastic.
Smooth Relatively large amount in small arteries and Small amount. All blood in veins is None.
arterioles. Contraction of this muscle travelling back to the heart, so there is no
muscle reduces the size of the lumen, which can advantage in being able to divert it to
in wall divert blood from one area to another. different tissues.
Thickness Relatively thick. Artery walls must be strong Relatively thin. The blood in veins is at low The wall is only one cell thick. Moreover,
enough to withstand the high pressure of pressure, so there is no need for a thick these cells are thin and flattened, so the
of the blood flowing inside them. wall. wall is as thin as possible. This allows rapid
wall transfer of substances by diffusion
between blood and tissue fluid.
Endothelium Very smooth. This allows blood to flow As arteries. The wall of a capillary is made of
freely and quickly. A rough wall would endothelium only, with no other layers of
(inner lining) present more resistance to blood flow. tissue. The thin endothelium and pores
Intact endothelium decreases the likelihood speed up exchange of substances with the
of a thrombus (blood clot) forming. tissues.
Presence There are no valves in arteries, except those Veins have valves, which allow blood to There are no valves in capillaries.
in the aorta and pulmonary artery as they flow towards the heart but not away from
of leave the heart. it. They are necessary because of the low
valves pressure of blood in the veins.
Diameter Relatively small compared with veins. Relatively large. The wide lumen of a vein Tiny. Many capillaries are only 8m wide.
provides less resistance to blood flow This brings the blood as close as possible to
of than the narrow lumen of an artery, the cells in the tissues with which it is
lumen allowing blood at low pressure to blood in exchanging materials such as oxygen and
the veins. carbon dioxide.
Oxygen state Oxygenated Deoxygenated Depends on site of exchange can be