2.68 understand how the structure of arteries, veins and capillaries relate to their function

Arteries:
-very thick muscular walls to withstand high pressure of blood.
-blood travels through arteries in surges (pulse) every time the heart beats.
-to cope with the surges, arteries contain elastic fibres. Elastic fibres stretch when surge of blood passes, and recoil in between surges to keep blood moving.
*remember: blood travels TO the organs in arteries, but once it's in the organ, the blood flows through capillaries.

 Capillaries:
-when the blood passes through capillaries, substances such as glucose and oxygen diffuse from blood to cells.
-alternatively, carbon dioxide diffuse from cells to blood.
-capillaries have THIN WALLS therefore a very short diffusion distance to allow substances to diffuse rapidly between blood and body cells.
*remember: once the blood has passed through organs, it makes its way back to heart in VEINS. The blood is now traveling slowly and at low pressure. This means it could stop or even go backwards.


Veins:
-veins have a thin wall because blood pressure is low so wall doesn't have to be thick.
-many veins contain valves. This stops blood from flowing backwards.