Blood vessels and tissue fluid

Arteries branch into narrower blood vessels called arterioles which transport blood into narrow capillaries. They lower the pressure of blood before entering capillaries to prevent bursting and they also have a muscular layer

The walls of the artery are relatively thick with layers of collagen, smooth muscle and elastic fibres. The elastic fibres allow the walls of the artery to slightly stretch to withstand high pressures of blood.

The walls of the vein are very thin however the lumen is much larger than the artery. They also contain valves to prevent the backflow of deoxygenated blood, helping blood return to the heart

They are another type of blood vessel between arteries and veins and allow substances to leave the blood like oxygen to be transport to other regions of the body where it is needed (Respiring muscles)

Capillaries branch between cells - This is useful as it shortens diffusion distance so substances can diffuse quickly between cells Walls of capillaries are made from one single layer of endothelial cells - This greatly reduced the diffusion distance for oxygen and carbon dioxide between blood and tissues of body Pores - The cell walls have gaps that allow plasma to leak out to form tissue fluid

A liquid that constitutes for 55% of blood it is 95% of water as water is an universal solvent so many substances can dissolve in it

Tissue fluid is formed from plasma leaking out capillaries

Plasma contains proteins whilst tissue fluid doesn’t as it is too large to go with plasma through the pores