Blood vessels |

Table of Contents

Mammals have a transport mechanism called circulatory system. The circulatory system is composed of the heart and the associated blood vessels

Carry blood away from the heart.
Blood that flows through arteries is pulsing and at a high pressure.
Contain elastic fibres and collagen fibres
Arteries have narrow lumen maintaining high pressure facilitate faster movement of blood
Have thick, elastic walls which can expand and recoil as the blood pulses through.
The artery wall contains variable amounts of smooth muscle.
It carries oxygenated blood except in pulmonary artery

Arteries transport swiftly and at high pressure to the tissues
made up of an inner endothelium
- this layer is very smooth, minimizing friction with the moving blood.
also made up of tunica media
- Contain smooth muscle and elastic fibres
Tunica extern
- Contain elastic fibres and collagen fibres.
- Arteries have narrow lumen maintaining high pressure facilitate faster movement of blood.
- Elastic walls to allow for expansion when pressure increases
semilunar valves to prevent backflow of blood

Carry low-pressure blood back to the heart
the lumen is larger than in arteries, reducing friction which would otherwise slow down blood movement
Have thin muscular wall with little elastic tissue
Contain valves, to prevent the backflow of blood
No pulses and blood flows slowly.
Deoxygenated blood except pulmonary vein

Tiny vessels with just enough space for red blood cells to squeeze through
Have no muscles or elastic tissue.
Blood flows slowly and no pulses.
Large lumen relative to diameter
single cell walled and they are permeable and unable to constrict.
there are often gaps in the walls through which plasma (the liquid component of blood) can leak out
deliver nutrients, hormones and other requirements to body cells, and take away their waste products
Small size and thin walls minimize diffusion distance
this enables the exchange to take place rapidly between the blood and the body cells.