Biology 3.1.2 Blood vessels

Blood go away from the heart through the , blood goes back to the heart through the

The largest arteries divide into smaller ones called , then divide into , which then join up to form which finally merge to form

The inner layer of blood vessels ( ) is a thin layer of tissue allowing it to

The middle layer of blood vessels ( ) contain muscle and fibres

The outer layer of blood vessels ( ) contain and tissue

Arteries are lined with cells so it is a very surface

Arterioles contain more which allows them to and

The lumen of capillaries are very so there is a small

The walls of capillaries are so and disolved substances can leave the blood

Blood flows towards the heart the valve and if blood flows away from the heart, the valve , preventing