1.3 Blood vessels

Blood vessels

An important part of the cardiovascular system as this is how blood travels around the body.

Lumen

Hollow space inside the blood vessel through which blood flows through.

The three main types of blood vessels

• Arteries

• Veins

• Capillaries

Arteries

A type of blood vessel that carries blood away from the heart, under high pressure.

Function of arteries

To carry blood away from the heart.

Features of Arteries

• Thick, muscular walls

• Elastic tissue

• Narrow lumen

Structural adaptations of arteries

• Thick, muscular walls allows the arteries to control blood flow by tightening or relaxing.

• The elastic tissue helps the arteries to stretch and recoil as blood moves through.

• The narrow lumen helps maintain the high pressure needed to move blood efficiently.

Veins

A type of blood vessel that carries blood towards the heart, under low pressure.

Function of veins

To carry blood towards the heart.

Features of veins

• Fairly thin walls

• Very little elastic tissue

• Wide lumen

• Semilunar valves

Structural adaptations of veins

• Fairly, thin walls because blood travels under much lower pressure, so thick walls are not required.

• Little elastic tissue compared to arteries because blood pressure in veins is low.

• The wide lumen allows the blood to flow more easily despite the low pressure.

• Semilunar valves at regular intervals along the vein, prevent blood from flowing backwards.

Capillaries

Very small blood vessels that connects arteries to veins.

Functions of capillaries

• Connects arteries to veins

• Carries blood under low blood pressure, through tissues and cells, to exchange substances with them by diffusion.

Features of capillaries

• One cell thick walls

• Porous walls

• Very narrow lumen

Structural adaptations of capillaries

• One cell thick walls to allow substances to diffuse in and out of the blood easily.

• Porous walls (small holes in the walls), that aid substance exchange between surrounding cells.

• They have a narrow lumen as red blood cells must pass through in a single file.

Substances exchanged in the capillaries

• Oxygen and glucose move out of the blood to supply the surrounding tissues and cells.

• Waste products; carbon dioxide and urea, move into the blood to be transported away and excreted.