The Blood Vessels:

Arteries:

• Carry blood from the heart to the organs

• Carry bright-red oxygenated blood

• Can stretch

• Have thick walls

  • Containing muscle and elastic fibres

• Have small lumens

  • The central hole which allows blood to flow

Veins:

• Carry blood from the organs to the heart

• Carry purple-red, low-oxygen blood

• Have thin walls

• Have valves

  • To make sure blood can only flow in one direction

• Blood is squeezed by the skeletal muscles

• Have large lumens

Capillaries:

• Form a huge network of tiny vessels that link the arteries and the veins

• Have narrow, thin walls

  • Suited for the diffusion of oxygen and glucose

  • Carbon dioxide can easily pass through

Double Circulation:

Pulmonary Circulation System:

• Connects the heart and the lungs

• Allows for gas exchange to take place

Systemic Circulation System:

• Connects the heart and the cells of the body

• Allows cells to be provided with oxygen

• Takes carbon dioxide from the cells

Key Facts:

• Vital in warm-blooded animals

• Efficient

• Ensures all cells are provided with oxygenated blood

The Heart: