Biology – The circulatory system | e-Consult

Arteries: Arteries are adapted for carrying blood away from the heart under high pressure. Key adaptations include:

• Thick, elastic walls: This allows them to withstand the high pressure of blood being pumped from the heart and also allows for expansion and recoil with each heartbeat, maintaining a relatively constant blood flow.
• Smooth muscle layer: This allows for vasoconstriction (narrowing) and vasodilation (widening) to regulate blood flow and blood pressure.
• Elastic fibres: Contribute to the elasticity of the artery walls.

Veins: Veins are adapted for returning blood to the heart under low pressure. Key adaptations include:

• Thin walls: Veins experience lower blood pressure than arteries, so they don't need thick walls.
• Valves: These prevent the backflow of blood, ensuring that blood flows in one direction towards the heart, especially in the limbs.
• Less smooth muscle: Veins have less smooth muscle than arteries, as they don't need to regulate blood flow as much.

Capillaries: Capillaries are adapted for the exchange of substances between blood and tissues. Key adaptations include:

• Single layer of endothelial cells: This thin layer allows for easy diffusion of substances between the blood and the surrounding tissues.
• Thin walls: Facilitates the short diffusion distance.
• Large surface area: The extensive network of capillaries provides a large surface area for exchange.