L2 - Blood vessels

Main function of arteries

• Carry blood away from heart

Main function of veins

• Transport blood to the heart

Main function of capillaries

• Site of gas exchange through thin walls

Features of arteries

• Maintains high blood pressure

  • by stretching/recoiling elastic fibres

• Strong, thick walls w/ collagen

• Endothelium folded, allowing artery to expand

Features of veins

• Blood flows at lower pressure

• Thinner layers of collagen, smooth muscle and elastic tissue

• Valves to prevent backflow

Features of capillaries

• Narrow lumen - 7 micrometers wide

  • enough to fit 1 erythrocyte

• Walls have fenestrations to allow plasma and dissolves substances to pass through

Features of arterioles

Small blood vessels that split from arteries to capillaries

• Lowers pressure of blood before entering capillaries to prevent bursting/damage.

• Arteriole wall contains rings of smooth muscle that can contract

  • Allows redirection of blood flow

Features of venules

Small blood vessels from capillaries join to form venules.

• Collect blood from capillary bed into veins