Mass transport and blood vessels

What is mass transport?

Bulk movement of substances in a fluid over distances within an organism.

Why do large organisms need mass transport?

They have a low surface-area-to-volume ratio and long diffusion distances; diffusion alone is too slow to meet metabolic demands.

How are arteries adapted to their function?

Thick muscular and elastic walls withstand high pressure; elastic tissue stretches and recoils; a relatively narrow lumen helps maintain pressure.

How are veins adapted to their function?

A wide lumen reduces resistance; thin walls suit low pressure; valves prevent backflow and skeletal muscle contraction assists venous return.

How are capillaries adapted for exchange?

Walls are one endothelial cell thick

How does elastic recoil help arteries?

Arteries stretch during ventricular systole and recoil during diastole

How do valves in veins work?

They open when blood moves towards the heart and close if blood starts to flow backwards.

Compare arteries and veins.

Arteries carry blood away from the heart at higher pressure; veins carry blood towards the heart at lower pressure and contain valves.

Why is capillary blood flow relatively slow?

Extensive branching creates a large total cross-sectional area