Summary 2.2.2 Transport systems in mammals

2.2.2 Transport systems in mammals


Once organisms reach a certain size, diffusion is no longer sufficient to
Transport provide all body cells with the oxygen and nutrients they need.
systems in
mammals This is when a mass transport system is needed. In mammals this is
the circulatory system.

Unicellular organisms don't need a specialist transport system because
they have a high surface area : volume ratio. These cells use diffusion,
osmosis and active transport.

Mass transport = a system that transports all substances in the same
direction at the same speed.

A good transport system in humans has:
 Large surface area
 Pump to move substances
 Fluid to suspend substances so they can be moved

Human circulatory system
Double circulation:
 Pulmonary circuit – between the lungs and the heart
 Systemic circuit – between the body and the heart.
 Advantages
o Blood pressure maintained
o Oxygenated and deoxygenated blood does not mix
o Delivery of O and nutrients to tissues is more efficient
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Closed system:
 The blood in the human circulatory system always moves within
blood vessels, and can be maintained at pressure.
 Advantages
o Blood pressure maintained
o Pressures can differ in pulmonary and systemic
systems
o Blood supply to organs can be varied due to functions

Blood vessels
Arteries:
 Take blood away from the heart under high pressure
 Narrow lumen
 Thick wall, large amounts of smooth muscle and elastic fibres
 Stretches during ventricular systole and recoils during diastole
 Inner endothelium lining smooth to reduce friction

Veins:
 Return blood to the heart
 Thin walls, small amount of muscle and elastic tissue
 Contain semilunar valves which prevent backflow