Page 112 - Biology Form Two

Biology for Secondary Schools

Table 5.2 summarises the structural and functional differences between arteries,
veins, and capillaries.
Table 5.2: Comparison of structure and function of arteries, veins, and capillaries

FOR ONLINE READING ONLY
Feature Arteries Veins Capillaries
Lumen Have narrow Have wide irregular Have narrow
smooth lumens lumens smooth lumens

Valves Lack valves except Have valves at regular Lack valves
where they are intervals
connected to the
heart
Pressure Transport blood at Transport blood at low Blood pressure
high pressure pressure varies from high to
low

Direction of Transport blood Transport blood Transport blood
blood flow away from the heart towards the heart within the tissues

Function Transport Transport deoxygen- Transport either
oxygenated ated blood, except the oxygenated or
blood, except the pulmonary vein deoxygenated blood
pulmonary artery
Blood flow Contract and relax Blood flows smoothly Blood flows
to create a pulse smoothly

Wall layers Have three wall Have three wall layers Have one wall layer
layers
Wall thickness Have thick muscular Have thin muscular Extremely thin
walls walls walls (single cell
thick)

Permeability of Not permeable Not permeable Permeable
walls

Elasticity of Very elastic Less elastic Not elastic
walls (inelastic)

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