Blood vessels

Arteries Transport blood to tissues from heart Tunica intima – squamous epithelium Tunica media – smooth muscle, collagen, elastic fibres Tunica externa – elastic and collagen fibres.

Transport blood to tissues from heart

Tunica intima – squamous epithelium

Tunica media – smooth muscle, collagen, elastic fibres

Tunica externa – elastic and collagen fibres.

Arteries Strength to blood at high pressure Composition of walls Tunica Media – thickest layer. Large amount of elastic fibres so wall can stretch at high pressures. This means that they will not burst but “give”. They recoil when blood passes through which pushes the blood increasing the pressure a little bit

Strength to blood at high pressure

Composition of walls

Tunica Media – thickest layer. Large amount of elastic fibres so wall can stretch at high pressures. This means that they will not burst but “give”.

They recoil when blood passes through which pushes the blood increasing the pressure a little bit

Arterioles Smaller than arteries Have more muscle Muscle can contract making vessels narrower Amount of blood entering tissues can then be regulated. Eg during exercise

Smaller than arteries

Have more muscle

Muscle can contract making vessels narrower

Amount of blood entering tissues can then be regulated.

Eg during exercise

Capillaries Tiniest Allow rapid transfer between blood and cells 7 µm thick Extremely thin walls – 1 cell thick only Tiny gaps between the cells Pressure drops significantly in capillary bed – from 35mm Hg to 10mm Hg

Tiniest

Allow rapid transfer between blood and cells

7 µm thick

Extremely thin walls – 1 cell thick only

Tiny gaps between the cells

Pressure drops significantly in capillary bed – from 35mm Hg to 10mm Hg

Vein Return blood to heart Pressure = 5mm Hg or less No need for thick walls so tunic media much thinner and with less elastic and muscle Semi-lunar valves prevent blood from flowing backwards

Return blood to heart

Pressure = 5mm Hg or less

No need for thick walls so tunic media much thinner and with less elastic and muscle

Semi-lunar valves prevent blood from flowing backwards