4. Arteries:
– Transport blood swiftly and at high pressure to the tissues
– Walls have 3 layer:
Inner endothelium (lining tissue) – squamous epithelium, layer very
smooth and rests on elastic fibres (tunica intima)
Middle layer – smooth muscle, collagen and elastic fibres (tunica
media)
Outer layer – elastic fibres and collagen fibres (tunica externa)
– Distinctive characteristic: strength
– Have the thickest wall
– Large amounts of elastic fibres in tunica media allow the wall to
stretch
– Arteries further from the heart have fewer elastic fibres but
more muscle fibres
– Elasticity important to ‘even out’ blood flow
– Branch into arterioles in tissues having greater proportion of
smooth muscle. Muscles contract , narrowing the diameter and
reducing blood flow. Helps to control the volume of blood
flowing into tissues at different times.
ALBIO9700/2006JK
5. Veins:
– Capillaries join to form venules. These join to
form veins.
– To return blood to the heart
– Pressure has dropped to very low
– No need for thick walls, tunica media thinner,
fewer elastic fibres and muscle fibres
– Muscles squeeze inwards on the veins to raise
pressure
– To keep blood flowing in right direction, veins
contain half-moon valves or semilunar
valves
ALBIO9700/2006JK
8. Capillaries:
– Arterioles continue to branch into capillaries
– Takes blood as close as possible to all cells,
allowing rapid transfer of substances
between cells and blood
– Form networks throughout every tissue in
body except cornea and cartilage called
capillary beds
– Small size, thin walls (single layer endothelial
cells), tiny gaps
– Pressure will have dropped
ALBIO9700/2006JK
