6/7) Blood vessels

Vein structure

• walls are thin

• 4 layers of tissue

• epithelium

• elastic tissue/muslce

• collagen shell

What blood pressure are veins under?

Low blood pressure(10-20mmHg)

Veins lead towards the …

heart

What do valves do?

stop the backflow fo blood

Where are veins found?

through out the tissue

Diameter of lumen

very large - many RBCs flow at once

Why are the vein walls thin?

blood flows through them at low pressure

Artery structure

• walls are very thick

• 4 layers

• epithelium

• muscle layer

• elastic layer

• collagen layer

What pressure is blood carried in arteries?

systolic pressure (120mmHg)

Artery leads away from…

the heart

Where are arteries found?

mostly deep beneath the skin

lumen of artery

• fairly large

• many RBCs flow but closely packed together

artery wall thickness

• thick muscle layer

• cope with very high internal pressure

Capillary walls

one layer of epithelim cells

Capillary blood pressure

very low (1-2mmHg)

Where are the capillary’s located?

mostly under the surface of the skin

Capillary diameter lumen

• lumen diameter is small

• one RBC passes through at a time

What happens to the capillaries when pressure changes?

walls burst

Where does blood flow fastest/slowest?

• arteries because the pump from the heat is the closest

• capillaries so that the rate of diffusion increases

Role of epithelium

a: smooth lining, reducing friction and resistance as blood flows at high pressure.

v:smooth lining, reducing friction and resistance as blood flows at low pressure

c: one cell thick, giving a short diffusion distance for rapid exchange of substances between blood and tissues.

Elastic layer role

a: Stretches as blood enters under high pressure, then recoils to maintain blood pressure and smooth blood flow.

v: Have a thinner elastic layer, allowing some stretch and recoil, but this is less important because blood pressure is low.

Muscle layer role

a:Thick muscle layer contracts to narrow the lumen (vasoconstriction) and relaxes to widen it (vasodilation), controlling blood flow.

v:Thin muscle layer can contract and relax, changing the lumen diameter, but this plays a smaller role in controlling blood flow.

Collagen shell/connective tissue role

• Provide strength to the blood vessel wall.

• Prevent the vessel from bursting when blood pressure is high.

• Prevent overstretching of the blood vessel.