3.4.1 mass transport in animals

what is the function of arteries

carry blood away from the heart at high pressure

explain how the structure of arteries relates to their function

• thick smooth muscle tissue - can contract and control/maintain blood flow/ pressure

• thick elastic tissue - can stretch as ventricles contract and recoil as ventricles relax to reduce pressure surges / even out blood pressure / maintain high pressure

• thick wall - withstand high pressure/ stop bursting

• smooth / folded endothelium - reduces friction

• narrow lumen - increases/ maintains high pressure

what is the function of arterioles

division of arteries to smaller vessels which can direct blood to different capillaries/ tissues

explain how the structure of arterioles relates to their function

thicker smooth muscle layers than arteries

• contracts - narrow lumen (vasoconstriction) - reduces blood flow to capillaries

• relaxes - widens lumens (vasodilation) - increases blood flow to capillaries

thinner elastic layer - pressure surges are lower

what is the function of veins

carry blood back to the heart at lower pressure

explain how the structure of veins relates to their function

wider lumen than arteries - less resistance to blood flow

very little elastic and muscle tissue - blood pressure lower

valves - prevent backflow of blood

what is the function of capillaries

allow efficient exchange of substances between blood and tissue fluid (exchange surface)

explain how the structure of capillaries relates to their function

• wall is thin (one cell) layer of endothelial cells - reduces diffusion distance

• capillary bed is a large network of branched capillaries - increases surface area for diffusion

• smaller diameter / narrow lumen - reduces blood flow rate so more time for diffusion

• pores in walls between cells - allow larger substances through

explain the formation of tissue fluid at the arteriole end

1. higher blood/ hydrostatic pressure inside capillaries than tissue fluid

2. forcing water out of capillaries

3. large plasma proteins remain in capillary

explain the formation of tissue fluid at the venule end of capillaries

1. hydrostatic pressure reduces as fluid leaves capillaries

2. an increasing concentration of plasma proteins lowers water potential in capillary below that of tissue fluid

3. water enter capillaries from tissue fluid by osmosis down a water potential gradient

4. excess water taken up by lymph capillaries and returned to circulatory system through veins

suggest and explain causes of excess tissue fluid accumulation

low concentration of protein in blood plasma or high salt concentration

• water potential in capillary not as low - water potential gradient is reduced

• so more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis

high blood pressure - high hydrostatic pressure

• increases outward pressure from arterial end AND reduces inward pressure at venule end

• so more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis

• lymph system may not be able to drain excess fast enough

what is a risk factor

an aspect of a person’s lifestyle or substances in a person’s body/ environment

that has been shown to be linked to an increased rate of disease

examples for cardiovascular disease

age

diet

high in salt or saturated fat

smoking

lack of exercise

genes