Thick and muscular walls-resists damage due to high pressure
Elastic tissue to stretch and recoil-maintains high pressure
Folded endothelium layer-allows stretching to
maintain high pressure
Also smooth to reduce friction
Arterioles
Contract to restrict flow and relax to
aloow flow to organs
Veins
Take blood INTO heart
Low pressure
Wide lumen
Little elastic and muscle tissue
Valves stop back flow of blood
Capillaries
One cell thick-increases rate of diffusion
Large number to increase surface area
Numerous and Branched- increases surface area
Narrow diameter- ensures RBC in contact with wall
Wall spaces- gaps between cells allow
rapid formation of tissue fluid
Tissue Fluid
Surrounds cells in tissues
Made from small molecules (oxygen, water and nutrients)
No big proteins- too large to
push through capillary walls
Cells take in O2 and nutrients
from T.F. and release metabolic
waste into it
Fluid leaves capillaries at arteriole
end but large proteins remain-due
to larger force pushing out than
forces pulling in
Lower water potential in venule end than
in tissue fluid
Force pulling in is stronger than force
pushing out
Water moves into capillary via osmosis
Excess T.F. is drained into LYMPHATIC SYSTEM
High blood pressure = High hydrostatic pressure
Cardiac Cycle
1. When ventricle relaxes, the atria
contracts-decreasing volume and increasing
pressure. This pushes blood into the ventricles.
AV valve opens and SL valves close.
2. Atria now relax. Ventricles contract (decreasing
volume and increasing pressure). Pressure is
higher in ventricles than atria so AV valves shut
(stops back flow). Pressure in ventricles higher
than Aorta so SL valves open
3. Both ventricles and atria relax. Higher pressure in
Aorta (than ventricle) close SL valves (stops back flow). Atria fill again
due to high pressure in Vena Cava. Increases
pressure in atria. Ventricles relax so pressure falls
below that in atria so AV valves open.
AV vales OPEN when pressure in Atria HIGHER than Ventricle
AV valves CLOSE when pressure in Atria LOWER than Ventricle
SL valves OPEN when pressure in Ventricle HIGHER than Aorta
SL valves CLOSE when pressure in Ventricle LOWER than Aorta