Circulatory system Flashcards
how are molecules transported in single-celled organisms
through diffusion
why cant diffusion work for large organisms
- too great of distance
- high energy requirements so the delivery of reactents must be quick
mass transport
bulk movement of gases or liquids in one direction via vessels and tubes
advantages of mass transport
- bring substances quickly
- maintains diffusion gradients between sites
- ensures effective cell activity
Ateries
- carries blood away from heart
- high pressure to tissues
arterioles
- transports blood into capillaries
veins
- transports blood to the heart
- low pressure
venules
- narrow blood vessels which transports blood from the capillaries to the veins
what are the three layers of the arteries
tunica intima
tunica media
tunica externa
tunica intinma
- endothelium is one cell thick and lines the lumen of blood vessels
- smooth-> reduce friction
- highly folded, so it can expand under high pressure
tunica media
- contains smooth muscle and elastic tissue
- thick in arteries
- layer of muscle to withstand high pressure and so it can constrict and narrow the lumen for reduced blood flow
- elastic tissue to help maintin b.p which streches and recoils to even out any fluctuations in presure
what does contraction of muscle in tunica media cause
constriction of the lumen which is useful to divert blood away from certain locations
tunica externa
- contains collagen to help protect the blood vessel to prevent over stretching
lumen of artery
narrow to help maintain blood pressure
what helps arteries accomodate increased volume of blood
a pulse
smooth muscle and elastic layer in veins
- much thinner as it doesnt need to withstand high pressure
lumen in vein
wider, to help ensure blood returns to heart at the right speed
- reduces friction between blood and the endothelium of the vein
rate of blood flow in veins
slower but the volume of blood per unit is equal to arteries
why do veins have valves
to prevent backflow of blood
why dont veins have a pulse
due to increased distance from the heart
what do capillaries from
capillary beds which are important exchange surfaces
why do a large numbers of capillaries branch between cells
so substances can diffuse between the blood and calls quickly as there is a short distance
lumen in capillaries
narrow as red blood cells need to pass through in single file, so blood travels slowly and provides time for diffusion to occur
what is the wall of the capillary made of
endothelial cells
capillary wall
one cell thick to reduce the diffusion distance
- contains pores so blood plasma can leak out as tissue fluid
