The Circulatory System - created from Mind Map

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Heart

Arteries

Arterioles

Blood Capillaries

Venules

Veins

blood is kept circulating throughout the body by means of a muscular pump; the heart

relaxes

contracts

fills up with blood

blood is squeezed out

blood circulates through blood vessels which direct blood flow round the body

blood vessels that carry blood away from heart

need to be able to withstand the immense pressure of the blood as it is forced out of the heart

constricts

dilates

most arteries carry oxygenated blood

have thick, muscular and elastic walls

elastic layer is much thicker in arteries near the heart

elasticity enables artery wall to stretch and recoil or spring back

this helps to push the blood in spurts along the artery and also gives rise to the pulse

lumen becomes narrower & less blood flows through per unit time

lumen becomes wider & more blood flows through it per unit time

except pulmonary arteries

carry deoxygenated blood from heart to lungs

aorta -> arteries -> arterioles -> capillaries

found between the cells of almost all tissues

have walls made up of only a single layer of flattened cells (endothelium)

branch repeatedly

total cross-sectional area increases when arteriole branch into capillaries

endothelium is partially permeable

enables certain substances to diffuse quickly through the capillary walls

numerous branches provide a large surface area for exchange of substances between blood & tissue cells

this lowers blood pressure in capillaries

flow of blood is slowed down, giving more time for exchange of substances

before the capillaries leave an organ or tissue, they unite to form small veins called venules

venules in turn join to form bigger veins

carry blood back to the heart

blood pressure in veins is much lower than in the arteries

contain less elastic tissue

semi-lunar valves

blood flows more slowly and smoothly

walls do not need to be as thick and muscular as of those arteries of about the same size

prevent blood from flowing backwards