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SBI3U
BLOOD VESSELS
 Total length of human blood vessels = ~ 160 000 km
ARTERIES
FUNCTION:
 Rapid transport of high pressure blood from the heart to the capillary
blood.
STRUCTURE:
 Thick layer of muscle and elastic tissue
 walls stretch when blood pumped from the heart
 walls recoil when heart relaxes
 Elasticity helps maintain the blood pressure
NOTE: arterioles are smaller and less elastic
VEINS
FUNCTION:
 Carry blood from capillary beds to the heart
STRUCTURE:
 Thinner walls due to thinner layer of muscle
 walls stretch more easily
 blood under low pressure
 Contains valves
maintain flow towards the heart (prevents back flow)
NOTE:
 Contraction of skeletal muscles squeezes the veins
 blood is moved through the veins
CAPILLARIES
FUNCTION:
 Link arterial and venous systems
 Exchange of material between blood and cells of the body
 Forms dense capillary beds
STRUCTURE:
 Smallest blood vessels
 large enough to let a single red blood cell pass
 Walls consist of only 1 layer of cells
 allows for rapid exchange of materials between blood and interstitial
fluid (fluid that lies outside of circulatory system)
NOTE:
 Amount of blood flowing in a particular capillary bed is regulated
 corresponds to the activity of the particular tissue/organ
 When skeletal muscles are at rest only 5-10% of the capillary beds will be
open at any one time.