Download Capillary exchange

Blood Vessels, Blood Flow
and Capillary Exchange
Learning Outcomes:
C5 - analyze the functional interrelationships of
the vessels of the circulatory system
• Describe and differentiate among the five types of
blood vessels
• Relate blood pressure and blood velocity to the total
cross-sectional area of the five types of blood vessels
• Describe capillary-tissue fluid exchange
Review:
• What are the 5 types of blood vessels,
in the order that blood flows through
them?
• arteries  arterioles  capillaries 
venules  veins
Fig. 13.2
Flow of Blood
• Arteries bring oxygen- and nutrient- rich
blood to all tissues of the body
• Arterioles branch into capillary networks
in tissues
• At the capillaries, oxygen and nutrients
leave the blood
• CO2 and wastes enter the blood
• Capillaries flow into venules and veins
Blood Vessels and Blood
Pressure
• Blood pressure is greatest in the
arteries
• Decreases moving away from the heart
and into smaller vessels (arterioles and
capillaries)
• Increases again as it moves into
venules and veins
• Capillaries have a very large crosssectional area, so blood pressure and
velocity are very low
• This is where substances move
between the blood and tissues
• Walls are very thin so substances can
pass through
Fig. 13.15
Capillary-Tissue Exchange
• At the arterial end of the capillary, blood
pressure is high
• Water and small molecules are pushed
out of the capillary into the surrounding
fluid
• Nutrients and oxygen diffuse into
surrounding cells
• At the venous end, blood pressure is
lower
• Osmotic pressure (due to salts and
proteins in the blood) brings water back
into the capillaries
• CO2 and other cellular wastes diffuse
into capillaries from tissue fluids
Fig. 13.16
• Excess water enters the lymph
capillaries and is returned to the blood
at lymphatic ducts