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CARDIOVASCULAR
SYSTEM
Blood Vessels and Blood Pressure
Chapter 15
Topics 4 - 7
Differences Between the Vessels
Arteries  arterioles  capillaries  venules 
veins
 Arteries - carry blood away from heart

– Round Cross Section
– Tough and Elastic
 Elastic recoil helps keep blood flowing
– 3 Layers:
 Tunica Adventitia – Outer
– CT to connect arteries in place
 Tunica Media – middle
– Smooth muscle
 Vasoconstriction  sympathetic N.S.
 Vasodilation  inhibition of sympathetic NS
– Elastic CT – pulse
 Tunica Intima – inner endothelium
– Needs to be smooth
DIAGRAM
Differences Between the Vessels

Arterioles – small arteries
– Precapillary sphincters – open and close capillary
beds
– Metaterioles
– Major part of vasodilation and vasoconstriction

Veins – carry blood toward heart (atria)
– 3 layers
 Tunica adventitia
 Tunica Media – less developed
 Tunica Intima – one way valves
– Blood Resevoir
– Skeletal Muscles help move blood

Venules – small veins
DIAGRAM
CAPILLARIES

Smallest; walls one cell thick
– Largest total cross sectional area
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
Connect arteriole and venous systems
Capillary permeability varies
DIAGRAM
– Muscle tissue cap small
– Gland, intestinal cap. Larger
– Liver, spleen and bone marrow cap. Largest 
sinusoids

Capillary Arrangement
– Nearly every tissue has associated cap. Bed
– High metabolic  extensive cap. Bed
– Can be shut off or opened up
 Precapillary sphincters
CAPILLARIES

Only place for exchange
– Diffusion
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At Tissues: O2, nutrients out; CO2, wastes in
At alveoli (lungs): CO2 out; O2 in
Sm. Intestines: Nutrients in
Lipid soluble and small molecules diffuse easily
Plasma Proteins remain in blood
– Filtration – hydrostatic pressure
 Pressure decreases as distance increases
 Filtration greater at arteriole end
 Water is lost
DIAGRAM
– Movement depends on osmotic and hydrostatic pressures
– Lymph system returns fluid
Arteries VS Veins
Capillary Structure
Fluid Pressure at Capillaries