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Characteristics of blood vessels
Blood vessels must be resilient, flexible and remain open
1
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Tunica intima- endothelium, basal lamina of the epithelial cells, subendothelial connective
tissue
3
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Tunica externa- connective tissue, merges with surrounding connective tissue

Arteries
Arteries have thick walls and the blood is under high pressure
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1
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b) Diameter: 2
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Muscular, distributing arteries
a) Example; brachial and femoral
b) Diameter: 0
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4cm
c) Distributes blood to muscles and organs
d) Capable of vasodilation and vasoconstriction to control rate of flow
e) Smooth muscle cells in tunica media
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Thick tunica externa
3
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Poorly defined tunica
externa
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It is the site of gas exchange
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Blood flow is slow
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It is 8 micrometre in
diameter
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Continuous capillaries
a
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Connective tissue
c
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Fenestrated
a
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Rapid exchange of water or large solutes
c
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Sinusoidal
a
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Incomplete or absent basement membrane
c
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Specialised lining cells
e
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Each metarteriole continues as a thoroughfare
channel which leads to a vein
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Precapillary sphincter- guards the entrance to each capillary
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Relaxation dilates entrance so it increases flow
Arteriovenous anastomoses- direct communication between arterioles and venules
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Venules
1
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3
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Collects blood from capillary bed and deliver it to small veins
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Contain valves



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