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Chapter 22

BISC 3221 Chapter 22: Chapter 22 Notes- Blood Vessels and Circulation

Biological Sciences
Course Code
BISC 3221
Craig Frank

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Chapter 22: The Cardiovascular System (Vessels and Circulation)
22.1 Histological Organization of Blood Vessels
Walls of arteries and veins have 3 distinct layers (inner intima, middle media, outer adventitia)
o Innermost layer of blood vessel
o Includes endothelial lining of vessel, underlying layer of connective tissue with elastic
o In arteries, outer margin contains internal elastic membrane (layer of elastic fibers)
o In largest arteries, more connective tissue + thicker intima
o Middle layer of blood vessel
o Has concentric sheets of smooth muscle tissue in framework of loose connective tissue
o Smooth muscle encircles lumen of blood vessel, perform vasoconstriction/dilation
o Changes in vessel diameter affect BP and blood flow
o Collagen fibers bind media to intima and adventitia
o Arteries have external elastic membrane (elastic fiber band) between media and
o Connective tissue sheath around vessel
o Very thick, made of collagen, scattered bands of elastic fibers
o Fibers blend with adjacent tissues, stabilizing/anchoring blood vessel
o In veins, this layer is thicker than the media
Layered walls give vessels a lot of strength; too thick to allow diffusion to
bloodstream/surrounding tissues
Vasa vasorum: vessels that supply the muscle cells, fibroblasts, fibrocytes of the media and
Distinguishing Arteries from Veins
Walls of arteries are thicker than those of veins
Media of artery contains more smooth muscle and elastic fibers than those of vein
When not opposed by blood pressure, arterial walls contract (appear smaller in dissection or c.s.),
they retain their circular shape
Cut veins tend to collapse, look flattened/distorted
Endothelial lining of artery can’t contract, endothelium appears pleated when contracting; veins
lack these folds
Elastic Arteries
o AKA conducting arteries
o Large vessels, diameters up to 1 inch
o Transport large volumes away from heart
o i.e. pulmonary, common carotid, subclavian, common iliac arteries
o Not very thick walls compared to diameter, very resilient walls
o Media contains relatively few smooth muscle cells, more elastic fibers
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