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BIOB34H3 Lecture Notes - Tunica Intima, Tunica Externa, Vasa Vasorum

Biological Sciences
Course Code
Ted Petit

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Chapter 20 Blood Vessels
General Pattern
- heart → arteries → arterioles → capillaries → venules → veins → heart
Basic Structure
- Three tunics surrounding a lumen
1. tunica intima
a. endothelium- slick surface reduces friction
b. basement membrane
c. elastic lamina
2. tunica media
a. smooth muscle and elastin sheets
b. regulates circulation by vasoconstriction or vasodilation
3. tunica externa
a. collagen and elastin fibers protect vessel and anchor it to other structures
b. larger vessels have their own blood vessels to supply outer tissues (called vasa vasorum)
- Carry blood away from heart
- Withstand high pressure
- Three groups
1. elastic arteries (conducting)
a. aorta and major branches
b. large (1 - 2.5 cm in diameter)
c. lots of elastin allows expansion and recoil (recoil keeps blood moving between heartbeats)
2. muscular arteries
a. deliver blood to specific body organs
b. .3 mm 1 cm in diameter
c. more smooth muscle, less elastin
d. active in vasoconstriction
3. arterioles
a. 10 m - .3 mm in diameter
b. larger ones have all three tunics
c. smaller ones are just smooth muscle surrounding endothelium
- Anastomoses
1. most tissues receive blood from more than one artery
2. anastomoses are branches between arteries
3. also occur between veins
4. called collateral circulation (allows alternate pathways for blood flow)
- Smallest vessels, 3 10 m in diameter
- Thin tunica intima only
- Allow exchanges between blood and tissues
- Near almost all cells (epithelial sheets, cartilage, some parts of eye have none)
- Varying distribution based on need
1. e.g., muscles, liver, kidneys, lungs, and nervous system have lots
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