1. BLOOD VESSELS
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2. Delivery system of dynamic structures that begins and ends at heart
Blood Vessels
Delivery system of dynamic structures that begins and ends at heart
Arteries: carry blood away from heart; oxygenated except for pulmonary circulation and umbilical vessels of fetus
Capillaries: contact tissue cells; directly serve cellular needs
Veins: carry blood toward heart
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3. Artery
Vein
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4. Structure of Blood Vessel Walls
Lumen
Central blood-containing space
Three wall layers in arteries and veins
Tunica intima,
Tunica media, and
Tunica externa
Capillaries
Endothelium with sparse basal lamina
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5. • Internal elastic membrane • External elastic membrane
Tunica intima
• Endothelium
• Subendothelial layer
• Internal elastic membrane
Tunica media
(smooth muscle and
elastic fibers)
Valve
• External elastic membrane
Tunica externa
(collagen fibers)
• Vasa vasorum
Lumen
Lumen
Artery
Capillary network
Vein
Basement membrane
Endothelial cells
Capillary
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6. Tunics Tunica intima Endothelium lines lumen of all vessels
Continuous with endocardium
Slick surface reduces friction
Subendothelial layer in vessels larger than 1 mm; connective tissue basement membrane
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7. Tunics Tunica media Smooth muscle and sheets of elastin
Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels
Influence blood flow and blood pressure
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8. Tunica externa (tunica adventitia)
Tunics
Tunica externa (tunica adventitia)
Collagen fibers protect and reinforce; anchor to surrounding structures
Contains nerve fibers, lymphatic vessels
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9. Sinusoid Metarteriole
Venous system
Arterial system
Large veins
(capacitance
vessels)
Heart
Elastic
arteries
(conducting
arteries)
Large
lymphatic
vessels
Lymph
node
Muscular
arteries
(distributing
arteries)
Lymphatic
system
Small veins
(capacitance
vessels)
Arteriovenous
anastomosis
Lymphatic
capillaries
Sinusoid
Arterioles
(resistance
vessels)
Terminal
arteriole
Postcapillary
venule
Metarteriole
Thoroughfare
channel
Capillaries
(exchange
vessels)
Precapillary
sphincter
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10. Arterial System: Elastic Arteries
Large thick-walled arteries with elastin in all three tunics
Aorta and its major branches
Large lumen offers low-resistance
Act as pressure reservoirs—expand and recoil as blood ejected from heart
Smooth pressure downstream
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11. Arterial System: Muscular Arteries
Distal to elastic arteries
Deliver blood to body organs
Thick tunica media with more smooth muscle
Active in vasoconstriction
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12. Arterial System: Arterioles
Smallest arteries
Lead to capillary beds
Control flow into capillary beds via vasodilation and vasoconstriction
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14. Microscopic blood vessels Walls of thin tunica intima
Capillaries
Microscopic blood vessels
Walls of thin tunica intima
In smallest one cell forms entire circumference
Pericytes help stabilize their walls and control permeability
Diameter allows only single RBC to pass at a time
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15. In all tissues except for cartilage, epithelia, cornea and lens of eye
Capillaries
In all tissues except for cartilage, epithelia, cornea and lens of eye
Provide direct access to almost every cell
Functions
Exchange of gases, nutrients, wastes, hormones, etc., between blood and interstitial fluid
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16. Three structural types
Capillaries
Three structural types
Continuous capillaries
Fenestrated capillaries
Sinusoid capillaries (sinusoids)
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17. Continuous Capillaries
Abundant in skin and muscles
Intercellular clefts allow passage of fluids and small solutes
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18. Pericyte Tight junction
Red blood
cell in lumen
Intercellular
cleft
Endothelial
cell
Basement
membrane
Tight junction
Pinocytotic
vesicles
Endothelial
nucleus
Continuous capillary. Least permeable, and most
common (e.g., skin, muscle).
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19. Fenestrated Capillaries
Some endothelial cells contain pores (fenestrations)
Permeable
Function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys)
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20. Basement membrane Tight junction
Pinocytotic
vesicles
Red blood
cell in lumen
Fenestrations
(pores)
Endothelial
nucleus
Intercellular
cleft
Basement membrane
Tight junction
Endothelial
cell
Fenestrated capillary. Large fenestrations (pores)
increase permeability. Occurs in areas of active
absorption or filtration (e.g., kidney, small intestine).
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21. Blood flow sluggish – allows modification
Sinusoid Capillaries
Fewer tight junctions; usually fenestrated; larger intercellular clefts; large lumens
Blood flow sluggish – allows modification
Large molecules and blood cells pass between blood and surrounding tissues
Found only in the liver, bone marrow, spleen, adrenal medulla
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22. Sinusoid capillary. Most permeable. Occurs in special
Endothelial
cell
Red blood
cell in lumen
Large
intercellular
cleft
Tight junction
Incomplete
basement
membrane
Nucleus of
endothelial
cell
Sinusoid capillary. Most permeable. Occurs in special
locations (e.g., liver, bone marrow, spleen).
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23. Blood Flow Through Capillary Beds
Precapillary sphincters regulate blood flow into true capillaries
Blood may go into true capillaries or to shunt
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24. Precapillary sphincters
Vascular shunt
Precapillary sphincters
Metarteriole
Thoroughfare
channel
True
capillaries
Terminal arteriole
Postcapillary venule
Sphincters open—blood flows through true capillaries.
Terminal arteriole
Postcapillary venule
Sphincters closed—blood flows through metarteriole – thoroughfare
channel and bypasses true capillaries.
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25. Venous System: Venules
Formed when capillary beds unite
Smallest postcapillary venules
Very porous; allow fluids and WBCs into tissues
Consist of endothelium and a few pericytes
Larger venules have one or two layers of smooth muscle cells
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26. Formed when venules converge
Veins
Formed when venules converge
Have thinner walls, larger lumens compared with corresponding arteries
Blood pressure lower than in arteries
Thin tunica media; thick tunica externa of collagen fibers and elastic networks
Called capacitance vessels (blood reservoirs); contain up to 65% of blood supply
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27. Pulmonary blood vessels 12% Systemic arteries and arterioles 15%
Heart 8%
Capillaries 5%
Systemic veins
and venules 60%
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28. Adaptations ensure return of blood to heart despite low pressure
Veins
Adaptations ensure return of blood to heart despite low pressure
Venous valves prevent backflow of blood
Most abundant in veins of limbs
Venous sinuses: flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain)
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29. © 2013 Pearson Education, Inc.

30. Artery
Vein
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31. Systemic Blood Pressure
Pumping action of heart generates blood flow
Pressure results when flow is opposed by resistance
Systemic pressure
Highest in aorta
Declines throughout pathway
0 mm Hg in right atrium
Steepest drop occurs in arterioles
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32. 120 Systolic pressure 100 Mean pressure 80 Blood pressure (mm Hg) 60
Diastolic
pressure 40 20
Aorta
Veins
Arteries
Venules
Arterioles
Capillaries
Venae cavae
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