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Copyright © 2011 Pearson Education, Inc.
Overview
Structure:
Arteries
Veins
Capillaries
Copyright © 2011 Pearson Education, Inc.
Blood Vessels
• Transport blood
• Arteries: carry blood away from the heart
• Usually ↑ O2
• Pulmonary circulation exception
• Veins: carry blood toward the heart
• Usually ↓ O2
• Capillaries: contact tissue directly
Copyright © 2011 Pearson Education, Inc. Figure 18.2
Large veins
Arteriovenousanastomosis
Postcapillaryvenule
SinusoidArterioles
Muscular arteries
Elastic arteries
Small veins
Capillaries(exchange vessels)
sphincter
Venous system Arterial systemHeart
Copyright © 2011 Pearson Education, Inc.
BLOOD VESSEL STRUCTURE
Tunics (extera, media, intima)
Copyright © 2011 Pearson Education, Inc.
Structure of Blood Vessel Walls
• Arteries and veins
1. Tunica intima
2. Tunica media
3. Tunica externa
• Lumen
• Central space, contains blood
• Capillaries
• Endothelium with basal layer
Copyright © 2011 Pearson Education, Inc. Figure 18.1b
Tunica media(smooth muscle andelastic fibers)
Tunica externa(collagen fibers)
LumenArtery
LumenVein
Internal elastic lamina
External elastic lamina
Valve
(b)
Endothelial cellsBasement membrane
Capillarynetwork
Capillary
Tunica intima• Endothelium• Subendothelial layer
Copyright © 2011 Pearson Education, Inc.
Tunics
• Tunica intima
• Endothelium
• lines the lumen
• Subentothelial layer
• In larger vessels (>1 mm)
EndotheliumSubendothelial layer
Copyright © 2011 Pearson Education, Inc.
Tunics
• Tunica media
• Smooth muscle
• Controls:
• Vasoconstriction
• Vasodilation
Smooth muscle
Copyright © 2011 Pearson Education, Inc.
Tunics
• Tunica externa
• Outer most layer
• Collagen fibers reinforce
• Large vessels have vasa vasorum
• “vessels to the vessels”
Tunica externa
Copyright © 2011 Pearson Education, Inc.
TYPES OF ARTERIES
Elastic, Muscular and Arterioles
Copyright © 2011 Pearson Education, Inc.
Elastic (Conducting) Arteries
• Largest thick-walled arteries
• Aorta / major branches
• elastin in all tunics
• Blood directly from heart
• Resist high pressure
• Large volume
• Large lumen = low-resistance
Copyright © 2011 Pearson Education, Inc.
Muscular (Distributing) Arteries
• Distal to elastic arteries
• Deliver blood to organs
• Have thick tunica media
• smooth muscle
• Vasoconstriction
• Vasodilation
Copyright © 2011 Pearson Education, Inc.
Arterioles
• Smallest arteries
• Lead to capillary beds
• Control of flow w/
• vasodilation and vasoconstriction
Copyright © 2011 Pearson Education, Inc. Table 18.1 (1 of 2)
Copyright © 2011 Pearson Education, Inc.
Capillaries
• Smallest blood vessels
• thin tunica intima
• one cell thick
• Only one RBC wide
• Pericytes support and control permeability
Copyright © 2011 Pearson Education, Inc.
CAPILLARIES
Copyright © 2011 Pearson Education, Inc.
Capillaries
• Location-
• all tissues except for:
• cartilage, epithelia, cornea and lens of eye
• Functions-
• Exchange:
• gases, nutrients, wastes, hormones, etc.
Copyright © 2011 Pearson Education, Inc. Figure 18.2
Large veins(capacitancevessels)
Arteriovenousanastomosis
Postcapillaryvenule
SinusoidArterioles
Muscular arteries
Elastic arteries
Small veins(capacitancevessels)
Capillaries(exchange vessels)
Venous system Arterial systemHeart
Copyright © 2011 Pearson Education, Inc.
Capillaries
• Three structural types
1. Continuous capillaries
2. Fenestrated capillaries
3. Sinusoidal capillaries
Copyright © 2011 Pearson Education, Inc.
Continuous Capillaries
• Location:
• skin & muscles
• Cells connected with tight junctions
• Clefts allow passage
• Blood-brain barrier
• ↑ Tight junctions
• Limits passage
Copyright © 2011 Pearson Education, Inc. Figure 18.3a
Red bloodcell in lumen
IntercellularcleftEndothelialcell
Endothelialnucleus
Tight junction Pinocytoticvesicles
Pericyte
Basementmembrane
(a) Continuous capillary. Least permeable, and most common (e.g., skin, muscle).
Copyright © 2011 Pearson Education, Inc.
Fenestrated Capillaries
• Endothelial cells contain pores “fenestrations”
• Function:
• Absorption / Filtration
• Location:
• small intestines, endocrine glands, and kidneys
Copyright © 2011 Pearson Education, Inc. Figure 18.3b
Red bloodcell in lumen
Intercellularcleft
Fenestrations(pores)
Endothelialcell
EndothelialnucleusBasement membrane
Tight junction
Pinocytoticvesicles
(b) Fenestrated capillary. Large fenestrations (pores) increase permeability. Occurs in special locations (e.g., kidney, small intestine).
Copyright © 2011 Pearson Education, Inc.
Sinusoidal Capillaries
• Larger intercellular clefts
• Function:
• Passage of large molecules and blood cells
• Location:
• liver, bone marrow, spleen
Copyright © 2011 Pearson Education, Inc. Figure 18.3c
Nucleus ofendothelialcell
Red bloodcell in lumen
Endothelialcell
Tight junction
Incompletebasementmembrane
Largeintercellularcleft
(c) Sinusoidal capillary. Most permeable. Occurs in special locations (e.g., liver, bone marrow, spleen).
Copyright © 2011 Pearson Education, Inc.
Capillary Beds
• Networks connecting arterioles and venules
• Sphincters control flow into capillaries
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Venules & Anastomosis
• Venules (smallest vein)
• Form from capillary beds
• “Postcapillary venules”
• Anastomosis
• Alternative connections between arteries and veins
Copyright © 2011 Pearson Education, Inc.
Veins
• Return blood flow to heart
• Converging venules
• larger lumens w/ thin walls
• ↓ blood pressure
• Blood reservoirs
• contain ~65% of blood supply
Copyright © 2011 Pearson Education, Inc.
Veins
• Adaptations to ensure blood return
1. Low resistance
• Large lumen
2. Valves
• Prevent backflow
• in limbs
• Venous sinuses: flattened veins
• Ex. Coronary sinus
Copyright © 2011 Pearson Education, Inc. Figure 18.1a
Artery
Vein
(a)
Copyright © 2011 Pearson Education, Inc.
Arteries Veins
Delivery Blood pumped into single systemic artery—the aorta
Blood returns via superior and interior venae cavae and the coronary sinus
Location Deep, and protected by tissues Both deep and superficial
Pathways Fairly distinct Numerous interconnections
Supply/drainage Predictable supply Usually similar to arteries, except dural sinuses and hepatic portal circulation
Differences Between Arteries and Veins