2. Blood Vessels

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Chapter 19

The Cardiovascular System: Blood Vessels: Part A

1. Intro

2. Blood Vessels

• Delivery system of dynamic structures that begins and ends at the heart

• Arteries: carry blood away from the heart; oxygenated except for pulmonary circulation and umbilical vessels of a fetus

• Capillaries: contact tissue cells and directly serve cellular needs

• Veins: carry blood toward the heart

3. Fig. 19.2 pg. 697

4. Structure of Blood Vessel Walls

Arteries and veins

• Tunica intima, tunica media, and tunica externa

• Lumen

• Central blood-containing space

• Capillaries

• Endothelium with sparse basal lamina

5. Fig. 19.1 pg. 696

6. Tunics

• Tunica intima

• Endothelium lines the lumen of all vessels

• In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present

7. Tunics

• Tunica media

• Smooth muscle and sheets of elastin

• Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels

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8. Tunics

• Tunica externa (tunica adventitia)

• Collagen fibers protect and reinforce

• Larger vessels contain vasa vasorum to nourish the external layer

9. Table 19.1a pg. 698

10. Table 19.1b pg. 698

11. Elastic (Conducting) 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 is ejected from the heart

12. Muscular (Distributing) Arteries and Arterioles

• Distal to elastic arteries; deliver blood to body organs

• Have thick tunica media with more smooth muscle

• Active in vasoconstriction

13. Arterioles

• Smallest arteries

• Lead to capillary beds

• Control flow into capillary beds via vasodilation and vasoconstriction

14. Capillaries

• Microscopic blood vessels

• Walls of thin tunica intima, one cell thick

• Pericytes help stabilize their walls and control permeability

• Size allows only a single RBC to pass at a time

15. Capillaries

• In all tissues except for cartilage, epithelia, cornea and lens of eye

• Functions: exchange of gases, nutrients, wastes, hormones, etc.

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16. Fig. 19.2

17. Capillaries

• Three structural types

1.

Continuous capillaries

2.

Fenestrated capillaries

3.

Sinusoidal capillaries (sinusoids)

18. Continuous Capillaries

• Abundant in the skin and muscles

• Tight junctions connect endothelial cells

• Intercellular clefts allow the passage of fluids and small solutes

• Continuous capillaries of the brain

• Tight junctions are complete, forming the blood-brain barrier

19. Fig. 19.3a Pg. 699

20. Fenestrated Capillaries

• Some endothelial cells contain pores (fenestrations)

• More permeable than continuous capillaries

• Function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys)

21. Fig. 19.3b Pg. 699

22. Sinusoidal Capillaries

• Fewer tight junctions, larger intercellular clefts, large lumens

• Usually fenestrated

• Allow large molecules and blood cells to pass between the blood and surrounding tissues

• Found in the liver, bone marrow, spleen

23. Fig. 19.3c Pg. 699

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24. Capillary Beds

• Interwoven networks of capillaries form the microcirculation between arterioles and venules

• Consist of two types of vessels

1.

Vascular shunt (metarteriole

—thoroughfare channel):

• Directly connects the terminal arteriole and a postcapillary venule

25. Capillary Beds

2.

True capillaries

• 10 to 100 exchange vessels per capillary bed

• Branch off the metarteriole or terminal arteriole

26. Blood Flow Through Capillary Beds

• Precapillary sphincters regulate blood flow into true capillaries

• Regulated by local chemical conditions and vasomotor nerves

27. Fig 19.4 pg. 700

28. Venules

• Formed when capillary beds unite

• Very porous; allow fluids and WBCs into tissues

• Postcapillary venules consist of endothelium and a few pericytes

• Larger venules have one or two layers of smooth muscle cells

29. Veins

• Formed when venules converge

• Have thinner walls, larger lumens compared with corresponding arteries

• Blood pressure is lower than in arteries

• Thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks

• Called capacitance vessels (blood reservoirs); contain up to 65% of the blood supply

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30. Fig: Isn’t in your book

31. Fig. 19.5 pg. 701

32. Veins

• Adaptations that ensure return of blood to the heart

1.

Large-diameter lumens offer little resistance

2.

Valves prevent backflow of blood

• Most abundant in veins of the limbs

• Venous sinuses: flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain)

33. Vascular Anastomoses

• Interconnections of blood vessels

• Arterial anastomoses provide alternate pathways (collateral channels) to a given body region

• Common at joints, in abdominal organs, brain, and heart

• Vascular shunts of capillaries are examples of arteriovenous anastomoses

• Venous anastomoses are common

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