Chapter 21: Blood Vessels and Circulation

1. Chapter 21:Blood Vessels and Circulation Primary sources for figures and content: Marieb, E. N. Human Anatomy & Physiology. 6th ed. San Francisco: Pearson Benjamin Cummings, 2004. Martini, F. H. Fundamentals of Anatomy & Physiology. 6th ed. San Francisco: Pearson Benjamin Cummings, 2004.

2. The types of blood vessels, their structures and functions.

3. 6 Classes of Blood Vessels • Arteries: • carry blood away from heart • Branch and decrease in diameter • Arterioles: • Are smallest branches of arteries • Connect to capillaries • Capillaries: • are smallest blood vessels • location of exchange between blood and interstitial fluid

4. 6 Classes of Blood Vessels • Venules: • Smallest veins • collect blood from capillaries • Veins: • return blood to heart • Converge and increase in diameter • Anastomoses: - Bypass connection between vessels

6. The Largest Blood Vessels • Attach to heart • Pulmonary trunk: • carries blood from right ventricle • to pulmonary circulation • Aorta: • carries blood from left ventricle • to systemic circulation

7. The Smallest Blood Vessels • Capillaries • Have small diameter and thin walls • Chemicals and gases diffuse across walls

8. The Anatomy of Blood Vessels • Arteries, veins, and capillaries • Have different functions • Have different structures

10. Arteries and Veins • Walls have 3 layers: 1. tunica intima 2. tunica media 3. tunica externa

11. The Tunica Intima/Tunica interna • Is the innermost layer • Includes: • the endothelial cell lining • Endothelium = simple squamous epithelial-like cells connected by tight junctions • With basal lamina of loose connective tissue containing elastic fibers (elastin) • Arteries have internal elastic membrane • extra layer of elastic fibers on the outer edge

12. Tunica Media • Is the middle layer • Contains smooth muscle cells in loose connective tissue with sheets of elastin • Binds to inner and outer layers • Arteries have external elastic membrane • extra layer of elastic fibers on the outer edge

13. Tunica Externa/Tunica adventitia • Is outer layer • Contains collagen rich external connective tissue sheath • Infiltrated with nerve fibers and lymphatic vessels • Large vessels contain vasa vasorum • Arteries = more collagen, scattered elastic fiber bands • Veins = extensive fiber networks, bundles of smooth muscle cells

14. Vasa Vasorum • Small arteries and veins • Found: • in walls of large arteries and veins • Function: • Supply cells of tunica media and tunica externa

15. Structure of Vessel Walls Figure 21-1

17. Structure of Blood Vessels Figure 21-2

18. 1. Arteries • Designed to change diameter, elastic and muscular, thick walls • Tunica externa contains collagen • Pressure • Elasticity allows arteries to absorb pressure waves that come with each heartbeat • Contractility • Arteries change diameter • Controlled by sympathetic division of ANS

19. Vasoconstriction and Vasodilation • Vasoconstriction • The contraction of arterial smooth muscle by the ANS • Vasodilatation • The relaxation of arterial smooth muscle • Enlarging the lumen • Affect: • afterload on heart • peripheral blood pressure • capillary blood flow

20. Artery Characteristics • From heart to capillaries, arteries change: • from elastic arteries • to muscular arteries • to arterioles

21. Elastic Arteries • Also called conducting arteries • Diameter up to 2.5cm • Elastin in all three tunics • Elasticity evens out pulse force • Stretch (ventricular systole) and rebound (ventricular diastole) • Not involved in systemic vasoconstriction

22. Muscular Arteries • Also called distribution arteries • Are medium-sized (most arteries) • Transport blood to organs and tissues • Diameter 10mm – 0.3mm • More smooth muscle and less elastin in tunica media than elastic arteries • Involved in systemic vasoconstriction via sympathetic stimulation

24. 2. Arterioles • Also known as resistance vessels • Connect blood supply to capillary beds • Are small – diameters 300µm – 10µm • All three tunics thin with few elastic fibers • Involved in local vasoconstriction via endocrine or sympathetic stimulation

25. Health Problems with Arteries 1. Aneurysm: • Pressure of blood exceeds elastic capacity of wall • Causes bulge or weak spot prone to rupture • Caused by chronic high blood pressure or arteriosclerosis

26. Health Problems with Arteries 2. Arteriosclerosis: • Variety of pathological conditions causing changes in walls that decrease elasticity (“thickenings”) • Focal calcification = smooth muscle degenerates, replaced by calcium salts • Atherosclerosis 3. Atherosclerosis: lipid deposits

27. Health Problems with Arteries 4. Stroke = cerebrovascular accident (CVA) • Interruption of arterial supply to portion of brain due to embolism or atherosclerosis • Brain tissue dies and function is lost

28. 3. Capillaries • Only vessels with thin enough wall structure to allow complete diffusion • Designed to allow diffusion to/from the tissue • Diameter 8 µm • Consists of tunica intima only • endothelium + basal lamina • Human body contains 25,000 miles of capillaries

29. Capillary Structure Figure 21-4

30. Capillary Function • Location of all exchange functions of cardiovascular system • Materials diffuse between blood and interstitial fluid

31. Capillary Structure • Endothelial tube, inside thin basal lamina • No tunica media • No tunica externa • Diameter is similar to red blood cell

32. Capillaries

33. Types of Capillaries • Continuous capillaries • Normal diffusion to all tissues except epithelium and cartilage • Complete endothelium, tight junctions • Functions: • Permit diffusion of: water, small solutes, lipid-soluble materials • Block: blood cells and plasma proteins • e.g., the blood–brain barrier

34. Types of Capillaries 2. Fenestrated capillaries • High volume fluids or large solute transfer • Pores/fenestrations span endothelium • Permit rapid exchange of water and larger solutes between plasma and interstitial fluid

35. Fenestrated Capillaries • Are found in: • choroid plexus • endocrine organs • kidneys • intestinal tract

36. Sinusoids • Areas in: • liver • spleen • bone marrow • endocrine organs • Have gaps between adjacent endothelial cells

37. Types of CapillariesSinusoids 3. Sinusoids • Cell or large protein exchange • Gaps between endothelial cells • Permit free exchange of water and large plasma proteins between blood and interstitial fluid • Phagocytic cells monitor blood at sinusoids • Found: liver, bone marrow, lymphoid tissues

38. Capillary Networks Figure 21-5

39. Capillaries Networks • Organized into Capillary bed or capillary plexus • Connect 1 arteriole and 1 venule • Not enough total blood to fill all capillaries at once • Flow through capillary bed must be controlled based on need via precapillary spincters

40. Capillary Sphincter • Guards entrance to each capillary • Opens and closes, causing capillary blood to flow in pulses

41. Vasomotion • Contraction and relaxation cycle of capillary sphincters • Spincter relaxed = flow in capillary bed • Spincter constricted = capillary bed empty, flow through anastomoses • Causes blood flow in capillary beds to constantly change routes

42. Structure of Blood Vessels Figure 21-2

43. Veins vs. Arteries • Are larger in diameter • Have thinner walls • Carry lower blood pressure

44. 4. Veins • Collect blood from capillaries in tissues and organs • Return blood to heart • Can serve as blood reservoir • Thin walls but large lumens • Thin tunica media = little smooth muscle or elastin • Tunica externa = elastin and smooth muscle • Tunica intima = valves to prevent back-flow

45. 3 Vein Categories • Venules (5th type of vessel): • very small veins • Average diameter 20 µm • collect blood from capillary beds • Small venules lack tunica media • Medium-sized veins: - Diameter 2-9 mm • Large Veins: - Diameters up to 3 cm

46. Valves in the Venous System Valves in tunica intima insure one way movement Figure 21-6

47. Vein Valves • Valves = Folds of tunica intima • Prevent blood from flowing backward • Pressure from heart drives blood flow in arteries, but pressure in veins often too low to oppose gravity • Compression pushes blood toward heart • Skeletal muscle movement required to “squish” blood through veins

48. Health Problems with Veins • Resistance to flow (gravity, obesity) causes pooling above valves, veins stretch out • Varicose veins • Hemorrhoids

49. Blood Reservoirs in Venous System • Venous system contains 65-70% total blood volume • Can constrict during hemorrhage to keep volume in capillaries and arteries near normal

50. 6. Anastomoses • Bypass routes between vessels • Bypass the capillary bed • Not present in retina, kidney, or spleen • More common in veins