1. Blood Vessels
Ch 21

2. Blood Vessels
Blood is carried in a closed system of vessels that begins and ends at the heart
The three major types of vessels are arteries, capillaries, and veins
Arteries carry blood away from the heart, veins carry blood toward the heart
Capillaries contact tissue cells and directly serve cellular needs

3. Tunics Tunica interna (tunica intima) Tunica media
Endothelial layer that lines the lumen of all vessels
In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present
Tunica media
Smooth muscle and elastic fiber layer, regulated by sympathetic nervous system
Controls vasoconstriction/vasodilation of vessels

4. Tunics Tunica externa (tunica adventitia)
Collagen fibers that protect and reinforce vessels
Larger vessels contain vasa vasorum

5. Blood Vessel Structure
simple squamous epithelium
smooth muscle tissue
Blood Vessel Structure
connective tissue

6. • Subendothelial layer Internal elastic lamina
Tunica intima
• Endothelium
Valve
• Subendothelial layer
Internal elastic lamina
Tunica media
(smooth muscle and
elastic fibers)
External elastic lamina
Tunica externa
(collagen fibers)
Lumen
Vein
Lumen
Artery
Capillary
network
Basement membrane
Endothelial cells
(b)
Capillary
Figure 19.1b

7. Artery
vein

8. Arteries 1. Carry blood away from the heart.
2. Thick-walled to withstand hydrostatic pressure of the blood during ventricular systole.
3. Blood pressure pushes blood through the vessel

9. Elastic (Conducting) Arteries
Thick-walled arteries near the heart; the aorta and its major branches
Large lumen allow low-resistance conduction of blood
Contain elastin in all three tunics
Withstand and smooth out large blood pressure fluctuations
Allow blood to flow fairly continuously through the body

10. Muscular (Distributing) Arteries and Arterioles
Muscular arteries – distal to elastic arteries; deliver blood to body organs
Have thick tunica media with more smooth muscle and less elastic tissue
Active in vasoconstriction
Arterioles – smallest arteries; lead to capillary beds
Control flow into capillary beds via vasodilation and constriction

11. Pressure reservoir function of elastic arteries
Fig.21.02
Pressure reservoir function of elastic arteries

12. Veins Carry blood to the heart. Thinner-walled than arteries.
Possess one-way valves that prevent backwards flow of blood.
Blood flow due to body movements, not from blood pressure.

13. One-Way Valves in Veins
open valve
closed valve

14. Capillaries One cell thick, endothilium Function: Diffusion Filtration
Transcytosis

15. Diffusion O2
CO2

16. Filtration

17. Transcytosis Caveolae Pinocytotic vesicles Endothelial fenestration
Lumen
Caveolae
Pinocytotic
vesicles
Endothelial
fenestration
(pore)
Intercellular
cleft
Transport
via vesicles or
caveolae (large
substances) 4
Movement
through
fenestrations
(water-soluble
substances) 3
Basement
membrane
Movement
through intercellular
clefts (water-soluble
substances) 2
Diffusion
through
membrane
(lipid-soluble
substances) 1
Figure (2 of 2)

18. Capillaries Capillaries are the smallest blood vessels
Walls consisting of a thin tunica interna, one cell thick
Allow only a single RBC to pass at a time
Pericytes on the outer surface stabilize their walls
There are three structural types of capillaries: continuous, fenestrated, and sinusoids

19. Continuous Capillaries
Continuous capillaries are abundant in the skin and muscles, and have:
Endothelial cells that provide an uninterrupted lining
Adjacent cells that are held together with tight junctions
Intercellular clefts of unjoined membranes that allow the passage of fluids

20. Continuous Capillaries
Continuous capillaries of the brain:
Have tight junctions completely around the endothelium
Constitute the blood-brain barrier

21. Continuous Capillaries
Figure 19.3a

22. Fenestrated Capillaries
Found wherever active capillary absorption or filtrate formation occurs (e.g., small intestines, endocrine glands, and kidneys)
Characterized by:
An endothelium riddled with pores (fenestrations)
Greater permeability to solutes and fluids than other capillaries

23. Fenestrated Capillaries
Figure 19.3b

24. Sinusoids
Highly modified, leaky, fenestrated capillaries with large lumens
Found in the liver, bone marrow, lymphoid tissue, and in some endocrine organs
Allow large molecules (proteins and blood cells) to pass between the blood and surrounding tissues
Blood flows sluggishly, allowing for modification in various ways

25. Sinusoids
Figure 19.3c

26. Capillary Beds
A microcirculation of interwoven networks of capillaries, consisting of:
Vascular shunts – metarteriole–thoroughfare channel connecting an arteriole directly with a postcapillary venule
True capillaries – 10 to 100 per capillary bed, capillaries branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed

27. Capillaries
capillary vessel

28. arteriole
capillaries
venule

29. (a) Sphincters open—blood flows through true capillaries.
Vascular shunt
Precapillary
sphincters
Metarteriole
Thoroughfare channel
True capillaries
Terminal arteriole
Postcapillary venule
(a) Sphincters open—blood flows through true capillaries.
Terminal arteriole
Postcapillary venule
(b) Sphincters closed—blood flows through metarteriole
thoroughfare channel and bypasses true capillaries.
Figure 19.4

30. Blood pressure (BP)
Force per unit area exerted on the wall of a blood vessel by the blood
Expressed in mm Hg
Measured as systemic arterial BP in large arteries near the heart
The pressure gradient provides the driving force that keeps blood moving from higher to lower pressure areas

31. Resistance (peripheral resistance)
Opposition to flow
Measure of the amount of friction blood encounters
Generally encountered in the peripheral systemic circulation
Three important sources of resistance
Blood viscosity
Total blood vessel length
Blood vessel diameter

32. Systemic Blood Pressure
The pumping action of the heart generates blood flow
Pressure results when flow is opposed by resistance
Systemic pressure
Is highest in the aorta
Declines throughout the pathway
Is 0 mm Hg in the right atrium
The steepest drop occurs in arterioles

33. Systolic pressure
Mean pressure
Diastolic
pressure
Figure 19.6

34. Resistance Factors that remain relatively constant: Blood viscosity
The “stickiness” of the blood due to formed elements and plasma proteins
Blood vessel length
The longer the vessel, the greater the resistance encountered

35. Resistance Frequent changes alter peripheral resistance
Varies inversely with the fourth power of vessel radius
E.g., if the radius is doubled, the resistance is 1/16 as much

36. Resistance
Small-diameter arterioles are the major determinants of peripheral resistance
Abrupt changes in diameter or fatty plaques from atherosclerosis dramatically increase resistance
Disrupt laminar flow and cause turbulence

37. 120-
80-
Mm Hg
Artery
Arteriole
Capillary
Venule
Vein

38. Sphygmomanometer
Used to estimate pressure

39. Measuring Blood Pressure

40. Blood Pressure
120/80 is good

41. Superficial Pulse Points- arteries, not veins
temporal
60 beats/minute
facial
carotid
Temporal artery
Facial artery
Common carotid artery
Brachial artery
Radial artery
Femoral artery
Popliteal artery
Posterior tibial artery
Dorsal pedis artery
brachial
radial
femoral
popliteal
Posterior tibial
Dorsal pedis

42. Homeostatic Imbalances
Tachycardia: abnormally fast heart rate (>100 bpm)
If persistent, may lead to fibrillation
Bradycardia: heart rate slower than 60 bpm
May result in grossly inadequate blood circulation
May be desirable result of endurance training

43. Circulatory Shock Any condition in which
Blood vessels are inadequately filled
Blood cannot circulate normally
Results in inadequate blood flow to meet tissue needs

44. Circulatory Shock
Hypovolemic shock: results from large-scale blood loss
Vascular shock: results from extreme vasodilation and decreased peripheral resistance
Cardiogenic shock: results when an inefficient heart cannot sustain adequate circulation

45. Three Types of Circulation
Pulmonary
Systemic
Coronary

46. Pulmonary Circulation
Figure 19.17b

47. Pulmonary Circulation
Figure 19.17a

48.                                                                                                                         
Systemic Circulation

49. Systemic Circulation
Figure 19.18

50. Coronary Circulation Aorta Pulmonary Superior trunk vena cava
Left atrium
Anastomosis
(junction of
vessels)
Left
coronary
artery
Right
atrium
Circumflex
artery
Right
coronary
artery
Left
ventricle
Right
ventricle
Anterior
interventricular
artery
Right
marginal
artery
Posterior
interventricular
artery
(a) The major coronary arteries
Figure 18.7a

51. Coronary Circulation Superior vena cava Great Anterior cardiac cardiac
vein
Anterior
cardiac
veins
Coronary
sinus
Small cardiac vein
Middle cardiac vein
(b) The major cardiac veins
Figure 18.7b

52. Major Arteries

53. Fig.21.18b

54. Fig.21.20

55. Fig.21.20

56. Fig.21.22a

57. Fig.21.23

58. Major Veins

59. Fig.21.25

60. Fig.21.26

61. Fig.21.27

62. Fig.21.28

63. Hepatic Portal Circulation
Inferior Vena cava
Hepatic Vein
Left Gastric Vein
Hepatic Portal
Splenic Vein
Inferior Mesentaric Vein
Renal Vein
Inferior Mesentaric Vein
Right Gastropiplore Vein
Superior Mesentaric Vein

64. Superior mesenteric vein
Abdominal aorta
Inferior vena cava
Proper hepatic artery
Tributaries from portions of stomach. pancreas & lg intestine
Hepatic veins
Splenic vein
Tributaries from sm intestine &
portions of stomach, lg intestine & pancreas
liver
Hepatic portal vein
Superior mesenteric vein

65. Fetal circulation and changes at birth

66. INQUIRY
Sedentary people with elevated triglyceride levels who continue to eat fatty foods are likely to have a high level of _____.
Which vessels have valves?
Which vessel is the thickest walled?
What type of blood vessels carry blood away from the heart?
What happens when blood is pumped into the thin- walled vessels of the lungs?
Which blood vessel delivers blood to the brain?
Which blood vessel delivers blood to the liver?
The distinctive Korotkoff sounds heard when taking blood pressure are produced by ____.