1. Arteries
• AWAY
• Branch
• Typically oxygenated.

2. Capillaries • Smallest. • Most abundant. • Exchange – How many??
– Why?
• Exchange

3. Veins
• TOWARDS
• Converge.
• Typically deoxygenated.

4. 3 Layers of the Vascular Wall
• Tunica interna
• Tunica media
• Tunica externa.

5. Tunica Interna/Intima
• Lining.
• Endothelium.
• Supported by loose CT.
• Only layer in capillaries.

6. Tunica Media • Primarily smooth muscle plus elastic fibers.
• Most prominent layer in arteries.

7. Tunica Media • Smooth muscle tone • Regulated by: – Metabolites
– Hormones
– Sympathetic vasomotor
neurons.

8. • Vasomotor neurons constantly release NE onto TM smooth muscle.
– What does the NE do?
– Why have a constant release?

9. Increased NE release by a vasomotor neuron causes:
– Tunica media smooth muscle tone to:
– Vessel diameter to:
– Resistance to blood flow in the vessel to:
– Blood flow thru the vessel to:

10. This gentleman has fatty plaques in his lower
leg arteries.
How do you think they affect blood flow?
How does that relate to his facial
expression?
His doctor recommends that the sympathetic
nerves to those arteries be cut.
Why?

11. Tunica Externa/Adventitia
• Primarily collagen
• Function?
• Most prominent
layer in veins

12. Elastic Arteries
• Aorta and major branches.
• Act as AUXILIARY PUMPS.

14. Muscular Arteries
• Regional distribution
• Significant layer

15. Arterioles • Smallest. • May or may not have an externa.
• Highly innervated by vasomotor neurons.

16. Arterioles • Regulation of blood pressure and flow.
• Easy to change the diameter.
– How would you do it?
– Why would you want to?

17. Capillaries • Smallest. • Thin walls • Billions • Function?
• Almost everywhere.

18. Continuous capillaries–
Most common and least permeable.
No endothelial “holes”
Intercellular clefts.
Abundant in…

19. Fenestrated capillaries
– Endothelial “holes”
– Intercellular clefts
– Found in…

20. Sinusoidal capillaries.–
Most permeable and least common.
Big endothelial “holes”
Intercellular clefts.
Can have macrophages in their
lining. Why?
– Found in…

21. Why are capillaries organized into beds?
What tissues will have high densities of capillary beds?

22. What do precapillary sphincters do?
What determines whether the
sphincters are open or closed?
Vascular shunt vs.
True capillaries

23. If you were running,
1. Precapillary sphincters in your biceps femoris would …
2. Precapillary sphincters in your large intestine would…

24. Veins • All 3 tunics. • TE is the largest. • Thin walls
• Large lumens.
• Low resistance
• High compliance

25. Veins • Smooth muscle tone prevents too much distention.
• Capacitance vessels/Blood
reservoirs.
• 65%

26. Veins • Low pressure vessels. • Contain valves.
– What do they do?
– Where are they needed?

27. Venous Sinuses
• Thin-walled veins made of endothelium only.

28. Blood Flow • Volume per time.
• Flow thru systemic circuit = cardiac output.
• Flow to individual organs varies.
– How is this achieved?

29. Blood Pressure • Force per unit area exerted on
the vessel wall by blood.
• Millimeters of mercury (mmHg).
• All vessels

30. Resistance • Opposition to flow • Measure of friction.
• Peripheral resistance.
• Direction!

31. While this guy is running,
- the resistance of the arterioles
of his quadriceps needs to…
- the resistance of arterioles in
his colon needs to…

32. Sources of Resistance • Blood viscosity. • Total vessel length.
• Vessel radius.

33. Viscosity • Viscosity resistance. • Can you drink one of these with
a straw?
• What makes it challenging?

34. • What are the major contributors to blood
viscosity?
• Does viscosity change often in a healthy
person?
• An increase in plasma EPO will cause
resistance to…

35. Total Vessel Length • Length resistance.
• Does total vessel length change in a normal person?

36. • Which tube has greater intrinsic resistance?
• As total vessel length increases, resistance will…
• As total vessel length decreases, blood flow will…

37. Vessel Radius
• (1/radius4)
resistance

38. • Does vessel radius change in a normal healthy
person?
• Which vessels?
• How is the change achieved?

39. Which tube has the greater intrinsic resistance?
What layer of the vessel wall has the greatest effect on
vessel resistance? a. b. c.
Interna
Media
Externa

40. Resistance  (length)(viscosity)
(radius)4

41. Which tube has the LEAST resistance?
Which tube has the GREATEST resistance?

42. FLOW 
PRESSURE GRADIENT
RESISTANCE

43. • As resistance decreases, flow will…
• As the pressure gradient increases, flow will…
• Which does the heart influence more: pressure
gradient or resistance?

44. Blood Pressure • Why do all blood vessels have a BP?
• Which vessel do we usually care about?
• Where is systemic BP the highest?
• Where is systemic BP the lowest?

45. Arterial Blood Pressure Model

46. • What would happen to AP if the amount of blood
pumped into the arteries increased?
• Thus, arterial pressure varies directly with…

47. • What would happen to AP if the resistance in the
arterioles went up?
• Thus, arterial pressure varies directly with…

48. • What would happen to AP if there was more blood
in the entire system?
• Thus, arterial pressure varies directly with…

49. Systolic Blood Pressure

50. Diastolic Blood Pressure

52. Pulse • What creates it? • How/Where do you measure it?
• What’s its relationship to heart rate?

53. Pulse Pressure • Change in arterial pressure caused by ventricular
systole.
• Varies directly with…
• PP = SBP – DBP.

54. Mean Arterial Pressure (MAP)
• Arterial BP fluctuates. Why?
• MAP is the pressure driving blood flow.
• MAP is a weighted average of SBP and DBP.

55. Mean Arterial Pressure (MAP)
• MAP = ⅔DBP + ⅓SBP
• MAP = DBP + ⅓PP

56. Capillary Blood Pressure
• Low BP.
• Why is this good? (Think about the structure of a
capillary.)

57. Venous Blood Pressure
• Even lower BP.
• Very small gradient.

58. What is responsible for venous return?
• Remaining force imparted by ventricular systole.
• Gravity.
• Skeletal muscle pump.
• Respiratory pump.
• Venomotor action.

61. Skeletal Muscle Pump

62. Respiratory Pump Pressure in thoracic veins will…
Deep Inspiration
Thoracic volume will…
Pressure in thoracic cavity will…
Pressure in thoracic veins will…
Blood flow into thoracic veins and
towards the heart will…

63. Venomotor Tone • An increase in sympathetic activity causes:
– NE release on the TM of medium/large veins to…
– Venous pressure to…
– Venous return to…

64. Controlling MAP • Why do we need to control it? • Short term
• Long term

65. Brain Centers for Short Term MAP Control
• Vasomotor
• Cardioinhibitory
• Cardioacceleratory

66. Increased vasomotor center activity
__creased sympathetic output to arterioles
Vaso__________
__creased peripheral resistance
__creased blood pressure
What about a decrease in vasomotor activity?

67. Increased cardioacceleratory center activity
__creased sympathetic output to heart
__creased heart rate and stroke volume
__creased cardiac output
__creased blood pressure
What about a decrease in cardioacceleratory activity?

68. Increased cardioinhibitory center activity
__creased parasympathetic output to heart
__creased heart rate
__creased cardiac output
__creased blood pressure
What about a decrease in cardioacceleratory activity?

69. Baroreceptor Reflex

70. Baroreceptor Reflex • Frequency of these impulses is proportional
• Baroreceptors signals the
cardiac and vasomotor
centers via CN IX and X.
• Frequency of these
impulses is proportional
to MAP.
• Cardiac and vasomotor
centers adjust their
output accordingly.

71. Demonstrating the Baroreceptor Reflex
• Take the subject’s radial pulse.
• Find the carotid pulse point and GENTLY press
on it.
• What will happen to the radial pulse?
• Why?

72. Adrenal Medullary Mechanism
• Release epinephrine (and a
small amt of NE) in response
to:
– Large drops in MAP.
– Increases in physical activity.
– Stressful situations.

73. • How would activation of the adrenal
Adrenal Medullary Mechanism
• How would activation of the adrenal
medulla affect: – HR SV CO PR BP

74. Renin-Angiotensin-Aldosterone System
Angiotensin II

75. Indirect Mechanism Renin-Angiotensin-Aldosterone System
Angiotensin II
Vasoconstriction
Aldosterone &
Thirst
Antidiuretic
hormone
Increased TPR
Increased BV
Increased BP

76. Indirect Mechanism Renin-Angiotensin-Aldosterone System
• In response to a fall in MAP, renin release
by the kidney would:
• In response to a rise in MAP, renin release
by the kidney would:

77. A 25yo woman complains to her doctor of
headaches and blurred vision. Her blood pressure is
200/130 mmHg. After the BP has been reduced,
investigations are made to find the cause of the
problem. It’s discovered that her left renal artery is
narrowed.
Why would this cause the rise in BP?

78. Long Term BP Control • Achieved by the...
• Primarily done by altering...

79. Long Term BP Control ____________ _________BP Large increase in BP
urine formation
urine output
____________
blood volume
_________BP

80. • As we go from the
aorta to the
billions of
capillaries, what
happens to the
total cross-
sectional area?
• What happens to
the velocity of
blood flow?

81. • As we go from the
billions of
capillaries to the
venae cavae, what
happens to the
total cross-
sectional area?
• What happens to
the velocity of
blood flow?

82. The Paradoxical Problem of the
Vasomotor Center

83. Local Regulation of Blood Flow
• Autoregulation - adjustment of blood flow to
each tissue according to its immediate needs.
• Surplus or deficiency of local chemicals
influences local vessel diameter and blood flow.

84. Local Regulation of Blood Flow
Tissue temp. ____
Working
Muscle Tissue
Tissue CO2 levels ___
Tissue O2 levels ___
Arterioles
serving tissue
vaso________
Lactic acid levels ___
______blood
flow to tissue
CO2 _______
Lactic acid _______
Heat _______
O2 ________

85. Capillary Exchange • Btwn blood plasma and tissue fluid.
• Nutrients, wastes,
signaling molecules
• FLUID

86. Capillary Fluid Exchange
• 4 forces
– Capillary osmotic pressure.
– Capillary hydrostatic pressure.
– Interstitial osmotic pressure.
– Interstitial hydrostatic pressure.

87. Capillary Hydrostatic Pressure
• A.k.a…
• What does it do?
ISF
CAPILLARY HP

88. Capillary Osmotic Pressure
• Mostly due to…
• What does it do?
ISF
CAPILLARY OP

89. Interstitial Hydrostatic Pressure
• Usually inconsequential b/c…
• What would it do?
ISF HP
CAPILLARY

90. Interstitial Osmotic Pressure
• Usually inconsequential b/c…
• What would it do?
ISF OP
CAPILLARY

91. Capillary Fluid Exchange
• Thebalance of what 2 forces typically determines if
fluid enters or exits the capillary?
• Net filtration pressure

92. Capillary Filtration • If capillary HP >> capillary OP,
– What kind of fluid movement will occur?
ISF
CAPILLARY

93. Capillary Reabsorption
• If capillary HP << capillary OP,
– What kind of fluid movement will occur?
ISF
CAPILLARY

94. • Is capillary HP constant?? • Is capillary OP constant??
Capillary Fluid Exchange
• Is capillary HP constant??
• Is capillary OP constant??
Pressure
Arterial end
Venous end
Distance along the capillary

95. • At which end of the capillary is filtration likely to occur?
Capillary Fluid Exchange
• At which end of the capillary is filtration likely to occur?
• At which end is reabsorption likely to occur?
Pressure
Arterial end
Venous end
Distance along the capillary

96. Capillary Fluid Exchange
• Capillary HP usually slightly exceeds capillary OP.
• Why does this matter?