1. The Blood Vessels and Blood Pressure
Chapter 10
The Blood Vessels and Blood Pressure
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

2. Outline Vessel types and flow Arteries Blood pressure Arterioles
Capillaries
Lymphatic system
Veins

3. Outline Vessel types and flow Vessel anatomy
Flow, flow rate, pressure gradients
Blood distribution, Poiselle’s law

4. Credit: © Biodisc/Visuals Unlimited
Human Coronary Artery. LM X6.
Human artery showing atherosclerosis. LM X3.
Human artery cross-section, elastic tissue stain. X80.
Credit: © Biodisc/Visuals Unlimited
213940

5. Red and white blood cells within an arteriole.
Arteries branch into arterioles within organs
and deliver blood to the capillaries. SEM X6130.
Artery and Vein. A distributing artery (right)
and a medium-sized vein (left) surrounded
by connective tissue. Arteries and veins
are part of the extensive network of vessels
that make up the vascular system. SEM X305.
Credit: © Dr. Richard Kessel & Dr. Randy Kardon/Tissues & Organs/Visuals Unlimited
900019

6. Blood Flow
Blood is constantly reconditioned so composition remains relatively constant
Reconditioning organs receive more blood than needed for metabolic needs
Digestive organs, kidneys, skin
Adjust extra blood to achieve homeostasis
Blood flow to other organs can be adjusted according to metabolic needs
Brain can least tolerate disrupted supply

7. Distribution of Cardiac Output at Rest

8. Blood Flow
Flow rate through a vessel (volume of blood passing through per unit of time) is directly proportional to the pressure gradient and inversely proportional to vascular resistance
F = ΔP R
F = flow rate of blood through a vessel
ΔP = pressure gradient
R = resistance of blood vessels

9. Blood Flow
Pressure gradient is pressure difference between beginning and end of a vessel
Blood flows from area of higher pressure to area of lower pressure
Resistance is measure of opposition of blood flow through a vessel
Depends on three things
Blood viscosity, vessel length, vessel radius
Major determinant of resistance to flow is vessel’s radius
Slight change in radius produces significant change in blood flow
R is proportional to 1 r4

10. Relationship of Resistance and Flow to Vessel Radius

11. Vascular Tree Closed system of vessels Consists of Arteries Arterioles
Carry blood away from heart to tissues
Arterioles
Smaller branches of arteries
Capillaries
Smaller branches of arterioles
Smallest of vessels across which all exchanges are made with surrounding cells
Venules
Formed when capillaries rejoin
Return blood to heart
Veins
Formed when venules merge

12. Basic Organization of the Cardiovascular System

13. Outline
Arteries
“pressure reservoir”
anatomy

14. Arteries Specialized to
Serve as rapid-transit passageways for blood from heart to organs
Due to large radius, arteries offer little resistance to blood flow
Act as pressure reservoir to provide driving force for blood when heart is relaxing
Arterial connective tissue contains
Collagen fibers
Provide tensile strength
Elastin fibers
Provide elasticity to arterial walls

15. Arteries as a Pressure Reservoir

16. Outline Blood pressure Systolic/diastolic Measurements
Pressure and pulse
Mean arterial pressure
Pressure abnormalities

17. Blood Pressure Force exerted by blood against a vessel wall Depends on
Volume of blood contained within vessel
Compliance of vessel walls
Systolic pressure
Peak pressure exerted by ejected blood against vessel walls during cardiac systole
Averages 120 mm Hg
Diastolic pressure
Minimum pressure in arteries when blood is draining off into vessels downstream
Averages 80 mm Hg

18. Blood Pressure
Can be measured indirectly using sphygmomanometer and stethascope
Sounds heard when determining blood pressure
Sounds are distinct from heart sounds associated with valve closure

19. Blood
Pressure

20. Pulse Pressure
Pressure difference between systolic and diastolic pressure
Example
If blood pressure is 120/80, pulse pressure is 40 mm Hg (120mm Hg – 80mm Hg)
Pulse that can be felt in artery lying close to surface of skin is due to pulse pressure

21. Mean Arterial Pressure
Average pressure driving blood forward into tissues throughout cardiac cycle
Formula for approximating mean arterial pressure
Mean arterial pressure = diastolic pressure + ⅓ pulse pressure
At 120/80, mean arterial pressure = 80 mm Hg +
⅓ (40 mm Hg) = 93 mm Hg

22. Outline Arterioles Resistance vessels
Vasoconstriction and vasodilation
Regulation of arteiolar diameter
Local factors
Endothelial cells, nitric oxide

23. Arterioles Major resistance vessels
Radius supplying individual organs can be adjusted independently to
Distribute cardiac output among systemic organs, depending on body’s momentary needs
Help regulate arterial blood pressure

24. Arterioles Mechanisms involved in adjusting arteriolar resistance
Vasoconstriction
Refers to narrowing of a vessel
Vasodilation
Refers to enlargement in circumference and radius of vessel
Results from relaxation of smooth muscle layer
Leads to decreased resistance and increased flow through that vessel

25. Arteriolar Vasoconstriction and Vasodilation

26. Arterioles Only blood supply to brain remains constant
Changes within other organs alter radius of vessels and adjust blood flow to organ
Local chemical influences on arteriolar radius
Local metabolic changes
Histamine release
Local physical influences on arteriolar radius
Local application of heat or cold
Chemical response to shear stress
Myogenic response to stretch

27. Magnitude and Distribution
Of the Cardiac Output at Rest
and During Moderate Exercise

28. Arterioles
Specific local chemical factors that produce relaxation of arteriolar smooth muscle
Decreased O2
Increased CO2
Increased acid
Increased K+
Increased osmolarity
Adenosine release
Prostaglandin release

29. Arterioles Local vasoactive mediators Endothelial cells
Release chemical mediators that play key role in locally regulating arteriolar caliber
Release locally acting chemical messengers in response to chemical changes in their environment
Among best studied local vasoactive mediators is nitric oxide (NO)

30. Functions of Endothelial Cells

31. Functions of
Nitric Oxide (NO)

32. Arterioles Extrinsic control
Accomplished primarily by sympathetic nerve influence
Accomplished to lesser extent by hormonal influence over arteriolar smooth muscle

33. Arterioles Cardiovascular control center In medulla of brain stem
Integrating center for blood pressure regulation
Other brain regions also influence blood distribution
Hypothalamus
Controls blood flow to skin to adjust heat loss to environment
Hormones that influence arteriolar radius
Adrenal medullary hormones
Epinephrine and norepinephrine
Generally reinforce sympathetic nervous system in most organs
Vasopressin and angiotensin II
Important in controlling fluid balance

34. Outline
Capillaries
Exchange and anatomy
Pressures driving diffusion

35. Capillaries Thin-walled, small-radius, extensively branched
Sites of exchange between blood and surrounding tissue cells
Maximized surface area and minimized diffusion distance
Velocity of blood flow through capillaries is relatively slow
Provides adequate exchange time
Two types of passive exchanges
Diffusion
Bulk flow

36. Factors affecting diffusion Ficks law of diffusion Slow blood velocity
Permeability
Metarterioles and precapillary sphincters
Exchanges
Blood to interstitial fluid to cell
Passive
Active
Bulk Flow
Ultrafiltration
reabsorption

37. Table 3-1, p. 62

38. Figure 10.16: Comparison of blood flow rate and velocity of flow in relation to total cross-sectional area.
The blood flow rate (red curve) is identical through all levels of the circulatory system and is equal to the cardiac output (5 liters/min at rest). The velocity of flow (purple curve) varies throughout the vascular tree and is inversely proportional to the total cross-sectional area (green curve) of all the vessels at a given level. Note that the velocity of flow is slowest in the capillaries, which have the largest total cross-sectional area.
Fig , p. 355

39. Capillary blood pressure Plasma colloid osmotic pressure
Figure 10.22: Bulk flow across the capillary wall.
Schematic representation of ultrafiltration and reabsorption as a result of imbalances in the physical forces acting across the capillary wall.
Capillary blood pressure
Plasma colloid osmotic pressure
Interstitial fluid hydrostatic pressure
Interstitial fluid colloid osmotic pressure
Fig , p. 359

40. Figure 10.9: Pressures throughout the systemic circulation.
Left ventricular pressure swings between a low pressure of 0 mm Hg during diastole to a high pressure of 120 mm Hg during systole. Arterial blood pressure, which fluctuates between a peak systolic pressure of 120 mm Hg and a low diastolic pressure of 80 mm Hg each cardiac cycle, is of the same magnitude throughout the large arteries. Because of the arterioles’ high resistance, the pressure drops precipitously and the systolic-to-diastolic swings in pressure are converted to a nonpulsatile pressure when blood flows through the arterioles. The pressure continues to decline but at a slower rate as blood flows through the capillaries and venous system.
Fig. 10-9, p. 345

41. Myogenic tone Stopcock Local metabolic changes Arteriole
Smooth muscles
Precapillary
sphincter
Myogenic tone
Stopcock
Local metabolic
changes
Metarteriole
Capillary
Venule
Fig , p. 357

42. Capillaries
Narrow, water-filled gaps (pores) lie at junctions between cells
Permit passage of water-soluble substances
Lipid soluble substances readily pass through endothelial cells by dissolving in lipid bilayer barrier
Size of pores varies from organ to organ

43. Capillaries Under resting conditions many capillaries are not open
Capillaries surrounded by precapillary sphincters
Contraction of sphincters reduces blood flowing into capillaries in an organ
Relaxation of sphincters has opposite effect
Metarteriole
Runs between an arteriole and a venule

44. Outline
Lymphatic system
Drainage of tissue
Immune function
Edema

45. Lymphatic
System

46. Lymphatic System Extensive network of one-way vessels
Provides accessory route by which fluid can be returned from interstitial to the blood
Initial lymphatics
Small, blind-ended terminal lymph vessels
Permeate almost every tissue of the body
Lymph
Interstitial fluid that enters a lymphatic vessel
Lymph vessels
Formed from convergence of initial lymphatics
Eventually empty into venous system near where blood enters right atrium
One way valves spaced at intervals direct flow of lymph toward venous outlet in chest

47. Lymphatic System Functions Return of excess filtered fluid
Defense against disease
Lymph nodes have phagocytes which destroy bacteria filtered from interstitial fluid
Transport of absorbed fat
Return of filtered protein

48. To venous system Arteriole Interstitial fluid Tissue cells Venule
Blood capillary
Initial
lymphatic
Fig , p. 362

49. Fluid pressure on the outside of the vessel
pushes the endothelial cell’s free edge inward,
permitting entrance of interstitial fluid
(now lymph).
Overlapping
endothelial cell
Interstitial
fluid
Lymph
Fluid pressure on the inside of the vessel
forces the overlapping edges together so
that lymph cannot escape.
Fig , p. 362

50. Edema Swelling of tissues
Occurs when too much interstitial fluid accumulates
Causes of edema
Reduced concentration of plasma proteins
Increased permeability of capillary wall
Increased venous pressure
Blockage of lymph vessels

51. Outline Veins Capacitance vessels Regulation of pressure and flow
Venous return

52. Veins Venous system transports blood back to heart
Capillaries drain into venules
Venules converge to form small veins that exit organs
Smaller veins merge to form larger vessels
Veins
Large radius offers little resistance to blood flow
Also serve as blood reservoir

53. Capacitance! Pulmonary vessels Systemic arteries 9% 13%
Systemic arterioles 2%
Heart 7%
Systemic capillaries 5%
Systemic veins
64%
Capacitance!
Fig , p. 364

54. Veins Factors which enhance venous return
Driving pressure from cardiac contraction
Sympathetically induced venous vasoconstriction
Skeletal muscle activity
Effect of venous valves
Respiratory activity
Effect of cardiac suction

55. Skeletal muscle pump Fig. 10-29, p. 366
Figure 10.29: Skeletal muscle pump enhancing venous return.
Fig , p. 366

56. Effects of Gravity Fig. 10-30, p. 367
Figure 10.30: Effect of gravity on venous pressure.
In an upright adult, the blood in the vessels extending between the heart and foot is equivalent to a 1.5 m column of blood. The pressure exerted by this column of blood as a result of the effect of gravity is 90 mm Hg. The pressure imparted to the blood by the heart has declined to about 10 mm Hg in the lower-leg veins because of frictional losses in preceding vessels. Together these pressures produce a venous pressure of 100 mm Hg in the ankle and foot veins. Similarly, the capillaries in the region are subjected to these same gravitational effects.
Fig , p. 367

57. Standing Walking Heart Thigh 150 cm Calf 34 cm Foot 100 mm Hg Venous
pressure
in foot 27
mm Hg
Foot vein supporting
column of blood 1.5 m
(150 cm) in height
Foot vein supporting
column of blood
34 cm in height
Fig , p. 367

58. Vein Open venous valve permits flow of blood toward heart Contracted
skeletal muscle
Closed venous valve
prevents backflow
of blood
Stepped art
Fig , p. 368

59. Respiratory activity and venous return
5 mm Hg less than
atmospheric pressure
Atmospheric pressure
Atmospheric pressure
5 mm Hg less than
atmospheric pressure
Cardiac suction also
Fig , p. 368

60. Factors that Influence Venous Return
summary

61. Blood pressure Mean Arterial Pressure
Blood pressure that is monitored and regulated in the body
Regulation is important:
Provides adequate driving pressure (brain and organs)
Prevents extra work
Primary determinants
Cardiac output
Total peripheral resistance
Mean arterial pressure = cardiac output x total peripheral resistance

62. Determinants of Mean Arterial Pressure

63. Mean Arterial Pressure
Constantly monitored by baroreceptors (pressure sensors) within circulatory system
Short-term control adjustments
Occur within seconds
Adjustments made by alterations in cardiac output and total peripheral resistance
Mediated by means of autonomic nervous system influences on heart, veins, and arterioles
Long-term control adjustments
Require minutes to days
Involve adjusting total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst

64. Figure 10.11: Flow rate as a function of resistance.
Fig , p. 347

65. Carotid sinus baroreceptor
Neural signals to
cardiovascular
control center
in medulla
Common carotid arteries
(Blood to the brain)
Aortic arch baroreceptor
Aorta
(Blood to rest of body)
Fig , p. 371

66. Cardiac output Heart rate Heart Heart rate Cardiac output Heart Stroke
Parasympathetic
stimulation
Heart
rate
Blood
pressure
Heart
Heart
rate
Sympathetic
stimulation
Cardiac
output
Blood
pressure
Heart
Contractile
strength
of heart
Stroke
volume
Total peripheral
resistance
Blood
pressure
Arterioles
Vasoconstriction
Venous
return
Stroke
volume
Cardiac
output
Blood
pressure
Veins
Vasoconstriction
Fig , p. 372

67. Baroreceptor Reflexes to Restore Blood Pressure to Normal

68. Normal Increased Decreased Arterial pressure (mm Hg) 120 80
Firing rate in
afferent neuron
arising from carotid
sinus baroreceptor
Time
Fig , p. 371

69. Blood Pressure
Additional reflexes and responses that influence blood pressure
Left atrial receptors and hypothalamic osmoreceptors affect long-term regulation of blood pressure by controlling plasma volume
Chemoreceptors in carotid and aortic arteries are sensitive to low O2 or high acid levels in blood – reflexly increase respiratory activity
Associated with certain behaviors and emotions mediated through cerebral-hypothalamic pathway
Exercise modifies cardiac responses
Hypothalamus controls skin arterioles for temperature regulation
Vasoactive substances released from endothelial cells play role

70. Blood Pressure Abnormalities
Hypertension
Blood pressure above 140/90 mm Hg
Two broad classes
Primary hypertension
Secondary hypertension
Hypotension
Blood pressure below 100/60 mm Hg

71. Hypertension Most common of blood pressure abnormalities
Primary hypertension
Catchall category for blood pressure elevated by variety of unknown causes rather than by a single disease entity
Potential causes being investigated
Defects in salt management by the kidneys
Excessive salt intake
Diets low in K+ and Ca2+
Plasma membrane abnormalities such as defective Na+-K+ pumps
Variation in gene that encodes for angiotensinogen
Endogenous digitalis-like substances
Abnormalities in NO, endothelin, or other locally acting vasoactive chemicals
Excess vasopressin

72. Hypertension Secondary hypertension
Accounts for about 10% of hypertension cases
Occurs secondary to another known primary problem
Examples of secondary hypertension
Renal hypertension
Endocrine hypertension
Neurogenic hypertension

73. Hypertension Complication of hypertension Congestive heart failure
Stroke
Heart attack
Spontaneous hemorrhage
Renal failure
Retinal damage

74. Hypotension Low blood pressure Occurs when
There is too little blood to fill the vessels
Heart is too weak to drive the blood
Orthostatic (postural) hypotension
Transient hypotensive condition resulting from insufficient compensatory responses to gravitational shifts in blood when person moves from horizontal to vertical position

75. Hypotension Circulatory shock
Occurs when blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained
Four main types
Hypovolemic (“low volume”) shock
Cardiogenic (“heart produced”) shock
Vasogenic (“vessel produced”) shock
Neurogenic (“nerve produced”) shock

76. ( mean arterial pressure)
Circulatory shock
( mean arterial pressure)
Cardiac output
Cardiac output
Total peripheral resistance
Widespread
vasodilation
Loss of blood volume
Vasodilator
substances
released from
bacteria
Histamine
released
in severe
allergic
reaction
Loss of fluids
derived from
plasma
Loss of
vascular tone
Excessive
vomiting,
diarrhea,
urinary losses,
etc.
Severe
hemorrhage
Weakened
heart
Septic
shock
Anaphylactic
shock
Sympathetic
nerve activity
Hypovolemic
shock
Cardiogenic
shock
Cardiogenic
shock
Neurogenic
shock
Fig , p. 377

77. Figure 10.40: Consequences and compensations of hemorrhage.
The reduction in blood volume resulting from hemorrhage leads to a fall in arterial pressure. (Note the blue boxes, representing consequences of hemorrhage.) A series of compensations ensue (light pink boxes) that ultimately restore plasma volume, arterial pressure, and the number of red blood cells toward normal (dark pink boxes). Refer to the text (pp. 376–377) for an explanation of the circled numbers and a detailed discussion of the compensations.
Fig , p. 378