the cardiovascular system blood and vessels

human anatomy and physiology

1. Chapter 19
The Cardiovascular
system: Blood
Vessels

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. Figure 19.2
Large veins
(capacitance
vessels)
Large
lymphatic
vessels
Arteriovenous
anastomosis
Lymphatic
capillary
Postcapillary
venule
Sinusoid
Metarteriole
Terminal arteriole
Arterioles
(resistance vessels)
Muscular arteries
(distributing
vessels)
Elastic arteries
(conducting
vessels)
Small veins
(capacitance
vessels)
Lymph
node
Capillaries
(exchange vessels)
Precapillary sphincterThoroughfare
channel
Lymphatic
system
Venous system Arterial system
Heart

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

6. 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
•In all tissues except for cartilage, epithelia, cornea
and lens of eye
•Functions: exchange of gases, nutrients, wastes,
hormones, etc.

7. Capillaries
•Three structural types
1.Continuous capillaries
2.Fenestrated capillaries
3.Sinusoidal capillaries (sinusoids)

8. 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

9. Figure 19.3a
Red blood
cell in lumen
Intercellular
cleft
Endothelial
cell
Endothelial
nucleus
Tight junction Pinocytotic
vesicles
Pericyte
Basement
membrane
(a) Continuous capillary. Least permeable, and
most common (e.g., skin, muscle).

10. 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)

11. Figure 19.3b
Red blood
cell in lumen
Intercellular
cleft
Fenestrations
(pores)
Endothelial
cell
Endothelial
nucleus
Basement membrane
Tight junction
Pinocytotic
vesicles
(b) Fenestrated capillary. Large fenestrations
(pores) increase permeability. Occurs in special
locations (e.g., kidney, small intestine).

12. 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

13. Figure 19.3c
Nucleus of
endothelial
cell
Red blood
cell in lumen
Endothelial
cell
Tight junction
Incomplete
basement
membrane
Large
intercellular
cleft
(c) Sinusoidal capillary. Most permeable. Occurs in
special locations (e.g., liver, bone marrow, spleen).

14. 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
2.True capillaries
•10 to 100 exchange vessels per capillary bed
•Branch off the metarteriole or terminal arteriole

15. Blood Flow Through Capillary Beds
•Precapillary sphincters regulate blood flow
into true capillaries
•Regulated by local chemical conditions and
vasomotor nerves

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

17. 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

18. 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

19. Figure 19.1a
Artery
Vein
(a)

20. Figure 19.5
Heart 8%
Capillaries 5%
Systemic arteries
and arterioles 15%
Pulmonary blood
vessels 12%
Systemic veins
and venules 60%

21. 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)

22. 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

23. Physiology of Circulation: Definition of Terms
•Blood flow
–Volume of blood flowing through a vessel, an organ, or the
entire circulation in a given period
•Measured as ml/min
•Equivalent to cardiac output (CO) for entire vascular
system
•Relatively constant when at rest
•Varies widely through individual organs, based on
needs

24. Physiology of Circulation: Definition of Terms
•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

25. Physiology of Circulation: Definition of Terms
•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

26. 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

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

28. 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

29. Relationship Between Blood Flow, Blood
Pressure, and Resistance
•Blood flow (F) is directly proportional to the
blood (hydrostatic) pressure gradient (P)
–If P increases, blood flow speeds up
•Blood flow is inversely proportional to
peripheral resistance (R)
–If R increases, blood flow decreases: F = P/R
•R is more important in influencing local blood
flow because it is easily changed by altering
blood vessel diameter

30. 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

31. Figure 19.6
Systolic pressure
Mean pressure
Diastolic
pressure

32. Arterial Blood Pressure
•Reflects two factors of the arteries close to the
heart
–Elasticity (compliance or distensibility)
–Volume of blood forced into them at any time

33. Arterial Blood Pressure
•Systolic pressure: pressure exerted during
ventricular contraction
•Diastolic pressure: lowest level of arterial
pressure
•Pulse pressure = difference between systolic
and diastolic pressure

34. Arterial Blood Pressure
•Mean arterial pressure (MAP): pressure that
propels the blood to the tissues
MAP = diastolic pressure + 1/3 pulse pressure
•Pulse pressure and MAP both decline with
increasing distance from the heart

35. Capillary Blood Pressure
•Ranges from 15 to 35 mm Hg
•Low capillary pressure is desirable
–High BP would rupture fragile, thin-walled
capillaries
–Most are very permeable, so low pressure forces
filtrate into interstitial spaces

36. Venous Blood Pressure
•Changes little during the cardiac cycle
•Small pressure gradient, about 15 mm Hg
•Low pressure due to cumulative effects of
peripheral resistance

37. Factors Aiding Venous Return
1.Respiratory “pump”: pressure changes created
during breathing move blood toward the heart by
squeezing abdominal veins as thoracic veins
expand
2.Muscular “pump”: contraction of skeletal muscles
“milk” blood toward the heart and valves prevent
backflow
3.Vasoconstriction of veins under sympathetic
control

38. Figure 19.7
Valve (open)
Contracted
skeletal
muscle
Valve (closed)
Vein
Direction of
blood flow

39. Maintaining Blood Pressure
•Requires
–Cooperation of the heart, blood vessels, and
kidneys
–Supervision by the brain

40. Maintaining Blood Pressure
•The main factors influencing blood pressure:
–Cardiac output (CO)
–Peripheral resistance (PR)
–Blood volume

41. Maintaining Blood Pressure
•Flow = P/PR and CO = P/PR
•Blood pressure = CO x PR (and CO depends on
blood volume)
•Blood pressure varies directly with CO, PR, and
blood volume
•Changes in one variable are quickly
compensated for by changes in the other
variables

42. Cardiac Output (CO)
•Determined by venous return and neural and
hormonal controls
•Resting heart rate is maintained by the
cardioinhibitory center via the
parasympathetic vagus nerves
•Stroke volume is controlled by venous return
(EDV)

43. Cardiac Output (CO)
•During stress, the cardioacceleratory center
increases heart rate and stroke volume via
sympathetic stimulation
–ESV decreases and MAP increases

44. Figure 19.8
Venous return
Exercise
Contractility of cardiac muscle
Sympathetic activity Parasympathetic
activity
Epinephrine in blood
EDV ESV
Stroke volume (SV) Heart rate (HR)
Cardiac output (CO = SV x HR
Activity of respiratory pump
(ventral body cavity pressure)
Activity of muscular pump
(skeletal muscles)
Sympathetic venoconstriction
BP activates cardiac centers in medulla
Initial stimulus
Result
Physiological response

45. Control of Blood Pressure
•Short-term neural and hormonal controls
–Counteract fluctuations in blood pressure by
altering peripheral resistance
•Long-term renal regulation
–Counteracts fluctuations in blood pressure by
altering blood volume

46. Short-Term Mechanisms: Neural Controls
•Neural controls of peripheral resistance
–Maintain MAP by altering blood vessel diameter
–Alter blood distribution in response to specific
demands

47. Short-Term Mechanisms: Neural Controls
•Neural controls operate via reflex arcs that
involve
–Baroreceptors
–Vasomotor centers and vasomotor fibers
–Vascular smooth muscle

48. The Vasomotor Center
•A cluster of sympathetic neurons in the
medulla that oversee changes in blood vessel
diameter
•Maintains vasomotor tone (moderate
constriction of arterioles)
•Receives inputs from baroreceptors,
chemoreceptors, and higher brain centers

49. Short-Term Mechanisms: Baroreceptor-
Initiated Reflexes
•Baroreceptors are located in
–Carotid sinuses
–Aortic arch
–Walls of large arteries of the neck and thorax

50. Short-Term Mechanisms: Baroreceptor-
Initiated Reflexes
•Increased blood pressure stimulates
baroreceptors to increase input to the
vasomotor center
–Inhibits the vasomotor center, causing arteriole
dilation and venodilation
–Stimulates the cardioinhibitory center

51. Figure 19.9
Baroreceptors
in carotid sinuses
and aortic arch
are stimulated.
Baroreceptors
in carotid sinuses
and aortic arch
are inhibited.
Impulses from baroreceptors
stimulate cardioinhibitory center
(and inhibit cardioacceleratory
center) and inhibit vasomotor
center.
Impulses from baroreceptors stimulate
cardioacceleratory center (and inhibit cardioinhibitory
center) and stimulate vasomotor center.
CO and R
return blood
pressure to
homeostatic range.
CO and R
return blood pressure
to homeostatic range.

Rate of
vasomotor impulses
allows vasodilation,
causing R
Vasomotor
fibers stimulate
vasoconstriction,
causing R
Sympathetic
impulses to heart
cause HR,
contractility, and
CO.
Sympathetic
impulses to heart
cause HR,
contractility, and
CO.
Stimulus:
Blood pressure
(arterial blood
pressure falls below
normal range).
Stimulus:
Blood pressure
(arterial blood
pressure rises above
normal range).
3
2
1
5
4a
4b
Homeostasis: Blood pressure in normal range
4b
3
2
1
5
4a

52. Short-Term Mechanisms:
Baroreceptor-Initiated Reflexes
•Baroreceptors taking part in the carotid sinus
reflex protect the blood supply to the brain
•Baroreceptors taking part in the aortic reflex
help maintain adequate blood pressure in the
systemic circuit

53. Short-Term Mechanisms:
Chemoreceptor-Initiated Reflexes
•Chemoreceptors are located in the
–Carotid sinus
–Aortic arch
–Large arteries of the neck

54. Short-Term Mechanisms:
Chemoreceptor-Initiated Reflexes
•Chemoreceptors respond to rise in CO
2, drop
in pH or O
2
–Increase blood pressure via the vasomotor center
and the cardioacceleratory center
•Are more important in the regulation of
respiratory rate (Chapter 22)

55. Influence of Higher Brain Centers
•Reflexes that regulate BP are integrated in the
medulla
•Higher brain centers (cortex and
hypothalamus) can modify BP via relays to
medullary centers

56. Short-Term Mechanisms: Hormonal Controls
•Adrenal medulla hormones norepinephrine
(NE) and epinephrine cause generalized
vasoconstriction and increase cardiac output
•Angiotensin II, generated by kidney release of
renin, causes vasoconstriction

57. Short-Term Mechanisms: Hormonal Controls
•Atrial natriuretic peptide causes blood volume
and blood pressure to decline, causes
generalized vasodilation
•Antidiuretic hormone (ADH)(vasopressin)
causes intense vasoconstriction in cases of
extremely low BP

58. Long-Term Mechanisms: Renal Regulation
•Baroreceptors quickly adapt to chronic high
or low BP
•Long-term mechanisms step in to control BP
by altering blood volume
•Kidneys act directly and indirectly to regulate
arterial blood pressure
1.Direct renal mechanism
2.Indirect renal (renin-angiotensin) mechanism

59. Direct Renal Mechanism
•Alters blood volume independently of
hormones
–Increased BP or blood volume causes the kidneys
to eliminate more urine, thus reducing BP
–Decreased BP or blood volume causes the kidneys
to conserve water, and BP rises

60. Indirect Mechanism
•The renin-angiotensin mechanism
– Arterial blood pressure  release of renin
–Renin production of angiotensin II
–Angiotensin II is a potent vasoconstrictor
–Angiotensin II  aldosterone secretion
•Aldosterone  renal reabsorption of Na
+
and  urine
formation
–Angiotensin II stimulates ADH release

61. Figure 19.10
Arterial pressure
Baroreceptors
Indirect renal
mechanism (hormonal)
Direct renal
mechanism
Sympathetic stimulation
promotes renin release
Kidney
Renin release
catalyzes cascade,
resulting in formation of
ADH release
by posterior
pituitary
Aldosterone
secretion by
adrenal cortex
Water
reabsorption
by kidneys
Blood volume
Filtration
Arterial pressure
Angiotensin II
Vasoconstriction
( diameter of blood vessels)
Sodium
reabsorption
by kidneys
Initial stimulus
Physiological response
Result

62. Figure 19.11
Activity of
muscular
pump and
respiratory
pump
Release
of ANP
Fluid loss from
hemorrhage,
excessive
sweating
Crisis stressors:
exercise, trauma,
body
temperature
Bloodborne
chemicals:
epinephrine,
NE, ADH,
angiotensin II;
ANP release
Body size
Conservation
of Na
+
and
water by kidney
Blood volume
Blood pressure
Blood pH, O
2
,
CO
2
Dehydration,
high hematocrit
Blood
volume
Baroreceptors Chemoreceptors
Venous
return
Activation of vasomotor and cardiac
acceleration centers in brain stem
Heart
rate
Stroke
volume
Diameter of
blood vessels
Cardiac output
Initial stimulus
Result
Physiological response
Mean systemic arterial blood pressure
Blood
viscosity
Peripheral resistance
Blood vessel
length

63. Monitoring Circulatory Efficiency
•Vital signs: pulse and blood pressure, along
with respiratory rate and body temperature
•Pulse: pressure wave caused by the expansion
and recoil of arteries
•Radial pulse (taken at the wrist) routinely used

64. Figure 19.12
Common carotid
artery
Brachial artery
Radial artery
Femoral artery
Popliteal artery
Posterior tibial
artery
Dorsalis pedis
artery
Superficial temporal
artery
Facial artery

65. Measuring Blood Pressure
•Systemic arterial BP
–Measured indirectly by the auscultatory method
using a sphygmomanometer
–Pressure is increased in the cuff until it exceeds
systolic pressure in the brachial artery

66. Measuring Blood Pressure
•Pressure is released slowly and the examiner
listens for sounds of Korotkoff with a
stethoscope
•Sounds first occur as blood starts to spurt
through the artery (systolic pressure, normally
110–140 mm Hg)
•Sounds disappear when the artery is no longer
constricted and blood is flowing freely (diastolic
pressure, normally 70–80 mm Hg)

67. Variations in Blood Pressure
•Blood pressure cycles over a 24-hour period
•BP peaks in the morning due to levels of
hormones
•Age, sex, weight, race, mood, and posture may
vary BP

68. Alterations in Blood Pressure
•Hypotension: low blood pressure
–Systolic pressure below 100 mm Hg
–Often associated with long life and lack of
cardiovascular illness

69. Homeostatic Imbalance: Hypotension
•Orthostatic hypotension: temporary low BP
and dizziness when suddenly rising from a
sitting or reclining position
•Chronic hypotension: hint of poor nutrition
and warning sign for Addison’s disease or
hypothyroidism
•Acute hypotension: important sign of
circulatory shock

70. Alterations in Blood Pressure
•Hypertension: high blood pressure
–Sustained elevated arterial pressure of 140/90 or
higher
•May be transient adaptations during fever, physical
exertion, and emotional upset
•Often persistent in obese people

71. Homeostatic Imbalance: Hypertension
•Prolonged hypertension is a major cause of
heart failure, vascular disease, renal failure,
and stroke
•Primary or essential hypertension
–90% of hypertensive conditions
–Due to several risk factors including heredity, diet,
obesity, age, stress, diabetes mellitus, and
smoking

72. Homeostatic Imbalance: Hypertension
•Secondary hypertension is less common
–Due to identifiable disorders, including kidney
disease, arteriosclerosis, and endocrine disorders
such as hyperthyroidism and Cushing’s syndrome

73. Blood Flow Through Body Tissues
•Blood flow (tissue perfusion) is involved in
–Delivery of O
2
and nutrients to, and removal of
wastes from, tissue cells
–Gas exchange (lungs)
–Absorption of nutrients (digestive tract)
–Urine formation (kidneys)
•Rate of flow is precisely the right amount to
provide for proper function

74. Figure 19.13
Brain
Heart
Skeletal
muscles
Skin
Kidney
Abdomen
Other
Total blood flow during strenuous
exercise 17,500 ml/min
Total blood
flow at rest
5800 ml/min

75. Velocity of Blood Flow
•Changes as it travels through the systemic
circulation
•Is inversely related to the total cross-sectional
area
•Is fastest in the aorta, slowest in the
capillaries, increases again in veins
•Slow capillary flow allows adequate time for
exchange between blood and tissues

76. Figure 19.14
Relative cross-
sectional area of
different vessels
of the vascular bed
Total area
(cm
2
) of the
vascular
bed
Velocity of
blood flow
(cm/s)
A
o
rta
A
rte
rie
s
A
rte
rio
le
s
C
a
p
illa
r
ie
s
V
e
n
u
le
s
V
e
in
s
V
e
n
a
e
c
a
v
a
e

77. Autoregulation
•Automatic adjustment of blood flow to each
tissue in proportion to its requirements at any
given point in time
•Is controlled intrinsically by modifying the
diameter of local arterioles feeding the
capillaries
•Is independent of MAP, which is controlled as
needed to maintain constant pressure

78. Autoregulation
•Two types of autoregulation
1.Metabolic
2.Myogenic

79. Metabolic Controls
•Vasodilation of arterioles and relaxation of
precapillary sphincters occur in response to
–Declining tissue O
2

–Substances from metabolically active tissues (H
+
,
K
+
, adenosine, and prostaglandins) and
inflammatory chemicals

80. Metabolic Controls
•Effects
–Relaxation of vascular smooth muscle
–Release of NO from vascular endothelial cells
•NO is the major factor causing vasodilation
•Vasoconstriction is due to sympathetic
stimulation and endothelins

81. Myogenic Controls
•Myogenic responses of vascular smooth
muscle keep tissue perfusion constant despite
most fluctuations in systemic pressure
•Passive stretch (increased intravascular
pressure) promotes increased tone and
vasoconstriction
•Reduced stretch promotes vasodilation and
increases blood flow to the tissue

82. Figure 19.15
Metabolic
controls
pH Sympathetic
a Receptors
b Receptors
Epinephrine,
norepinephrine
Angiotensin II
Antidiuretic
hormone (ADH)
Atrial
natriuretic
peptide (ANP)
Dilates
Constricts
Prostaglandins
Adenosine
Nitric oxide
Endothelins
Stretch
O
2
CO
2
K
+
Amounts of:
Amounts of:
Nerves
Hormones
Myogenic
controls
Intrinsic mechanisms
(autoregulation)
• Distribute blood flow to individual
organs and tissues as needed
Extrinsic mechanisms
• Maintain mean arterial pressure (MAP)
• Redistribute blood during exercise and
thermoregulation

83. Long-Term Autoregulation
•Angiogenesis
–Occurs when short-term autoregulation cannot
meet tissue nutrient requirements
–The number of vessels to a region increases and
existing vessels enlarge
–Common in the heart when a coronary vessel is
occluded, or throughout the body in people in
high-altitude areas

84. Blood Flow: Skeletal Muscles
•At rest, myogenic and general neural mechanisms
predominate
•During muscle activity
–Blood flow increases in direct proportion to the
metabolic activity (active or exercise hyperemia)
–Local controls override sympathetic vasoconstriction
•Muscle blood flow can increase 10 or more during
physical activity

85. Blood Flow: Brain
•Blood flow to the brain is constant, as neurons are
intolerant of ischemia
•Metabolic controls
–Declines in pH, and increased carbon dioxide cause
marked vasodilation
•Myogenic controls
–Decreases in MAP cause cerebral vessels to dilate
–Increases in MAP cause cerebral vessels to constrict

86. Blood Flow: Brain
•The brain is vulnerable under extreme
systemic pressure changes
–MAP below 60
 mm Hg can cause syncope
(fainting)
–MAP above 160 can result in cerebral edema

87. Blood Flow: Skin
•Blood flow through the skin
–Supplies nutrients to cells (autoregulation in
response to O
2 need)
–Helps maintain body temperature (neurally
controlled)
–Provides a blood reservoir (neurally controlled)

88. Blood Flow: Skin
•Blood flow to venous plexuses below the skin
surface
–Varies from 50 ml/min to 2500 ml/min, depending
on body temperature
–Is controlled by sympathetic nervous system
reflexes initiated by temperature receptors and
the central nervous system

89. Temperature Regulation
•As temperature rises (e.g., heat exposure,
fever, vigorous exercise)
–Hypothalamic signals reduce vasomotor
stimulation of the skin vessels
–Heat radiates from the skin

90. Temperature Regulation
•Sweat also causes vasodilation via bradykinin
in perspiration
–Bradykinin stimulates the release of NO
•As temperature decreases, blood is shunted to
deeper, more vital organs

91. Blood Flow: Lungs
•Pulmonary circuit is unusual in that
–The pathway is short
–Arteries/arterioles are more like veins/venules
(thin walled, with large lumens)
–Arterial resistance and pressure are low (24/8
 mm
Hg)

92. Blood Flow: Lungs
•Autoregulatory mechanism is opposite of that
in most tissues
–Low O
2
levels cause vasoconstriction; high levels
promote vasodilation
–Allows for proper O
2
loading in the lungs

93. Blood Flow: Heart
•During ventricular systole
–Coronary vessels are compressed
–Myocardial blood flow ceases
–Stored myoglobin supplies sufficient oxygen
•At rest, control is probably myogenic

94. Blood Flow: Heart
•During strenuous exercise
–Coronary vessels dilate in response to local
accumulation of vasodilators
–Blood flow may increase three to four times

95. Blood Flow Through Capillaries
•Vasomotion
–Slow and intermittent flow
–Reflects the on/off opening and closing of
precapillary sphincters

96. Capillary Exchange of Respiratory Gases and
Nutrients
•Diffusion of
–O
2 and nutrients from the blood to tissues
–CO
2 and metabolic wastes from tissues to the blood
•Lipid-soluble molecules diffuse directly through
endothelial membranes
•Water-soluble solutes pass through clefts and
fenestrations
•Larger molecules, such as proteins, are actively
transported in pinocytotic vesicles or caveolae

97. Figure 19.16 (1 of 2)
Red blood
cell in lumen
Endothelial cell
Intercellular cleft
Fenestration
(pore)Endothelial cell nucleus
Tight junction
Basement membrane
Pinocytotic vesicles

98. Figure 19.16 (2 of 2)
Basement
membrane
Endothelial
fenestration
(pore)
Intercellular
cleft
Pinocytotic
vesicles
Caveolae
4 Transport
via vesicles or
caveolae (large
substances)
3 Movement
through
fenestrations
(water-soluble
substances)
2 Movement
through intercellular
clefts (water-soluble
substances)
1 Diffusion
through
membrane
(lipid-soluble
substances)
Lumen

99. Fluid Movements: Bulk Flow
•Extremely important in determining relative
fluid volumes in the blood and interstitial
space
•Direction and amount of fluid flow depends
on two opposing forces: hydrostatic and
colloid osmotic pressures

100. Hydrostatic Pressures
•Capillary hydrostatic pressure (HP
c) (capillary
blood pressure)
–Tends to force fluids through the capillary walls
–Is greater at the arterial end (35
 mm Hg) of a bed
than at the venule end (17
 mm Hg)
•Interstitial fluid hydrostatic pressure (HP
if)
–Usually assumed to be zero because of lymphatic
vessels

101. Colloid Osmotic Pressures
•Capillary colloid osmotic pressure (oncotic
pressure) (OP
c)
–Created by nondiffusible plasma proteins, which
draw water toward themselves
–~26 mm Hg
•Interstitial fluid osmotic pressure (OP
if)
–Low (~1
 mm Hg) due to low protein content

102. Net Filtration Pressure (NFP)
•NFP—comprises all the forces acting on a
capillary bed
•NFP = (HP
c—HP
if)—(OP
c—OP
if)
•At the arterial end of a bed, hydrostatic forces
dominate
•At the venous end, osmotic forces dominate
•Excess fluid is returned to the blood via the
lymphatic system

103. Figure 19.17
HP = hydrostatic pressure
• Due to fluid pressing against a wall
• “Pushes”
• In capillary (HP
c
)
• Pushes fluid out of capillary
• 35 mm Hg at arterial end and
17 mm Hg at venous end of
capillary in this example
• In interstitial fluid (HP
if
)
• Pushes fluid into capillary
• 0 mm Hg in this example

OP = osmotic pressure
• Due to presence of nondiffusible
solutes (e.g., plasma proteins)
• “Sucks”
• In capillary (OP
c
)
• Pulls fluid into capillary
• 26 mm Hg in this example
• In interstitial fluid (OP
if
)
• Pulls fluid out of capillary
• 1 mm Hg in this example
Arteriole
Capillary
Interstitial fluid
Net HP—Net OP
(35—0)—(26—1)
Net HP—Net OP
(17—0)—(26—1)
Venule
NFP (net filtration pressure)
is 10 mm Hg; fluid moves out
NFP is ~8 mm Hg;
fluid moves in
Net
HP
35
mm
Net
OP
25
mm
Net
HP
17
mm
Net
OP
25
mm

104. Circulatory Pathways
•Two main circulations
–Pulmonary circulation: short loop that runs from
the heart to the lungs and back to the heart
–Systemic circulation: long loop to all parts of the
body and back to the heart

105. Figure 19.19a
R. pulmon-
ary veins
Pulmonary
trunk
Pulmonary capillaries
of the R. lung
Pulmonary capillaries
of the L. lung
R. pulmonary
artery
L. pulmonary
artery
To
systemic
circulation
L. pulmonary
veins
(a) Schematic flowchart.
From
systemic
circulation
RA
RVLV
LA

106. Figure 19.20
Azygos
system
Venous
drainage
Arterial
blood
Thoracic
aorta
Inferior
vena
cava
Abdominal
aorta
Inferior
vena
cava
Superior
vena cava
Common
carotid arteries
to head and
subclavian
arteries to
upper limbs
Aortic
arch
Aorta
RA
RVLV
LA
Capillary beds of
head and
upper limbs
Capillary beds of
mediastinal structures
and thorax walls
Diaphragm
Capillary beds of
digestive viscera,
spleen, pancreas,
kidneys
Capillary beds of gonads,
pelvis, and lower limbs

107. Arteries Veins
Delivery Blood pumped into single
systemic artery—the aorta
Blood returns via
superior and interior
venae cavae and the
coronary sinus
Location Deep, and protected by tissuesBoth deep and superficial
Pathways Fairly distinct Numerous
interconnections
Supply/drainagePredictable supply Usually similar to
arteries, except dural
sinuses and hepatic
portal circulation
Differences Between Arteries and Veins

108. Figure 19.21b
Internal carotid artery
Common carotid arteries
Subclavian artery
Subclavian artery
Aortic arch
Ascending aorta
Coronary artery
Thoracic aorta (above
diaphragm)
Renal artery
Superficial palmar arch
Radial artery
Ulnar artery
Internal iliac artery
Deep palmar arch
Vertebral artery
Brachiocephalic trunk
Axillary artery
Brachial artery
Abdominal aorta
Superior mesenteric artery
Gonadal artery
Common iliac artery
External iliac artery
Digital arteries
Femoral artery
Popliteal artery
Anterior tibial artery
Posterior tibial artery
Arcuate artery
(b) Illustration, anterior
view
Inferior mesenteric artery
Celiac trunk
External carotid artery
Arteries of the head and trunk
Arteries that supply
the upper limb
Arteries that supply
the lower limb

109. Figure 19.22b
• Superficial
temporal artery
• Maxillary artery
• Occipital artery
• Facial artery
• Lingual artery
• Superior thyroid
artery

Ophthalmic artery

Larynx
Thyroid gland
(overlying trachea)
Clavicle (cut)
Brachiocephalic
trunk
Internal thoracic
artery
Basilar artery
Vertebral artery
Internal
carotid artery
Subclavian
artery
Axillary
artery
(b) Arteries of the head and neck, right aspect
External
carotid artery
Common
carotid artery
Thyrocervical
trunk
Costocervical
trunk
Branches of
the external
carotid artery

110. Figure 19.22d
Frontal lobe
Optic chiasma
Middle
cerebral
artery
Internal
carotid
artery
Mammillary
body
Temporal
lobe
Occipital lobe
Cerebral arterial
circle
(circle of Willis)
• Posterior
cerebral artery
Basilar artery
Vertebral artery
Cerebellum
• Posterior
communicating
artery
(d) Major arteries serving the brain (inferior view, right side
of cerebellum and part of right temporal lobe removed)
Pons
• Anterior
cerebral artery
• Anterior
communicating
artery
Posterior
Anterior

111. Figure 19.23b
Vertebral artery
Costocervical trunk
Thoracoacromial artery
Axillary artery
Subscapular artery
Radial artery
Ulnar artery
Brachial artery
Suprascapular artery
Thyrocervical trunk
Posterior circumflex
humeral artery
Anterior circumflex
humeral artery
Deep artery of arm
Common
interosseous
artery
Deep palmar arch
Superficial palmar arch
Digital arteries
Common carotid
arteries
Right subclavian artery
Left subclavian artery
Brachiocephalic trunk
Posterior intercostal
arteries
Anterior intercostal
artery
Internal thoracic artery
Lateral thoracic artery
Descending aorta
(b) Illustration, anterior view

112. Figure 19.24c
(c) Major branches of the abdominal aorta.
Hiatus (opening)
for inferior
vena cava
Diaphragm
Inferior
phrenic artery
Middle
suprarenal
artery
Renal artery
Superior
mesenteric
artery
Median sacral
artery
Common
iliac artery
Ureter
Gonadal
(testicular or
ovarian) artery
Hiatus (opening)
for esophagus
Celiac trunk
Adrenal
(suprarenal)
gland
Kidney
Abdominal aorta
Lumbar arteries
Inferior
mesenteric
artery

113. Figure 19.25b
Common iliac artery
Deep artery of thigh
Obturator artery
Femoral artery
Adductor hiatus
Popliteal artery
Anterior tibial artery
Posterior tibial artery
Fibular artery
Dorsalis pedis artery
Arcuate artery
Dorsal metatarsal
arteries
(b) Anterior view
Internal iliac artery
Superior gluteal artery
External iliac artery
Lateral circumflex
femoral artery
Medial circumflex
femoral artery

114. Figure 19.25c
(c) Posterior view
Popliteal artery
Anterior tibial artery
Fibular artery
Dorsalis pedis artery
(from top of foot)
Plantar arch
Medial plantar
artery
Lateral plantar
artery
Posterior tibial
artery

115. Figure 19.26b
Renal vein
Splenic vein
Basilic vein
Brachial vein
Cephalic vein
Dural venous sinuses
External jugular vein
Vertebral vein
Internal jugular vein
Superior vena cava
Right and left
brachiocephalic veins
Axillary vein
Great cardiac vein
Hepatic veins
Hepatic portal vein
Superior mesenteric
vein
Inferior vena cava
Ulnar vein
Radial vein
Common iliac vein
External iliac vein
Internal iliac vein
Digital veins
Femoral vein
Great saphenous vein
Popliteal vein
Posterior tibial vein
Anterior tibial vein
Small saphenous vein
Dorsal venous arch
(b) Illustration, anterior
view. The vessels of the
pulmonary circulation
are not shown.
  Dorsal metatarsal veins
Inferior mesenteric vein
Median cubital vein
Subclavian vein
Veins of the head and trunk Veins that drain
the upper limb
Veins that drain
the lower limb

116. Figure 19.27b
(b) Veins of the head and neck, right superficial aspect
Vertebral vein
Ophthalmic vein
External
jugular vein
Superficial temporal
vein
Facial vein
Occipital vein
Posterior
auricular vein
Internal jugular
vein
Superior and middle
thyroid veins
Brachiocephalic
vein
Subclavian vein
Superior
vena cava

117. Figure 19.27c
(c) Dural venous sinuses of the brain
Confluence
of sinuses
Superior sagittal
sinus
Falx cerebri
Inferior sagittal
sinus
Straight sinus
Cavernous
sinus
Transverse
sinuses
Sigmoid sinus
Jugular foramen
Right internal
jugular vein

118. Figure 19.28b
Right subclavian vein
Brachiocephalic veins
Axillary vein
Brachial vein
Cephalic vein
Basilic vein
Median cubital vein
Median antebrachial
vein
Basilic vein
Internal jugular vein
External jugular vein
Left subclavian vein
Superior vena cava
Azygos vein
Inferior vena cava
Ascending lumbar vein
Accessory hemiazygos
vein
Hemiazygos vein
Posterior intercostals
Ulnar vein
Deep palmar venous arch
Superficial palmar venous arch
Digital veins
Cephalic vein
Radial vein
(b) Anterior view

119. Figure 19.29a
Inferior
vena cava
Inferior phrenic veins
Hepatic veins
Hepatic portal vein
Superior mesenteric vein
Splenic vein
Inferior
mesenteric
vein
L. ascending
lumbar vein
R. ascending
lumbar vein
Gonadal veins
Renal veins
Suprarenal
veins
Lumbar veins
Hepatic
portal
system
Cystic vein
External iliac vein
Internal iliac veins
Common iliac veins
(a) Schematic flowchart.

120. Figure 19.29b
(b) Tributaries of the inferior vena cava. Venous drainage
of abdominal organs not drained by the hepatic portal vein.
Hepatic veins
Inferior phrenic
vein
Left suprarenal
vein
Left ascending
lumbar vein
Lumbar veins
Left gonadal vein
Common iliac
vein
Internal iliac vein
Renal veins
Inferior vena cava
Right suprarenal
vein
Right gonadal
vein
External iliac
vein

121. Figure 19.29c
(c) The hepatic portal circulation.
Hepatic veins
Liver
Spleen
Gastric veins
Inferior vena cava
Inferior vena cava
(not part of hepatic
portal system)
Splenic vein
Right gastroepiploic
vein
Inferior
mesenteric vein
Superior
mesenteric vein
Large intestine
Hepatic portal
vein
Small intestine
Rectum

122. Figure 19.30b
Popliteal vein
Common iliac vein
Fibular vein
Anterior tibial vein
Dorsalis pedis vein
Dorsal venous arch
Dorsal metatarsal
veins
(b) Anterior view
Internal iliac vein
External iliac vein
Inguinal ligament
Femoral vein
Great saphenous
vein (superficial)
Small saphenous
vein

123. Figure 19.30c
(c) Posterior view
Great saphenous
vein
Popliteal vein
Anterior tibial vein
Fibular vein
Small saphenous
vein (superficial)
Posterior tibial vein
Plantar veins
Deep plantar arch
Digital veins