1. Chapter 10 The Blood Vessels and Blood Pressure

2. Blood Flow
Blood is transported to all parts of the body through a system of vessels.
Reconditioning organs (digestive organs, kidneys, skin) receive a disproportionally high blood flow.
This allows them replenish nutrient supplies and remove metabolic wastes to help maintain homeostasis.
Blood flow to other organs can be adjusted according to metabolic needs.
Brain function requires constant blood flow
Maintaining adequate flow to the brain is a priority of the circulatory system.

3. 100% Lungs Right side of heart Left side of heart 21% 6% Liver 20%
Digestive system
(Hepatic portal system) 6%
Liver
20%
Kidneys 9%
Skin
13%
Brain
Figure 10.1: Distribution of cardiac output at rest.
The lungs receive all the blood pumped out by the right side of the heart, whereas the systemic organs each receive some of the blood pumped out by the left side of the heart. The percentage of pumped blood received by the various organs under resting conditions is indicated. This distribution of cardiac output can be adjusted as needed. 3%
Heart muscle
15%
Skeletal muscle 5%
Bone 8%
Other
Fig. 10-1, p. 344

4. Flow Rate directly proportional to the pressure gradient
Flow rate through a vessel (volume of blood passing through per unit of time):
directly proportional to the pressure gradient
inversely proportional to vascular resistance
F = ΔP R
F = flow rate of blood through a vessel
ΔP = pressure gradient
R = resistance of blood vessels
Pressure gradient is the difference in pressure between the beginning and end of a vessel.
Blood flows from an area of higher pressure to an area of lower pressure down a pressure gradient.
The greater the pressure gradient the greater the flow rate through that vessel

5. Resistance Resistance is the hindrance to blood flow through a vessel.
Factors affecting resistance include:
blood viscosity-friction between molecules of a fluid during flow
vessel length- the longer the vessel the greater the resistance to flow
vessel radius-the smaller the radius the greater the resistance
Major determinant of resistance to flow is vessel radius.
Small change in radius produces significant change in blood flow.
R is proportional to 1/r4
Doubling the radius reduces resistance to 1/16th original value and increases flow 16-fold.

6. (a) Comparison of contact of a given volume of blood with the
10 ml 10 ml
FIGURE 10.3 Relationship of resistance and fl ow to the vessel radius.
(a) The smaller-radius vessel off ers more resistance to blood flow, because the blood “rubs” against a larger surface area. (b) Doubling the radius decreases the resistance to 1/16th and increases
the flow 16 times, because the resistance is inversely proportional to the fourth power of the radius.
(a) Comparison of contact of a given volume of blood with the
surface area of a small-radius vessel and a large-radius vessel
Fig. 10-3, p. 346

7. Radius in vessel 2 = 2 times that of vessel 1
Same
pressure
gradient
Vessel 2
Radius in vessel 2 = 2 times that of
vessel 1
Resistance in vessel 2 = 1/16 that of
vessel 1
FIGURE 10.3 Relationship of resistance and fl ow to the vessel radius.
(a) The smaller-radius vessel off ers more resistance to blood flow, because the blood “rubs” against a larger surface area. (b) Doubling the radius decreases the resistance to 1/16th and increases
the flow 16 times, because the resistance is inversely proportional to the fourth power of the radius.
Flow in vessel 2 = 16 times that of
vessel 1
Relationship of resistance and flow to the vessel radius.
The smaller-radius vessel offers more resistance to blood flow, because the blood “rubs” against a larger surface area.
Doubling the radius decreases the resistance to 1/16th and increases
the flow 16 times, because the resistance is inversely proportional to the fourth power of the radius.
Fig. 10-3, p. 346

8. Vascular Tree
Blood flows in a closed loop between the heart and the organs.
Arteries transport blood from the heart throughout the body.
Arterioles control the amount of blood that flows through each organ.
Capillaries are vessels where materials are exchanged between blood and surrounding tissue cells.
Veins return blood from the tissue back to the heart.

9. PULMONARY CIRCULATION SYSTEMIC CIRCULATION
Airway
Lungs
Air sac
Pulmonary
capillaries
Blood flows in a closed loop between the heart and the organs.
Arteries transport blood from the heart throughout the body.
Arterioles control the amount of blood that flows through each organ.
Capillaries are vessels where materials are exchanged between blood and surrounding tissue cells.
Veins return blood from the tissue back to the heart.
Arterioles
Venules
Pulmonary
artery
PULMONARY
CIRCULATION
Pulmonary
veins
Aorta
(major
systemic
artery)
Systemic
veins
Figure 10.4: Basic organization of the cardiovascular system.
Arteries progressively branch as they carry blood from the heart to the organs. A separate small arterial branch delivers blood to each of the various organs. As a small artery enters the organ it is supplying, it branches into arterioles, which further branch into an extensive network of capillaries. The capillaries rejoin to form venules, which further unite to form small veins that leave the organ. The small veins progressively merge as they carry blood back to the heart.
SYSTEMIC
CIRCULATION
Systemic
capillaries
Tissues
Venules
Arterioles
For simplicity, only
two capillary beds within
two organs are illustrated.
Smaller arteries branching off to supply various tissues
Fig. 10-4, p. 349

10. 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

11. Connective tisssue coat (mostly collagen fibers)
Endothelium
Venous
valve
Elastin
fibers
Endothelium
Smooth
muscle
Smooth
muscle;
elastin
fibers
Elastin
fibers
Connective
tisssue coat
(mostly
collagen
fibers)
Connective
tisssue coat
(mostly
collagen
fibers)
Capillary
Large artery
Arteriole
Large vein
Relative Thickness
of Layers in Wall
Endothelium
Elastin fibers
Smooth muscle
Collagen fibers
Table 10-1, p. 348

12. Arteries - large radius, rapid transit, low resistance, elastic pressure vessels
Arterioles
To capillaries
From veins
(a) Heart contracting and emptying
Arteries
Figure 10-6 Arteries as a pressure reservoir. Because of their elasticity, arteries act as a pressure reservoir.
(a) The elastic arteries distend during cardiac systole as more blood is ejected into them than drains
off into the narrow, high-resistance arterioles downstream. (b) The elastic recoil of arteries during cardiac diastole
continues driving the blood forward when the heart is not pumping.
Arterioles
To capillaries
From veins
Force exerted by blood against a vessel wall.
Pressure depends on:
the volume of blood contained within the vessel
compliance of the vessel walls; how easily the vessel distends when it fills with blood
(b) Heart relaxing and filling

13. Blood Pressure Systolic pressure: Diastolic 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
Pulse Pressure: the difference between systolic and diastolic pressures
Mean Arterial Pressure (MAP): the average driving pressure throughout the cardiac cycle=
diastolic pressure + 1/3 (pulse pressure)
Mean arterial pressure is monitored and regulated by blood pressure reflexes

14. Arterial pressure (mm Hg)
Notch caused
by closure
of aortic valve
120
Systolic pressure
Pulse
pressure
Arterial pressure (mm Hg)
Mean
pressure 93
Figure 10-7 Arterial blood pressure. The systolic pressure is the peak pressure
exerted in the arteries when blood is pumped into them during ventricular
systole. The diastolic pressure is the lowest pressure exerted in the arteries when
blood is draining off into the vessels downstream during ventricular diastole. The
pulse pressure is the difference between systolic and diastolic pressure. The mean
pressure is the average pressure throughout the cardiac cycle. 80
Diastolic pressure
Time (msec)
Fig. 10-7, p. 350

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

16. Systolic pressure 120 110 100 90 80 70 60 50 40 30 20 10 Mean pressure
Mean pressure
Diastolic
pressure
Pressure (mm Hg)
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.
Left
ventricle
Large
arteries
Arterioles
Capillaries
Venules and veins
Fig. 10-9, p. 352

17. Arterioles Major resistance vessels.
High resistance produces a large drop in mean pressure between the arteries and capillaries.
This decline enhances blood flow by contributing to the pressure gradient between the heart and organs.
Have a thick layer of circular smooth muscle.
The radius of arterioles can be adjusted to accomplish two functions:
to variably distribute cardiac output among the organs depending on body needs
to help regulate arterial blood pressure
Video

18. Vascular Tone
Arteriolar vasodilation decreases resistance and increases blood flow through the vessel.
Arteriole vasoconstriction increases resistance and decreases flow.

19. Vascular tone is the state of partial constriction that establishes a baseline of arteriolar resistance.
SEM of arteriole
Shows smooth muscle
Cross section
of arteriole
Figure 10.10: Arteriolar vasoconstriction and vasodilation.
(b) Normal arteriolar tone
Fig , p. 353

20. Arteriolar tone is controlled by local (intrinsic) controls and extrinsic controls.
Video
Caused by:
Myogenic activity O2
CO2 and other metabolites
Nitric oxide
Sympathetic stimulation
Histamine release
Heat
Caused by:
Myogenic activity
Oxygen (O2)
Carbon dioxide (CO2)
And other metabolites
Endothelin
Sympathetic stimulation
Vasopression; angiotensin II
Cold
Figure 10.10: Arteriolar vasoconstriction and vasodilation.
(d) Vasodilation (decreased contraction of circular smooth
muscle in the arteriolar wall, which leads to decreased
resistance and increased flow through the vessel)
(c) Vasoconstriction (increased contraction of circular
smooth muscle in the arteriolar wall, which leads to
increased resistance and decreased flow through the vessel)
Fig , p. 353

21. Intrinsic Control Extrinsic Control
Extrinsic sympathetic control of arteriolar radius is important in regulating blood pressure.
Increased sympathetic activity produces generalized arteriolar vasoconstriction.
Decreased sympathetic activity leads to generalized arteriolar vasodilation.
Changes in arteriolar resistance bring about changes in mean arterial pressure.
Local chemical changes associated with changes in the level of metabolic activity affect arteriole resistance.
Increased blood flow in response to enhanced tissue activity is called active hyperemia.

22. Total peripheral resistance
Arteriolar radius
Blood
viscosity
Number of
red blood cells
Local (intrinsic) control
(local changes acting on arteriolar smooth muscle in the vicinity)
Extrinsic control
(important in
regulation of blood
pressure)
Heat, cold application
(therapeutic use)
Response to shear stress
(compensates for
changes in longitudinal
force of blood flow)
Vasopressin
(hormone important
in fluid balance; exerts vasoconstrictor effect)
Myogenic responses to stretch (important in autoregulation)
Angiotensin II
(hormone important
in fluid balance; exerts
vasoconstrictor effect)
Figure 10.14: Factors affecting total peripheral resistance. The primary determinant of total peripheral resistance is the adjustable arteriolar radius. Two major categories of factors influence arteriolar radius: (1) local (intrinsic) control, which is primarily important in matching blood flow through a tissue with the tissue’s metabolic needs and is mediated by local factors acting on the arteriolar smooth muscle; and (2) extrinsic control, which is important in regulating blood pressure and is mediated primarily by sympathetic influence on arteriolar smooth muscle.
Epinephrine and nor-epinephrine (hormones that generally reinforce sympathetic nervous system)
Histamine release
(involved with injuries
and allergic responses)
Local metabolic changes
In O2 and other
Metabolites (important in matching blood flow with metabolic needs)
Sympathetic activity
(exerts generalized
vasoconstrictor effect)
Major factors affecting arteriolar radius
Fig , p. 360

23. Capillaries
Capillaries are thin-walled, small-radius, extensively branched vessels.
Surface area for exchange is maximized.
Diffusion distance is minimized.
Large cross-sectional area results in slow blood velocity to maximize time for exchange.

24. Endothelial cell nucleus Capillary lumen
Figure Capillary anatomy. (a) Electron micrograph showing that the
capillary wall consists of a single layer of endothelial cells. The nucleus of one of
these cells is shown. (b) The capillaries are so narrow that red blood cells must
pass through the capillary bed in single file.
(a) Cross section of a capillary
Fig , p. 361

25. Red blood cell Capillary
Figure Capillary anatomy. (a) Electron micrograph showing that the
capillary wall consists of a single layer of endothelial cells. The nucleus of one of
these cells is shown. (b) The capillaries are so narrow that red blood cells must
pass through the capillary bed in single file.
Fig , p. 361

26. Total cross-sectional area (cm2)5
Blood flow rate
(liters/min)
3000
Total cross-sectional area (cm2)
4.0
Anatomical
distribution
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.
200
Velocity of flow
(mm/sec)
0.3
Aorta
Arteries
Veins
Venae
cavae
Arterioles
Venules
Capillaries
Fig , p. 362

27. precapillary sphincters Arteriolar vasodilation
Tissue metabolic activity
O2, CO2 and other metabolites
Relaxation of
precapillary sphincters
Arteriolar vasodilation
Capillary blood flow
Number of open capillaries
Delivery of O2,
more rapid removal of
CO2 and other metabolites
Figure Complementary action of precapillary sphincters and arterioles in adjusting blood
flow through a tissue in response to changing metabolic needs.
Concentration gradient for
these materials between
blood and tissue cells
Capillary surface area
available for exchange
Diffusion distance from
cell to open capillary
Exchange between blood and tissue
to support increased metabolic activity
Fig , p. 365

28. Capillary Exchange
Exchanges between blood and tissues across the capillary are accomplished in two ways:
passive diffusion down concentration gradients is the primary mechanism for exchanging solutes
bulk flow determines the distribution of the ECF volume between the vascular and the interstitial fluid compartments

29. Capillary Exchange
Individual solutes are exchanged primarily by diffusion down concentration gradients.
Lipid-soluble substances pass directly through endothelial cells lining a capillary.
Water-soluble substances pass through water-filled pores between the endothelial cells.
Plasma proteins generally do not escape.

30. Endothelial cell Pores (a) Typical capillary
Figure 10.18: Exchanges across a continuous capillary wall, the most common type of capillary. (a) Slitlike gaps between adjacent endothelial cells form pores within the capillary wall. (b) As depicted in this cross section of a capillary wall, small water-soluble substances are exchanged between the plasma and the interstitial fluid by passing through the water-filled pores, whereas lipid-soluble substances are exchanged across the capillary wall by passing through the endothelial cells. Proteins to be moved across are exchanged by vesicular transport. Plasma proteins generally cannot escape from the plasma across the capillary wall.
Pores
(a) Typical capillary
Fig , p. 363

31. (b) Transport across a typical capillary wall
Interstitial fluid
Endothelial cell
Water-filled pore
Plasma proteins
generally cannot
cross the capillary
wall
Plasma
Plasma
proteins
Plasma
membrane
Lipid-soluble
substances
pass through
the
endothelial
cells
typical
Cytoplasm
O2, CO2
Exchangeable
proteins
Na+, K+, glucose,
amino acids
Figure 10.18: Exchanges across a continuous capillary wall, the most common type of capillary. (a) Slitlike gaps between adjacent endothelial cells form pores within the capillary wall. (b) As depicted in this cross section of a capillary wall, small water-soluble substances are exchanged between the plasma and the interstitial fluid by passing through the water-filled pores, whereas lipid-soluble substances are exchanged across the capillary wall by passing through the endothelial cells. Proteins to be moved across are exchanged by vesicular transport. Plasma proteins generally cannot escape from the plasma across the capillary wall.
Exchangeable
proteins are
moved across
by vesicular
transport
Small
water-soluble
substances pass
through the pores
(b) Transport across a typical capillary wall
Fig , p. 363

32. Glucose O2 CO2 Plasma Interstitial fluid Facilitated diffusion
by carrier
Figure 10.21: Independent exchange of individual solutes down their own concentration gradients across the capillary wall.
Glucose + O2
CO2 + H2O + ATP
Tissue cell
Fig , p. 366

33. Bulk Flow
Bulk flow occurs when protein-free plasma filters out of the capillary, mixes with the interstitial fluid and then is reabsorbed.
Important in regulating the distribution of ECF between plasma and interstitial fluid to help maintain arterial blood pressure.
Depends on two processes:
ultrafiltration
reabsorption

34. Bulk Flow
Ultrafiltration occurs when pressure inside the capillary exceeds pressure outside and fluid is pushed out through the pores.
Reabsorption occurs when inward-driving pressures exceed outward pressures and net movement of fluid back into the capillaries occurs.

35. Bulk Flow Forces Bulk flow occurs because of differences in the:
hydrostatic pressure PC (capillary) PIF (interstitial fluid)
colloid osmotic pressures πP (capillary) π I (interstitial fluid)
between plasma and interstitial fluid.
Capillary hydrostatic pressure pushes fluid out of the capillary bed.
Plasma colloid osmotic pressure draws fluid back into the capillary bed.

36. All values are given in mm Hg. Blood capillary
FORCES AT ARTERIOLAR
END OF CAPILLARY
FORCES AT VENULAR
END OF CAPILLARY
Initial
lymphatic
vessel
• Outward pressure
• Outward pressure
Interstitial
fluid
11 mm Hg
(ultrafiltration)
9 mm Hg
(reabsorption)
• Inward pressure
• Inward pressure
Net outward pressure
of 11 mm Hg =
Ultrafiltration pressure
Net inward pressure
of 9 mm Hg =
Reabsorption pressure
Figure 10.22: Bulk flow across the capillary wall. Ultrafiltration occurs at the arteriolar end and reabsorption occurs at the venule end of the capillary as a result of imbalances in the physical forces acting across the capillary wall.
From arteriole
To venule
All values are given in mm Hg.
Blood capillary
Fig , p. 367

37. Bulk Flow Forces
Slightly more fluid is filtered out of the capillaries into the interstitial fluid than is reabsorbed from the interstitial fluid back into the plasma.
Excess fluid is picked up by the lymphatic system and returned to general circulation.

38. (a) Relationship between initial lymphatics and blood capillaries
To venous
system
Arteriole
Tissue
cells
Interstitial
fluid
Venule
Figure 10.24: Initial lymphatics. (a) Blind-ended initial lymphatics pick up excess fluid filtered by blood capillaries and return it to the venous system in the chest. (b) Note that the overlapping edges of the endothelial cells create valvelike openings in the vessel wall.
Blood capillary
Initial
lymphatic
(a) Relationship between initial lymphatics and blood capillaries
Fig p. 368

39. Fluid pressure on the outside of the vessel
pushes the endothelial cell's free edge
inward, permitting entrance of
interstitial fluid
(now lymph).
Interstitial
fluid
Lymph
Overlapping
endothelial cells
Figure 10.24: Initial lymphatics. (a) Blind-ended initial lymphatics pick up excess fluid filtered by blood capillaries and return it to the venous system in the chest. (b) Note that the overlapping edges of the endothelial cells create valvelike openings in the vessel wall.
Fluid pressure on the inside of the vessel
forces the overlapping edges together so
that lymph cannot escape.
(b) Arrangement of endothelial cells in an initial lymphatic
Fig p. 368

40. Lymphatic System
The extra fluid, any leaked proteins, and bacteria in the tissue are picked up by the lymphatic system.
Bacteria are destroyed as lymph passes through lymph nodes on the way to being returned to the venous system.
Transports absorbed digestive fats.

41. (a) Relationship of lymphatic system to circulatory system
Systemic
circulation
Lymph node
Pulmonary
circulation
Initial
lymphatics
Lymph vessel
Valve
Blood
capillaries
Arteries
Veins
Heart
Figure 10.25: Lymphatic system. (a) Lymph empties into the venous system near its entrance to the right atrium. (b) Lymph flow averages 3 liters per day, whereas blood flow averages 7200 liters per day.
Lymph
node
Blood
capillaries
Initial
lymphatics
(a) Relationship of lymphatic system to circulatory system
Fig , p. 369

42. Veins
Venules communicate chemically with nearby arterioles to control capillary flow.
Veins serve as a blood reservoir containing 60% of blood volume.
Veins return blood back to the heart.

43. Pulmonary Systemic vessels arteries 9% 13% Systemic arterioles 2%
Heart 7%
Systemic
capillaries 5%
Systemic
veins
64%
Figure 10.27: Percentage of total blood volume in different parts of the circulatory system.
Fig , p. 371

44. (b) Action of venous valves, permitting flow of blood toward
Open venous valve
permits flow of
blood toward heart
Vein
Contracted
skeletal muscle
Closed venous valve
prevents backflow
of blood
Figure Function of venous valves.
(b) Action of venous valves,
permitting flow of blood toward
heart and preventing backflow
of blood
Fig , p. 374