1. Chapter 20 Lecture PowerPoint
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2. Blood Vessels and Circulation
General Anatomy of Blood Vessels
Blood Pressure
Capillary Exchange
Venous Return and Circulatory Shock
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3. Anatomy of Blood Vessels
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Capillaries
Artery:
Tunica interna
Tunica media
Tunica externa
Nerve
Vein
Figure 20.1a
(a)
1 mm
© The McGraw-Hill Companies, Inc./Dennis Strete, photographer
arteries carry blood away from heart
veins carry blood back to heart
capillaries connect smallest arteries to veins
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4. Vessel Wall tunica interna (tunica intima)
lines the blood vessel and is exposed to blood
endothelium – simple squamous epithelium overlying a basement membrane and a sparse layer of loose connective tissue
selectively permeable barrier
secretes chemicals that stimulate dilation or constriction of the vessel
normally repels blood cells and platelets (prevents clots)
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5. Vessel Wall tunica media middle layer
smooth muscle, collagen, and elastic tissue
strengthens vessel and prevents blood pressure from rupturing them
vasomotion – changes in diameter of the blood vessel brought about by smooth muscle
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6. Vessel Wall tunica externa (tunica adventitia) outermost layer
loose connective tissue that often merges with that of neighboring blood vessels, nerves, or other organs
anchors the vessel and provides passage for small nerves, lymphatic vessels
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7. Figure 20.2
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8. Arteries
arteries - sometimes called resistance vessels because they have strong, resilient tissue structure that resists blood pressure
small arteries are called arterioles
carry blood away from heart
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9. Aneurysm aneurysm - weak point in an artery or heart wall
forms thin-walled, bulging sac that pulses with each heartbeat
may rupture at any time, causing hemorrhage
dissecting aneurysm - blood accumulates between the tunics of the artery and separates them
can cause pain by putting pressure on other structures
result from congenital weakness of the blood vessels or result of trauma or bacterial infections such as syphilis
most common cause is atherosclerosis and hypertension
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10. Arterial Sense Organs
sensory structures in the walls of certain vessels that monitor blood pressure and chemistry
send info to brainstem that serves to regulate heart rate, vasomotion, and respiration
carotid sinuses – baroreceptors (pressure sensors)
in walls of internal carotid artery
monitor blood pressure
carotid bodies - chemoreceptors (monitor blood chemistry)
oval bodies near branch of common carotids
adjust respiratory rate to stabilize pH, CO2, and O2
aortic bodies - chemoreceptors
one to three in walls of aortic arch
same function as carotid bodies
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11. Capillaries
capillaries - site where nutrients, wastes, and hormones are exchanged between the blood and tissue fluid (exchange vessels)
the ‘business end’ of the cardiovascular system
absent or scarce in tendons, ligaments, epithelia, cornea and lens of the eye
three capillary types distinguished by structural differences that account for their greater or lesser permeability
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12. Three Types of Capillaries
1. continuous capillaries - occur in most tissues
endothelial cells have tight junctions forming a continuous tube with intercellular clefts
allow passage of solutes such as glucose
pericytes wrap around the capillaries and contain the same contractile protein as muscle
contract and regulate blood flow
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13. Continuous Capillary Figure 20.5 Pericyte Basal lamina Intercellular
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Pericyte
Basal
lamina
Intercellular
cleft
Pinocytotic
vesicle
Endothelial
cell
Erythrocyte
Tight
junction
Figure 20.5
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14. Three Types of Capillaries
2. fenestrated capillaries - kidneys, small intestine
organs that require rapid absorption or filtration
endothelial cells riddled with holes called filtration pores (fenestrations)
spanned by very thin glycoprotein layer
allows passage of only small molecules
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15. Fenestrated Capillary
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Endothelial
cells
Nonfenestrated
area
Erythrocyte
Filtration pores
(fenestrations)
Basal
lamina
Intercellular
cleft
(a)
(b)
400 µm
b: Courtesy of S. McNutt
Figure 20.6a
Figure 20.6b
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16. Three Types of Capillaries
3. sinusoids (discontinuous capillaries) - liver, bone marrow, spleen
irregular blood-filled spaces with large fenestrations
allow proteins (albumin), clotting factors, and new blood cells to enter the circulation
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17. Sinusoid in Liver Figure 20.7 Macrophage Endothelial cells
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Macrophage
Endothelial
cells
Erythrocytes
in sinusoid
Liver cell
(hepatocyte)
Microvilli
Sinusoid
Figure 20.7
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18. Capillary Beds
capillaries organized into networks called capillary beds
usually supplied by a single metarteriole
thoroughfare channel - metarteriole that continues through capillary bed to venule
precapillary sphincters control which beds are well perfused
when sphincters open
capillaries perfused with blood and exchange substances with tissue fluid
when sphincters closed
blood bypasses the capillaries
flows through thoroughfare channel to venule
3/4 of the body’s capillaries are shut down at a given time
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19. Capillary Bed Sphincters Open
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Precapillary
sphincters
Thoroughfare
channel
Metarteriole
Capillaries
Figure 20.3a
Arteriole
Venule
(a) Sphincters open
when sphincters are open, the capillaries are well perfused
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20. Capillary Bed Sphincters Closed
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Figure 20.3b
Arteriole
Venule
(b) Sphincters closed
when the sphincters are closed, little to no blood flow occurs
(skeletal muscles at rest)
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21. Veins (Capacitance Vessels)
greater capacity for blood containment than arteries
thinner walls, flaccid, less muscule and elastic tissue
collapse when empty, expand easily
have steady blood flow
merge to form larger veins
subjected to relatively low blood pressure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Distribution of Blood
Pulmonary
circuit
18%
Veins
54%
Systemic
circuit
70%
Heart
12%
Arteries
11%
Capillaries 5%
Figure 20.8
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22. Veins postcapillary venules – smallest veins
even more porous than capillaries so also exchange fluid with surrounding tissues
medium veins have venous valves
skeletal muscle pump propels venous blood back towards heart
venous sinuses
veins with especially thin walls, large lumens, and no smooth muscle
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23. Varicose Veins
blood pools in the lower legs in people who stand for long periods, stretching the veins
cusps of the valves pull apart in enlarged superficial veins further weakening vessels
blood backflows and further distends the vessels, their walls grow weak and develop into varicose veins
hereditary weakness, obesity, and pregnancy also contribute
hemorrhoids are varicose veins of the anal canal
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24. ?

25. Blood Pressure
blood pressure (bp) – the force that blood exerts against a vessel wall
measured at brachial artery of arm using sphygmomanometer
two pressures are recorded:
systolic pressure: peak arterial BP taken during ventricular contraction (ventricular systole)
diastolic pressure: minimum arterial BP taken during ventricular relaxation (diastole) between heart beats
normal value, young adult: 120/75 mm Hg
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26. Abnormalities of Blood Pressure
hypertension – high blood pressure
chronic is resting BP > 140/90
consequences
can weaken small arteries and cause aneurysms
hypotension – chronic low resting BP
caused by blood loss, dehydration, anemia
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27. Blood Pressure
one of the body’s chief mechanisms in preventing excessive blood pressure is the ability of the arteries to stretch and recoil during the cardiac cycle
importance of arterial elasticity
expansion and recoil maintains steady flow of blood throughout cardiac cycle, smoothes out pressure fluctuations and decreases stress on small arteries
BP rises with age
arteries less elastic and absorb less systolic force
BP determined by cardiac output, blood volume and peripheral resistance
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28. BP Changes With Distance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
120
100
Systolic pressure 80
Systemic blood pressure (mm Hg) 60
Diastolic
pressure 40 20
Figure 20.10
Aorta
Small
veins
Large
veins
Large
arteries
Small
arteries
Venae
cavae
Arterioles
Venules
Capillaries
Increasing distance from left ventricle
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29. Two Purposes of Vasomotion
general method of raising or lowering BP throughout the whole body
important in supporting brain during hemorrhage or dehydration
method of rerouting blood from one region to another for perfusion of individual organs
either centrally or locally controlled
during exercise, blood flow reduced to kidneys and digestive tract and increased to skeletal muscles
metabolite accumulation in a tissue affects local circulation without affecting circulation elsewhere in the body
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30. Blood Flow in Response to Needs
Aorta
Superior
mesenteric
artery
Dilated
Constricted
Increased flow
to intestines
Reduced
flow to
intestines
Common iliac
arteries
Figure 20.14
Constricted
Dilated
Reduced flow to legs
Increased flow to legs
(a)
(b)
arterioles shift blood flow with changing priorities
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31. Total cardiac output 5 L/min Total cardiac output 17.5 L/min
Blood Flow Comparison
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
At rest
Total cardiac output 5 L/min
Moderate exercise
Total cardiac output 17.5 L/min
Other
350 mL/min
(7.0%)
Other
400 mL/min
(2.3%)
Coronary
200 mL/min
(4.0%)
Coronary
750 mL/min
(4.3%)
Cutaneous
1,900 mL/min
(10.9%)
Cutaneous
300 mL/min
(6.0%)
Muscular
1,000 mL/min
(20.0%)
Cerebral
750 mL/min
(4.3%)
Cerebral
700 mL/min
(14.0%)
Renal
600 mL/min
(3.4%)
Digestive
1,350 mL/min
(27.0%)
Muscular
12,500 mL/min
(71.4%)
Renal
1,100 mL/min
(22.0%)
Digestive
600 mL/min
(3.4%)
Figure 20.15
during exercise
increased perfusion of lungs, myocardium, skeletal muscles
decreased perfusion of kidneys and digestive tract
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32. Capillary Exchange
only through capillary walls are exchanges made between the blood and surrounding tissues
capillary exchange – two way movement of fluid across capillary walls
water, oxygen, glucose, amino acids, lipids, minerals, antibodies, hormones, wastes, carbon dioxide, ammonia
chemicals pass through the capillary wall by three routes
through endothelial cell cytoplasm
intercellular clefts between endothelial cells
filtration pores (fenestrations) of the fenestrated capillaries
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33. Capillary Exchange - Diffusion
diffusion is the most important form of capillary exchange
glucose and oxygen diffuse out of the blood
carbon dioxide and other waste diffuse into the blood
capillary diffusion can only occur if:
the solute can permeate the plasma membranes of the endothelial cell, or
lipid soluble substances diffuse easily through plasma membranes
can find passages large enough to pass through
water soluble substance must pass through filtration pores and intercellular clefts
large particles like proteins are held back
Always down conc. gradient
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34. Capillary Exchange - Transcytosis
endothelial cells 1. pick up material on one side of the plasma membrane by pinocytosis or receptor-mediated endocytosis, 2. transport vesicles across cell, and 3. discharge material on other side by exocytosis
important for fatty acids, albumin and some hormones (insulin)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Filtration pores
Transcytosis
Figure 20.16
Diffusion through
endothelial cells
Intercellular
clefts
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35. Filtration and Reabsorption
fluid filters out of the arterial end of the capillary and osmotically reenters at the venous end
delivers materials to the cell and removes metabolic wastes
opposing forces
blood hydrostatic pressure drives fluid out of capillary (physical)
high on arterial end of capillary, low on venous end
colloid osmotic pressure (COP) draws fluid into capillary
results from plasma proteins (albumin)- more in blood
oncotic pressure = net COP (blood COP - tissue COP)
capillaries reabsorb about 85% of the fluid they filter
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36. Capillary Filtration and Reabsorption
capillary filtration at arterial end
capillary reabsorption at venous end
Figure 20.17
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37. Capillary Filtration and Reabsorption
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 20.17
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39. Edema three primary causes
edema – the accumulation of excess fluid in a tissue
occurs when fluid filters into a tissue faster than it is absorbed
three primary causes
increased capillary filtration
kidney failure, histamine release, old age, poor venous return
reduced capillary absorption
hypoproteinemia, liver disease, dietary protein deficiency
obstructed lymphatic drainage
surgical removal of lymph nodes
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40. Consequences of Edema tissue necrosis pulmonary edema cerebral edema
oxygen delivery and waste removal impaired
pulmonary edema
suffocation threat
cerebral edema
headaches, nausea, seizures, and coma
severe edema - circulatory shock
excess fluid in tissue spaces causes low blood volume and low blood pressure
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41. ?

42. Mechanisms of Venous Return
venous return – the flow of blood back to the heart
pressure gradient
blood pressure is the most important force in venous return
gravity drains blood from head and neck
skeletal muscle pump in the limbs
thoracic (respiratory) pump
inhalation - thoracic cavity expands and thoracic pressure decreases, abdominal pressure increases forcing blood upward
cardiac suction of expanding atrial space
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43. Skeletal Muscle Pump Figure 20.19 a-b 20-43 To heart Valve open Venous
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To heart
Valve open
Venous
blood
Valve closed
(a) Contracted skeletal muscles
(b) Relaxed skeletal muscles
Figure a-b
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44. Venous Return and Physical Activity
exercise increases venous return in many ways:
heart beats faster, harder increasing CO and BP
vessels of skeletal muscles, lungs, and heart dilate
increased respiratory rate, increased action of thoracic pump
increased skeletal muscle pump
venous pooling occurs with inactivity
venous pressure not enough force blood upward
with prolonged standing, CO may be low enough to cause dizziness
prevented by tensing leg muscles, activate skeletal muscle pump
jet pilots wear pressure suits
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45. Circulatory Shock
circulatory shock – cardiac output is insufficient to meet the body’s metabolic needs
cardiogenic shock - inadequate pumping of heart (MI)
low venous return (LVR) – cardiac output is low because too little blood is returning to the heart
hypovolemic shock - most common
-loss of blood volume: trauma, burns, dehydration
obstructed venous return shock
-tumor or aneurysm compresses a vein
venous pooling (vascular) shock
-next slide
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46. Vascular Shock and Others
venous pooling (vascular) shock
long periods of standing, sitting or widespread vasodilation
neurogenic shock - loss of vasomotor tone, vasodilation
emotional shock, brainstem injury
septic shock
bacterial toxins trigger vasodilation and increased capillary permeability
anaphylactic shock
severe immune reaction to antigen, histamine release, generalized vasodilation, increased capillary permeability
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47. TIAs and CVAs
transient ischemic attacks (TIAs ) – brief episodes of cerebral ischemia
caused by spasms of diseased cerebral arteries
dizziness, loss of vision, weakness, paralysis, headache or aphasia
lasts from a moment to a few hours
often early warning of impending stroke
stroke - cerebral vascular accident (CVA)
sudden death of brain tissue caused by ischemia
atherosclerosis, thrombosis, ruptured aneurysm
effects range from unnoticeable to fatal
blindness, paralysis, loss of sensation, loss of speech common
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48. Hypertension
hypertension – most common cardiovascular disease affecting about 30% of Americans over 50
“the silent killer”
major cause of heart failure, stroke, and kidney failure
damages heart by increasing afterload
myocardium enlarges until overstretched and inefficient
renal arterioles thicken in response to stress
drop in renal BP leads to salt retention (aldosterone) and worsens the overall hypertension
primary hypertension
obesity, sedentary behavior, diet, nicotine
secondary hypertension – secondary to other disease
kidney disease, hyperthyroidism
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49. END