1. Blood Vessels Part 1 Slides by Barbara Heard and W. Rose.
HESC310
4/28/2017
Blood Vessels
Part 1
Slides by Barbara Heard and W. Rose.
figures from Marieb & Hoehn 9th eds.
Portions copyright Pearson Education
Axial Skeleton

2. Delivery system of dynamic structures that begins and ends at heart
Blood Vessels
Delivery system of dynamic structures that begins and ends at heart
Arteries: carry blood away from heart; oxygenated except for pulmonary circulation and umbilical vessels of fetus
Capillaries: contact tissue cells; directly serve cellular needs
Veins: carry blood toward heart
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3. Figure 19.1a Generalized structure of arteries, veins, and capillaries.
Artery
Vein
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4. Structure of Blood Vessel Walls
Lumen
Central blood-containing space
Three wall layers in arteries and veins
Tunica intima, tunica media, and tunica externa
Capillaries
Endothelium with sparse basal lamina
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5. • Internal elastic membrane • External elastic membrane
Figure 19.1b Generalized structure of arteries, veins, and capillaries.
Tunica intima
• Endothelium
• Subendothelial layer
• Internal elastic membrane
Tunica media
(smooth muscle and
elastic fibers)
Valve
• External elastic membrane
Tunica externa
(collagen fibers)
• Vasa vasorum
Lumen
Lumen
Artery
Capillary network
Vein
Basement membrane
Endothelial cells
Capillary
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6. Tunics Tunica intima Endothelium lines lumen of all vessels
Continuous with endocardium
Slick surface reduces friction
Subendothelial layer in vessels larger than 1 mm; connective tissue basement membrane
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7. Tunics Tunica media Smooth muscle and sheets of elastin
Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels
Influence blood flow and blood pressure
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8. Tunica externa (tunica adventitia)
Tunics
Tunica externa (tunica adventitia)
Collagen fibers protect and reinforce; anchor to surrounding structures
Contains nerve fibers, lymphatic vessels
Vasa vasorum of larger vessels nourishes external layer
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9. Vessels vary in length, diameter, wall thickness, tissue makeup
Blood Vessels
Vessels vary in length, diameter, wall thickness, tissue makeup
See figure 19.2 for interaction with lymphatic vessels
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10. Sinusoid Metarteriole
Figure The relationship of blood vessels to each other and to lymphatic vessels.
Venous system
Arterial system
Large veins
(capacitance
vessels)
Heart
Elastic
arteries
(conducting
arteries)
Large
lymphatic
vessels
Lymph
node
Muscular
arteries
(distributing
arteries)
Lymphatic
system
Small veins
(capacitance
vessels)
Arteriovenous
anastomosis
Lymphatic
capillaries
Sinusoid
Arterioles
(resistance
vessels)
Terminal
arteriole
Postcapillary
venule
Metarteriole
Thoroughfare
channel
Capillaries
(exchange
vessels)
Precapillary
sphincter
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11. Arterial System: Elastic Arteries
Large thick-walled arteries with elastin in all three tunics
Aorta and its major branches
Large lumen offers low resistance
Inactive in vasoconstriction
Act as pressure reservoirs—expand and recoil as blood ejected from heart
Smooth pressure downstream
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12. Arterial System: Muscular Arteries
Distal to elastic arteries
Deliver blood to body organs
Thick tunica media with more smooth muscle
Active in vasoconstriction
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13. Arterial System: Arterioles
Smallest arteries
Lead to capillary beds
Control flow into capillary beds via vasodilation and vasoconstriction
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14. Table 19.1 Summary of Blood Vessel Anatomy (1 of 2)
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15. Microscopic blood vessels Walls of thin tunica intima
Capillaries
Microscopic blood vessels
Walls of thin tunica intima
In smallest one cell forms entire circumference
Pericytes help stabilize their walls and control permeability
Diameter allows only single RBC to pass at a time
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16. In all tissues except for cartilage, epithelia, cornea and lens of eye
Capillaries
In all tissues except for cartilage, epithelia, cornea and lens of eye
Provide direct access to almost every cell
Functions
Exchange of gases, nutrients, wastes, hormones, etc., between blood and interstitial fluid
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17. Three structural types
Capillaries
Three structural types
Continuous capillaries
Fenestrated capillaries
Sinusoid capillaries (sinusoids)
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18. Continuous Capillaries
Abundant in skin and muscles
Tight junctions connect endothelial cells
Intercellular clefts allow passage of fluids and small solutes
Continuous capillaries of brain unique
Tight junctions complete, forming blood brain barrier
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19. Pericyte Tight junction
Figure 19.3a Capillary structure.
Pericyte
Red blood
cell in lumen
Intercellular
cleft
Endothelial
cell
Basement
membrane
Tight junction
Pinocytotic
vesicles
Endothelial
nucleus
Continuous capillary. Least permeable, and most
common (e.g., skin, muscle).
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20. 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)
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21. Basement membrane Tight junction
Figure 19.3b Capillary structure.
Pinocytotic
vesicles
Red blood
cell in lumen
Fenestrations
(pores)
Endothelial
nucleus
Intercellular
cleft
Basement membrane
Tight junction
Endothelial
cell
Fenestrated capillary. Large fenestrations (pores)
increase permeability. Occurs in areas of active
absorption or filtration (e.g., kidney, small intestine).
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22. Blood flow sluggish – allows modification
Sinusoid Capillaries
Fewer tight junctions; usually fenestrated; larger intercellular clefts; large lumens
Blood flow sluggish – allows modification
Large molecules and blood cells pass between blood and surrounding tissues
Found only in the liver, bone marrow, spleen, adrenal medulla
Macrophages in lining to destroy bacteria
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23. Sinusoid capillary. Most permeable. Occurs in special
Figure 19.3c Capillary structure.
Endothelial
cell
Red blood
cell in lumen
Large
intercellular
cleft
Tight junction
Incomplete
basement
membrane
Nucleus of
endothelial
cell
Sinusoid capillary. Most permeable. Occurs in special
locations (e.g., liver, bone marrow, spleen).
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24. Capillary Beds Microcirculation
Interwoven networks of capillaries between arterioles and venules
Terminal arteriole  metarteriole
Metarteriole continuous with thoroughfare channel (intermediate between capillary and venule)
Thoroughfare channel  postcapillary venule that drains bed
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25. Capillary Beds: Two Types of Vessels
Vascular shunt (metarteriole—thoroughfare channel)
Directly connects terminal arteriole and postcapillary venule
True capillaries
10 to 100 exchange vessels per capillary bed
Branch off metarteriole or terminal arteriole
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26. Blood Flow Through Capillary Beds
True capillaries normally branch from metarteriole and return to thoroughfare channel
Precapillary sphincters regulate blood flow into true capillaries
Blood may go into true capillaries or to shunt
Regulated by local chemical conditions and vasomotor nerves
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27. Precapillary sphincters
Figure Anatomy of a capillary bed.
Vascular shunt
Precapillary sphincters
Metarteriole
Thoroughfare
channel
True
capillaries
Terminal arteriole
Postcapillary venule
Sphincters open—blood flows through true capillaries.
Terminal arteriole
Postcapillary venule
Sphincters closed—blood flows through metarteriole – thoroughfare
channel and bypasses true capillaries.
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28. Venous System: Venules
Formed when capillary beds unite
Smallest postcapillary venules
Very porous; allow fluids and WBCs into tissues
Consist of endothelium and a few pericytes
Larger venules have one or two layers of smooth muscle cells
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29. Formed when venules converge
Veins
Formed when venules converge
Have thinner walls, larger lumens compared with corresponding arteries
Blood pressure lower than in arteries
Thin tunica media; thick tunica externa of collagen fibers and elastic networks
Called capacitance vessels (blood reservoirs); contain up to 65% of blood supply
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30. Pulmonary blood vessels 12% Systemic arteries and arterioles 15%
Figure Relative proportion of blood volume throughout the cardiovascular system.
Pulmonary blood
vessels 12%
Systemic arteries
and arterioles 15%
Heart 8%
Capillaries 5%
Systemic veins
and venules 60%
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31. Adaptations ensure return of blood to heart despite low pressure
Veins
Adaptations ensure return of blood to heart despite low pressure
Large-diameter lumens offer little resistance
Venous valves prevent backflow of blood
Most abundant in veins of limbs
Venous sinuses: flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain)
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32. Table 19.1 Summary of Blood Vessel Anatomy (2 of 2)
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33. Figure 19.1a Generalized structure of arteries, veins, and capillaries.
Artery
Vein
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34. Interconnections of blood vessels
Vascular Anastomoses
Interconnections of blood vessels
Arterial anastomoses provide alternate pathways (collateral channels) to given body region
Common at joints, in abdominal organs, brain, and heart; none in retina, kidneys, spleen
Vascular shunts of capillaries are examples of arteriovenous anastomoses
Venous anastomoses are common
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35. Physiology of Circulation: Definition of Terms
Blood flow
Volume of blood flowing through vessel, organ, or entire circulation in 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
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36. Physiology of Circulation: Definition of Terms
Blood pressure (BP)
Force per unit area exerted on wall of blood vessel by blood
Expressed in mm Hg
Measured as systemic arterial BP in large arteries near heart
Pressure gradient provides driving force that keeps blood moving from higher to lower pressure areas
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37. Physiology of Circulation: Definition of Terms
Resistance (peripheral resistance)
Opposition to flow
Measure of amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation
Three important sources of resistance
Blood viscosity
Total blood vessel length
Blood vessel diameter
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38. Factors that remain relatively constant:
Resistance
Factors that remain relatively constant:
Blood viscosity
The "stickiness" of blood due to formed elements and plasma proteins
Increased viscosity = increased resistance
Blood vessel length
Longer vessel = greater resistance encountered
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39. Frequent changes alter peripheral resistance
Blood vessel diameter
Greatest influence on resistance
Frequent changes alter peripheral resistance
Varies inversely with fourth power of vessel radius
E.g., if radius is doubled, the resistance is 1/16 as much
E.g., Vasoconstriction  increased resistance
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40. Small-diameter arterioles major determinants of peripheral resistance
Abrupt changes in diameter or fatty plaques from atherosclerosis dramatically increase resistance
Disrupt laminar flow and cause turbulent flow
Irregular fluid motion  increased resistance
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41. Relationship Between Blood Flow, Blood Pressure, and Resistance
R = resistance
ν = viscosity
L = vessel length
r = vessel radius
 = “proportional to”

42. Relationship Between Blood Flow, Blood Pressure, and Resistance
Blood flow (F) directly proportional to blood pressure gradient ( P)
If  P increases, blood flow speeds up
Blood flow inversely proportional to peripheral resistance (R)
If R increases, blood flow decreases:
F =  P/R
R more important in influencing local blood flow because easily changed by altering blood vessel diameter
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43. 120 Systolic pressure 100 Mean pressure 80 Blood pressure (mm Hg) 60
Figure Blood pressure in various blood vessels of the systemic circulation.
120
Systolic pressure
100
Mean pressure 80
Blood pressure (mm Hg) 60
Diastolic
pressure 40 20
Aorta
Veins
Arteries
Venules
Arterioles
Capillaries
Venae cavae
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44. Arterial Blood Pressure
Systolic pressure: pressure exerted in aorta during ventricular contraction
Averages 120 mm Hg in normal adult
Diastolic pressure: lowest level of aortic pressure
Pulse pressure = difference between systolic and diastolic pressure
Throbbing of arteries (pulse)
Larger if elastic arteries are less distensible
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45. Arterial Blood Pressure
Mean arterial pressure (MAP): pressure that propels blood to tissues
MAP = diastolic pressure + 1/3 pulse pressure
Pulse pressure and MAP both decline with increasing distance from heart
Ex. BP = 120/80; MAP = 93 mm Hg
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46. Capillary Blood Pressure
Ranges from 17 to 35 mm Hg
Low capillary pressure is desirable
High BP would rupture fragile, thin-walled capillaries
Most very permeable, so low pressure forces filtrate into interstitial spaces
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47. Changes little during cardiac cycle
Venous Blood Pressure
Changes little during cardiac cycle
Small pressure gradient from venules to great veins (i.e. from caps back to heart); about 15 mm Hg
Low pressure in veins due to cumulative effects of “upstream” peripheral resistance
Energy of blood pressure lost as heat during each circuit
Central venous pressure approx. zero
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48. Factors Aiding Venous Return
Muscular pump: contraction of skeletal muscles "milks" blood toward heart; valves prevent backflow
Respiratory pump: pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand
Venoconstriction under sympathetic control pushes blood toward heart
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49. Direction of blood flow
Figure The muscular pump.
Venous valve (open)
Contracted skeletal
muscle
Venous valve
(closed)
Vein
Direction of blood flow
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50. Maintaining Blood Pressure
Requires
Cooperation of heart, blood vessels, and kidneys
Supervision by brain
Main factors influencing blood pressure
Cardiac output (CO)
Peripheral resistance (PR)
Blood volume
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51. Blood pressure, again
For the entire systemic circulation, Flow = cardiac output, so we replace “F” with “C.O.” The resistance of the whole systemic circulation is called total peripheral resistance (TPR), so we replace “R” with “TPR”:

52. CO = SV × HR; normal = 5.0-5.5 L/min
Cardiac Output (CO)
CO = SV × HR; normal = L/min
Determined by venous return, and neural and hormonal controls
Resting heart rate maintained by cardioinhibitory center via parasympathetic vagus nerves
Stroke volume controlled by venous return (EDV)
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53. Cardiac Output (CO)
During stress, cardioacceleratory center increases heart rate and stroke volume via sympathetic stimulation
ESV decreases and MAP increases
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54. Figure 19.8 Major factors enhancing cardiac output.
Exercise
BP activates cardiac centers in medulla
Activity of respiratory pump
(ventral body cavity pressure)
Activity of muscular pump
(skeletal muscles)
Sympathetic venoconstriction
Sympathetic activity
Parasympathetic activity
Epinephrine in blood
Venous return
Contractility of cardiac muscle
EDV
ESV
Stroke volume (SV)
Heart rate (HR)
Initial stimulus
Physiological response
Result
Cardiac output (CO = SV x HR)
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55. Control of Blood Pressure
Short-term neural and hormonal controls
Counteract fluctuations in blood pressure by altering peripheral resistance and CO
Long-term renal regulation
Counteracts fluctuations in blood pressure by altering blood volume
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56. Short-term Mechanisms: Neural Controls
Neural controls of peripheral resistance
Maintain MAP by altering blood vessel diameter
If low blood volume all vessels constricted except those to heart and brain
Alter blood distribution to organs in response to specific demands
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57. Short-term Mechanisms: Neural Controls
Neural controls operate via reflex arcs that involve
Baroreceptors
Cardiovascular center of medulla
Vasomotor fibers to heart and vascular smooth muscle
Sometimes input from chemoreceptors and higher brain centers
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58. The Cardiovascular Center
Clusters of sympathetic neurons in medulla oversee changes in CO and blood vessel diameter
Consists of cardiac centers and vasomotor center
Vasomotor center sends steady impulses via sympathetic efferents to blood vessels  moderate constriction called vasomotor tone
Receives inputs from baroreceptors, chemoreceptors, and higher brain centers
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59. Short-term Mechanisms: Baroreceptor Reflexes
Baroreceptors located in
Carotid sinuses
Aortic arch
Walls of large arteries of neck and thorax
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60. Short-term Mechanisms: Baroreceptor Reflexes
Increased blood pressure stimulates baroreceptors to increase input to vasomotor center
Inhibits vasomotor and cardioacceleratory centers, causing arteriolar dilation and venodilation
Stimulates cardioinhibitory center
 decreased blood pressure
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61. Short-term Mechanisms: Baroreceptor Reflexes
Decrease in blood pressure due to
Arteriolar vasodilation
Venodilation
Decreased cardiac output
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62. Short-term Mechanisms: Baroreceptor Reflexes
If MAP low
 Reflex vasoconstriction  increased CO  increased blood pressure
Ex. Upon standing baroreceptors of carotid sinus reflex protect blood to brain; in systemic circuit as whole aortic reflex maintains blood pressure
Baroreceptors ineffective if altered blood pressure sustained
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63. Figure 19.9 Baroreceptor reflexes that help maintain blood pressure homeostasis.
Slide 1
Impulses from baroreceptors stimulate cardioinhibitory center (and inhibit cardioacceleratory center) and inhibit vasomotor center. 3
Sympathetic impulses to heart
cause HR, 4a
contractility, and
CO.
Baroreceptors in carotid sinuses and aortic arch are stimulated. 2
Rate of vasomotor impulses allows vasodilation, causing R. 4b
IMBALANCE
CO and R return blood pressure to homeostatic range. 5
Stimulus:
Blood pressure (arterial blood pressure rises above normal range). 1
Homeostasis: Blood pressure in normal range
Stimulus:
Blood pressure (arterial blood pressure falls below normal range). 1
IMBALANCE
CO and R return blood pressure to homeostatic range. 5
Vasomotor fibers stimulate vasoconstriction, causing R. 4b
Baroreceptors in carotid sinuses and aortic arch are inhibited. 2 4a
Sympathetic impulses to heart cause HR,
contractility, and
CO.
Impulses from baroreceptors activate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center. 3
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64. Short-term Mechanisms: Chemoreceptor Reflexes
Chemoreceptors in aortic arch and large arteries of neck detect increase in CO2, or drop in pH or O2
Cause increased blood pressure by
Signaling cardioacceleratory center  increase CO
Signaling vasomotor center  increase vasoconstriction
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65. Short-term Mechanisms: Influence of Higher Brain Centers
Reflexes in medulla
Hypothalamus and cerebral cortex can modify arterial pressure via relays to medulla
Hypothalamus increases blood pressure during stress
Hypothalamus mediates redistribution of blood flow during exercise and changes in body temperature
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66. Short-term Mechanisms: Hormonal Controls
Short term regulation via changes in peripheral resistance
Long term regulation via changes in blood volume
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67. Short-term Mechanisms: Hormonal Controls
Cause increased blood pressure
Epinephrine and norepinephrine from adrenal gland  increased CO and vasoconstriction
Angiotensin II stimulates vasoconstriction
High ADH levels cause vasoconstriction
Cause lowered blood pressure
Atrial natriuretic peptide causes decreased blood volume by antagonizing aldosterone
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68. Inhibits baroreceptors
Figure Direct and indirect (hormonal) mechanisms for renal control of blood pressure.
Direct renal mechanism
Indirect renal mechanism (renin-angiotensin-aldosterone)
Initial stimulus
Physiological response
Result
Arterial pressure
Arterial pressure
Inhibits baroreceptors
Sympathetic nervous
system activity
Filtration by kidneys
Angiotensinogen
Renin release
from kidneys
Angiotensin I
Angiotensin converting
enzyme (ACE)
Angiotensin II
Urine formation
ADH release by
posterior pituitary
Thirst via
hypothalamus
Vasoconstriction;
peripheral resistance
Adrenal cortex
Secretes
Aldosterone
Blood volume
Sodium reabsorption
by kidneys
Water reabsorption
by kidneys
Water intake
Blood volume
Mean arterial pressure
Mean arterial pressure
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69. Long-term Mechanisms: Renal Regulation
Baroreceptors quickly adapt to chronic high or low BP so are ineffective
Long-term mechanisms control BP by altering blood volume via kidneys
Kidneys regulate arterial blood pressure
Direct renal mechanism
Indirect renal (renin-angiotensin-aldosterone) mechanism
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70. Direct Renal Mechanism
Alters blood volume independently of hormones
Increased BP or blood volume causes elimination of more urine, thus reducing BP
Decreased BP or blood volume causes kidneys to conserve water, and BP rises
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71. The renin-angiotensin-aldosterone mechanism
Indirect Mechanism
The renin-angiotensin-aldosterone mechanism
 Arterial blood pressure  release of renin
Renin catalyzes conversion of angiotensinogen from liver to angiotensin I
Angiotensin converting enzyme, especially from lungs, converts angiotensin I to angiotensin II
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72. Functions of Angiotensin II
Increases blood volume
Stimulates aldosterone secretion
Causes ADH release
Triggers hypothalamic thirst center
Causes vasoconstriction directly increasing blood pressure
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73. Inhibits baroreceptors
Figure Direct and indirect (hormonal) mechanisms for renal control of blood pressure.
Direct renal mechanism
Indirect renal mechanism (renin-angiotensin-aldosterone)
Initial stimulus
Physiological response
Result
Arterial pressure
Arterial pressure
Inhibits baroreceptors
Sympathetic nervous
system activity
Filtration by kidneys
Angiotensinogen
Renin release
from kidneys
Angiotensin I
Angiotensin converting
enzyme (ACE)
Angiotensin II
Urine formation
ADH release by
posterior pituitary
Thirst via
hypothalamus
Vasoconstriction;
peripheral resistance
Adrenal cortex
Secretes
Aldosterone
Blood volume
Sodium reabsorption
by kidneys
Water reabsorption
by kidneys
Water intake
Blood volume
Mean arterial pressure
Mean arterial pressure
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74. Activation of vasomotor and cardio- acceleratory centers in brain stem
Figure Factors that increase MAP.
Activity of
muscular
pump and
respiratory
pump
Release
of ANP
Fluid loss from
hemorrhage,
excessive
sweating
Crisis stressors:
exercise, trauma,
body
temperature
Vasomotor tone;
bloodborne
chemicals
(epinephrine,
NE, ADH,
angiotensin II)
Dehydration,
high hematocrit
Body size
Conservation
of Na+ and
water by kidneys
Blood volume
Blood pressure
Blood pH O2
CO2
Blood
volume
Baroreceptors
Chemoreceptors
Venous
return
Activation of vasomotor and cardio-
acceleratory centers in brain stem
Diameter of
blood vessels
Blood
viscosity
Blood vessel
length
Stroke
volume
Heart
rate
Cardiac output
Peripheral resistance
Initial stimulus
Physiological response
Result
Mean arterial pressure (MAP)
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