1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 19 The Cardiovascular System: Blood Vessels: Part A p.695

2. Copyright © 2010 Pearson Education, Inc. Blood Vessel fun facts Your system of blood vessels -- arteries, veins and capillaries -- is over 60,000 miles long. That's long enough to go around the world more than twice! Blood takes about 20 seconds to circulate throughout the entire vascular system.

3. Copyright © 2010 Pearson Education, Inc.

5. Body World - Plastination

6. Copyright © 2010 Pearson Education, Inc. 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

7. Copyright © 2010 Pearson Education, Inc. 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 sphincter Thoroughfare channel Lymphatic system Venous system Arterial system Heart

8. Copyright © 2010 Pearson Education, Inc. 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

9. Copyright © 2010 Pearson Education, Inc. 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

10. Copyright © 2010 Pearson Education, Inc. Tunics Tunica intima Endothelium lines the lumen of all vessels In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present

11. Copyright © 2010 Pearson Education, Inc. Tunics Tunica media Smooth muscle and sheets of elastin Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels

12. Copyright © 2010 Pearson Education, Inc. Tunics Tunica externa (tunica adventitia) Collagen fibers protect and reinforce Larger vessels contain vasa vasorum to nourish the external layer

13. Copyright © 2010 Pearson Education, Inc. Table 19.1 (1 of 2)

14. Copyright © 2010 Pearson Education, Inc. Table 19.1 (2 of 2)

15. Copyright © 2010 Pearson Education, Inc. Elastic (Conducting) Arteries Large thick-walled arteries with elastin in all three tunics Aorta and its major branches Large lumen offers low-resistance Act as pressure reservoirs—expand and recoil as blood is ejected from the heart

16. Copyright © 2010 Pearson Education, Inc. Muscular (Distributing) Arteries and Arterioles Distal to elastic arteries; deliver blood to body organs Have thick tunica media with more smooth muscle Active in vasoconstriction

17. Copyright © 2010 Pearson Education, Inc. Arterioles Smallest arteries Lead to capillary beds Control flow into capillary beds via vasodilation and vasoconstriction

18. Copyright © 2010 Pearson Education, Inc. Capillaries Microscopic blood vessels Walls of thin tunica intima, one cell thick Pericytes help stabilize their walls and control permeability Mesenchyml cell that wraps around the vessel Size allows only a single RBC to pass at a time

19. Copyright © 2010 Pearson Education, Inc. Capillaries In all tissues except for cartilage, epithelia, cornea and lens of eye Functions: exchange of gases, nutrients, wastes, hormones, etc.

20. Copyright © 2010 Pearson Education, Inc. 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 sphincter Thoroughfare channel Lymphatic system Venous system Arterial system Heart

21. Copyright © 2010 Pearson Education, Inc. Capillaries Three structural types 1.Continuous capillaries 2.Fenestrated capillaries 3.Sinusoidal capillaries (sinusoids)

22. Copyright © 2010 Pearson Education, Inc. 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

23. Copyright © 2010 Pearson Education, Inc. 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).

24. Copyright © 2010 Pearson Education, Inc. 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)

25. Copyright © 2010 Pearson Education, Inc. 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).

26. Copyright © 2010 Pearson Education, Inc. 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

27. Copyright © 2010 Pearson Education, Inc. 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).

28. Copyright © 2010 Pearson Education, Inc. 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

29. Copyright © 2010 Pearson Education, Inc. Capillary Beds 2.True capillaries 10 to 100 exchange vessels per capillary bed Branch off the metarteriole or terminal arteriole

30. Copyright © 2010 Pearson Education, Inc. Blood Flow Through Capillary Beds Precapillary sphincters regulate blood flow into true capillaries Regulated by local chemical conditions and vasomotor nerves

31. Copyright © 2010 Pearson Education, Inc. 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 arteriolePostcapillary venule Terminal arteriolePostcapillary venule Thoroughfare channel True capillaries

32. Copyright © 2010 Pearson Education, Inc. 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

33. Copyright © 2010 Pearson Education, Inc. 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

34. Copyright © 2010 Pearson Education, Inc. Figure 19.1a Artery Vein (a)

35. Copyright © 2010 Pearson Education, Inc. Figure 19.5 Heart 8% Capillaries 5% Systemic arteries and arterioles 15% Pulmonary blood vessels 12% Systemic veins and venules 60%

36. Copyright © 2010 Pearson Education, Inc. STOP 3/16

37. Copyright © 2010 Pearson Education, Inc. 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)

38. Copyright © 2010 Pearson Education, Inc. 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

39. Copyright © 2010 Pearson Education, Inc. 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

40. Copyright © 2010 Pearson Education, Inc. 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

41. Copyright © 2010 Pearson Education, Inc. 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

42. Copyright © 2010 Pearson Education, Inc. 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

43. Copyright © 2010 Pearson Education, Inc. Resistance Frequent changes alter peripheral resistance Varies inversely with the fourth power of vessel radius E.g., if the radius is doubled, the resistance is 1/16 as much

44. Copyright © 2010 Pearson Education, Inc. 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

45. Copyright © 2010 Pearson Education, Inc. 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

46. Copyright © 2010 Pearson Education, Inc. 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

47. Copyright © 2010 Pearson Education, Inc. Figure 19.6 Systolic pressure Mean pressure Diastolic pressure

48. Copyright © 2010 Pearson Education, Inc. 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 Blood pressure near the heart is pulsatile

49. Copyright © 2010 Pearson Education, Inc. 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 Video

50. Copyright © 2010 Pearson Education, Inc. 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

51. Copyright © 2010 Pearson Education, Inc. 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

52. Copyright © 2010 Pearson Education, Inc. 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

53. Copyright © 2010 Pearson Education, Inc. 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

54. Copyright © 2010 Pearson Education, Inc. Figure 19.7 Valve (open) Contracted skeletal muscle Valve (closed) Vein Direction of blood flow

55. Copyright © 2010 Pearson Education, Inc. Maintaining Blood Pressure Requires Cooperation of the heart, blood vessels, and kidneys Supervision by the brain

56. Copyright © 2010 Pearson Education, Inc. Maintaining Blood Pressure The main factors influencing blood pressure: Cardiac output (CO) Peripheral resistance (PR) Blood volume

57. Copyright © 2010 Pearson Education, Inc. Maintaining Blood Pressure F =  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

58. Copyright © 2010 Pearson Education, Inc. 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)

59. Copyright © 2010 Pearson Education, Inc. Cardiac Output (CO) During stress, the cardioacceleratory center increases heart rate and stroke volume via sympathetic stimulation ESV decreases and MAP increases

60. Copyright © 2010 Pearson Education, Inc. Figure 19.8 Venous return Exercise Contractility of cardiac muscle Sympathetic activity Parasympathetic activity Epinephrine in blood EDVESV 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

61. Copyright © 2010 Pearson Education, Inc. 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

62. Copyright © 2010 Pearson Education, Inc. 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

63. Copyright © 2010 Pearson Education, Inc. Short-Term Mechanisms: Neural Controls Neural controls operate via reflex arcs that involve Baroreceptors Vasomotor centers and vasomotor fibers Vascular smooth muscle

64. Copyright © 2010 Pearson Education, Inc. The Vasomotor Center A cluster of sympathetic neurons in the medulla that oversee changes in blood vessel diameter Part of the cardiovascular center, along with the cardiac centers Maintains vasomotor tone (moderate constriction of arterioles) Receives inputs from baroreceptors, chemoreceptors, and higher brain centers

65. Copyright © 2010 Pearson Education, Inc. Short-Term Mechanisms: Baroreceptor- Initiated Reflexes Baroreceptors are located in Carotid sinuses Aortic arch Walls of large arteries of the neck and thorax

66. Copyright © 2010 Pearson Education, Inc. 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

67. Copyright © 2010 Pearson Education, Inc. 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

68. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 1 Stimulus: Blood pressure (arterial blood pressure rises above normal range). 1 Homeostasis: Blood pressure in normal range

69. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 2 Baroreceptors in carotid sinuses and aortic arch are stimulated. Stimulus: Blood pressure (arterial blood pressure rises above normal range). 2 1 Homeostasis: Blood pressure in normal range

70. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 3 Baroreceptors in carotid sinuses and aortic arch are stimulated. Impulses from baroreceptors stimulate cardioinhibitory center (and inhibit cardioacceleratory center) and inhibit vasomotor center. Stimulus: Blood pressure (arterial blood pressure rises above normal range). 2 3 1 Homeostasis: Blood pressure in normal range

71. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 4a Sympathetic impulses to heart cause HR, contractility, and CO. Baroreceptors in carotid sinuses and aortic arch are stimulated. Impulses from baroreceptors stimulate cardioinhibitory center (and inhibit cardioacceleratory center) and inhibit vasomotor center. Stimulus: Blood pressure (arterial blood pressure rises above normal range). 2 3 1 4a Homeostasis: Blood pressure in normal range

72. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 4b Sympathetic impulses to heart cause HR, contractility, and CO. Rate of vasomotor impulses allows vasodilation, causing R Baroreceptors in carotid sinuses and aortic arch are stimulated. Impulses from baroreceptors stimulate cardioinhibitory center (and inhibit cardioacceleratory center) and inhibit vasomotor center. Stimulus: Blood pressure (arterial blood pressure rises above normal range). 2 3 1 4b 4a Homeostasis: Blood pressure in normal range

73. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 5 Sympathetic impulses to heart cause HR, contractility, and CO. CO and R return blood pressure to homeostatic range. Rate of vasomotor impulses allows vasodilation, causing R Baroreceptors in carotid sinuses and aortic arch are stimulated. Impulses from baroreceptors stimulate cardioinhibitory center (and inhibit cardioacceleratory center) and inhibit vasomotor center. Stimulus: Blood pressure (arterial blood pressure rises above normal range). 2 3 1 4b 4a 5 Homeostasis: Blood pressure in normal range

74. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 1 Stimulus: Blood pressure (arterial blood pressure falls below normal range). 1 Homeostasis: Blood pressure in normal range

75. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 2 Baroreceptors in carotid sinuses and aortic arch are inhibited. Stimulus: Blood pressure (arterial blood pressure falls below normal range). 2 1 Homeostasis: Blood pressure in normal range

76. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 3 Baroreceptors in carotid sinuses and aortic arch are inhibited. Impulses from baroreceptors stimulate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center. Stimulus: Blood pressure (arterial blood pressure falls below normal range). 2 3 1 Homeostasis: Blood pressure in normal range

77. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 4a Baroreceptors in carotid sinuses and aortic arch are inhibited. Impulses from baroreceptors stimulate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center. Sympathetic impulses to heart cause HR, contractility, and CO. Stimulus: Blood pressure (arterial blood pressure falls below normal range). 2 3 1 4a Homeostasis: Blood pressure in normal range

78. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 4b Baroreceptors in carotid sinuses and aortic arch are inhibited. Impulses from baroreceptors stimulate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center. Vasomotor fibers stimulate vasoconstriction, causing R Sympathetic impulses to heart cause HR, contractility, and CO. Stimulus: Blood pressure (arterial blood pressure falls below normal range). 2 3 1 4b 4a Homeostasis: Blood pressure in normal range

79. Copyright © 2010 Pearson Education, Inc. Figure 19.9 step 5 Baroreceptors in carotid sinuses and aortic arch are inhibited. Impulses from baroreceptors stimulate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center. CO and R return blood pressure to homeostatic range. Vasomotor fibers stimulate vasoconstriction, causing R Sympathetic impulses to heart cause HR, contractility, and CO. Stimulus: Blood pressure (arterial blood pressure falls below normal range). 2 3 1 4b 4a 5 Homeostasis: Blood pressure in normal range

80. Copyright © 2010 Pearson Education, Inc. 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

81. Copyright © 2010 Pearson Education, Inc. 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

82. Copyright © 2010 Pearson Education, Inc. Short-Term Mechanisms: Chemoreceptor-Initiated Reflexes Chemoreceptors are located in the Carotid sinus Aortic arch Large arteries of the neck

83. Copyright © 2010 Pearson Education, Inc. 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)

84. Copyright © 2010 Pearson Education, Inc. Influence of Higher Brain Centers Reflexes that regulate BP are integrated in the medulla

85. Copyright © 2010 Pearson Education, Inc. 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

86. Copyright © 2010 Pearson Education, Inc. 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

87. Copyright © 2010 Pearson Education, Inc. 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

88. Copyright © 2010 Pearson Education, Inc. 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

89. Copyright © 2010 Pearson Education, Inc. 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

90. Copyright © 2010 Pearson Education, Inc. 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

91. Copyright © 2010 Pearson Education, Inc. 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 BaroreceptorsChemoreceptors 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