ch 19

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ch 19
2014-06-16 16:40:38

blood vessels exam
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  1. blood vessels
    delivery system of dynamic structures that begins and ends at heart
  2. arteries
    carry blood away from heart; oxygenated except for pulmonary circulation and umbilical vessels of fetus
  3. capillaries
    contact tissue cells; directly serve cellular needs
  4. veins
    carry blood toward heart
  5. lumen
    central blood containing space
  6. three wall layers in arteries and veins
    tunica intima, tunica media and tunica externa
  7. capillaries (structure of blood vessel walls)
    endothelium with sparse basal lamina
  8. 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
  9. tunica media
    • smooth muscle and sheets of elastin
    • sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels
    • influence blood flow and blood pressure
  10. 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
  11. 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
  12. muscular arteries
    • distal to elastic arteries -deliver blood to body organs
    • thick tunica media with more smooth muscle
    • active in vasoconstriction
  13. arterioles
    • smallest arteries
    • lead to capillary beds
    • control flow into capillary beds via vasodilation and vasoconstriction
  14. anatomy of capillaries
    • microscopic blood vessels
    • walls of thin tunica intima
    • pericytes help stabilize their walls and control permeability
    • diameter allows only single rBC to pass at a time
    • 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, between blood and interstitial fluid
  15. three structural types of capillaries
    • continuous
    • fenestrated
    • sinusoid
  16. 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
  17. fenestrated capillaries
    • some endothelial cells contain pores (fenestrations)
    • more permeable than continuous capillaries
    • function in absorption of filtrate formation (small intestines, endocrine glands, kidneys)
  18. 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
  19. capillary beds
    • interwoven networks of capillaries between arterioles and venules
    • terminal arteriole > metarteriole
    • metarteriole continuous with thoroughfare channel
    • thoroughfare channel > postcapillary venule that drains bed
  20. two types of vessels
    • vascular shunt: directly connects terminal arteriole and postcapillary venule
    • true capillaries: 10-100 exchange vessels per capillary bed. branch of metartiole or terminal arteriole
  21. precapillary sphincters
    regulate blood flow into true capillaries blood may go into true capillaries or to shunt
  22. venules
    formed when capillary beds unite. smallest postcapillary venues, very porous, allow fluids and WBCs into tissues, consist of endothelium and a few pericytes larger venules have one or two layers of smooth muscles cells
  23. veins (structure)
    • 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
    • adaptations ensure return of blood to heart despite low pressure
  24. venous valves
    prevent backflow of blood. most abundant in veins of limbs
  25. venous sinuses
    flattened veins with extremely thin walls e.g. coronary sinus of the heart and dural sinuses of the brain
  26. vascular anastomoses
    • interconnections of blood vessels
    • arterial anastomoses provide alternate pathways (collateral channels) to given body region. common at joints in abdominal organs, brain, heart, kidneys, spleen
    • vascular shunts of capillaries are examples of arteriovenous anastomoses
    • venous anastomoses are common
  27. blood flow
    • volume of blood flowing through vessel, organ, or entire circulation in given period. measured as ml/min
    • equivalents to cardiac output for entire vascular system
    • relatively constant when at rest
    • varies widely through individual organs, based on needs
  28. blood pressure
    • 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.
  29. resistance (peripheral resistance)
    • opposition to flow
    • measure of amount of friction blood encounters with vessel walls, generally in peripheral circulation
    • three important sources of resistance: blood viscosity, total blood vessel length, blood vessel diameter
  30. blood vessel diameter
    • greatest influence on resistance
    • frequent changes alter peripheral resistance
  31. abrupt changes in diameter or fatty plaques from atheroschlerosis dramatically increase ______
  32. systemic pressure
    • highest in aorta
    • declines throughout pathway
    • 1 mm Hg in right atrium
  33. pressure results when flow is opposed by
  34. arterial blood pressure
    • reflects two factors of arteries close to heart: elasticity and volume
    • blood pressure near heart is pulsatile
  35. systolic pressure
    pressure exerted in aorta during ventricular contraction. averages 120 mm Hg in normal adult
  36. diastolic pressure
    lowest level of aortic pressure
  37. pulse pressure
    difference between systolic and diastolic pressure. throbbing of arteries (pulse)
  38. MAP
    • mean arterial pressure: prssure that propels blood to tissues
    • MAP=diastolic pressure + 1/3 pulse pressure
    • pulse pressure and MAP both decline with increasing distance from heart
  39. capillary blood pressure
    • ranges from 17-35 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.
  40. venous blood pressure
    • changes little during cardiac cycle
    • small pressure gradient, about 15 mm Hg
    • low pressure due to cumulative effects of peripheral resistance -energy of blood pressure lost as heat during each circuit
  41. factors aiding venous return
    • muscular pump: contraction of skeletal msucles 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.
  42. maintaing blood pressure requires
    • cooperation of heart blood vessels and kidneys
    • supervision by brain
  43. what are the main factors influencing blood pressure
    • cardiac output
    • peripheral resistance
    • blood volume
  44. 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
  45. neural control of blood pressure
    • maintain MAP by altering blood vessel diameter. if low blood volume all vessels contracted except those to heart and brain
    • alter blood distribution to organs in response to specific demands
    • 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
  46. where are baroreceptors located
    • carotid sinuses
    • aortic arch
    • walls of large arteries of neck and thorax
  47. baroreceptor reflexes
    • increased blood pressure stimnulates baroreceptors to increase input to vasomotor center. 
    • inhibits vasomotor and cardioacceleratory centers, causing arteriole dilation and venodilation. 
    • stimulates cardioinhibitory center
    • decreased blood pressure
  48. when are baroreceptors ineffective
    if altered blood pressure is sustained
  49. chemoreceptors 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
  50. role of hypothalamus
    • increases blood pressure during stress
    • mediates redistribution of blood flow during exercise and changes in body temperature
  51. hormonal controls
    • short term regulation via changes in peripheral resistance
    • long term regulation via changes in blood volume
    • E and NE from adrenal gland: increased CO and vasocontriction
    • angiotensin II: stimulates vasoconstriction
    • high ADH levels: cause vasoconstriction
    • ANP: causes decreased blood volume by antagonizing aldosterone
  52. renal regulation
    • altering blood volume via kidneys
    • kidneys regulate arterial blood pressure: direct renal mechanism, indirect renal mechanism
  53. direct renal mechanism
    • alters blood volume indepdently 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
  54. indirect mechanism
    the renin angiotensin aldosterone mechanism

    • decrease in arterial BP causes release of renin
    • renin catalyzes conversion of angiotensinogen from liver to angiotensin I
    • angiotensin converting enzyme, esp. form lungs, converts angiotensin I to angiotensin II
  55. angiotensin II
    • increases blood volume
    • stimulates aldosterone secretion
    • causes ADH release
    • triggers hypothalamic thirst center
    • causes vasocontriction directly increasing blood pressure
  56. vital signs
    pulse and blood pressure, along with respiratory rate and body temperature
  57. pulse
    pressure wave caused by expansion and recoil of arteries
  58. radial pulse
    taken at wrist routinely used
  59. pressure points
    where arteries close to body surface can be compressed to stop blood flow
  60. systemic arterial BP
    • measured indirectly by auscultatory method using a sphygmomanometer
    • pressure increased in cuff until it exceeds systolic pressure in brachial artery
    • pressure released slowly and examiner listens for sounds of Korotkoff with a stethoscope
  61. systolic pressure
    normally less than 120 mm Hg, is pressure when sounds first occur as blood starts to spurt through artery
  62. diastolic pressure
    normally less than 80 mm Hg, is pressure when sounds disappear because artery no longer constricted; blood flowing freely
  63. hypertension
    • high blood pressure
    • sustained elevated arterial pressure of 140/90 or higher
    • prehypertension if values elevated but not yet in hypertension range
  64. prolonged hypertension may cause
    major heart failure, vascular disease, renal failure, stroke
  65. secondary hypertension
    • due to identifiable disorders including obstructed renal arteries, kidney disease, endocrine disorders, etc.
    • treatment focuses on correcting underlying problem
  66. hypotension
    • blood pressure below 90/60 mm Hg
    • usually not a concern, only if not enough blood to tissues
    • often associated with long life and lack of cardiovascular illness
  67. orthostatic hypotension
    temporary low BP and dizziness when suddenly rising from sitting or reclining position
  68. chronic hypotension
    hint of poor nutrition and warning sign for Addison's disease or hypothyroidism
  69. acute hypotension
    important sign of circulatory shock; threat for surgical patients and those in ICU
  70. tissue perfusion involved in
    • delivery of O2 and nutrients to and removal of wastes from tissue cells
    • gas exchange (lungs)
    • absorption of nutrients (digestive tract)
    • urine formation (kidneys)
    • rate of flow is precisely right amount to provide proper function
  71. bood flow is fastest and slowest where
    • fastest: aorta
    • slowest: capillaries
  72. autoregulation
    • automatic adjustment of blood flow to each tissue relative to its varying requirements
    • organs regulate own blood flow by varying resistance of own arterioles
  73. what are the two types of autoregulation
    • metabolic controls
    • myogenic controls
  74. metabolic controls of autoregulation
    • vasodilation of arterioles and relaxation of precapillary sphincters occur in response to auto deckinging tissue O2, substances from metabolically active tissues H+, K+, etc. and inflammatory chemicals
    • effects: relaxation of vascuar smooth muscle, release of NO (powerful dilater) by endothelial cells
    • endotehlins released from endothelium are potent vasoconstrictors
  75. myogenic controls of autoregulation
    • myogenic responses keep tissue perfusion constant despite most fluctuations in systemic pressure
    • vascular smooth muscle responds to stretch
  76. long term autoregulation
    occurs when short term autoregulation cannot meet tissue nutrient requirements
  77. angiogenesis
    • number of vessels to region increases and existing vessels enlarge
    • common in heart when coronary vessel occluded, or throughout body in people in high altitude areas
  78. blood flow through skin
    • supplies nutrients to cells
    • helps regulate body temp (primary function)
    • provides a blood reservoir
  79. blood flow in the lungs
    • pathways is short
    • arteries and arterioles are more like veins and venues.(thin walled with lumen)
    • arterial resistance and pressure are low
    • low O2 levels cause vasoconstriction, high levels promote vasodilation
  80. blood flow in the heart
    • during strenuous exercise: coronary vessels dilate in response to local accumulation of vasodilators.
    • blood flow may increase three to four times
  81. blood flow through capillaries
    vasomotion: slow, intermittent flow; reflects on/off opening and closing of precapillary sphincters
  82. diffusions for gas and nutrient exchange in the capillary is done how?
    • through diffusion down concentration gradients.
    • 02 and nutrients from blood to tissues
    • C02 and metabolic wastes from tissues to blood
  83. capillary hydrostatic pressure (HPc)
    • (capillary blood pressure)
    • tends to force fluids through capillary walls
    • greater at arterial end (35 mm Hg) of bed than at venule end (17 mm Hg)
  84. interstitial fluid hydrostatic pressure (HP if)
    • pressure that would push fluid into vessel
    • usually assumed to be zero because of lymphatic vessels
  85. capillary colloid osmotic pressure (OPc)
    • created by nondiffusible plasma proteins, which draw water toward themselves
    • -26 mm Hg
  86. NFP
    • net filtration pressure; comprises all forces acting on capillary bed.
    • net fluid flod out at arterial end
    • net fluid flow in at venous end
    • more leaves than is returned
  87. circulatory shock
    • any condition in which blood vessels inadequately filled or blood cannot circulate normally.
    • results in inadequate blood flow to meet tissue needs
  88. two main circulations are
    • pulmonary circulation: short loop that runs from heart to lungs and back to heart
    • systemic circulation: long loop to all parts of body and back to heart