19Long-Term AutoregulationSlide 3Blood Flow: Skeletal MusclesBlood Flow: Skeletal Muscle RegulationSlide 6Blood Flow: BrainSlide 8Blood Flow: SkinSlide 10Temperature RegulationBlood Flow: LungsSlide 13Blood Flow: HeartSlide 15Capillary Exchange of Respiratory Gases and NutrientsSlide 17Slide 18Capillary Exchange: Fluid MovementsNet Filtration Pressure (NFP)Slide 21Slide 22Circulatory ShockSlide 24PowerPoint PresentationCirculatory PathwaysDifferences Between Arteries and VeinsDevelopmental AspectsSlide 29Pulmonary CirculationSystemic CirculationSlide 32Slide 33Arteries of the BrainSlide 35Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsHuman Anatomy & PhysiologySEVENTH EDITIONElaine N. MariebKatja HoehnPowerPoint® Lecture Slides prepared by Vince Austin, Bluegrass Technical and Community CollegeC H A P T E R19The Cardiovascular System: Blood VesselsP A R T BCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsLong-Term AutoregulationIs evoked when short-term autoregulation cannot meet tissue nutrient requirementsMay evolve over weeks or months to enrich local blood flowCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsLong-Term AutoregulationAngiogenesis takes place:As the number of vessels to a region increasesWhen existing vessels enlargeWhen a heart vessel becomes partly occluded Routinely in people in high altitudes, where oxygen content of the air is lowCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: Skeletal MusclesResting muscle blood flow is regulated by myogenic and general neural mechanisms in response to oxygen and carbon dioxide levelsWhen muscles become active, hyperemia is directly proportional to greater metabolic activity of the muscle (active or exercise hyperemia) Arterioles in muscles have cholinergic, and alpha () and beta () adrenergic receptors  and  adrenergic receptors bind to epinephrineCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: Skeletal Muscle RegulationMuscle blood flow can increase tenfold or more during physical activity as vasodilation occurs Low levels of epinephrine bind to  receptors Cholinergic receptors are occupiedCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: Skeletal Muscle RegulationIntense exercise or sympathetic nervous system activation results in high levels of epinephrine High levels of epinephrine bind to  receptors and cause vasoconstriction This is a protective response to prevent muscle oxygen demands from exceeding cardiac pumping abilityCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: BrainBlood flow to the brain is constant, as neurons are intolerant of ischemiaMetabolic controls – brain tissue is extremely sensitive to declines in pH, and increased carbon dioxide causes marked vasodilationMyogenic controls protect the brain from damaging changes in blood pressureDecreases in MAP cause cerebral vessels to dilate to ensure adequate perfusionIncreases in MAP cause cerebral vessels to constrictCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: BrainThe brain can regulate its own blood flow in certain circumstances, such as ischemia caused by a tumorThe brain is vulnerable under extreme systemic pressure changes MAP below 60mm Hg can cause syncope (fainting)MAP above 160 can result in cerebral edemaCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: SkinBlood flow through the skin:Supplies nutrients to cells in response to oxygen needHelps maintain body temperature Provides a blood reservoirCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: SkinBlood flow to venous plexuses below the skin surface:Varies from 50 ml/min to 2500 ml/min, depending on body temperatureIs controlled by sympathetic nervous system reflexes initiated by temperature receptors and the central nervous systemCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsTemperature RegulationAs temperature rises (e.g., heat exposure, fever, vigorous exercise):Hypothalamic signals reduce vasomotor stimulation of the skin vesselsHeat radiates from the skin Sweat also causes vasodilation via bradykinin in perspirationBradykinin stimulates the release of NO As temperature decreases, blood is shunted to deeper, more vital organsCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: LungsBlood flow in the pulmonary circulation is unusual in that:The pathway is shortArteries/arterioles are more like veins/venules (thin-walled, with large lumens)They have a much lower arterial pressure (24/8 mm Hg versus 120/80 mm Hg)Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: LungsThe autoregulatory mechanism is exactly opposite of that in most tissues Low oxygen levels cause vasoconstriction; high levels promote vasodilationThis allows for proper oxygen loading in the lungsCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: HeartSmall vessel coronary circulation is influenced by:Aortic pressureThe pumping activity of the ventriclesDuring ventricular systole:Coronary vessels compressMyocardial blood flow ceasesStored myoglobin supplies sufficient oxygenDuring ventricular diastole, oxygen and nutrients are carried to the heartCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsBlood Flow: HeartUnder resting conditions, blood flow through the heart may be controlled by a myogenic mechanismDuring strenuous exercise:Coronary vessels dilate in response to local accumulation of carbon dioxideBlood flow may increase three to four times Blood flow remains constant despite wide variation in coronary perfusion pressureCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsCapillary Exchange of Respiratory Gases and NutrientsOxygen, carbon dioxide, nutrients, and metabolic wastes diffuse between the blood and interstitial fluid along concentration gradientsOxygen and nutrients pass from the blood to tissuesCarbon dioxide and metabolic wastes pass from tissues to the bloodWater-soluble solutes pass through