Presentation on theme: "Chapter 21: The Cardiovascular System: Blood Vessels and Hemodynamics"— Presentation transcript:
1Chapter 21: The Cardiovascular System: Blood Vessels and Hemodynamics Copyright 2009, John Wiley & Sons, Inc.
2Structure and function of blood vessels 5 main typesArteries – carry blood AWAY from the heartArteriolesCapillaries – site of exchangeVenulesVeins – carry blood TO the heartCopyright 2009, John Wiley & Sons, Inc.
3Copyright 2009, John Wiley & Sons, Inc. Basic structure3 layers or tunicsTunica interna (intima)Tunica mediaTunica externaModifications account for 5 types of blood vessels and their structural/ functional differencesCopyright 2009, John Wiley & Sons, Inc.
5Copyright 2009, John Wiley & Sons, Inc. StructureTunica interna (intima)Inner lining in direct contact with bloodEndothelium continuous with endocardial lining of heartActive role in vessel-related activitiesTunica mediaMuscular and connective tissue layerGreatest variation among vessel typesSmooth muscle regulates diameter of lumenTunica externaElastic and collagen fibersVasa vasorumHelps anchor vessel to surrounding tissueCopyright 2009, John Wiley & Sons, Inc.
6Copyright 2009, John Wiley & Sons, Inc. Arteries3 layers of typical blood vesselThick muscular-to-elastic tunica mediaHigh compliance – walls stretch and expand in response to pressure without tearingVasoconstriction – decrease in lumen diameterVasodilation – increase in lumen diameterCopyright 2009, John Wiley & Sons, Inc.
7Copyright 2009, John Wiley & Sons, Inc. Elastic ArteriesLargest arteriesLargest diameter but walls relatively thinFunction as pressure reservoirHelp propel blood forward while ventricles relaxingAlso known as conducting arteries – conduct blood to medium-sized arteriesCopyright 2009, John Wiley & Sons, Inc.
8Copyright 2009, John Wiley & Sons, Inc. ArteriesMuscular arteriesTunica media contains more smooth muscle and fewer elastic fibers than elastic arteriesWalls relatively thickCapable of great vasoconstriction/ vasodilatation to adjust rate of blood flowAlso called distributing arteriesAnastomosesUnion of the branches of 2 or more arteries supplying the same body regionProvide alternate routes – collateral circulationCopyright 2009, John Wiley & Sons, Inc.
9Copyright 2009, John Wiley & Sons, Inc. ArteriolesAbundant microscopic vesselsMetarteriole has precapillary sphincter which monitors blood flow into capillarySympathetic innervation and local chemical mediators can alter diameter and thus blood flow and resistanceResistance vessels – resistance is opposition to blood flowVasoconstriction can raise blood pressureCopyright 2009, John Wiley & Sons, Inc.
10Copyright 2009, John Wiley & Sons, Inc. CapillariesCapillariesSmallest blood vessels connect arterial outflow and venous returnMicrocirculation – flow from metarteriole through capillaries and into postcapillary venuleExchange vessels – primary function is exchange between blood and interstitial fluidLack tunica media and tunica externaSubstances pass through just one layer of endothelial cells and basement membraneCapillary beds – arise from single metarterioleVasomotion – intermittent contraction and relaxationThroughfare channel – bypasses capillary bedCopyright 2009, John Wiley & Sons, Inc.
11Arteries, Capillaries, and Venule Copyright 2009, John Wiley & Sons, Inc.
12Copyright 2009, John Wiley & Sons, Inc. Types of Capillaries3 typesContinuousEndothelial cell membranes from continuous tubeFenestratedHave fenestrations or poresSinusoidsWider and more windingUnusually large fenestrationsCopyright 2009, John Wiley & Sons, Inc.
13Copyright 2009, John Wiley & Sons, Inc. Portal vein – blood passes through second capillary bedHepatic or hypophysealVenulesThinner walls than arterial counterpartsPostcapillary venule – smallest venuleForm part of microcirculatory exchange unit with capillariesMuscular venules have thicker walls with 1 or 2 layers of smooth muscleCopyright 2009, John Wiley & Sons, Inc.
14Copyright 2009, John Wiley & Sons, Inc. VeinsStructural changes not as distinct as in arteriesIn general, very thin walls in relation to total diameterSame 3 layersTunica interna thinner than arteriesTunica interna thinner with little smooth muscleTunica externa thickest layerNot designed to withstand high pressureValves – folds on tunica interna forming cuspsAid in venous return by preventing backflowCopyright 2009, John Wiley & Sons, Inc.
15Copyright 2009, John Wiley & Sons, Inc. Venous ValvesCopyright 2009, John Wiley & Sons, Inc.
16Copyright 2009, John Wiley & Sons, Inc. Blood DistributionLargest portion of blood at rest is in systemic veins and venulesBlood reservoirVenoconstriction reduces volume of blood in reservoirs and allows greater blood volume to flow where neededCopyright 2009, John Wiley & Sons, Inc.
17Copyright 2009, John Wiley & Sons, Inc. Capillary exchangeMovement of substances between blood and interstitial fluid3 basic methodsDiffusionTranscytosisBulk flowCopyright 2009, John Wiley & Sons, Inc.
18Copyright 2009, John Wiley & Sons, Inc. DiffusionMost important methodSubstances move down their concentration gradientO2 and nutrients from blood to interstitial fluid to body cellsCO2 and wastes move from body cells to interstitial fluid to bloodCan cross capillary wall through intracellular clefts, fenestrations or through endothelial cellsMost plasma proteins cannot crossExcept in sinusoids – proteins and even blood cells leaveBlood-brain barrier – tight junctions limit diffusionCopyright 2009, John Wiley & Sons, Inc.
19Copyright 2009, John Wiley & Sons, Inc. TranscytosisSmall quantity of materialSubstances in blood plasma become enclosed within pinocytotic vessicles that enter endothelial cells by endocytosis and leave by exocytosisImportant mainly for large, lipid-insoluble molecules that cannot cross capillary walls any other wayCopyright 2009, John Wiley & Sons, Inc.
20Copyright 2009, John Wiley & Sons, Inc. Bulk FlowPassive process in which large numbers of ions, molecules, or particles in a fluid move together in the same directionBased on pressure gradientDiffusion is more important for solute exchangeBulk flow more important for regulation of relative volumes of blood and interstitial fluidFiltration – from capillaries into interstitial fluidReabsorption – from interstitial fluid into capillariesCopyright 2009, John Wiley & Sons, Inc.
21NFP = (BHP + IFOP) – (BCOP + IFHP) Net filtration pressure (NFP) balance of 2 pressures2 pressures promote filtrationBlood hydrostatic pressure (BHP) generated by pumping action of heartFalls over capillary bed from 35 to 16 mmHgInterstitial fluid osmotic pressure (IFOP)1 mmHgCopyright 2009, John Wiley & Sons, Inc.
22NFP = (BHP + IFOP) – (BCOP + IFHP) 2 pressures promote reabsorptionBlood colloid osmotic pressure (BCOP) promotes reabsorptionDue to presence of blood plasma proteins to large to cross wallsAverages 36 mmHgInterstitial fluid hydrostatic pressure (IFHP)Close to zero mmHgCopyright 2009, John Wiley & Sons, Inc.
23Copyright 2009, John Wiley & Sons, Inc. Starling’s LawNearly as much reabsorbed as filteredAt the arterial end, net outward pressure of 10 mmHg and fluid leaves capillary (filtration)At the venous end, fluid moves in (reabsoprtion) due to -9 mmHgOn average, about 85% of fluid filtered in reabsorpbedExcess enters lymphatic capillaries (about 3L/ day) to be eventually returned to bloodCopyright 2009, John Wiley & Sons, Inc.
25Dynamics of Capillary Exchange Copyright 2009, John Wiley & Sons, Inc.
26Hemodynamics: Factors affecting blood flow Blood flow – volume of blood that flows through any tissue in a given period of time (in mL/min)Total blood flow is cardiac output (CO)Volume of blood that circulates through systemic (or pulmonary) blood vessels each minuteCO = heart rate (HR) x stroke volume (SV)Distribution of CO depends onPressure differences that drive blood through tissueFlows from higher to lower pressureResistance to blood flow in specific blood vesselsHigher resistance means smaller blood flowCopyright 2009, John Wiley & Sons, Inc.
27Copyright 2009, John Wiley & Sons, Inc. Blood PressureContraction of ventricles generates blood pressureSystolic BP – highest pressure attained in arteries during systoleDiastolic BP – lowest arterial pressure during diastolePressure falls progressively with distance from left ventricleBlood pressure also depends on total volume of bloodCopyright 2009, John Wiley & Sons, Inc.
28Copyright 2009, John Wiley & Sons, Inc. Vascular resistanceOpposition to blood flow due to friction between blood and walls of blood vesselsDepends onSize of lumen – vasoconstriction males lumen smaller meaning greater resistanceBlood viscosity – ratio of RBCs to plasma and protein concentration, higher viscosity means higher resistanceTotal blood vessel length – resistance directly proportional to length of vessel400 miles of additional blood vessels for each 2.2lb. of fatCopyright 2009, John Wiley & Sons, Inc.
29Copyright 2009, John Wiley & Sons, Inc. Venous returnVolume of blood flowing back to heart through systemic veinsOccurs due to pressure generated by constriction of left ventricleSmall pressure difference from venule (16 mmHg) to right ventricle (0 mmHg) sufficientCopyright 2009, John Wiley & Sons, Inc.
30Copyright 2009, John Wiley & Sons, Inc. Skeletal Muscle Pump2 other mechanismsSkeletal muscle pump – milks blood in 1 direction due to valvesRespiratory pump – due to pressure changes in thoracic and abdominal cavitiesCopyright 2009, John Wiley & Sons, Inc.
33Copyright 2009, John Wiley & Sons, Inc. Velocity of blood flowSpeed in cm/sec in inversely related to cross-sectional areaVelocity is slowest where total cross sectional area is greatestBlood flow becomes slower farther from the heartSlowest in capillariesAids in exchangeCirculation time – time required for a drop of blood to pass from right atrium, through pulmonary and systemic circulation and back to right atriumNormally 1 minute at restCopyright 2009, John Wiley & Sons, Inc.
34Copyright 2009, John Wiley & Sons, Inc. Relationship between Velocity of Blood Flow and Total Cross-sectioned area in Different Types of Blood VesselsCopyright 2009, John Wiley & Sons, Inc.
35Control of blood pressure and blood flow Interconnected negative feedback systems control blood pressure by adjusting heart rate, stroke volume, systemic vascular resistance, and blood volumeSome act faster that othersSome shorter- or longer-termCopyright 2009, John Wiley & Sons, Inc.
36Role of cardiovascular center (CV) In medulla oblongataHelps regulate heart rate and stroke volumeAlso controls neural, hormonal, and local negative feedback systems that regulate blood pressure and blood flow to specific tissuesGroups of neurons regulate heart rate, contractility of ventricles, and blood vessel diameterCardiostimulatory and cardioinhibitory centersVasomotor center control blood vessel diameterReceives input from both higher brain regions and sensory receptorsCopyright 2009, John Wiley & Sons, Inc.
37Copyright 2009, John Wiley & Sons, Inc. CV CenterCopyright 2009, John Wiley & Sons, Inc.
383 main types of sensory receptors Proprioceptors – monitor movements of joints and muscles to provide input during physical activityBaroreceptors – monitor pressure changes and stretch in blood vessel wallsChemoreceptors – monitor concentration of various chemicals in the bloodOutput from CV flows along neurons of ANSSympathetic (stimulatory) opposes parasympathetic (inhibitory)Copyright 2009, John Wiley & Sons, Inc.
39Neural regulation of blood pressure Negative feedback loops from 2 types of reflexesBaroreceptor reflexesPressure-sensitive receptors in internal carotid arteries and other large arteries in neck and chestCarotid sinus reflex helps regulate blood pressure in brainAortic reflex regulates systemic blood pressureWhen blood pressure falls, baroreceptors stretched less, slower rate of impulses to CVCV decreases parasympathetic stimulation and increases sympathetic stimulationCopyright 2009, John Wiley & Sons, Inc.
40Neural regulation of blood pressure Chemoreceptor reflexesReceptors located close to baroreceptors of carotid sinus (carotid bodies) and aortic arch (aortic bodies)Detect hypoxia (low O2), hypercapnia (high CO2), acidosis (high H+) and send signals to CVCV increases sympathetic stimulation to arterioles and veins, producing vasoconstriction and an increase in blood pressureReceptors also provide input to respiratory center to adjust breathing rateCopyright 2009, John Wiley & Sons, Inc.
43Hormonal regulation of blood pressure Renin-angiotensin-aldosterone (RAA) systemRenin (released by kidney when blood volume falls or blood flow decreases) and angiotensin converting enzyme (ACE) act on substrates to produce active hormone angiotensin IIRaises BP by vasoconstriction and secretion of aldosterone (increases water reabsorption in kidneys to raise blood volume and pressure)Copyright 2009, John Wiley & Sons, Inc.
44Hormonal regulation of blood pressure Epinephrine and norepinephrineAdrenal medulla releases in response to sympathetic stimulationIncrease cardiac output by increasing rate and force of heart contractionsAntidiuretic hormone (ADH) or vasopressinProduced by hypothalamus, released by posterior pituitaryResponse to dehydration or decreased blood volumeCauses vasoconstriction which increases blood pressureCopyright 2009, John Wiley & Sons, Inc.
45Atrial natriuretic peptide (ANP) Released by cells of atriaLowers blood pressure by causing vasodilation and promoting loss of salt and water in urineReduces blood volumeCopyright 2009, John Wiley & Sons, Inc.
46Autoregulation of blood pressure Ability of tissue to automatically adjust its blood flow to match metabolic demandsDemand of O2 and nutrients can rise tenfold during exercise in heart and skeletal musclesAlso controls regional blood flow in the brain during different mental and physical activities2 general types of stimuliPhysical – temperature changes, myogenic responseVasodilating and vasoconstricting chemicals alter blood vessel diameterCopyright 2009, John Wiley & Sons, Inc.
47Copyright 2009, John Wiley & Sons, Inc. CirculationImportant difference between pulmonary and systemic circulation in autoregulatory responseSystemic blood vessel walls dilate in response to low O2 to increase O2 deliveryWalls of pulmonary blood vessels constrict under low O2 to ensure most blood flows to better ventilated areas of lungCopyright 2009, John Wiley & Sons, Inc.
48Copyright 2009, John Wiley & Sons, Inc. End of Chapter 21Copyright 2009 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.Copyright 2009, John Wiley & Sons, Inc.