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BIOL 273
Katherine Wood

Unit 4Cardiovascular System Chapter 15 Blood Flow and the Control of Blood PressureVasovagal syncopesyncopefainting o Emotional reaction to blood or other frightening things o CV system homoeostatic control maintains blood flood from the heart to the brainperfusion o V Syncopesignals from nervous system cause a sudden decrease in blood pressurePerson faints from lack of blood to brain Heart two separate pumps o Right pumpblood to lungs o Left pumpblood to bodyBlood leaving enters systemic arteriesProduces pressure by elastic recoilArteriespressure reservoirPressure is maintain for blood flow during ventricular relaxationelastic recoilDownstream from arteriesarterioles o Small vessels o Create highresistance outlet for arterial flow o Transport blood to the bodys tissues be contracting or dilatingvariable resistanceDiameter controlled by local factorsex oxygen concentrations of the tissuesBlood flows into capillariesleaky epithelium allows exchange of material between plasma interstitial fluid and body cells o Distal endblood flows into venous side of circulationVeinsact as volume reservoirsIf blood pressure falls to low the blood can be sent to the arterial side of circulation o From veinsto heartarteriesTotal blood flowcardiac output o Ex 5 Lmincardiac output 5 Lminblood flow through systemic capillaries blood flow through pulmonary side of circulationsystemic blood flow THE BLOOD VESSELS Blood Vessels Contain Vascular Smooth MuscleIn blood vessels smooth muscles maintain a state of partial contractionmuscle tone o Contraction of smooth muscle depends on calcium ion flow from the ECM through calcium ion channels o Neurotransmitters hormones paracrines influence smooth muscle toneVasoactive paracrinessecreted by endothelium cells lining the blood vessels of by the tissue surrounding the blood vessels Arteries and Arterioles Carry Blood Away from the HeartAorta and artery wallsstiff and springyArteriesthick smooth muscle o Large amounts of elastic and fibrous connective tissueA lot of fibrous connective tissuemore stiffnessNeed more energy to stretch blood vesselenergy storedEnergy regained byelastic recoilArteries and arteriolesdivergent pathway of blood flow o Arteries divide into smaller and smaller arteriesWalls of vessels become more muscular and less elastic o Walls of arteriolesseveral layers of smooth musclesContract and relax under chemical control Some arterioles branchmetarterioles o True arteriolescontinuous smooth muscle layer o Metarteriolesonly partially surrounded by smooth muscleBlood can take two pathsPercapillary sphincters muscle rings are relaxedblood directed to joining capillary bedsPercapillary sphincters are constrictedblood bypass capillary bed and goes straight to venous circulationLet WBCs pass straight through from arterial to venous circulationWBCs cannot pass through capillariesWBCs too largeMicrocirculationformed by arterioles capillaries and small postcapillary vessels venules Exchange Takes Place in the CapillariesCapillariessmallest blood vessel in the cardiovascular system o Postcapillary venulessite of exchange between blood and interstitial fluid o Lack smooth muscle and elastic and fibrous reinforcement so they can exchange materials o Wallsflat layers of endotheliumOne cell thickSupported on an acellular matrixbasal laminaCapillaries associated with cellspericytes o Highly branched contractile cells that surround capillariesMeshlike outer layer between capillary endothelium and the interstitial fluid o Contribute to tightness of capillaryMore pericytesless leaky capillary endothelium
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