The Vertebrate Circulatory SystemTransportationRespiratoryErythrocytes (red blood cells) transport oxygen from lungs to tissuesHemoglobin of red blood cells is transporterCO2 is released by cells into blood - carried back to lungsNutritiveNutrients enter blood through wall of intestineCarried to liver and to all body cellsExcretoryMetabolic wastes carried to kidney for removalFiltered through capillaries - Excreted in urineRegulationHormone transportHormones produced in endocrine glands - transported to targettissues throughout bodyTemperature regulationWarm-blooded vertebrates are homeothermsHeat distributed by circulating bloodTemperature adjusted by directing flow to or from extremitiesProtectionBlood clottingProtects against blood loss when vessels are damagedInvolves proteins in plasma and plateletsImmune defenseLeukocytes, white blood cells, provide immunity against disease agentsAre phagocytic, produce antibodies or have other actionsBlood VesselsArteries - carry blood away from heartArterioles - network of microscopic vessels of arterial treeCapillaries - fine network of thin-walled tubesVenules - small vessels that collect blood from capillariesVeins - return blood to heartArteries, arterioles, veins and venules have similar structurefour layers of tissueendothelium, elastic fibers, smooth muscle, connective tissuetoo thick to permit exchange of materials with surrounding tissuesExchange with tissues occurs in capillaries, endothelium is only layermolecules and ions leave blood plasma by filtration (pressurized)travel through pores in capillary walls or transported through endothelial cellsArteries and Arterioleselastic fibers allow large arteries toexpand and recoil when receivingblood from heart - helps to buffereffect of pulsing on capillary bedssmaller arteries and arterioles are less elastic, but have thickersmooth muscle - allows change in diametersmall diameter arteries and arterioles cause greatest resistanceto blood flowVasoconstriction - through contraction of smooth muscleincreases resistance, decreases flow volumeVasodilation - through relaxation of smooth muscledecreases resistance, increases flow volumeBlood around some organs regulated by precapillary sphinctersrings of smooth muscle around arterioles at capillary bedcan regulate or stop blood flow to capillary bedExample - close beds in skin to limit heat loss in cold environmentsHigh tissue perfusion Low tissue perfusionCapillary ExchangeHeart provides sufficient pressure to pump against resistance of arterial tree and into capillariesEvery cell is within 100 µm of a capillaryAverage capillary 1 mm long, 8 µm diameter, slightly larger than ared blood cellCapillaries have greatestcross-sectional areaBlood velocity decreases in capillary bedsProvides greater time for exchange of materials with tissuesBlood pressure is greatly reduced when blood enters veinsVenules and VeinsVeins and venules have thinner layer of smooth muscle than arteriespressure one-tenth that of arteriescan expand to hold greater quantities - most blood in body is in veinsVenous pressure is insufficient toreturn blood to heart from feet- aided by contraction of skeletal musclesOne-way venous valves direct flow toward heartVaricose veins - caused by blood pooling in veins when valves failCirculatory system delivers by diffusion through capillary wallsFiltration driven by pressure of blood - supplies cells with nutrientsMost fluid returned by osmosis due to concentration of protein in bloodHigh capillary blood pressure causes production of too much interstitial fluid - “edema” - a swelling of tissues in extremitiesEdema commonlyoccurs in feet ofpregnant womenEdema also resultswhen plasma proteinconcentration is toolowMay be caused byliver disease orprotein malnutritionThe lymphatic system recovers lost fluid and returns it to bloodComposed of lymphatic capillaries, lymphatic vessels, lymph nodesand lymphatic organs like spleen and thymusFluid in tissues diffuses into blind-end lymph capillariesLymph passes into larger vesselsLymphatic vessels also contain one-way valvesMajor lymphatic ducts drain into veins on sides of neckLymph fluid movement assisted by movement of musclesSome lymph vessels contract rhythmicallyLymph modified by phagocytic cells in lymph nodes and lymphatic organsThe Heart - has two pairs of valvesAtrioventricular (AV) valves lie between atria and ventricleson right side - tricuspid valveon left side - bicuspid or mitral valveSemilunar valves lie between ventricles and main arteriesright - pulmonary valveleft - aortic valveRight side sends blood to lungsLeft side sends blood to rest of bodyHow the Heart Is Stimulated to ContractCaused by transmission of membrane depolarizationtriggered by sinoatrial (SA) node - the “pacemaker”SA cells depolarize spontaneously with regular rhythmdepolarization passes from one cardiac muscle cell to anothercardiac cells are “electrically” coupled by gap junctionsAtria contract first - ventricular depolarization delayed by ~ 0.1 secSeparated by nonconductive connective tissueWave passes via atrioventricular (AV) nodeDelay permits atria to empty before ventricles contractVentricles contract together - signal carried through atrioventricular bundle of fibers - “Bundle of His”Signal transmitted by Purkinje fibers to bottom of ventricles stimulates ventricular cells to contractRight and left ventricles contract almost simultaneously from bottom to top, emptying ventriclesECG readings and contractionT =VentricularrepolarizationBlood Pressure and the Baroreceptor ReflexArterial blood pressure depends on two factorsCardiac output - how much ventricles pumpResistance to flowIncreased blood pressure caused byIncreased heart rate or blood volume or resistanceVasoconstriction - produces increased resistance to flowBlood pressure will fall ifHeart rate slows or blood volume reduced or vasodilationBaroreceptors are sensitive to changes in arterial blood pressureLocated in walls of aortic arch and carotid arteriesConnected to cardiovascular control center in medullaWhen baroreceptors detect decrease in blood pressureStimulates an increased heart rate and vasoconstriction of vessels in skin and visceraRaises blood pressureBaroreceptors act to maintain blood flow to brain with rapid standingRapid standing changes venous pressure in lower body, reduces pressure above the heartIncreases volume of blood in lower bodyReduced return of blood to heart and reduced cardiac outputLow blood