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module 9 - circulatory system II blood vessels.docx

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Western University
Physiology 2130
Ingrid L.Stefanovic

Module 9Circulatory System II Blood Vessels Circulatory System IIBlood Vessels Divided into 2 distinct loopsPulmonary circulationSystemic circulationAnatomyGeneral OrganizationCirculatory system is essentially a closed system of tubes blood vessels filled with fluid blood that is moved around by a central pump heartBlood vessels consist of arteries and arterioles that transport the blood away from the heart capillaries where gas exchange occurs and venules and veins that return the blood back to the heartAortalarge arteriessmaller arteriessmaller arteriolessmaller vessels that lead to capillaries smallest of all the blood vessels and are the functional units of the circulatory system where substances enter and leavesmall venulessmall veinslarge veinsvena cavaTwo principle loops that the blood takes through the body o Pulmonary circulationbegins on right side of the heart sends blood through arteries to the lungsThrough arteriescapillaries where oxygen diffuses into the blood and carbon dioxide outveins to return to the left side of the heart o Systemic circulationbegins on the left side of the heart and freshly oxygenated blood is now pumped to the rest of the bodyLeft ventricleaortaarteriesarteriolescapillaries oxygen nutrients hormones delivered to cells and carbon dioxide and waste products picked upvenuleslarger veins to the right side of the heartAlso two smaller circulatory loops with systemic circulationHepatic portal loopdigestive systemHypothalamichypophyseal portal systembrainendocrineBlood Volume DistributionTotal blood volume TBV of an avg person5 litresThe largest portion 70 is contained in the veins o Since they contain the most capacity the veins are often referred to as the capacitance vessels or blood resevoirThe arteries contain 10 of TBVHeart and lungs contain 15Capillaries contain 5Blood Velocity and CrossSectional Area of VesselsArteries o Highest BP and velocity o Very low crosssectional area1 Module 9Circulatory System II Blood Vessels o Rapidly distribute the blood throughout the bodyArterioles o Lower BP and velocity o Higher crosssectional area o Site of highest resistance in the circulation and help regulate blood flow to an organCapillaries o Lowest blood velocity o Highest crosssectional area o Helps maximize the exchange of substancesVenules and veins o Decreased BP and crosssectional area o Increase blood velocity o Return blood back to the heart while also storing a largeof total blood volume o Pressure Flow and ResistanceConcentration gradientdriving force moving ions during diffusion Pressure gradientforce that moves the blood through the entire circulatory system o Large drop in pressure from high in aorta to low in veins o The higher the pressure gradient the higher the blood flow Blood flows through vessels as a result of the pressure gradient o As it flows it encounters resistance o This resistance is the result of blood dragging along the walls of the vessels o The higher the resistance that the blood encounters the lower the flow o Laminar streamlined flowblood flow through a vessel o There are thin layers of flow whose velocity varies across the vesselflow is slower at the edges and faster in the centerFlowpressure gradientresistanceFlowP1P2 Resistance R2
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