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USC BISC 307L - Vessels and Pressure
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Blood VesselsTension in wall of vessels proportional to radius and pressure insideconclusion: aorta gives a lot of wall tension where as a capillary is not very much tension in the walls. Aneurisms only occur in arteries3 have smooth muscle: arteries and arterioles and veinsvascular smooth muscle is capable of contracting and not contracting (vaso constriction and dilation)vasoconstriction of arteries and arterioles increases resistance to blood flow make it possible to redirect blood flow in systemic system. Regional vasoconstriction will redirect blood flow one way or the other (after a meal vasodilation in intestine is coming from other areas that are inducing vasoconstriction2 do not: capillaries and venulesMicrocirculationDow from the top and across from the right and up is the flowThe artery is heavily reinforced by strong fibrous connective tissueArterioles don’t have this protective sheathSmooth muscle cells can generate force for long periods of time can maintain contraction all night and day longAlways contracted to some extent 24 hours a dayThe amount of contraction is called MUSCLE TONECapillaries have no smooth muscle besides the pre-capillary sphincters that regulate the amount of blood flowing through the capillariesIn most tissues, most cells are no further than a couple cells away from a capillaryIn order to get from the arteries to the veins it gets though either arteriovenous bypasses or thoroughfare channelsInner diameter of the capillaries is about the size of a red blood cellSome white blood cells are actually bigger so they must go through these other channels instead of capillary bedsAngiogenesisTumor that is attracting blood vesselsGrowth factors that promote angiogenesisVEGF-formation of abnormal formation of blood vessels in the retina for diabetesFGF- proteases that digest molecules in the extracellular matrix which is important in angiogenesis because they stimulates endothelial cells to migrate and form new blood vessels. Migration to a site that needs vascularization.Angiostatin and endostatin inhibit angiogenesisPressure In Blood VesselsGraph in upper right shows pressure in various places in the systemic circulationIn arteries in general the pressure goes down as you go deeper in the vascular systempressure driveIn the left ventricle the pressure changes are extremeArteries are moderalteyl compliant and highly elasticCompliance- tendency of an object to deform under pressureElasticity- ability to come back to original form after stretchingDue to high elasticity, the stretching of the elastic walls stores some of the energy that the forward rushing blood hasKeeps the arterial diastolic pressure form going as low as the ventricle goes (12080 instead of 0)Pulse pressure is the difference between the diastolic and systolic pressureArterioles are a lot smaller and therefore the resistance is much higher and this diminishes the pressure changesno more surges of pressure. Makes for more efficient exchange of materials in the capillariesIf the arteries were to lose elasticity there would be more pulsingCalled hardening of the arteries when this elasticity is lost or arteriosclerosisCauses: calcification of arteries and atherosclerosis. PlaquesResult: stiffer arteriole wallspressure fluctuations in artery biggerpressure pulses propagate further even in the capillaries inhibiting function. Their pulse is very largeCan calculate MAP just by calculating blood pressure1. Cardiac output X peripheral resistance2. Diastolic + 1/3 pulseLow blood pressure: hypotensionResults in poor vascularization of organsLack of adequate blood flow to the brain (dizziness)High blood pressure: HypertensionIf MAP is too high because peripheral resistance is too highAneurisms, damage to kidney, increased probability of bleeding (especially in brain)It is in the arterioles that blood encounters first resistanceThis resistance is adjustableMany factors that regulate thisRegulation of Arteriolar ResistanceChanging arteriolar resistance- main way systemic blood pressure is regulated1. Myogenic autoregulationstretch activated ca2+ channels in arterioles so they can respond actively to change in blood pressure. When the pressure goes up, the resistance of the arteriole squeezes and increases causing less flow. In a perfect world the increase in blood pressure would cause the stretching to be just enough to increase the resistance just enough to keep the flow constant. And this is what happensif didn’t have this the flow would change as the pressure changes2. Local hormones1. Vasopressin (ADH)2. Angiotenson 2 (made by liver)3. Autonomic innervations (sympathetic)Vasoconstriciton1. Norepi on smooth muscle cellsbaroreceptor reflex2. ADH increases BP by causing arteriolar vasoconstriction which maintains BP during hemorrhage3. Angiotensin 2 – maintains sodium reabsorption in the kidney. Builds up blood volumebuild up blood pressureVasodilationEpinephrineBinds to beta 2 adrenergic receptors in the heart and on arterioler smooth muscle but the binding is weak.Part of fight or flight response. Vasodilation in skeletal muscle and heart and liverAChMostly arterioles don’t have parasympathetic nerves except for in penis and clitoris and release of ACh in these releases NO which causes erection.Also coronary arterioles have parasympathetic ACh releasers. Why nitroglycerine are useful in pain in the chest associated with hypoxia. Serves as a substrate for NONOLook aboveAdenosineSigns of metabolism- change when local tissue is metabolizing moreBISC 307L 1st Edition Lecture 27 Current Lecture- Blood Vesselsoo Tension in wall of vessels proportional to radius and pressure insideconclusion: aorta gives a lot of wall tension where as a capillary is notvery much tension in the walls. Aneurisms only occur in arterieso 3 have smooth muscle: arteries and arterioles and veins vascular smooth muscle is capable of contracting and not contracting (vaso constriction and dilation) vasoconstriction of arteries and arterioles increases resistance to blood flow make it possible to redirect blood flow in systemic system. Regional vasoconstriction will redirect blood flow one way or the other (after a meal vasodilation in intestine is coming from other areas that are inducing vasoconstrictiono 2 do not: capillaries and venules- Microcirculationoo Dow from the top and across from the right and up is the flowo The artery is heavily reinforced by strong fibrous


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