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Kinesiology & Health Science
KINE 2011
Gillian Wu

Local Control of Blood Flow 1. Active or Reactive Hyperemia Hyperaemia= increase in flow Active or Reactive hyperaemia= relationship between disturbance in metabolites that will cause vasodilation of arterioles. 2 diff ways to disturbance of metabolites (i)Enhancing metabolic activity of cells surrounding blood vessels (ii)Accumulation because we have reduced flow to the area Key dilators is Adenosine Concept of Vasodilation As the Adenosine diffuses and reaches the smooth muscle causes and starts smooth muscle cells it to relax, we see a much larger increase in diameter of blood vessels and now u can see rich network of blood flow. A large flow occurs, vasodilation allows opening of low resistance pathway so much more flow is distributed to downstream capillaries that will assist in deliverance of oxygen and removal of waste products which will once those signals are removed allow the blood vessels to come to their original size again. Norepinephrine is added which causes vasoconstriction and prevents blood from moving downstream capillaries. Once its removed, it comes to its resting diameter again Vasodilator is added, adenosine is going on to the blood vessel, and the capacity of blood vessel to go in opposite direction and opens up a lot of capillaries. Local Control of Blood Flow is not associated with metabolic demands. Its associated with organ trying to maintain its blood flow aat constant level. Its to help ensure that’s there is no ups and down in perfusion of an orgran just based on fluctuation based on arterial pressure . Its called flow autoregulation coz its designed to maintain steady flow. Actual response that’s allowing auto-regulation to occur is called Myogenic response. The initiator is change in arterial pressure (nothing to do with metabolism) . The second graph on the left side how steady arterial pressure and it increases (prob due to infusion of fluid, or changed posture etc). When you increase pressure, that is inside the blood vseels pushing outside, pressure is pushing on the walls of blood vessels. Arterioles are somewhat elastic, when increase outward force, the tendency passively arterioles wall will be stretched out. Filling ballon with water).. Increasing the pressure will push out the walls of the arterioles, (i)PASSIVE RESPONSE just happens with the increase in pressure pushes out walls But smooth muscles react to this, they don’t like being stretched out, and the SECOND PART is the (ii)ACTIVE RESPONSE. The smooth muscle cells have stretched sensitive channels in their membranes, these channels become activated and allow Ca to enter smooth muscle cells. Increasing intracellular calcium in the muscle cell causes CONTRACTION to occur. Smooth muscle cells contract lowering the diameter and that will reduce BLOOD Flow (negative feedback but helps maintain steady blood flow) This response does not happen in a lot of responses, . Important in kidneys, brain also likes to maintain steady blood flow. Response to the stimulus (negative feedback) If blood pressure is changed ;increase /decrease, you will not see a change that goes with it Blood flow is able to maintained despite changes in pressure (small graph steady state result) Dashed line =where low or very high pressure , smooth muscle cells are not capable of maintain flow anymore. Line stays horizontal is the optimal range, for flow auto- regulation, if you increase pressure / decrease beyond that, then flow-auto regulation would not occur. SUMMARY: LOCAL REGULATION The two mechanisms are not exclusive of each other. They are both diff features, and used depending on the situation. Normal arteriolar time: has some level of tone and constriction Vasoconstriction: Endothelin increases Vasodilation All factors arein balance but any change will cause the change in arterioal Control of Blood –Systemic a.k.a intrinsic (since its not coming from inside the organ) TWO main influences that can cause blood vessels to change diameter 1. Neural – exerted Sympathetic nervous system Sympathetic nerves are running down the spinal cord and there is branches of them that go to heart to regulate cardiac function. Also, branches go out and go out to other parts as well and these nerves terminate in close proximity to arterioles. So whatever sympathetic nerves do will cause responses in arterioles 2. Hormonal influences can have broad ranging effects, since they are circulating and can affect a lot of organs. (VASOCONTRICTORS) Epinephrine Angiotension II Vasopressin (these haromnes have cross-over functions and also blood vessels) These are the effectors that body uses to homeostaticly regulate MAP Systematic regulation Sympathetic neuron comes in and terminating very close to an arterial, so it doesn’t actually synapse with it, (unlike motor neuron) . They relase norephinrine in close proxmitity so it can diffuse and reach arteriole. On smooth muscle cells on arterioles, is the adrenergic receptor (predominant receptors on arterioles) .. little horizontal line with vertical line is to illustrate action potential that are coming down the sympathetic nerve and causing release of norepinephrine. Under resting conditions, there is some level of sympathetic nerve activity. Action potential is being fired periodically ,so norepinephrine is present and adrenergic receptors are being activated by it. This resting level of norepinephrine being released from the nerve is helping to set the normal vascular tone where the arteriole is partially constricted. This is one of the things that leads to partial contstriction coz we always have little norpehinrpine being released and activating adregeneric receptors. But from this, basal or resting level of nerve activity , we can have increase or decrease in nerve activity. If we get activation of nerve to higher leve (exercise, stressed out) much more rapid of action potential. Every little line will cause more norphephrine wil be released, more frequent action potential , the more norpepinephrine will be released which means you will activate greater number of adregrencic receptors and cause more CONSTRICTION. This constriction will last as long as the nerve is releasing additional norepinephrine. Another pat
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