Blood pressure mechanism

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<ul><li>1.BLOOD PRESSURE MECHANISM<br />SHORT TERM CONTROL OF BLOOD PRESSURE<br /></li></ul> <p>2. Introduction<br />There are two basic mechanisms for regulating blood pressure:<br /> (1) short-term mechanisms.<br /> regulate blood vessel diameter, heart rateand contractility<br /> (2) long-term mechanisms.<br />regulate blood volume<br />Blood Pressure = cardiac outputxperipheral resistance<br />Any change in cardiac output, blood volume or peripheral resistance will lead to a change in blood pressure. <br />3. Short term control of Blood pressure is mediated by the :<br />nervous system <br />Chemicals<br />that control blood pressure by changing peripheral resistance. ( in sec or minutes)<br />Rapidity of response (beginning within seconds and often increasing the pressure to 2X normal(5 to 10 seconds).<br />Sudden inhibition of nervous cardiovascular stimulation can decrease the arterial pressure (one half normal)(10-40 seconds).<br />4. I. Nervous System<br />Control BP by changing blood distribution in the body and by changing blood vessel diameter.<br />Sympathetic &amp; Parasympathetic activity will affects veins, arteries &amp; heart tocontrol HR and force of contraction<br />The vasomotor center <br /> cluster of sympathetic neurons found in the medulla.<br />It sends efferent motor fibers that innervate smooth muscle of blood vessels. <br />Sympathetic activity<br /> Sympathetic activity<br />VASOCONSTRICTION<br /> VASODILATATION<br />5. Short-term Regulation of Rising Blood Pressure<br />Rising blood pressure<br />Stretching of arterial walls<br />Stimulation of baroreceptors in carotid sinus, aortic arch, and other large arteries of the neck and thorax<br /> Increased impulses to the brain<br />6. Baroreceptors<br />The best known of nervous mechanisms for arterial pressure control (baroreceptor reflex)<br />Baroreceptors are stretch receptors found in the carotid body, aortic body and the wall of all large arteries of the neck and thorax. <br />Respond progressively at60-180 mm Hg.<br />Respond more to a rapidly changing pressure than stationary pressure.<br />7. Baroreceptors<br />8. Effect of Baroreceptors<br />Baroreceptors entered the medulla (tractussolitarius)<br />Secondary signals inhibit the vasoconstrictor center of medulla and excite the vagal parasympathetic center<br />EFFECT<br />VASODILATATION OF THE VEINS AND ARTERIOLES<br />DECREASED HEART RATE AND STRENGTH OF HEART CONTRACTION<br />Therefore, excitation of baroreceptors by high pressure in the arteries reflexly causes arterial pressure to decrease (as decrease in PR and CO)<br />NOTE : Conversely, low pressure has opposite effects,reflexly causing the pressure rise back to normal.<br />9. Increased Parasympathetic Activity<br />Effect of increased parasympathetic and decreased sympathetic activity on heart and blood pressure:<br />Increased activity of vagus (parasympathetic) nerve<br />Decreased activity of sympathetic cardiacNerves<br />Reduction of heart rate<br />Lower cardiac output<br />Lower blood pressure<br />10. Decreased Sympathetic Activity<br />Effect of decreased sympathetic activity on arteries and blood pressure:<br />Decreased activity of vasomotor fibers (sympathetic nerve fibers)<br />Relaxation of vascular smooth muscle<br />Increased arterial diameter<br />Lower blood pressure<br />11. Short-term Regulation of Falling Blood Pressure<br />Baroreceptors inhibited<br />Decreased impulses to the brain<br />Decreased parasympathetic activity, increased sympathetic activity<br />Effects<br />Heart<br />increased heart rate and increased contractility<br />Vessels<br />increased vasoconstriction<br />Adrenal gland<br /> release of epinephrine and norepinephrine which enhance heart rate<br />Contractility and vasoconstriction<br />Increased blood pressure<br />12. Sympathetic Activity on Heart and Blood Pressure<br /> Effect of Increased Sympathetic Activity on Heart and Blood Pressure:<br /> Increased activity of sympathetic cardiac nerves<br /> Decreased activity of vagus (parasympathetic) nerve<br /> Increased heart rate and contractility<br /> Higher cardiac output<br /> Increased blood pressure<br />13. Vasomotor Fibers<br /> Effect of Increased Sympathetic Activity on Arteries and Blood Pressure:<br /> Increased activity of vasomotor fibers (sympathetic nerve fibers)<br /> Constriction of vascular smooth muscle<br /> Decreased arterial diameter<br /> Increased blood pressure<br />14. Sympathetic Activity on Adrenal Gland and Blood Pressure<br />Effect of increased sympathetic activity on adrenal glands and blood pressure:<br /> Increased sympathetic impulses to adrenal glands.<br /> Release of epinephrine and norepinephrineto bloodstream.<br /> Hormones increase heart rate, contractility and vasoconstriction. Effect is slower-acting and more prolonged than nervous system control.<br /> Increased blood pressure.<br />15. 16. II. Chemoreceptor<br />17. Chemoreceptor<br />Chemosensitive cellsthat respond to changes in pCO2 and pO2 and pH levels (Hydrogen ion).<br />pO2 and pH <br />pCO2<br />Stimulation of vasomotor center <br />vasoconstriction <br />CO <br />HR<br />BP (speeding return of blood to the heart and lungs)<br />18. Chemoreceptor<br />19. CNS Ischemic Response<br />Severe decrease blood flow to brain<br />Cerebral hypoxia<br />Vasomotor center stimulated causes powerful vasoconstriction<br />( INCREASE SYMPATHETIC DISCHARGE Norepinephrine)<br />Increase blood pressure &amp; blood flow<br />20. Cushing Reaction<br /></p> <ul><li>Special type of CNS Ischemic Response</li></ul> <p>Increased pressure of cerebrospinal fluid (cranial vault)<br />Increase intracranial tension<br />Compress whole brain &amp; arteries in the brain<br />Cuts off blood supply to brain<br />CNS Ischemic Response initiated &amp; arterial pressure rises<br />Relieve brain ischemia<br />21. THANK YOU!!<br />22. SHORT TERM REGULATION OF BLOOD PRESSURE<br />23. Innervation of blood vessels<br /></p> <ul><li>Sympathetic vasoconstrictor fiber </li></ul> <p>24. Distribution: Almost all segments of the circulation. 25. The innervation is powerful in the kidneys, gut, spleen and skin 26. is less potent in both skeletal and cardiac muscle and in the brain. </p>


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