Physio_18.txt

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c_sopkovich
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63153
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Physio_18.txt
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2011-01-31 11:41:14
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Physiology
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chapter 18
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  1. What part of the nervous system controls circulation
    the autonomic, mainly sympathetic with a little parasympathetic controlling the heart
  2. What are the two routes sympathetics leave the chain
    • specific sympathetic nerves that go to internal viscera and the heart
    • follow spinal nerves to the peripheral
  3. sympathetic innervation of blood vessels
    • innervates the arterioles to control resistance and blood flow to the tissue
    • innervates the veins to control amount of compliance, is able to shift blood to the heart when needed
    • capillaries are not innervated
  4. Main role of parasympathetics on circulation
    • control heart rate
    • causes a decrease in rate and a slight decrease in contractibility
  5. distribution of sympathetic constrictor fibers
    • powerful to the kidney, spleen, skin and intestines
    • less potent tot skeletal muscle
  6. where is vaso motor section of brain
    medulla and lower pons
  7. Important areas of the vasomotor section
    • vasoconstrictor - located bilaterally in the anteriolateral portion of the upper medulla
    • vasodilator - located bilaterally in the anterolateral portion of the lower medulla. The fibers from this area travel up to the vasoconstrictor area and inhibit these neurons thus causing vasodilation
    • sensory area - located bilaterally in the tracts solitarius in the posterolateral medula and lower pons. Receive input from the vagus nerve and the glossopharyngeal nerve. Nerve fibers from this area travel to the other two areas to elicit control
  8. Normal tone of vessels
    • vasomotor constrictive tone is usually maintained
    • If sympathetic nerve transmission os blocked the normal resting blood pressure will drop
  9. Role of the hypothalamus
    • the posterolateral section mainly excites the vasomotor area
    • the anterolateral section inhibits the vasomotor area
  10. Stimulation of the motor cortex
    causes stimulation of the vasomotor area as the AP pass down through hypothalamus
  11. Other then the vasculature where else do sympathetic impulses go to cause vasoconstriction
    To the adrenal medulla and causes the release of epinephrine and norepinephrine
  12. Sympathetic vasodilator
    epinephrine, stimulateds beta 2 receptors
  13. role of sympathetic vasodilator system
    • does not play an important role
    • may possible dilate sketal muscle vessels in anticipation of higher blood flow need
    • motor signal from the cortex to the hypothalamus may control this
  14. Emotional vasovagal syncope
    muscle vasodilator system becomes activated and at the sam time the vagal cardioinhibitor center fires
  15. Three major changes to increase arterial pressure
    • all arterioles of systemic circulation constrict, increases TPR
    • veins constrict, shifts blood from the venous system tot he arterial. This increases preload and in turn increases cardiac output
    • autonomic nervous system stimulates the heart
  16. Two effects that result in increased arterial pressure during exercise
    when the motor cortex fires it stimulates the vasoconstrictor center and the cardioaccelerator area of the vasomotor center
  17. two areas where baroreceptors are abundant
    • each carotid sinus
    • wall of the aortic arch
  18. Path of baroreceptor afferent nerves
    • carotid; through the herring's nerve to the glossopharyngeal nerve and then to the tracts solitarius, posterolateral medulla
    • Aortic; transmit through the vagus nerves to the tractus solitarius
  19. Active range of the carotid baroreceptors
    • between 50 and 180 mmHg
    • Aorta works at a pressure level about 30 mmHg higher
  20. response of baroreceptor
    • respond much more rapidly to a change in pressure then to a stationary pressure
    • work as a pressure buffer
    • allow you to stand suddenly and not pass out due to large sympathetic release
    • reduce the minute by minute variations in arterial pressure to about one third
  21. reflex initiated by barorecpetors after reaching the tractus solitarius
    • secondary signals inhibit the vasoconstrictor center and excite the vagal parasympathetic center
    • net effect is vasodilation and decreased rate and strength of contraction
  22. With loss of baroreceptors
    you pressure would fluctuate much more and over a larger range of pressures
  23. long term control of pressure by baroreceptors
    • not very important
    • they reset after 1-2 days of pressure exposure
    • long term control requires interaction with the kidneys
  24. chemoreceptors
    • chemosensitive cells sensitive to oxygen lack and carbon dioxide excess and hydrogen ion excess
    • two in the carotid bodies and three in the aortic bodies
    • afferent nerves pass through herring nerves
  25. chemoreceptor response
    • they respond to changes in blood pressure by monitoring the oxygen and CO2 in the blood, low pressure will decrease flow and oxygen will decrease and co2 will build up
    • Does not have a large effect until the pressure falls below 80mmHg
  26. Low pressure receptors
    • located in the pulmonary artery and the atria
    • respond more to blood volume changes then pressure
  27. Atrial volume reflex
    • stretch of the atria cause a reflex dilation of the afferent arterials of the kidney and signal the hypothalamus to stop secreting ADH
    • these two effects increase GFR and reduce the reabsorption of fluid
  28. Brainbridge reflex
    • increase in arterial pressure increases heart rate
    • stretch os the SA node itself
    • afferent nerve signal through the vagus nerve to the medulla, efferent signal increase rate, increase contractile strength,
  29. CNS ischemic response
    • when blood flow to the vasomotor area of the brain becomes decreased enough to cause ischemia
    • response of the vasomotor center is to become excited
    • arterial pressure raises as high as possible
    • though to be due to the rise in co2 concentration
    • response is great enough to totally occlude peripheral vessels
    • kidneys produce no urine
    • most powerful activator
  30. when does CNS ischemic response become activated
    • becomes activated at 60mmHg and reaches a maximum at a pressure of 15mmHg
    • operates as an emergency response
  31. Cushing reaction
    • response to CNS ischemia resulting from increased intercranial pressure of cerebral spinal fluid
    • When the CSF pressure equals the arterial pressure it compresses the brain as well as the cerebral vessels
    • this initiates the CNS ischemic response to increase blood pressure to restore flow to the brain
  32. abdominal compression reflex
    • when the baroreceptors elicited a low pressure response the abdominal muscles contract and force blood out of the venous reservoirs, the blood increases systemic filling pressure and increases cardiac output and arterial pressure
    • people with muscle paralysis are more prone to hypertensive episodes
  33. Muscle contraction during exercise
    muscle contraction forces blood back to the heart and is the main ingredient in raising arterial pressure during exercise
  34. respiratory waves in arterial pressure
    • breathing signals spill over into the vaso motor center
    • inspiration causes negative thoracic pressure and vessels expand decreasing venous return
    • pressure changes can elicit stretch responses
    • there is an increase in pressure during the beginning of expiration and a decrease during the rest of the cycle
  35. Oscillation of the CNS ischemic response
    increased CSF causes a sympathetic activation, when pressure raises the ischemia is relieved and sympathetics fall and ischemia is again initiating a response
  36. Oscillation in pressure
    due to a high responce to pressure change with a delayed response, the body keeps overshooting each way

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