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Physiology Lecture 60

Physiology Lecture 60. Tanveer Raza MD MS MBBS razajju2@yahoo.com. Vasomotor center. Areas of the brain that play important roles in the nervous regulation of the circulation. Nervous Regulation of Circulation. Vasomotor Center Located in Brain

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Physiology Lecture 60

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  1. Physiology Lecture 60 Tanveer Raza MD MS MBBS razajju2@yahoo.com

  2. Vasomotor center Areas of the brain that play important roles in the nervous regulation of the circulation Tanveer Raza MD MS MBBS razajju2@yahoo.com

  3. Nervous Regulation of Circulation • Vasomotor Center • Located in Brain • Bilaterally mainly in the reticular substance of the Medulla and lower third of the Pons • Autonomic Nervous System • Sympathetic • Parasympathetic (Vagus) Tanveer Raza MD MS MBBS razajju2@yahoo.com

  4. Nervous Regulation of Circulation • Vasomotor center • Vasoconstrictor area • Vasodilator area • Sensory area • Receive sensory nerve signals through CN X and CN IX Tanveer Raza MD MS MBBS razajju2@yahoo.com

  5. Nervous Regulation of Circulation • Vasomotor Center • Control of Heart Activity • Sympathetic impulses • Increase heart rate and contractility • Parasympathetic impulses (Vagus Nerve) • Decrease heart rate and contractility Tanveer Raza MD MS MBBS razajju2@yahoo.com

  6. Nervous Regulation of Circulation • Vasomotor Center • Control by Higher Nervous Centers • Can excite or inhibit vasomotor center • Hypothalamus plays a special role Tanveer Raza MD MS MBBS razajju2@yahoo.com

  7. Nervous Regulation of Circulation • Sympathetic Nervous System • Vasomotor nerve fibers • Leave spinal cord through all the thoracic spinal nerves and L1 and L2 spinal nerves Tanveer Raza MD MS MBBS razajju2@yahoo.com

  8. Nervous Regulation of Circulation • Sympathetic innervation of Blood Vessels Tanveer Raza MD MS MBBS razajju2@yahoo.com

  9. Nervous Regulation of Circulation • Sympathetic Innervation • Blood Vessels • Innervates all the vessels except capillaries, precapillary sphincters and metarterioles in most tissues • Innervation of small arteries and arterioles increase resistance • Innervation to the large veins increase venous return Tanveer Raza MD MS MBBS razajju2@yahoo.com

  10. Nervous Regulation of Circulation • Sympathetic Innervations • Blood Vessels • Vasoconstriction • Distributed to essentially all segments of the circulation • More to kidneys, intestines, spleen, and skin but less potent in skeletal muscle and the brain • Vasodilation • Only a few fibers Tanveer Raza MD MS MBBS razajju2@yahoo.com

  11. Nervous Regulation of Circulation • Sympathetic Innervations • Vasoconstrictor tone • Under normal condition a partial state of contraction in the blood vessels, called vasomotor tone is maintained by sympathetic impulses Tanveer Raza MD MS MBBS razajju2@yahoo.com

  12. Sympathetic Innervations Effect of total spinal anesthesia on the arterial pressure, showing marked decrease in pressure resulting from loss of "vasomotor tone." Tanveer Raza MD MS MBBS razajju2@yahoo.com

  13. Nervous Regulation of Circulation • Sympathetic Innervation • Secretes Norepinephrine (NE) at nerve endings • Adrenal Medullae • Secrete both Epinephrine and NE • Usually causes vasoconstriction • Epinephrine in certain cases cause vasodilation Tanveer Raza MD MS MBBS razajju2@yahoo.com

  14. Nervous Regulation of Circulation • Sympathetic Innervation • Vasodilation • To skeletal muscles • Carries constrictor fibers also • Of little or no importance • May cause anticipatory vasodilation in skeletal muscles before exercise Tanveer Raza MD MS MBBS razajju2@yahoo.com

  15. Nervous Regulation of Circulation • Parasympathetic innervations • Control of Heart function • through CN X • Marked decrease in heart rate and a slight decrease in heart muscle contractility Tanveer Raza MD MS MBBS razajju2@yahoo.com

  16. VASOVAGAL SYNCOPE Tanveer Raza MD MS MBBS razajju2@yahoo.com

  17. Vasovagal Syncope • Most common cause of Syncope (fainting) • Mechanism • Increased Parasympathetic activity • Decreased Sympathetic activity Tanveer Raza MD MS MBBS razajju2@yahoo.com

  18. Vasovagal Syncope • Mechanism • Increased Parasympathetic activity • Cardioinhibitory effect • Negative Ionotropic (heart contraction) and Chronotropic (heart rate) effect • Decreased Cardiac Output • Decreased Sympathetic activity • Vasodilation • Pooling of blood in the periphery, decreased venous return Tanveer Raza MD MS MBBS razajju2@yahoo.com

  19. Vasovagal Syncope • Mechanism • Decreased blood flow to brain • Loss of Consciousness • Person falls down, blood flow to brain restored and patient wakes up Tanveer Raza MD MS MBBS razajju2@yahoo.com

  20. Vasovagal Syncope • Cause • Many triggers • Prolong standing • Stress • Painful stimuli • Venepuncture • Extreme emotion • etc Tanveer Raza MD MS MBBS razajju2@yahoo.com

  21. Nervous Regulation of Circulation • Control of Arterial Pressure • Rapid • Sympathetic stimulation • Vasoconstriction • Increased cardiac Output • Increase in Total Peripheral resistance • Increased venous return • Positive Chronotropic & Ionotropic action • Parasympathetic inhibition (to heart) Tanveer Raza MD MS MBBS razajju2@yahoo.com

  22. Baroreceptor Reflex • Reflex Mechanisms for Maintaining Normal Arterial Pressure • Negative feedback reflex mechanism • Rise in arterial pressure • Stretching of baroreceptors • Receptors transmit signals into CNS • "Feedback" signals (by ANS) to circulation • Arterial pressure reduced to normal level Tanveer Raza MD MS MBBS razajju2@yahoo.com

  23. Baroreceptor Reflex • Reflex Mechanisms for Maintaining Normal Arterial Pressure • Negative feedback reflex mechanism • Rise in arterial pressure • Stretching of baroreceptors • Receptors transmit signals into CNS • "Feedback" signals (by ANS) to circulation • Arterial pressure reduced to normal level Tanveer Raza MD MS MBBS razajju2@yahoo.com

  24. Baroreceptor Reflex • Arterial pressure rise • In normal operating range of arterial pressure, around 100 mm Hg, a slight change in pressure causes a strong change in the baroreflex signal Activation of the baroreceptors at different levels of arterial pressure Tanveer Raza MD MS MBBS razajju2@yahoo.com

  25. Baroreceptor Reflex • Reflex Mechanisms for Maintaining Normal Arterial Pressure • Negative feedback reflex mechanism • Rise in arterial pressure • Stretching of baroreceptors • Receptors transmit signals into CNS • "Feedback" signals (by ANS) to circulation • Arterial pressure reduced to normal level Tanveer Raza MD MS MBBS razajju2@yahoo.com

  26. Baroreceptor Reflex • Baroreceptors • Stretch receptors • Stimulated when stretched • Spray-type nerve endings • Location • Carotid sinus • Wall of the aortic arch • Few in the wall of almost every large artery of thoracic and neck regions Tanveer Raza MD MS MBBS razajju2@yahoo.com

  27. Baroreceptor Reflex • Carotid Sinus • Localized dilation of Internal Carotid Artery at its origin • Function • Contains numerous baroreceptors • Innervated by Nerve of Hering (CN IX branch) • CN IX synapses in the Nucleus Tractus Solitarius located in the medulla oblongata Tanveer Raza MD MS MBBS razajju2@yahoo.com

  28. Baroreceptor Reflex • Carotid Sinus Tanveer Raza MD MS MBBS razajju2@yahoo.com

  29. Carotid and Vertebral angiography Carotid Sinus Tanveer Raza MD MS MBBS razajju2@yahoo.com

  30. Baroreceptor Reflex • Carotid body • Chemoreceptors and supporting cells located near the bifurcation of the carotid artery • Innervated by branches of CN IX and CN X • Function • Detects changes in arterial blood • O2 (mainly) • Also • CO2 • pH • Temperature Tanveer Raza MD MS MBBS razajju2@yahoo.com

  31. Baroreceptor Reflex • Baroreceptors at the wall of aortic arch • Innervated by branches of CN X and travels to the Nucleus Tractus Solitarius located in the medulla oblongata Tanveer Raza MD MS MBBS razajju2@yahoo.com

  32. Baroreceptor Reflex • Reflex Mechanisms for Maintaining Normal Arterial Pressure • Negative feedback reflex mechanism • Rise in arterial pressure • Stretching of baroreceptors • Receptors transmit signals into CNS • "Feedback" signals (by ANS) to circulation • Arterial pressure reduced to normal level Tanveer Raza MD MS MBBS razajju2@yahoo.com

  33. Baroreceptor Reflex • Receptors transmit signals in CNS • The baroreceptor signals entered the Nucleus of tractus solitarius of the medulla, secondary signals inhibit the vasoconstrictor center of the medulla and excite the vagal parasympathetic center. Tanveer Raza MD MS MBBS razajju2@yahoo.com

  34. Tanveer Raza MD MS MBBS razajju2@yahoo.com

  35. Baroreceptor Reflex • Reflex Mechanisms for Maintaining Normal Arterial Pressure • Negative feedback reflex mechanism • Rise in arterial pressure • Stretching of baroreceptors • Receptors transmit signals into CNS • "Feedback" signals (by ANS) to circulation • Arterial pressure reduced to normal level Tanveer Raza MD MS MBBS razajju2@yahoo.com

  36. Baroreceptor Reflex • "Feedback" signals (by ANS) to circulation • High pressure in the arteries reflexly causes the arterial pressure to decrease • Decrease in peripheral resistance • Decrease in cardiac output • Low pressure has opposite effects Tanveer Raza MD MS MBBS razajju2@yahoo.com

  37. Baroreceptor Reflex • Arterial baroreceptor system reduces the minute by minute variation in arterial pressure to about one third that which would occur were the baroreceptor system not present Tanveer Raza MD MS MBBS razajju2@yahoo.com

  38. Two-hour records of arterial pressure in a normal dog (above) and in the same dog (below) several weeks after the baroreceptors had been denervated Tanveer Raza MD MS MBBS razajju2@yahoo.com

  39. Baroreceptor Reflex • Long-Term Regulation • Important in short term (seconds to minutes) control • Long term regulation unimportant • Baroreceptors rapidly reset to new pressure • Total baroreceptor denervation has no lasting effect on the average daily arterial pressure • Recent studies in intact experimental animals suggest baroreceptor may play a role in long term regulation Tanveer Raza MD MS MBBS razajju2@yahoo.com

  40. Baroreceptor Reflex • Control of Arterial pressure by chemoreceptors • Chemoreceptors • Chemosensitive cells • Respond to • O2 , CO2 and H+ • Location • In several small chemoreceptor organs • two Carotid bodies • One to three aortic bodies adjacent to aorta Tanveer Raza MD MS MBBS razajju2@yahoo.com

  41. Tanveer Raza MD MS MBBS razajju2@yahoo.com

  42. Baroreceptor Reflex • Control of Arterial pressure by chemoreceptors • Impulse pass along with the baroreceptor fibers, hrough Hering's nerves (CN IX) and the CN X into the vasomotor center • When arterial pressure falls below critical level, chemoreceptors become stimulated because diminished blood flow causes decreased O2 as well as excess CO2 and H+ Tanveer Raza MD MS MBBS razajju2@yahoo.com

  43. Bainbridge Reflex • Atrial Reflex Control of Heart Rate • Increased atrial pressure increases in heart rate • Direct effect of the increased atrial volume to stretch the SA node • Bainbridge reflex • Helps prevent damming of blood in the veins, atria, and pulmonary circulation Tanveer Raza MD MS MBBS razajju2@yahoo.com

  44. Bainbridge Reflex • Atrial Reflex Control of Heart Rate • Increased atrial pressure increases in heart rate • Bainbridge reflex • Nervous reflex • Stretch receptors of atria elicit the reflex • Afferent signals through CN X to the medulla • Efferent signals through CN X and sympathetic nerves • Increase heart rate and strength of contraction Tanveer Raza MD MS MBBS razajju2@yahoo.com

  45. Renal Control Increases in cardiac output, urinary output, and arterial pressure caused by increased blood volume in dogs whose nervous pressure control mechanisms had been blocked Tanveer Raza MD MS MBBS razajju2@yahoo.com

  46. Renal-body fluid systems play a dominant role in long-term BP regulation Excess ECF Blood volume and arterial pressure rise Kidneys excrete extra ECF Pressure returns back to normal Renal Control Tanveer Raza MD MS MBBS razajju2@yahoo.com

  47. Renal Control • Pressure diuresis • Increased urinary output in response to increased pressure • In humans being, at an arterial pressure of • 50 mmHg urine output is essentially zero • 100 mm Hg urine output is normal • 200 mm Hg urine output is 6-8 times normal. • Pressure natriuresis • Increased arterial pressure also increases sodium output Tanveer Raza MD MS MBBS razajju2@yahoo.com

  48. Renal Control • Increased Fluid Volume Can Elevate Arterial Pressure • Increases Cardiac Output • Increases Total Peripheral Resistance Tanveer Raza MD MS MBBS razajju2@yahoo.com

  49. Tanveer Raza MD MS MBBS razajju2@yahoo.com

  50. Renal Control • Salt (NaCl) intake elevate the arterial pressure • Increased Salt in ECF • Increased osmolality of ECF • Increased thirst • Increased ADH secreton • Increased ECF • Raised Pressure Tanveer Raza MD MS MBBS razajju2@yahoo.com

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