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  1. 1. Neural Regulation of the Circulation
  2. 2. Neural control of blood flow  affects blood flow in large segments of the systemic circulation,  shifting blood flow from the non- muscular vascular bed to the muscles during exercise  changing the blood flow in the skin to control body temperature.
  3. 3. Innervation of the Circulatory System  Cardiac innervation  Innervation of blood vessels  Sympathetic vasoconstrictor fiber  Sympathetic vasodilator fiber  Parasympathetic nerve fiber to peripheral vessels
  4. 4. Cardiac innervation  Sympathetic nerve – noradrenergic fiber; Parasympathetic nerve- cholinergic fiber  Noradrenergic sympathetic nerve  to the heart increase the cardiac rate (chronotropic effect)  the force of cardiac contraction (inotropic effect).  Cholinergic vagal cardiac fibers decrease the heart rate.
  5. 5. Cardiac innervation (contin.)  moderate amount of tonic discharge in the cardiac sympathetic nerves at rest  a good deal of tonic vagal discharge (vagal tone) in humans  When the vagi are cut in experiment animals, the heart rate rises
  6. 6. Innervation of blood vessels  Sympathetic vasoconstrictor fiber  Distribution: Almost all segments of the circulation.  The innervation is powerful in the kidneys, gut, spleen and skin,  is less potent in both skeletal and cardiac muscle and in the brain.
  7. 7. Innervation of blood vessels Sympathetic vasoconstrictor fiber (contin.) Almost all vessels, such as arteries, arterioles, venules and veins are innervated, except the capillaries, precapillary sphincters and most of the metarterioles. Tone: Usually the sympathetic vasoconstrictor fibers keep tonic.
  8. 8. Innervation of blood vessels  3) Parasympathetic nerve fiber to peripheral vessels  Parasympathetic nerve fibers innervate vessels of the blood vessels in  Meninges  the salivary glands,  the liver  the viscera in pelvis  the external genitals.  Importance: Regulate the blood flow of these organs in some special situations.
  9. 9. Cardiovascular System Blood flow and blood pressure are monitored and ultimately controlled by the brain. Peripheral signals are fed to the brain on a beat to beat basis, so that alterations in blood flow can occur to meet the changing metabolic demands of the body’s tissues. Blood flow in part, depends on maintaining an appropriate BP. Three main factors influencing BP are: 1. Cardiac Output 2. Peripheral Resistance 3. Blood Volume Remember Blood Flow = D Pressure Resistance By rearranging so Pressure is isolated, this becomes Blood Pressure = Blood Flow X Resistance OR = CO X Peripheral Resistance
  10. 10. Arterial Blood Pressure • Systolic pressure – pressure exerted on arterial walls during ventricular contraction • Diastolic pressure – lowest level of arterial pressure during a ventricular cycle • Pulse pressure – the difference between systolic and diastolic pressure • Mean arterial pressure (MAP) – pressure that propels the blood to the tissues • MAP = diastolic pressure + 1/3 pulse pressure
  11. 11. Factors affecting ABP: Sex : M > F due to hormones/ equal at menopause. Age : Elderly > children due to atherosclerosis. Emotions : due to secretion of adrenaline & noradrenaline. Exercise : due to  venous return. Hormones : (e.g. Adrenaline, noradrenaline, thyroid H). Gravity :  Lower limbs > upper limbs. Sleep :  due to  venous return. Pregnancy : due to  metabolism.
  12. 12. Cardiovascular System Neural Control of Peripheral Resistance aims to: 1. Alter blood distribution in response to specific demands. 2. Maintain appropriate MAP by changing vessel diameter. Neural Control of the cardiovascular system originates in the Cardiac Centres found in the Medulla. Cardio -Acceleratory Centre sends Sympathetic Neurones down the spine to between T1 and T5, where they exit to the periphery. Cardio - Inhibitory Centre originates with the Vagus Nucleus in the medulla and this Parasympathetic Nerve leaves the cranium as the Vagus (X) Nerve. Vasomotor Centre - is a cluster of sympathetic fibres in the Medulla. - transmits impulses via sympathetic vasomotor fibres from T1 to L2 to blood vessels (arterioles) Vasoconstriction is caused by increased frequency of impulses (Noradrenaline) Vasodilation is caused by decreased frequency of impulses.
  13. 13. Cardiovascular System Brainstem contains: Pons Medulla In the Medulla are the: Cardiac Acceleratory Centre Cardiac Inhibitory Centre Vasomotor Centre
  14. 14. I. Short-Term Regulation of Blood Pressure: • Rapidly Acting Pressure Control Mechanisms, Acting Within Seconds or Minutes. A. Baroreceptor reflexes Change peripheral resistance, heart rate, and stroke volume in response to changes in blood pressure B. Chemoreceptor reflexes Sensory receptors sensitive to oxygen, carbon dioxide, and pH levels of blood C. Central nervous system ischemic response Results from high carbon dioxide or low pH levels in medulla and increases peripheral resistance
  15. 15. Local mechanisms affect MAP:
  16. 16. Baroreceptor Reflex Control
  17. 17. Cardiovascular System Baroreceptors are found in • Carotid Sinuses (blood going to brain) and • Aortic Arch (systemic blood going to body) As MAP increases this stretches the receptors and they send a fast train of impulses to the Vasomotor Centre. This results in a decrease in the frequency of impulses from the Vasomotor Centre and arterioles dilate. Final result is vasodilation and decreases MAP. At the same time impulses are also relayed to the Cardiac Centre where CIC activity increases (stimulating the Vagus nerve) - decreases HR and SV. CAC activity decreases (inhibiting Sympathetic nerves) - decreases CO.
  18. 18. Chemoreceptor Reflex Control
  19. 19. General control of MAP:
  20. 20. II. Pressure Control Mechanisms that Act After Many Minutes : Intermediate Mechanisms • Fluid shift • Renin – – Movement of fluid from Angiotensin interstitial spaces into capillaries in response to decrease in blood system pressure to maintain blood volume • Stress-relaxation – Adjustment of blood vessel smooth muscle to respond to change in blood volume
  21. 21. Renin-Angiotensin-Aldosterone Mechanism
  22. 22. Sequential events by which increased salt intake increases the arterial pressure, but feedback decrease in activity of the renin angiotensin system returns the arterial pressure almost to the normal level.
  23. 23. Hypertension Caused by a Renin-Secreting Tumor or by Infusion of Angiotensin II. Effect of placing a constricting clamp on the renal artery of one kidney after the other kidney has been removed. The resulting hypertension is called "one-kidney" Goldblatt hypertension.
  24. 24. III. Long-Term Regulation of Blood Pressure • Renal –Body fluid mechanism • Hormones: Vasopressin (ADH), Atrial natriuretic factor, erythropoietin, aldosterone. Importance:  It takes a few hours to show significant response for these mechanisms.  Return the arterial pressure all the way back.
  25. 25. • Typical renal urinary output curve measured in a perfused isolated kidney, showing pressure diuresis when the arterial pressure rises above normal.
  26. 26. Atrial natriuretic factor Hormone released from cardiac muscle cells when atrial blood pressure increases, simulating an increase in urinary production, causing a decrease in blood volume and blood pressure.
  27. 27. Vasopressin (ADH) Mechanism