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Blood pressure

Blood pressure. Factors maintaing blood pressure. Central factors Cardiac out put Heart Rate Peripheral factors Peripheral resistance Blood volume venous return Elasticity of blood vessels Diameter of blood vessel Viscosity of blood. Cardiac out put.

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Blood pressure

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  1. Blood pressure

  2. Factors maintaing blood pressure • Central factors • Cardiac out put • Heart Rate Peripheral factors Peripheral resistance Blood volume venous return Elasticity of blood vessels Diameter of blood vessel Viscosity of blood

  3. Cardiac out put • To Systolic blood pressure depend upon CO&stroke volume –directly proportional • Dystolic BP is directly Peripheral resistance when PR decreased dystolic pressure is decreased • BP is directly proportion to blood volume BP is directly pro to venous return BP is inverslyproport to elasticity of vessels& diameter of vessels

  4. Control of blood pressure Outline • Short term control (baroreceptors) • Location • Types of baroreceptor • Baroreceptor reflex • Other stretch receptors • Long-term control • Renin/ angiotensin/ aldosterone system • Vasopressin • Atrialnatiuretic peptide • Response to blood loss (shock)

  5. Regulation of blood pressure • Short term • Baroreceptors • Long term • Kidney via reninangiotensin system

  6. . • Baro-receptors • Nerve endings in all large thoracic and neck arteries • 2 major populations: Carotid sinus and Arch of the aorta • Activation on stretch • Carotid: Hering’s nerve to Glossopharyngeal nerve to tractussolitarius in brainstem • Aortic: Vagus nerve to tractussolitarius • If baro-receptors sense increased BP Secondary signals from tractussolitarius: Inhibition of vasoconstrictor centre and excitation of vagal parasympathetic centre

  7. Baro-receptors • Important in maintaining postural blood pressure • (When standing from lying down  strong sympathetic discharge) • Long term changes in blood pressure result in resetting of baroreflexes (i.e. not influential)

  8. Location of baroreceptors • Baroreceptors sense stretch and rate of stretch by generating action potentials (voltage spikes) • Located in highly distensible regions of the circulation to maximise sensitivity

  9. Overview of short-term control mechanisms

  10. . • Anatomy of the autonomic nervous control of blood pressure: • Sympathetic vasomotor nerve fibres leave cord through (T+L) spinal nerves • Sympathetic chain  • 1)Sympathetic nerves (viscera) • 2)Spinal nerves (vasculature) • Vagus nerve (PNS)

  11. . • Vasomotor centre: • Vasoconstrictor area • origin of excitatory pre-ganglionic vasoconstrictor neurones • Vasodilator area • internal inhibition of vasoconstrictor area • Sensory area • input from vagus and glossopharyngeal nerves modulate vasoconstrictor/dilator area activity

  12. . • To raise the arterial pressure: • SNS release NA from nerve terminals • NA acts on the α adrenergic receptors of the VSMC • All arterioles constricted • Veins strongly constricted • Heart directly stimulated

  13. ….It’s all about intracellular calcium VSMC Cardiovascular Physiology Concepts, Richard E Klabunde. www.cvphysiology.com

  14. Beta-adrenoceptors Heart: Increased contractility Blood vessel: reduced contractility Cardiovascular Physiology Concepts, Richard E Klabunde. www.cvphysiology.com

  15. Long term control of blood pressure • Involves control of blood volume/sodium balance by the kidneys • Hormonal control • Renin-angiotensin-aldosterone system • Antidiuretic hormone (vasopressin) • Atrialnatiuretic peptide • Pressure natriuresis

  16. Angiotensin II Flow rate in loop of Henle Macula Densa NaCL Glomerular Hydrostatic pressure Glomerular Filtration Pressure Na Cl resorption Arterial Pressure Renin Afferent arteriole Resistance GFR Efferent Arteriole Resistance

  17. Vasopressin

  18. Atrialnatiuretic peptide • Increases salt excretion via kidneys • By reducing water reabsorption in the collecting ducts • relaxes renal arterioles • inhibits sodium reabsorption in the distal tubule • Released in response to stimulation of atrial receptors

  19. Atrial volume reflex Reduced secretion of anti-diuretic hormone from hypothalamus Atrial stretch due to pressure Reflex dilation of renal afferent arteriole Reduction in water resorbtion from renal tubule Fluid loss by kidneys Increased glomerular capillary pressure Increased filtration of fluid into renal tubule

  20. Summary of long term BP control • Cardiac output and BP depend on renal control of extra-cellular fluid volume via: • Pressure natriuresis, (increased renal filtration) • Changes in: • Vasopressin • Aldosterone • Atrialnatiuretic peptide

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