1 / 26

Control of blood pressure

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 Atrial natiuretic peptide Response to blood loss (shock).

tabitha
Download Presentation

Control of blood pressure

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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 • Atrial natiuretic peptide • Response to blood loss (shock)

  2. Control of blood pressure • Mean blood pressure is controlled by changing total peripheral resistance and or cardiac output. P = CO x TPR (compare Ohm’s law) • Cardiac output is controlled by sympathetic and para sympathetic nerves which effect: • heart rate • force of contraction • TPR controlled by nervous and chemical means to effect constriction/dilatation of • arterioles and venules

  3. Regulation of blood pressure How is pressure “measured”? • Short term • Baroreceptors • Long term • Kidney via renin angiotensin system

  4. 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 http://www.cvphysiology.com/Blood Pressure/bp012 baroreceptor anat.gif

  5. Rapid increase in mean pressure Rapid decrease in mean pressure Response to pulse pressure Baroreceptor output(from single fibres) From: Introduction to Cardiovascular physiology. J.R. Levick. Arnold 4th edition (2003)

  6. From “An Introduction to Cardiovascular Physiology” J.R. Levick Two types of baroreceptor • Type A • High sensitivity • High firing rate • Type C • Lower sensitivity • Lower firing rate • Higher threshold (before firing starts) • Therefore can deal with higher pressures than type A which become “saturated”

  7. Response of single baroreceptor fibre to change in pressure From “An Introduction to Cardiovascular Physiology” J.R. Levick

  8. Aortic arch Carotid sinus Nucleus tractus solitarius Cardiac inhibition Vasoconstriction Cardiac stimulation Constriction of veins & arterioles Increased heart rate Increased stroke volume Increased peripheral resistance Increased cardiac output Baroreceptor reflex Blood pressure falls Sensors Neural integration Effectors Increased blood pressure

  9. Baroreceptor reflex is a feedback loop Example: central heating system Set temperature Read temperature Is temperature too high? Yes No Boiler on Negative feedback

  10. No Reduce CO Reduce TPR Baroreceptor reflex is a feedback loop “Read” pressure Is pressure too high? Yes Increase CO Increase TPR Two way negative feedback

  11. No Yes Positive feedback loop Unstable Set temperature Read temperature Is temperature too high? No Yes Boiler on Positive feedback

  12. Other stretch receptors • Coronary artery baroreceptors • Respond to arterial pressure but more sensitive than carotid and aortic ones • Veno-atrial mechanoreceptors • Respond to changes in central blood volume • Lie down, lift your legs and cause peripheral vasodilatation • Unmyelinated mechanoreceptors • Respond to distension of heart • Ventricular ones during systole; atrial ones during inspiration

  13. Location of receptors in and near the heart Nucleus tractus solitarius Cardiac vagal afferents Cardiac pain myelinated unmyelinated Spinal cord Baroreceptors in coronary arteries and aortic arch Sympathetic afferents & unmyelinated nociceptors From “An Introduction to Cardiovascular Physiology” J.R. Levick

  14. Other receptors • Heart chemosensors • Cause pain in response to ischaemia • K+, lactic acid, bradykinin, prostaglandins • Arterial chemosensors • Stimulated in response to • Hypoxaemia, hypercapnia*, acidosis, hyperkalaemia** • Regulate breathing • Lung stretch receptors • Cause tachycardia during inspiration *too much CO2 **too much K+

  15. Overview of short-term control mechanisms From: Introduction to Cardiovascular physiology. J.R. Levick. Arnold 4th edition (2003)

  16. 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) • Atrial natiuretic peptide • Pressure natriuresis

  17. Increased pre-load Increased after-load Veins Arteries Reduced renal blood flow Renin/angiotensin/ aldosterone system Increased blood volume Juxtaglomerular apparatus LV filling pressure) Fluid re-absorption Renin (LV pressure beginning of systole) Angiotensinogen Sodium retention Increased blood volume in the thorax Angiotensin I Increased aldosterone secretion Angiotensin II vasoconstriction

  18. Vasopressin • Enhances water retention • Causes vasoconstriction • Secretion increased by unloading of aortic Baroreceptors and atrial sensors http://www.cvphysiology.com/Blood%20Pressure/BP016.htm

  19. Atrial natiuretic 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

  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 • Atrial natiuretic peptide All under the control of altered cardiovascular receptor signaling

  21. Shock Definition: A pathophysiological disorder characterised by acute failure of the cardiovascular system to perfuse the tissues of the body adequately. Levick J.R. “An Introduction to Cardiovascular Physiology” Symptoms • Cold, clammy skin • Muscular weakness • Rapid and shallow breathing • Rapid and weak pulse • Low pulse pressure (and sometimes mean pressure) • Reduced urine output • Confusion

  22. Types of shock • Hypovolaemia • Caused by drop in blood (plasma) volume • e.g. haemorrhage, diarrhoea, vomiting, injury • Septic • Caused by bacterial endotoxins • e.g. salmonella • Cardiogenic • An acute interruption of of cardiac function • e.g. myocarditis (inflammation of the heart muscle) or myocardial infarction • Anaphylactic • Caused by allergic reaction

  23. Effect of blood loss • less than 10%, no serious symptoms • e.g. blood transfusion • 20 - 30% blood loss not usually life threatening • greater than 30%, severe drop in BP and, often, death due to impaired cerebral and coronary perfusion

  24. Response to moderate blood loss(compensated haemorrhage) • Blood volume falls therefore pulse pressure and stroke volume fall. (Frank-Starling mechanism: reduced LV contractile force) • Cardiopulmonary stretch receptor and baroreceptor activity falls • Arterial chemoreceptor activity increases, due to hypoxia and acidosis  rapid breathing  release of vasoconstrictors Vasopressin, angiotensin etc.

  25. Response to moderate blood loss More serious blood loss can be treated by transfusion to lessen the effects shown here

  26. Uncompensated shock If compensation is not sufficient, organ failure occurs due to inadequate perfusion • Heart • Kidney • Brain

More Related