control of blood pressure

Blood pressure (BP) is the pressure exerted by circulating blood upon the walls of blood vessels and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation, usually measured at a person's upper arm. A person’s blood pressure is usually expressed in terms of the systolic pressure over diastolic pressure and is measured in millimeters of mercury (mm Hg). Normal resting blood pressure for an adult is approximately 120/80 mm Hg.

1. Topic:Control of Blood pressure Md.Jabiur Rahaman Daffodil International University Dept. Of pharmacy

2. Control of blood pressure Mean blood pressure is controlled by changing total peripheral resistance and or cardiac output. 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

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

6. 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” From “An Introduction to Cardiovascular Physiology” J.R. Levick

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

8. 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

9. 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 CO 2 ** too much K +

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

11. 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

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

13. 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

14. 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