1. Blood pressure regulation and tissue blood flow Reverend Dr David CM Taylor http:/www.liv.ac.uk/~dcmt

2.  http://pcwww.liv.ac.uk/~dcmt/cvs10.ppt http://pcwww.liv.ac.uk/~dcmt/cvs10.ppt  intrinsic (Starling’s Law)  extrinsic (principally autonomic) The story so far... Stroke volume Heart rate Cardiac output

3.  Increased sympathetic activity  Leads to increased cardiac output  And peripheral vasoconstriction (to protect the capillary beds)  Drop in blood flow  Triggers renin-angiotensin system Postulated mechanism for hypertension

4.  Cross transplantation studies show that essential hypertension has its origins in the kidneys.  Human and animal studies  So does renal denervation  Little evidence that “stress” is involved  But, of course, drugs that decrease sympathetic activity lower blood pressure. Evidence

5. Control Volume Pressure Chemicals Autonomic N.S. ADH Local Blood Flow Angiotensin

6.  Sensed by baroreceptors  in carotid arteries and aortic arch  an increase in pressure causes a decrease in sympathetic activity  a decrease in pressure causes an increase in sympathetic activity Pressure

7.  Sensed by atrial volume receptors A decrease in volume  causes an increase in ADH secretion  and a decrease in ANF secretion Volume

8. A decrease in O 2, or more usually an increase in CO 2 or H 2 causes an increase in chemoreceptor activity which  increases sympathetic activity Chemicals

9. Local Blood Flow (kidney) Sodium reabsorption Potassium secretion Decreased renal blood flow Monitored by JGA cells Renin production Angiotensinogen Converting enzyme Angiotensin I Angiotensin II Aldosterone Vasoconstriction

10.  Angiotensin II is a vasoconstrictor  Aldosterone increases vascular sensitivity to Angiotensin II  ADH (anti-diuretic hormone) increases water reabsorption  ANF decreases sodium reabsorption Hormones

11. Overview Fluid loss Blood volume Venous return Cardiac output Arterial pressure Local blood flow Blood volume Venous return Cardiac output Arterial pressure vol baro chemo kidney renin/angiotensin aldosterone ADH CNS sympathetic heart rate contractility vasoconstriction capillary pressure veins