major sites of the vasoconstrictor activity being the afferent and effirent arterioles of the kidney (see lower flown

being the afferent and effirent arterioles of the kidney (see lower flown, for further details) Angotensin II is 40 times more powerful than noradrenatin, so far as the vasoconstrictor ability is concerned However, the vaso constrictor efect is rather transient 2. aldosterone. Na+, K+. Water Angiotensin II stimulates aidosterone secreton (chap 4 sec VI). Aldosterone. in turn, causes the followings Increased reabsorption of Na+ from the distal as well as collecting tubule it thus causes Na retention which in turn leads lo edema and hypertension Further, against each ion of Na+.either one ion of K+ or hydrogen (H+) ejected (secreted) from the tubular epithelium To the limen. Aldosterone, thus causes , potassium depletion and threatens alkalosis in diabetic coma, however, it is life saving, because, in diabetic ketosis, ejection of H+ tt a compensatory mechanism againet the acidosis (NB in diabetic coma, there is usually a fall of BP and the 'fall of BP can lead to activation of renin angiotensin system) 3. Heart Angiotensin causes increased entry of Ca++ within the myocardium D rise of myocardial contractility rise of cardiac output 4 Brain. Stimulation of certain regons of brain try angiotenem II produces thirst Vlsualize the situation and the inherert teleobgy Seven diarrnea fall of renal blood flow release of anpotensin ll thirst excessive drinking of water fluid loss compensated The flow chart drawn below, summartzes what has been said above 1 Fall of BP. low renal perftoim pressure 2 Decreased Some further details on renal vas onstnction should be noted Angolens in II can cause constrction Of both the afferent and efferent arleroles of the glomerulus Whthin the afferflnt is predominantly constncted, there is reduction of C-FR, where as the- GFR increases when the efferent is preoomnantly constncted Question arises, what then is the usual effect(s) of an elevated level of angotensin in normal persons ? Answer is (i)the GFR (ii) the renal blod flow and (PH) the volume of unnary output all fall The net result is Na and water are conserved However, the issue is controversial Renin It is an enzyme, secreted first as ororenin which is then degraded to renn The final product renin has 340 asmlno acids and is a glycoprotein Converting enzyme/angintinin converting enzyme (ACE) A large protein containing 1278 amno acids, cleavs not only the angitensin I but also some Other slructures Angiotensinogenase degrades anglotensin II into angiotensin III Applied Physiology ACE inhfcitors are drugs (eg captopnl) causing inhibnon of angiotensin II formation and thus increase the sodium and water excretion Captopnl. discovered recenty (on the 1980s). is a very popular drug in hypertension and congestive cardiac failuie FACTORS CONTROLLING Na* EXCRETION by THE KIDNEY The importance of Na* regulation Regulation of sodium excretion, in the eyes of the clinicians, is one of the most important aspects of renal