Renal Circulation Lecture 2 PDF

Renal module Course code: IMP-07- 20318 Phase: I Year/ semester: 2nd year / Semester (3) 2022-2023  Lecture 2 Renal circulation and autoregulation of renal blood flow By Prof. Dr. Aziza Khalil  Number- Title of lecture Intended Learning Outcomes (ILOs)...

Renal module Course code: IMP-07- 20318 Phase: I Year/ semester: 2nd year / Semester (3) 2022-2023  Lecture 2 Renal circulation and autoregulation of renal blood flow By Prof. Dr. Aziza Khalil  Number- Title of lecture Intended Learning Outcomes (ILOs) On completion of this lecture, the student will be able to: Describe the renal circulation and its significance. -Discuss Regulation of renal blood flow. -Identify plasma clearance and its measurement.  Renal circulation Renal artery → interlobar arteries → arcuate arteries → interlobular arteries. Afferent arteriole → glomerulus → efferent arteriole (arterial blood). Peritubular capillaries and vasa recta. both types of capillaries drain into inter lobular vein → arcuate vein →inter lobar vein → renal vein  1)Proximal tubule 3) Distal tubule Juxtaglomerular Collecting apparatus 4) duct Efferent arteriole Afferent arteriole 1 Artery 2 Vein Cortex Medulla Renal circulation Peritubular 2) capillaries Loop of Henle To renal pelvis  Renal circulation Is portal circulation (2 sets of capillaries) Glomerulus Only specialized in filtration Reabsorption occur in peritubular capillaries Renal blood flow = 20-25% of cardiac output Renal blood flow = 1140 ml/min > 90 % of renal blood flow supply the cortex  Renal fraction It’s the portion of cardiac output (COP) that passes to the kidney (21%)  Renal plasma flow = 625 ml/min (55% of RBF) Calculated by para-aminohipuric (PAH) acid clearance  Plasma Clearance Definition Volume of plasma cleared of a particular substance by kidney/ minutes Plasma Clearance ( C ) Volume of plasma cleared of a particular substance/ min Ux × V Cx = Px Ux = Urine concentration of a substance x V = Rate of urine flow Px = Plasma concentration of a substance x  PAH acid clearance Para-aminohippuric acid (PAHA) clearance is a method used to measure renal plasma flow, which is a measure of renal function. PAHA is completely removed from blood that passes through the kidneys (PAHA undergoes both glomerular filtration and tubular secretion), and therefore the rate at which the kidneys can clear PAHA from the blood reflects total renal plasma flow.  The clearance of a substance means the volume of plasma that is cleared from this substance. The concentration of PAHA is measured in one arterial blood sample(PPAH) and one urine sample(UPAH). The urine flow (V) is also measured. Renal perfusion flow is then calculated by: ERPF(effective renal plasma flow=U × V/P In the fact about 90% of PAHA in arterial plasma excreted in urine (effective renal plasma flow ), so actual RPF = effective RPF*100/90  GF TR 3 basic processes GF= glomerular TS filtration TR= tubular reabsorption TS= tubular secretion  Afferent Efferent arteriole arteriole Glomerulus GF 80% of the plasma that enters Bowman’s the glomerulus (=625 ml/min) is capsule not filtered and leaves through the efferent arteriole. 20% of the plasma that enters the TR Glomerulus is filtered, Peritubular (Glomerular filtrate) TS capillary (=125ml/min) Kidney tubule (entire length, To venous system uncoiled) (conserved for the body) Urine excretion (eliminated from the body) Regulation Of RBF  ↑ABP ↑Bl Flow ↑Cap P ↑GFR (1) ↑ABP ↑ Flow ↑ cap. p  ↑Diameter ↑flow ↑Cap. P ↑GFR RBF (2) Increased diameter of arteriole Increases capillary pressure  Regulation of diameter of afferent arteriole II. Extrinsic control I. Autoregulation (sympathetic) Aims to maintain Intentionally Constant Change RBF & GFR despite changes GFR In the mean arterial blood pressure To maintain ABP between 75-160 mmHg  I. Autoregulation Kidneys have self regulatory mechanism to keep constant RBF &GFR Fluctuations in ABP would change glomerular capillary pressure and GFR But with Autoregulation Kidneys Prevent this fluctuations Constant GFR is essential for normal kidney function  By autoregulation afferent ABP arteriole constricts Flow Flow Glom. Cap. P Glom. Cap. P. GFR Back to GFR GFR normal  By autoregulation ABP afferent arteriole dilates Flow Flow Glom. Cap. P Glom. Cap. P. GFR Back to GFR GFR normal Mechanisms 1- myogenic 2- tubulo glomerular feedback  1-myogenic a- Stretch of vessel due to increase pressure Glomerulus Glomerular capillary Afferent arteriole blood pressure Efferent arteriole Arterial blood pressure (increases blood flow into the Net filtration glomerulus) pressure GFR  Glomerulus Glomerular Afferent arteriole capillary Efferent arteriole blood pressure Net filtration Vasoconstriction pressure (decreases blood flow into the glomerulus) 1-myogenic b- (Stretch of vessel) GFR Causes its smooth muscle to contract (Inherent property)  Distal tubule Efferent arteriole Bowman’s capsule (see next slide) Afferent 2-tubulo- Site DCT contacts arteriole glomerular afferent arteriole feedback through juxtaglomerular apparatus  Arterial blood pressure Driving pressure into glomerulus Mechanism of action Glomerular capillary pressure of GFR Juxtaglomerular apparatus Rate of fluid flow through tubules Stimulation of macula densa cells to release vasoactive chemicals Chemicals released that induce afferent arteriolar vasoconstriction Blood flow into glomerulus Glomerular capillary pressure to normal GFR to normal Autoregulation within ABP ranges 75:160 mmHg above or below ranges,GFR changes despite of maximum autoregulation  II. Extrinsic control Change GFR on purpose even within the autoregulatory limit Aims to control ABP Extrinsic control override the Autoregulation Through sympathetic nervous system, kidneys Richly supplied with sympathetic especially afferent Short-term Arterial blood Long-term adjustment pressure adjustment for for Arterial Detection by aortic blood arch and carotid sinus pressure baroreceptors Cardiac Sympathetic activity output Total Generalized peripheral arteriolar vasoconstriction resistance Afferent arteriolar vasoconstriction Glomerular capillary blood pressure GFR Urine volume Conservation of fluid and salt Arterial blood pressure Extrinsic control Glomerulus ABP Afferent arteriole Glomerular capillary Generalized blood pressure sympathetic Net filtration Efferent arteriole stimulation pressure Vasoconstriction GFR (decreases blood flow Generalized into the glomerulus) GFR Flow in VC DCT Autoregulation VC of + Jaxta GA Afferent Extrinsic Vasodilator for arteriole overcomes afferent arteriole autoregulation GFR Aims to ↑GFR  Points to remember The renal blood flow is about ¼ the cardiac output. RBF is regulated by : Extrinsic regulation Intrinsic regulation =autoregulation Clearance of substance means the volume of plasma that is cleared from this substance/min. The renal plasma flow is measured by para- aminohippuric acid clearance (PAHC)  References  Ganong, W.F.: Review of medical physiology, 23 th ed. New York, Mc Graw- Hill Co, 2011. P642:645.  Gyton, A.A. and Hall, J.E.: Text book of medical physiology, 12 th ed. Philadelphia, Saunders Co., 2011.P 316:322.  Handbook of Physiology department, Faculty of medicine for girls, AL-Azhar University, P 12:16 Mark true “T” or false “F” in the front of each sentence and give reason for each of the following: 1-Renal circulation is a portal circulation. 2- Renal blood flow nearly constant despite changes in ABP ranging (75-160 mmHg). Answers 1-T 2-T