L3 Glomerular Filtration Rate PDF - Renal Module

Renal module Course code: IMP-07- 20318 Phase: I Year/ semester: 2nd year / Semester (3) Credit hours: Course duration: 5 weeks.  Lecture 3 Physiology of glomerular filtration rate and factors affecting it By Prof. Dr. Aziza Khalil ...

Renal module Course code: IMP-07- 20318 Phase: I Year/ semester: 2nd year / Semester (3) Credit hours: Course duration: 5 weeks.  Lecture 3 Physiology of glomerular filtration rate and factors affecting it By Prof. Dr. Aziza Khalil  Lecture 3 Physiology of glomerular filtration rate and factors affecting it Intended Learning Outcomes (ILOs) On completion of this lecture, the student will be able to: - Define glomerular filtration rate (GFR), identify its value. -List factors affecting GFR. -Discuss method of GFR measurement. Glomerular filtration  Glomerular Filtration Is a passive process (ultra filtration) Glomerular filtration rate(GFR) = is the volume filtered by both kidneys / minute GFR = 125 ml/ min = 20% of RPF ( RPF = 625ml/ min) Filtration fraction : is the fraction which is filtered from the plasma during its flow through the glomerular capillaries. Importance : it is indication of the efficiency of filter bed. Filtration fraction = GFR / RPF = 125 / 625 =20%  GF URINE 3 basic processes TR FORMATION GF= glomerular TS filtration TR= tubular reabsorption TS= tubular secretion  Afferent Efferent arteriol arteriol e e Glomerulus G F 80% of the plasma that enters Bowman’s the glomerulus (=625 ml/min) is capsule not filtered and leaves through 20% of the plasma the efferent arteriole. that enters the T Glomerulus is R filtered, Peritubular T (Glomerular filtrate) capillary S (=125ml/min) Kidney tubule (entire length, To venous system uncoiled (conserved ) for the body) Urine excretion (eliminated from the body)  Filtration surface is 2 cell layers Capillary Podocytes endothelium Inner cells of Bowman’s 100 times permeable than capsule any capillaries Has octopus foot processes encircle glomerular tuft Basement membrane between 2 layers Formed of 1- Collagen for support 2- Glycoprotein negatively charged  Filtered fluid through glomerular membrane passes the membrane extracellularly Pass between endothelial cells. Then through basement membrane. Then filtration slits between podocytes foot processes  Afferent arteriole Efferent arteriole Glomerulus Bowman’s Lumen of capsule glomerular capillary Lumen of Endothelia Bowman’s l capsule cell Basement membrane (see Outer layer of next Bowman’s capsule Podocyte slide) Inner layer foot process of Bowman’s capsule (podocytes) Proximal convoluted tubule Podocyte foot process Filtration slit Basement membrane Capillary pore (see next slide)  Capillary Endothelia pore l Filtering surface cell Lumen of glomerular capillary Basement membrane Formed of collagen & glycoprotein (- charged) Lumen of Bowman’s capsule Filtration Podocyte slit foot process  Characteristics of glomerular capillaries 1-Highly 3-High permeable glomerular capillary 2-Filtration pressure all through Less than 4nm freely pass No reabsorption Equal to 55 mmHg 8nm cannot Other capillaries pass Forces =27mmHg make Between 4-8 nm filtration Afferent short & depends on all through straight charges (albumin 6 nm Afferent larger Cannot pass) than efferent arteriole  Forces acting on Glomerulus 1- Glomerular capillary hydrostatic pressure (filtering force) =55mmHg 2- Plasma colloid osmotic pressure ( a reabsorbing force) =30mmHg 3- Bowman‘s capsule hydrostatic pressure (a reabsorbing force)= 15 mmHg 55 2 1 3 15 30 15  Net filtration pressure = Glomerular capillary hydrostatic pressure – (colloid osmotic pressure of PP + intra capsular hydrostatic pressure) = 55 - (30 + 15) = 10 mmHg No plasma proteins filtered, no intracapsular oncotic Regulation Of GFR  1-Renal blood flow: it is directly proportional to the glomerular filtration rate. 2-Arterial blood pressure: Variations in mean ABP within range of 75-160 mmHg, not affect the GFR due to autoregulation. -Outside this range, the GFR is directly proportional to that pressure.  ↑ABP ↑Bl Flow ↑Cap P ↑GFR (1) ↑ABP ↑ Flow ↑ cap. p  3-Changes in the glomerular colloid osmotic pressure -Increase in colloid OP as in case of dehydration decrease GFR. -Decrease in colloid OP increase GFR. 4-The hydrostatic pressure in bowman` s capsule: Its increase as in case of ureteric stones decrease GFR 5-The glomerular capillary permeability: GFR is directly proportional to the glomerular capillary permeability 6-Sympthetic stimulation: sever sympathetic stimulation marked VC decrease RBF and GFR 7-Diameter of afferent arteriole ↑ Diameter ↓ ↓ Resistance ↓ ↑ Flow ↓ ↑ Cap. Bl. P ↓ ↑ GFR  ↑Diameter ↑flow ↑Cap. P ↑GFR Increased diameter of arteriole Increases capillary pressure  Regulation of diameter of afferent arteriole I. II. Extrinsic Autoregulation control (sympathetic) Aims to Intentionally maintain Change Constant GFR GFR To maintain ABP  8-Diameter of efferent arteriole Mild VC: increase resistance to blood flow increase glomerular capillary pressure increase GFR. Sever VC: initial increase in GFR followed by marked decrease. 9-Effect of protein intake: High protein intake increase RBF &GFR 10-Number of functioning nephrons When the functioning kidney mass is decreased as in case of chronic renal failure, the GFR is markedly decreased.  GFR Is measured by inulin clearance  Inulin has the following properties:- It is non toxic, not metabolized and not stored in the kidney. It is freely filtered through the glomerular capillary membrane. It is neither reabsorbed nor secreted by the renal tubules, so the amount of inulin filtered in the glomeruli is equal to the amount present in urine. Inulin is given I.V The plasma and urinary inulin concentration are determined then inulin clearance is calculated as follows C=U*V/P P:concentration of inulin in one ml plasma U:concentarion of inulin in one ml urine V:volume of urine excreted in one min. Normal value of G.F.R=125 ml/min.  Importance of inulin clearance Its considered as a reference value, because its cleared from the plasma only the G.F, so its clearance value is equal to G.F.R. Substance that are reabsorbed in the renal tubules have a clearance value less than that of inulin e.g. Urea. If the substance is completely reabsorbed, as in case of glucose, the clearance value will be zero. If the substance is secreted from the tubules, it will give a clearance value higher than inulin clearance as PAHA =700 ml. If the substance has a clearance value more than 700ml/min. this means that this substance is synthesized by renal tubules.  Points to remember Glomerular filtration is the first step in the formation of urine by simple filtration of plasma. The filtration force in the glomerulus =[the filtration force- (colloid osmotic pressure+ hydrostatic capsular pressure)]. The glomerular filtration rate is measured by inulin clearance=125 ml/min.  References Ganong, W.F.: Review of medical physiology, 23 th ed. New York, Mc Graw- Hill Co, 2011. P 645:647. Gyton, A.A. and Hall, J.E.: Text book of medical physiology, 12 th ed. Philadelphia, Saunders Co., 2011. P 317:322 & 340:343. Handbook of the Physiology department, Faculty of medicine for girls, Al-Azhar university. P 18:27.  Questions What are the factors that determine the glomerular filtration rate? What is the normal glomerular filtration rate? Mention the factors affecting it? Mark true “T” or false “F” in the front of each sentence and give reason for each of the following: 1-Glomerular filtration is called primary urine 2-Hight protein diet intake increase glomerular filtration rate  Answers 1-T 2-T