SYSTEMS PHYSIOLOGY Module 3 Lecture 17 Intro to the Renal System Glomerular Filtration Chapter 14 Sections 14 1 14 3 Important Topics in Lecture 17 Introduction to the renal system Glomerular Filtration GFR Cortical radiate vein Cortical radiate artery Arcuate vein Arcuate artery Interlobar vein Interlobar artery Segmental arteries Renal vein Renal artery Renal pelvis Ureter Renal medulla Renal cortex Frontal section illustrating major blood vessels Blood kidneys cleanse blood and adjust its composition so it has a rich blood supply Nephrons are the structural and functional units that form urine Two main parts Renal corpuscle Renal tubule PCT Nephron loop Loop of Henle DCT Collecting duct Renal Corpuscle Two parts of renal corpuscle 1 Glomerulus Allows for efficient filtrate plasma derived formation 2 Glomerular Bowman s capsule Contains podocytes Filtration slits allow filtrate to pass into capsular space Regulating rate of filtrate formation and blood pressure Parietal layer of glomerular capsule Foot processes of podocytes Capsular space Glomerular capsule Efferent arteriole Glomerulus Afferent arteriole Efferent arteriole Juxtaglomerular complex Macula densa cells of the ascending limb of nephron loop Extraglomerular mesangial cells Granular cells Afferent arteriole Podocyte cell body visceral layer Red blood cell Proximal tubule cell Lumens of glomerular capillaries Endothelial cell of glomerular capillary Juxtaglomerular complex Renal corpuscle Glomerular mesangial cells Physiology of Kidney 180 L of fluid processed daily but only 1 5 L of urine is formed Kidneys filter body s entire plasma volume 60 times each day Urine is produced from filtrate Urine 1 of original filtrate 3 processes are involved in urine formation and adjustment of blood composition 1 Glomerular filtration cell and protein free filtrate 2 Tubular reabsorption returns 99 of substances from filtrate to blood 3 Tubular secretion moves substances from blood to filtrate Afferent arterioleGlomerular capillaries Efferent arteriole 1 Glomerular capsule Renal tubule and collecting duct containing filtrate Peritubular capillary To cortical radiate vein 2 3 Urine Cortical radiate artery Three major renal processes 1 2 3 Glomerular filtration Tubular reabsorption Tubular secretion The Filtration Membrane Porous membrane between blood and interior of glomerular capsule Allows water and solutes smaller than plasma proteins to pass Normally no cells can pass Contains three layers 1 Fenestrated endothelium of glomerular capillaries 2 Basement membrane 3 Foot processes of podocytes with filtration slits slit diaphragms repel macromolecules Allows molecules smaller than three nm to pass Water glucose amino acids nitrogenous wastes Plasma proteins remain in blood to maintain colloid osmotic pressure Prevents loss of all water to capsular space Proteins in filtrate indicate membrane problem The filtration membrane separates the blood in the glomerular capillaries from the Capillary endothelium Basement membrane filtrate in the glomerular Foot processes of podocyte capsule It has three layers of glomerular capsule Filtration slit Slit diaphragm Blood in glomerular capillary Filtrate in capsular Fenestration pore Filtration membrane spaceFoot processes of The Filtration Membrane Glomerular capsular space Efferent arteriole Afferent arteriole Cytoplasmic extensions of podocytes Filtration slits Podocyte cell body Proximal convoluted tubule Fenestrations pores Glomerular capillary covered by podocytes that form the visceral layer of glomerular capsule Renal corpuscle Parietal layer of glomerular capsule Glomerular capillary endothelium podocyte covering Foot processes and basement of podocyte membrane removed Glomerular capillary surrounded by podocytes Pressures That Affect Filtration Outward pressures Forces that promote filtrate formation Hydrostatic pressure H Pg c glomerular blood pressure Chief force pushing water solutes out of blood High 55 m m Hg compared to 26 m m H g seen in capillary Reason is that efferent arteriole is a high resistance vessel with a diameter smaller than afferent arteriole Inward Pressures Forces inhibiting filtrate formation Hydrostatic pressure in capsular space H Pc s filtrate pressure in capsule 15 m m H g Colloid osmotic pressure in capillaries O Pg c pull of proteins in blood 30 m m H g Net filtration pressure N F P sum of forces responsible for filtrate formation 55 m m Hg forcing out minus 45 m m H g opposing net outward force of 10 m m H g Main controllable factor determining glomerular filtration rate G F R Glomerular Filtration Rate G F R G F R volume of filtrate formed per minute by both kidneys normal 120 125 ml min G F R is directly proportional to Net filtration pressure N F P Main pressure is glomerular hydrostatic Efferent arteriole pressure Total surface area available for filtration Filtration membrane permeability Filtration pressure Glomerular hydrostatic pressure capsular hydrostatic pressure glomerular capillary osmotic pressure Afferent arteriole Glomerular capsule HPgc 55 mm Hg OPgc 30 mm Hg HPcs 15 mm Hg NFP Net filtration pressure outward pressures inward pressures HPgc HPcs OPgc 55 15 30 10 mm Hg Figure 14 9 Control of G F R by Constriction or Dilation of Afferent Arterioles A A or Efferent Arterioles E A a Constriction of afferent arteriole b Constriction of efferent arteriole c Dilation of efferent arteriole d Dilation of afferent arteriole 12 Regulation of Glomerular Filtration Constant G F R is important as it allows kidneys to make filtrate and maintain extracellular homeostasis Goal of local intrinsic controls renal autoregulation maintain G F R in kidney G F R affects systemic blood pressure Increased G F R causes increased urine output which lowers blood pressure and vice versa SUMMARY Figure 14 4 The Renal Corpuscle a Renal corpuscle b Podocytes and capillaries c Glomerular filtration membrane 15