The Urinary System PDF

The Urinary System Renal Function 18.1 Functions of the Urinary System  Regulate plasma ionic composition  Regulate plasma volume  Regulate plasma osmolarity  Regulate plasma pH  Remove metabolic waste products and foreign substances from plasma  Other functions  Secrete erythrop...

The Urinary System Renal Function 18.1 Functions of the Urinary System  Regulate plasma ionic composition  Regulate plasma volume  Regulate plasma osmolarity  Regulate plasma pH  Remove metabolic waste products and foreign substances from plasma  Other functions  Secrete erythropoietin and renin  Activate vitamin D3 to calcitriol  Gluconeogenesis 18.2 Anatomy of the Urinary System Structures of the urinary system Macroscopic anatomy of the kidney Microscopic anatomy of the kidney Blood supply to the kidney Structures of the Urinary System Kidneys: form urine Ureters: transport urine from kidneys to bladder Bladder: store urine Urethra: excrete urine from bladder to outside of body Figure 18.1 Structures of the urinary system. Inferior vena cava Abdominal aorta Kidney Adrenal gland (part of the Renal hilus endocrine system) Renal artery Renal vein Ureter Bladder Neck of bladder Urethra Macroscopic Anatomy of the Kidneys Paired, bean shaped Approximate size of fist; 115–170 grams Retroperitoneal  Figure 18.2 Anatomy of a kidney. Renal cortex Renal medulla Renal pyramid Renal artery Renal papilla Renal pelvis Renal Minor vein calyx Minor calyx Renal medullaRenal cortex Major Bowman's calyx capsule Ureter Blood vessels Nephron Collecting duct Microscopic Anatomy of the Kidney Nephron = functional unit Renal corpuscle Glomerulus = capillary network for filtration Bowman's capsule  Receives the filtrate  Inflow to renal tubules Microscopic Anatomy of the Kidney  Renal tubules  Proximal tubule  Proximal convoluted tubule  Proximal straight tubule  Loop of Henle  Descending limb  Thin ascending limb  Thick ascending limb  Distal convoluted tubule  Connecting tubule  Collecting duct  Figure 18.3 Anatomy of a nephron. Bowman's capsule Renal corpuscle Glomerulus Efferent arteriole Proximal Afferent arteriole convoluted Proximal tubule tubule Connecting tubule Distal convoluted tubule Cortex Medulla Proximal straight tubule Thick ascending limb of loop of Henle Collecting duct Descending limb of loop of Henle Thin ascending limb of loop of Henle Minor calyx Microscopic Anatomy of the Kidney Cortical versus juxtamedullary nephrons Cortical  Short loop of Henle  Most numerous, 80–85% Juxtamedullary nephron  Long loop of Henle extends into medulla  Responsible for the medullary osmotic gradient Both types produce urine  Figure 18.4 Locations of cortical and juxtamedullary nephrons. Bowman's capsule Renal Bowman's capsule cortex Proximal tubule Proximal tubule Distal Distal tubule tubule Loop of Henle Collecting duct Renal medulla Loop of Henle Collecting duct Cortical nephron Juxtamedullary nephron  Figure 18.5 The juxtaglomerular apparatus. Bowman's capsule Juxtaglomerular Glomerular capillary apparatus Efferent arteriole Lumen of Proximal Bowman's Distal tubule tubule capsule Afferent arteriole Efferent arteriole Distal tubule Macula densa Direction of Loop of blood flow Henle Afferent arteriole Granular cells (juxtaglomerular cells) Blood Supply Renal arteries enter kidney at hilus Receive 20% of cardiac output at rest Account for less than 1% of body weight Account for 16% of ATP usage by body Function is to filter blood Renal veins exit at hilus Figure 18.6a Blood supply to the kidneys. Interlobular artery Arcuate artery Interlobar artery Segmental artery Renal artery  Figure 18.6b Blood supply to the kidneys. Efferent arteriole Glomerulus Peritubular capillaries Afferent arteriole Interlobular artery Cortex Arcuate artery Medulla Arcuate vein Interlobular vein Vasa recta 18.3 Basic Renal Exchange Processes Glomerular filtration: from glomerulus to Bowman's capsule Reabsorption: from tubules to peritubular capillaries Secretion: from peritubular capillaries to tubules Excretion: from tubules out of body  Figure 18.7 The three exchange processes in the renal tubules. Direction of blood flow Peritubular capillaries Efferent arteriole Reabsorption Secretion Filtration Excretion Glomerulus Afferent Bowman's capsule arteriole Glomerular Filtration  Movement of protein-free plasma from glomerulus to Bowman's capsule GFR = 125 mL/min or 180 L/day  Glomerular filtrate must cross three barriers to enter Bowman's capsule  Capillary endothelial layer  Surrounding epithelial layer  Basement membrane sandwiched between these two layers Figure 18.8 Anatomy of the renal corpuscle. Bowman's capsule Efferent arteriole Proximal tubule Afferent arteriole Podocyte Foot processes Filtration slit Lumen of glomerular capillary Bowman's space Plasma in lumen of capillary Glomerular membrane Fenestration Capillary endothelial cell Basement membrane Epithelial cell (podocyte) Filtrate in Slit pore Bowman's space Glomerular Filtration Starling forces Glomerular capillary hydrostatic pressure Bowman's capsule oncotic pressure Bowman's capsule hydrostatic pressure Glomerular oncotic pressure Glomerular Filtration Starling forces favoring filtration Glomerular capillary hydrostatic pressure  60 mm Hg  High due to resistance of efferent arteriole Bowman's capsule oncotic pressure  0 mm Hg  Low due to lack of protein in filtrate Glomerular Filtration Starling forces opposing filtration Bowman's capsule hydrostatic pressure  15 mm Hg  Relatively high (compared to systemic capillaries) due to large volume of filtrate in closed space Glomerular oncotic pressure  29 mm Hg  Higher than in systemic capillaries due to plasma proteins in smaller volume of plasma  Figure 18.9a Glomerular filtration. Efferent arteriole PBC PGC GC BC Glomerular filtration pressure = (PGC + BC) – (PBC + GC) = (60 mm Hg + 0 mm Hg) (15 – mm Hg + 29 mm Hg) Afferent = 16 mm Hg arteriole Glomerular filtration pressure Glomerular Filtration Glomerular filtration rate (GFR) Filtration pressure = (PGC + BC) – (PBC + GC) = (60 + 0) – (15 + 29) = 16 mm Hg Renal plasma flow = 625 mL/min GFR = 125 mL/min = 180 L/day Compared to systemic capillaries  Filtration pressure = 2 mm Hg  Filtration rate = 3 L/day Glomerular Filtration Filtration fraction Filtration faction = GFR/renal plasma flow 625 mL plasma enters kidneys per minute 125 mL filtered into Bowman's capsule 125/625 = filtration fraction = 20%  Figure 18.9b Glomerular filtration. 500 mL/min plasma Efferent arteriole 125 mL/min filtrate Plasma flow rate = 625 mL/min Glomerular filtration rate = 125 mL/min Afferent Filtration fraction = arteriole 125 mL/min = 0.20 = 20% 625 mL/min 625 mL/min plasma Glomerular filtration rate and filtration fraction Glomerular Filtration  Filtered load = GFR  Px  Small molecules that are filtered without impedance are freely filterable  Quantity filtered = filtered load  Depends on plasma concentration of solute and GFR  Filtered load of glucose  GFR = 125 mL/min  Plasma [glucose] =100 mg/dL = 1 mg/mL Filtered load of glucose = (125 mL/min)  (1 mg/mL) = 125 mg/min Regulation of GFR 180 liters fluid filtered/day Only 1.5 liters urine is excreted/day (99% of filtered fluid is reabsorbed Small increase in GFR large increase in volume of fluid filtered and excreted GFR is highly regulated Glomerular Filtration Intrinsic regulation of GFR Myogenic regulation  Smooth muscle in wall of afferent arteriole  Contracts in response to stretch Tubuloglomerular feedback  Macula densa cells secrete paracrine factors in response to an increase in flow of fluid past them  Smooth muscles of arterioles contract in response to these paracrines Figure 18.10 Effect of mean arterial pressure on glomerular filtration rate.  Figure 18.11 Intrinsic controls of glomerular filtration rate. MAP MAP Afferent arteriole Afferent arteriole Pressure Pressure Stretch of arteriolar smooth muscle Constriction Constriction Resistance Resistance Glomerulus Glomerulus Glomerular Glomerular Glomerular Glomerular Negative Negative capillary capillary capillary capillary feedback feedback pressure pressure pressure pressure Glomerular Glomerular filtration filtration pressure pressure GFR GFR Myogenic regulation Macula densa Initial stimulus Flow Paracrine secretion Physiological response Result Tubuloglomerular feedback Glomerular Filtration Extrinsic control of GFR Decreases in BP can decrease GFR  Directly (decrease in filtration pressure)  Indirectly through extrinsic controls Figure 18.12 Extrinsic control of GFR and renal vascular resistance during fluid loss Slide 1 due to hemorrhage or sweating. Hemorrhage, sweating Blood volume Venous pressure Negative feedback Heart Venous return Cardiac output MAP Baroreceptors detect and respond Negative Sympathetic nervous activity feedback Renal sympathetic nervous activity Direct effect Kidneys Vasoconstriction of afferent and efferent arterioles MAP Renal vascular resistance TPR GFR Urine flow Fluid loss Initial stimulus Physiological response Result Reabsorption Movement from tubules into peritubular capillaries (returned to blood) Most occurs in proximal tubules Most is not regulated Reabsorption Solute reabsorption Most occurs in proximal convoluted tubules Some occurs in distal convoluted tubules Barrier for reabsorption  Epithelial cells of renal tubules  Endothelial cells of capillaries (minimal)  Figure 18.13 The barriers to reabsorption. Lumen Microvilli Peritubular space Peritubular Reabsorption capillary Apical Renal membrane tubule Tight junction Lumen Peritubular space Plasma Tubule Basolateral Basement Capillary epithelialmembrane membrane endothelial cell cell Figure 18.14 Mechanisms of solute and water reabsorption. Peritubular fluid Apical Tubule Basolateral Capillary membrane endothelial cell membraneepithelial cell Y Y X X Active solute reabsorption Solute Y Solute X H2O Water reabsorption (passive) High Z Low [Z] [Z] Tubular fluid Plasma Passive solute reabsorption via diffusion Transport Maximum Rate of transport when carriers are saturated When solute is transported across epithelium by carrier proteins, saturation of carriers can occur Renal threshold: for a solute that is normally 100% reabsorbed If solute in filtrate saturates carriers, then some solute is excreted in urine Solute in plasma that causes solute in filtrate to saturate carriers and spill over into urine = renal Transport Maximum Example: glucose reabsorption Freely filtered at glomerulus Normally 100% actively reabsorbed in proximal tubules Normally no glucose appears in urine Carrier proteins for glucose reabsorption Apical membrane: secondary active transport Basolateral membrane: facilitated diffusion Transport Maximum Renal handling of glucose Plasma [glucose] = 100 mg/dL Filtered load glucose = 125 mg/min Transport maximum for glucose reabsorption = 375 mg/min Theoretical renal threshold = 300 mg/dL  GFR  renal threshold = transport maximum Actual renal threshold = 160–180 mg/dL  Filtered load = 225 mg/min  Figure 18.15 Mechanism of glucose reabsorption. Apical Tubule Basolateral Capillary membrane epithelial cellmembrane endothelial cell Glucose Glucose K+ Na+ Na+ Tubular fluid Plasma Figure 18.16 Glucose filtration, reabsorption, and excretion as a function of plasma glucose concentration. Renal threshold Filtration Reabsorption Transport maximum Excretion Secretion  Solute moves from peritubular capillaries into tubules  Barriers are the same as for reabsorption  Transport mechanisms are the same, but in the opposite direction  Secreted substances  Potassium  Hydrogen ions  Choline  Creatinine  Penicillin 18.4 Regional Specialization of the Renal Tubules Nonregulated reabsorption in the proximal tubules Regulated reabsorption and secretion in the distal tubules and collecting ducts Water conservation in the loop of Henle Nonregulated Reabsorption in the Proximal Tubules Proximal tubule is the mass reabsorber 70% sodium and water 100% glucose Brush border provides for large surface area Leaky tight junctions allow paracellular transport  Figure 18.17a Epithelial cells in selected portions of a renal tubule. Apical "Leaky" membrane tight junction Brush border Microvilli Mitochondria Basolateral membrane Proximal tubule epithelium Regulated Reabsorption and Secretion in the Distal Tubules and Collecting Ducts Transport is regulated across epithelium Tight junctions limit paracellular transport  Figure 18.17b Epithelial cells in selected portions of a renal tubule. Apical "Tight" membrane tight junction Mitochondria Basolateral membrane Distal tubule and collecting duct epithelium Water Conservation in the Loop of Henle Loop of Henle establishes conditions necessary to concentrate urine Minimizes water loss