/6/0 About this Chapter Functions of the Kidneys Anatomy of the urinary system Overview of kidney function Secretion Micturition Regulation of extracellular fluid volume and blood pressure Regulation of osmolarity Maintenance of ion balance Homeostatic regulation of ph of wastes Proion of hormones THE URINARY SYSTEM Nephrons Cortex Medulla Kidney Ureter Urinary bladder Urethra Renal pelvis Ureter (a) The urinary system Figure 9-a (c) The kidney, in cross section. Capsule Figure 9-c Cortex Arterioles Nephrons Juxtaglomerular apparatus () Vasa recta Medulla Loop of (i) Some nephrons dip deep into the medulla. Figure 9-i (g) One nephron has two s and two sets of. (h) Juxtamedullary nephron with vasa recta Figure 9-g h
/6/0 Proximal tubule Distal tubule Descending limb of loop begins Ascending limb of loop ends Descending limb Ascending limb (j) Parts of a nephron Loop of Figure 9-d e To bladder Figure 9-j Kidney Function Kidney Function, reabsorption, secretion, and excretion Distal tubule Proximal tubule = : blood to lumen = : lumen to blood Loop of To renal vein = Secretion: blood to lumen To bladder and = : lumen to external external environment environment Figure 9- Table 9- Kidney Function The urinary excretion of substance depends on its filtration, reabsorption, and secretion Tubule To renal vein To bladder and external environment The Fraction Plasma volume entering afferent = 00% 80% 0% of volume filters. >9% of fluid is. Remainder of nephron >99% of plasma entering kidney returns to systemic circulation. 5 <% of volume is excreted to external environment. Amount filtered Amount + Amount = secreted amount of solute excreted Figure 9-
/6/0 The Renal Corpuscle Thick ascending limb of loop of Capsular epithelium Podocyte The Renal Corpuscle Pores in endothelium Foot process of podocyte slit Basal lamina Glomerular capillary Lumen of Proximal tubule Capillary lumen Filtered material Lumen of (a) The epithelium around glomerular is modified into podocytes. Figure 9-5a (d) Filtered substances pass through endothelial pores and filtrationslits. Figure 9-5d The Renal Corpuscle Mesangial cell: Can contract Cytokines Podocyte Mesangial cell Glomerular capillary Lumen of Capillary endothelium Podocyte foot processes (c) Podocyte foot processes surround each capillary, leaving slits through which filtration takes place. Figure 9-5c Pressure Depends on ) hydrostatic pressure (Blood Pressure) and is opposed by ) colloid osmotic pressure ) fluid pressure created in Bowmans Volume of filtrate that enters Capsule = GFR P H P fluid = net filtration pressure 55 0 5 = 0mm Hg P H 5 mm Hg 0 mm Hg 55 mm Hg P fluid P H = Hydrostatic pressure = Colloid osmotic pressure gradient due to proteins in plasma but not in P fluid = Fluid pressure created by fluid in Net filtration pressure = 0 mm Hg Autoregulation of Glomerular Rate GFR remains relatively constant Resistance changes in renal s alter renal blood flow and GFR Figure 9-7 Figure 9-8a
/6/0 Influences on GFR Figure 9-8b Figure 9-8c GFR Regulation Juxtaglomerular Apparatus Autoregulation (Instrinsic local responses). Myogenic response Stretch smooth muscle cells they contract High BP causes constriction = GFR Low BP no contraction -??. Tubuloglomerular feedback Paracrine control (juxtaglomerular apperatus) Extrinsic (Non-local) Response. Hormones and autonomic neurons (SNS) (a) Ascending limb of loop of Macula densa cells (b) Granular cells Endothelium Proximal tubule Figure 9-9 Tubuloglomerular Feedback GFR Regulation GFR increases. Flow through tubule increases. Distal tubule Extrinsic (Non-local) Response Can influence GFR Flow past macula densa increases. Macula densa 5 Granular cells Paracrine from macula densa to afferent Granular cells release renin Proximal 5 constricts. tubule Resistance in afferent increases. Hydrostatic pressure in glomerulus decreases. Loop of GFR decreases. PLAY Interactive Physiology Animation: Urinary System: Glomerular Figure 9-0 Sympathetic neurons innervate the s - If LOW BP or hemorrhage - Sympathetic vasoconstriction - GFR is reduced (conserves fluids) Hormones - Angiotensin II Vasoconstrictor! Increases BP & GFR
Transport rate of substrate (mg/min) /6/0 may be active or passive About Principles governing the tubular reabsorption of solutes and water Transepithelial transport Substances cross both apical and basolateral membrane Paracellular pathway Substances pass through the junction between two adjacent cells Filtrate is similar to interstitial fluid. Na + Anions H O Na + is by active transport. Electrochemical gradient drives anion reabsorption. Water moves by osmosis, following solute reabsorption. K +, Ca +, urea Tubule lumen Tubular epithelium Extracellular fluid Concentrations of other solutes increase as fluid volume in lumen decreases. Permeable solutes are by diffusion. Figure 9-, steps Sodium reabsorption in the proximal tubule Sodium-linked glucose reabsorption in the proximal tubule Filtrate is similar to interstitial fluid. Na + Na + enters cell through membrane proteins, moving down its electrochemical gradient. Filtrate is similar to interstitial fluid. Na + [Na + ] low Na + ATP K + Na + is pumped out the basolateral side of cell by the Na + -K + -ATPase. Glucose and Na + [Na + ] low [glu] low [glu] high [glu] low glu glu Na + Na+ Na + moving down its electrochemical gradient using the SGLT protein pulls glucose into the cell against its concentration gradient. Glucose diffuses out the basolateral side of the cell using the GLUT protein. Na + is pumped out by Na + -K + -ATPase. ATP K + Tubule lumen Proximal tubule cell Interstitial fluid = Membrane protein ATP = Active transporter Figure 9- Tubule lumen Proximal tubule cell Interstitial fluid ATP = Active transporter = SGLT secondary active transporter = GLUT facilitated diffusion carrier Urea Passive reabsorption by diffusion i.e., must have concentration gradient Plasma proteins Most proteins are not in filtrate!!!!!!!!!!!!!!!!!!!!!!! But tiny ones enter proximal tubule cells by endocytosis digested by lysosomes Capillary pressure favor reabsorption: PH in caps = 0; Colloid osmotic Pressure in Caps = 0 Difference of 0 favors reabsortion Saturation of mediated transport can occur and influence reabsorption Transport maximum (T m ) is transport rate at saturation. Saturation occurs. Renal threshold is plasma concentration at which saturation occurs. Plasma [substrate] (mg/ml) Figure 9-5
/6/0 Secretion doesn t Occur until threshold reached Transfer of from extracellular fluid into lumen of the nephron tubule Active process Important in homeostasis of K + and H + Increasing secretion enhances nephron excretion Figure 9-5d Inulin Clearance is equal to GFR = filtration (reabsorption + secretion) Clearance Rate at which a solute disappears from the body by excretion or by metabolism Non-invasive way to measure GFR Inulin and creatinine used to measure GFR A non-invasive way to measure GFR = 00 ml of Inulin concentration is /00 ml. GFR = 00 ml /min Inulin (00 ml/min) Nephron 00 ml, 0% inulin 00 ml plasma is. No inulin is. 00% of inulin is excreted so inulin clearance = 00 ml/min. 00% inulin excreted Inulin clearance = 00 ml/min GFR Filtered load of X = [X] plasma GFR Filtered load of inulin = excretion rate of inulin GFR = excretion rate of inulin/[inulin] plasma = inulin clearance GFR = inulin clearance Table 9-6
/6/0 The relationship between clearance and excretion (00 ml/min) = 00 ml of = 00 ml of (00 ml/min) Plasma concentration is /00 ml. GFR = 00 ml /min Glucose 00 ml plasma is. Clearance depends on renal handling of solute. 00 ml, 00% glucose Glucose No glucose clearance excreted = 0 ml/min (a) Glucose clearance Figure 9-7a Urea (b) Urea clearance 50% of urea excreted 00 ml, 50% of urea Urea clearance = 50 ml/min Plasma concentration is /00 ml. GFR = 00 ml /min 00 ml plasma is. Clearance depends on renal handling of solute. Figure 9-7b Micturition (00 ml/min) = 00 ml of The storage of urine and the micturition reflex Penicillin More penicillin is excreted than was filtered. Some additional penicillin secreted. 00 ml, 0 penicillin Penicillin clearance = 50 ml/min Plasma concentration is /00 ml. GFR = 00 ml /min 00 ml plasma is. Clearance depends on renal handling of solute. Internal sphincter (smooth muscle) passively contracted External sphincter (skeletal muscle) stays contracted Relaxed (filling) state (a) Bladder at rest Bladder (smooth muscle) Tonic discharge Higher CNS input (c) Penicillin clearance Figure 9-7c Figure 9-8a Micturition Stretch receptors Internal sphincter External sphincter (b) Micturition Sensory neuron Parasympathetic neuron Motor neuron Higher CNS input may facilitate or inhibit reflex Tonic discharge inhibited Stretch receptors fire. Parasympathetic neurons fire. Motor neurons stop firing. Smooth muscle contracts. Internal sphincter passively pulled open. External sphincter relaxes. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the Normal or Slide Sorter views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Figure 9-8b 7