25Tubular ReabsorptionSlide 3Slide 4PowerPoint PresentationSodium ReabsorptionSlide 7Reabsorption of Nutrients, Water, and IonsSlide 9Slide 10Reabsorptive Capabilities of Renal Tubules and Collecting DuctsSlide 12Slide 13Slide 14Tubular SecretionSlide 16Regulation of Urine Concentration and VolumeSlide 18Countercurrent MechanismSlide 20Slide 21Countercurrent Multiplier: Loop of HenleSlide 23Slide 24Slide 25Slide 26Urea RecyclingCountercurrent Exchanger: Vasa RectaSlide 29Formation of Dilute UrineSlide 31Formation of Concentrated UrineSlide 33DiureticsSlide 35Slide 36Slide 37Slide 38Slide 39Renal ClearanceSlide 41Slide 42Physical Characteristics of UrineSlide 44Slide 45Chemical Composition of UrineUretersSlide 48Slide 49Renal CalculiUrinary BladderSlide 52Slide 53Slide 54Slide 55UrethraSlide 57Slide 58Slide 59Slide 60Slide 61MicturitionSlide 63Slide 64Slide 65Developmental AspectsSlide 67Slide 68Slide 69Slide 70Slide 71Slide 72PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal CollegeC H A P T E RCopyright © 2010 Pearson Education, Inc.25 The Urinary System: Part)BCopyright © 2010 Pearson Education, Inc.Tubular Reabsorption•A selective transepithelial process• All organic nutrients are reabsorbed•Water and ion reabsorption are hormonally regulated•Includes active and passive process•Two routes• Transcellular• ParacellularCopyright © 2010 Pearson Education, Inc.Tubular Reabsorption•Transcellular route•Luminal membranes of tubule cells•Cytosol of tubule cells•Basolateral membranes of tubule cells•Endothelium of peritubular capillariesCopyright © 2010 Pearson Education, Inc.Tubular Reabsorption•Paracellular route•Between cells•Limited to water movement and reabsorption of Ca2+, Mg2+, K+, and some Na+ in the PCT where tight junctions are leakyCopyright © 2010 Pearson Education, Inc.Figure 25.13Activetransport Passivetransport Peri-tubularcapillary24433112 43Filtratein tubulelumenTranscellularParacellularParacellularTight junctionLateral intercellular spaceCapillaryendothelialcellLuminalmembraneSolutesH2OTubule cellInterstitialfluidTranscellularBasolateralmembranes1 Transport across the luminal membrane.2 Diffusion through the cytosol.4 Movement through the interstitial fluid and into the capillary.3 Transport across the basolateral membrane. (Often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces.)Movement via thetranscellular route involves:The paracellular routeinvolves: • Movement through leaky tight junctions, particularly in the PCT.Copyright © 2010 Pearson Education, Inc.Sodium Reabsorption•Na+ (most abundant cation in filtrate)•Primary active transport out of the tubule cell by Na+-K+ ATPase in the basolateral membrane •Na+ passes in through the luminal membrane by secondary active transport or facilitated diffusion mechanismsCopyright © 2010 Pearson Education, Inc.Sodium Reabsorption•Low hydrostatic pressure and high osmotic pressure in the peritubular capillaries•Promotes bulk flow of water and solutes (including Na+)Copyright © 2010 Pearson Education, Inc.Reabsorption of Nutrients, Water, and Ions•Na+ reabsorption provides the energy and the means for reabsorbing most other substances•Organic nutrients are reabsorbed by secondary active transport•Transport maximum (Tm) reflects the number of carriers in the renal tubules available •When the carriers are saturated, excess of that substance is excretedCopyright © 2010 Pearson Education, Inc.Reabsorption of Nutrients, Water, and Ions•Water is reabsorbed by osmosis (obligatory water reabsorption), aided by water-filled pores called aquaporins•Cations and fat-soluble substances follow by diffusionCopyright © 2010 Pearson Education, Inc.Figure 25.141 At the basolateral membrane, Na+ is pumped into the interstitial space by the Na+-K+ATPase. Active Na+ transport creates concentration gradients that drive:2 “Downhill” Na+ entry at theluminal membrane.4 Reabsorption of water byosmosis. Water reabsorptionincreases the concentration of the solutes that are left behind. These solutes can then be reabsorbed asthey move down their concentration gradients:3 Reabsorption of organic nutrients and certain ions by cotransport at the luminal membrane.5 Lipid-solublesubstances diffuse by the transcellular route.6 Cl– (and other anions), K+, and urea diffuse by the paracellular route.Filtratein tubulelumenGlucoseAmino acidsSome ionsVitaminsLipid-solublesubstancesNucleusTubule cellParacellularrouteInterstitialfluidPeri-tubularcapillaryTight junction Primary active transport Passive transport (diffusion) Secondary active transport Transport protein Ion channel or aquaporinCl–, Ca2+, K+and otherions, ureaCl–3Na+2K+3Na+2K+K+H2ONa+654321Copyright © 2010 Pearson Education, Inc.Reabsorptive Capabilities of Renal Tubules and Collecting Ducts•PCT•Site of most reabsorption•65% of Na+ and water•All nutrients•Ions•Small proteinsCopyright © 2010 Pearson Education, Inc.Reabsorptive Capabilities of Renal Tubules and Collecting Ducts•Loop of Henle•Descending limb: H2O •Ascending limb: Na+, K+, ClCopyright © 2010 Pearson Education, Inc.Reabsorptive Capabilities of Renal Tubules and Collecting Ducts•DCT (distal collect tubule) and collecting duct•Reabsorption is hormonally regulated•Ca2+ (PTH)•Water (ADH)•Na+ (aldosterone and ANP)Copyright © 2010 Pearson Education, Inc.Reabsorptive Capabilities of Renal Tubules and Collecting Ducts•Mechanism of aldosterone•Targets collecting ducts (principal cells) and distal DCT•Promotes synthesis of luminal Na+ and K+ channels•Promotes synthesis of basolateral Na+-K+ ATPasesCopyright © 2010 Pearson Education, Inc.Tubular Secretion•Reabsorption in reverse •K+, H+, NH4+, creatinine, and organic acids move from peritubular capillaries or tubule cells into filtrate•Disposes of substances that are bound to plasma proteinsCopyright © 2010 Pearson Education, Inc.Tubular Secretion•Eliminates undesirable substances that have been passively reabsorbed (e.g., urea and uric acid)•Rids the body of excess K+•Controls blood pH by altering amounts of H+ or HCO3– in urineCopyright © 2010 Pearson Education, Inc.Regulation of Urine Concentration and Volume•Osmolality•Number of solute particles in 1 kg of H2O•Reflects ability to cause osmosisCopyright © 2010 Pearson Education,