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UM BIOH 370 - The Renal Tubule
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BIOH 370 1st Edition Lecture 26Outline of Last Lecture Urinary SystemI. Urinary System FunctionsII. Renal AnatomyIII. Blood and Nerve SupplyIV. The NephronV. Renal CorpuscleVI. Glomerular FiltrationVII. Juxtaglomerular Apparatus (JGA) VIII. Renal AutoregulationIX. Renal TubuleOutline of Current Lecture Urinary System Day 2I. Substances Reabsorbed/Excreted in Urine DailyII. The Renal TubuleIII. Cortical and Juxtamedullary Nephronsa. Cortical Nephronsb. Juxtamedullary NephronsIV. Tubular Reabsorption and SecretionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. Transcellular Routeb. Paracellular RouteV. Transport Mechanisms in the PCTVI. Late PCT- Passive ReabsorptionVII. Reabsorption in the Loop of HenleVIII. Reabsorption in Early DCTIX. Reabsorption in the Late Convoluting Tubules and Collecting Ductsa. Principal Cellsb. Intercalated DiscsX. ADH Regulation of Water ReabsorptionXI. Hormonal Regulation of Reabsorption/Secretion ChartXII. Regulation of Urine Concentration and VolumeCurrent LectureUrinary System Day 2I. Substances Reabsorbed/Excreted in Urine Daily- Protein shouldn’t be in urine- neither should glucose (or very little) unless diabetic- Bunch of stuff goes into glomerular capsule- reabsorbs most of this into blood= blood pH remains the sameo Only a small amount reabsorbed into urine= urine pH can changeo Meat eaters= more acidic urineo Vegetarians= more basic urineII. The Renal Tubule: the filtrate passes form the glomerular capsule to the renal tubulea. PCTb. Nephron Loop (Loop of Henle)- Descending Loop- Ascending Loopc. DCTIII. Cortical and Juxtamedullary Nephronsa. Cortical Nephrons: 80-85% of nephrons- Renal corpuscle in outer portion of cortex - Short loops of Henle extend only into outer region of medulla- Create urine with osmolarity similar to bloodb. Juxtamedullary Nephrons- Renal corpuscle deep in cortex withlong nephron loops- Receive blood from peritubularcapillaries and vasa recta- Ascending limb has thick and thinregions- Enable kidney to secrete very concentrated urine- Concentrate urine- more organized blood capillariesIV. Tubular Reabsorption and Secretion: Much of the filtrate is reabsorbed by both active and passive processes.- Especially water, glucose, amino acids, and ions- Secretion helps to mange pH and rid the body of toxic and foreign substancesb. Transcellular Route:- Luminal membranes of tubule cells- Cytosol of tubule cells- Basolateral membranes of tubule cells- Endothelium of peritubular capillaries- Na+ reabsorbed via transcellular routec. Paracellular Route:- Between cells- Limited to water movement and reabsorption of Ca2+, Mg2+, K+, and some Na+ in the PCT where tight junctions are leaky-Microvilli (for absorption) on apical surface-Basolateral surface= absorbed into blood- Na/K ATPase= pulls 3 Na our and 2 K in- use gradient to pull things through to peritubullar capillares-V. Transport Mechanisms in the PCTAll occurring in the PCT:-Na-glucose symporter on apical side-Glucose facilitated diffusion on basolateral side- Increasing amounts of H+ going into the filtrate- on the apical side-Na-ion antiporter-CO2 dissolves in blood and can diffuse- carbonic anhydrase to make bicarbonate= adds to pH buffering system of blood- - reabsorbed some Na+-Na-ion antiporter-apical side= carbonic anhydrase= neutralizes the increasing H+ in urine/filtrateVI. Late PCT- Passive Reabsorption-in late PCT- Lots of diffusion into peritubular capillary (moves from high to low concentration)- water also diffuses because “water follows salt”VII. Reabsorption in the Loop of Henle- Relatively impermeable to water, especially the ascending limb- Little obligatory water reabsorption- Na+ - K+ - 2Cl– symporters- no microvilli= little absorption- Na-K-2Cl Symporter= allows reabsorption of Na, K, and 2Cl – some K will leak backout- This apical membrane totally impermeable to water= no water movement but ions (salts) still moving= increasing ion concentration= increasing osmolarity and osmolality= continues to increase as move further into medulla- Not much happens in descending loop of Henle= has simple squamous epithelium. Much more happening in ascending loop- Vasa recta=same as peritubular capillary except call it vasa recta injuxtamedullary nephrons (futher in medulla)VIII. Reabsorption in Early DCT- Na+ - Cl– symporters reabsorb ions- PTH stimulates reabsorption of Ca2+- It also inhibits phosphate reabsorption in the PCT, enhancing its excretionIX. Reabsorption in the Late Convoluting Tubules and Collecting Ductsa) Principal Cells- Na+-K+ pumps reabsorb Na+ - Aquaporin – 2 reabsorbs water= Stimulated by ADHb) Intercalated Discs- Reabsorb K+ + HCO3–, secrete H+ Reabsorption is hormonally regulatedo Ca2+ (PTH)o Water (ADH) Inserts aquaporins into collecting duct luminal membraneso Na+ (aldosterone and ANP) Synthesize and retain more K+ and Na+ channels and morebasolateral Na+K+ ATPases- lots of hormonal control- last step of filtration where can have an effectFluid intubulelumen Sodium–potassium pump Diffusion Leakage channels Key: Principalcell Peritubular capillary Interstitialfluid Na+ Na+ Na+ Na+ K+ K+ K+ ATP ADPX. ADH Regulation of Water Reabsorption- Facultative Reabsorption- Negative FeedbackXI. Hormonal Regulation of Reabsorption/Secretion ChartXII. Regulation of Urine Concentration and Volume- Osmolality- Number of solute particles in 1 kg of H2O- Reflects ability to cause osmosis- Osmolality of plasma~300mOsm Osmolality of body fluids- Expressed in milliosmols (mOsm)- The kidneys maintain osmolality of plasma at ~300 mOsm, using countercurrent


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