Renal Tubular Reabsorption and Secretion PDF

Renal module Course code: IMP-07- 20318 Phase: I Year/ semester: 2nd year / Semester (3) Credit hours: Course duration: 5 weeks.  Lecture 4 Renal tubular reabsorption and secretion By Prof. Dr. Aziza Khalil  Lecture 4 Renal tu...

Renal module Course code: IMP-07- 20318 Phase: I Year/ semester: 2nd year / Semester (3) Credit hours: Course duration: 5 weeks.  Lecture 4 Renal tubular reabsorption and secretion By Prof. Dr. Aziza Khalil  Lecture 4 Renal tubular reabsorption and secretion Intended Learning Outcomes (ILOs) On completion of this lecture, the student will be able to: Describe the function of various parts of renal tubules (Tubular reabsorption and secretion). -Identify tubular reabsorption and secretion its significance.  Tubular functions Reabsorption Secretion Tubular Reabsorption Tubular reabsorption Each material to be reabsorbed Concentrations is the amount of different required Tubularsubstances to maintain proper is reabsorption in glomerular composition and filtrate volume of highly selective is exactly internal fluid similar to environment its concentration in plasma  Tubular reabsorption Paracellular In between Transepithelium cells Through cells (H2O) (most of sub.)  Tubular Reabsorption Tubular Tubular Interstitial Peritubular lumen epithelial cell fluid capillary Filtrate Plasm Tight a junctio n Lateral Luminal space membrane 1 2 3 4 5 3 Basolatera l Capillary wall membrane Transepithelium: substance has to cross 5 barriers 1- luminal, 2- cytosole, 3- basolateral  Mechanisms of tubular reabsorption Passive dif fusion as HH2 2O Active transport CL urea 1- primary active ( e.g. Na, K, Ca, H) 2- secondary active ( e.g. glucose, amino  Sodium Reabsorption  Peritubular Lume Tubular cell Interstitial fluid capillary n Diffusio n Na+ Active transport channe l Basolateral Na+– K+ ATPase carrier Lateral Diffusio space n Mechanism of sodium GLUCOSE REABSORPTION  No Lumen of energy Luminal border tubule Cotransport carrier required (SGLT) Glucose reabsorption is by Sodium -dependent Tight Energy secondary junctio required active n transport Epithelial cell Na+–K+ lining pump (Occurs in tubular cells early portion of PCT) No energy Glucose Basolatera required Carrier l GLUT-2 border Blood vessel = Sodium = Potassium = Glucose = Phosphate  All filtered glucose is reabsorbed The plasma glucose level at which glucose start to appear in urine is 180 mg%  K Transport PCT reabsorb 65% (obligatory) Loop of Henle reabsorb 25-30% (obligatory) Mechanism of K K++ transport: Active, both 1ry and 2 2nd nd transport mechanisms Reabsorption in PCT 1 1ry ry active transport in Loop 2 2nd nd  phosphate and Calcium reabsorption  phosphate and Calcium reabsorption Kidneys regulates their plasma levels as Their renal threshold = normal plasma conc.  Phosphate Phosphate Reabsorption Reabsorption Phosphate added to blood more than body needs. Reabsorption is active through co-transport with Na. Only in proximal convoluted tubules Can only reabsorb up to normal plasma concentration (normally ingested PO4 exceeds the body needs) Controlled by parathyroid hormone (PTH) which inhibits its reabsorption by PCT.  Calcium Calcium Reabsorption Reabsorption Through Through 2nd 2nd active active transport transport or or by by passive passive reabsorption. reabsorption. Both Both PCT PCT & & DCT DCT reabsorb reabsorb calcium. calcium. Can Can only only reabsorb reabsorb up up to to normal normal plasma plasma conc. conc. Controlled Controlled by by parathyroid parathyroid hormone hormone (PTH) (PTH) which which stimulates stimulates its its reabsorption reabsorption by by PCT. PCT.  Substances Substances that that are are passively passively reabsorbed reabsorbed and and dependent dependent on on active active Na Na reabsorption reabsorption Cl, Cl, H H22O, O, Urea Urea  CL- CL- reabsorbed reabsorbed Passively Passively through tight junction in PCT (in other parts by 2 2nd nd active transport) Mechanism Mechanism 1- 1- Electrical Electrical gradient gradient (due to to Na reabsorption) reabsorption) 2- 2- Concentration Concentration gradient gradient (due to to HO HO22 reabsorption)  H H22O O reabsorbed reabsorbed Passively Passively (by (by Osmosis Osmosis all all through) through) 1- 1- 80 80 % % obligatory obligatory In In PCT PCT (65%) (65%) and and Loop Loop of of Henle(15%) Henle(15%) (due (due to to Na reab.) reab.) 2- 2- 20 20 % % is is facultative facultative (varied) Lume Proximal tubular cell Interstitial fluid Peritubular capillary n Osmosis Water channe l Hydrostati c Osmosis pressure Water Reabsorption in PCT  Urea Urea reabsorption is Passive Passive -- linked linked to to Na Na reabsorbtion reabsorbtion && removal removal ofof 65% 65% of of H H22O O Which Which increases increases urea urea concentration concentration 33 times times -- only only 50% 50% of of filtered filtered urea urea  Glomerulus Peritubular Bowman’s capillary capsule 125 ml Urea of filtrate Reabsorption Beginning of Na+ proximal (active) H2O tubule (osmosis) Na+ (active) H2O (osmosis) End of 44 ml proxima of l filtrate tubule Passive diffusion = Urea of urea down its molecules concentration When When kidney kidney function function decline decline GFR GFR decline decline Filtered Filtered urea urea decreases decreases Increases Increases blood blood urea urea causes causes uremia uremia  Waste Waste products that that are filtered filtered are are not not reabsorbed reabsorbed and lost lost in urine urine  Summary to Tubular Reabsorption (other than sodium) Active Passive Glucose & amino acids Proximal Proximal tubule tubule CL, H2O, urea K, Phosphate& calcium Loop Loop of of Henle Henle CL, K H2O Distal Distal and and Tubular Secretion  Tubular Hydrogen Ions Secretion ( PCT, DCT, CD ) Potassium Ions ( DCT , CD ) Endogenous Endogenous:: Creatinine Organic , Uric Compounds Acid ( PCT ) Exogenous Exogenous:: PAH , Drugs  All H+ excreted in urine is through secretion (filtered H + is very little)  H H++ secretion secretion -Active, -Active, 11ry ry and and 22nd nd transport transport mechanisms mechanisms -All -All tubules tubules secrete secrete H H++ -- H H++ secretion secretion is is directly directly proportional proportional to to plasma plasma [H [H++]]  H H++ secretion secretion In In PCT PCT Active, Active, 22nd nd transport transport mechanisms mechanisms Counter-transport Counter-transport with with sodium sodium Main Main H H++ secretion secretion is is in in PCT PCT  Proximal Tubule Reabsorbed Na+ Na+ CO 2  HH++ secretion secretion In In Distal Distal & Collecting Collecting Tubules Tubules Primary Primary active active transport transport mechanism mechanism (pump) (pump) Distal Tubule & collecting duct ATP ADP  Control Control of of H+ H+ Secretion Secretion by by renal renal tubules tubules Secretion Secretion is is directly proportional proportional to plasma plasma [H[H+ +]] (or (or P PCO CO CO22) Mechanism of H+ secretion Counter Primary transport pump on with Na + luminal in PCT membrane (>90%) of DCT & CT (about 5%)  H+ ion secretion coupled with HCO3- reabsorption Tubularincell PCT Tubular lumen Na-H peritubular capillary counter transport Filtered HCO3- + H+ H+ + HCO3- “Reabsorbe d” HCO3- N a H2CO3 H2CO3 ca ca H2O + CO2 CO2 H2O + CO2 Cellular metabolism HCO3- Disappearance Luminal isborder therefore isofimpermeable considered HCO3- fromtothe be the tubular “reabsorbed” fluidHCO3- filtered is coupled withalthough Ca carbonic anhydrase the appearance it is not oftheanother same HCO3- HCO3- in the plasma  K + Transport Both Both types types of of transport transport occur occur Reabsorption Reabsorption and and Secretion Secretion  K K secretion secretion almost almost K K excreted excreted in in urine urine is is due due to to secretion secretion by by DCT DCT && CT CT secretion secretion by by 11ry ry active active transport transport (Secretion= 10-15% of filtered load) Lume Distal tubular cell Interstitial fluid Peritubular capillary n Primary active Diffusio n transport K+ channe l Active transpor t Diffusio n K Secretion The only part of K transport that is hormonally regulated  Na+/ ECF volume/ arterial pressure Control of K Reni Secretion n by Angiotensin I Distal and Collecting Plasma K+ Angiotensin II Aldosterone Tubular K+ secretion Tubular Na+ reabsorption Urinary K+ excretion Urinary Na+ excretion  References Ganong, W.F.: Review of medical physiology, 23 th ed. New York, Mc Graw- Hill Co, 2011. P647:652, 659 & 679:682. Gyton, A.A. and Hall, J.E.: Text book of medical physiology, 12 th ed. Philadelphia, Saunders Co., 2011.P 323:339 & 361:369. Handbook of the Physiology department, Faculty of medicine for girls, Al-Azhar university, P29:47& 57:63.