Renal Tubules

A brief slides presenting function of renal tubules (includes PCT, Loop of Henle, DCT, Cortical and Medullary collecting ducts)
dividedinto reabsorptive and secretory functions

1. Renal Tubules Pashupati Pokharel(MBBS) Institute of Medicine, Tribhuwan University, Kathmandu Nepal 1

2. Objective To explain the function of renal tubules 2

3. Renal Tubule Part of nephron that extends from Bowman’s capsule to its junction with a collecting duct 55mm in length and is lined by a single layer of epithelial cells Convoluted in shape and has four distinct zones 3

4. Fig. Structure of a N ephron Source=http://1.bp.blogspot.com/renal6.jpg 4

5. Tubular function means alteration of glomerular ultrafiltrate into urine Divided into: A. Tubular reabsorption B. Tubular secretion 5

6. Tubular Reabsorption Glomerular filtrate contains useful substances; glucose, amino acids, vitamins, hormones, electrolytes( Na + , K + , Cl - , Ca ++ , Mg ++ , HCO 3 - and others) Waste products: urea, creatinine, drugs, toxins Useful substances are reabsorbed selectively at different sites 6

7. Proximal Convoluted Tubule Most convoluted part of tubule; contains brush border, increases surface area by 20 times Reabsorbs: 65% of Na + , Cl - and H 2 O 100% glucose and amino acids Proteins if present reabsorbed by pinocytosis 50% of urea Ions like Ca 2+ ,Mg 2+ , K + are reabsorbed by solvent drag( paracellular pathway) and transcellular pathway 7

8. Fig. Transport of Na + T hrough T ubular E pithelial Cell https://www.researchgate.net/281741919/figure/fig3 8

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10. Loop of Henle 1. Thin Descending Limb: Freely permeable to H 2 O, not to ions. Water continuously moves to the interstitium due to medullary hyperosmolarity 20% of H 2 O is reabsorbed here 2. Thin Ascending Segment: Permeability similar to descending limb As fluid moves up, little H 2 O is secreted to the tubule 10

11. 3.Thick Ascending Segment Impermeable to H 2 O Presence of Na + -K + -2Cl - symporter on luminal membrane and Na + -K + - ATPase pump in basolateral membrane Active reabsorption of Na + , 25% of Na + , K + and Cl - are reabsorbed here Reabsorption of Ca ++ and Mg ++ takes place by paracellular pathway HCO 3 - also reabsorbed 11

12. http://www.pathwaymedicine.org/images/renal/Thick-Ascending-Loop-of-Henle-Transport.png 12

13. Early Distal Tubule Na + - Cl - symporter is present in luminal membrane Reabsorbs Na + - Cl - driven by Na + -K + - ATPase pump Impermeable to H 2 O and urea Late Distal tubule and Cortical Collecting Duct Permeable to H 2 O in presence of Anti-diuretic hormone (ADH), impermeable to urea Principal cells reabsorb Na + in exchange to K + mediated by aldosterone 13

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15. Fig. Aldosterone Mediated Na+ Reabsorption in Late DCT and CD 15

16. Medullary Collecting Duct Permeable to H 2 O in presence of ADH Passive diffusion of urea mediated by ADH Urea transporters UT-A 1 and UT-A 3 16

17. Tubular Secretion A. Proximal Convoluted Tubule H + is secreted in exchange with Na + Creatinine, K + , organic acids like bile acids, oxalate, uric acid, para amino hippuric acid are secreted Drugs like penicillins , salicylates , probenicid , thiazides are also secreted 17

18. Fig. H + Secretion in Lumen of PCT 18

19. B.Late Distal tubules and Collecting Tubules Principal cells : Na + reabsorption coupled with K+ secretion. Driven by Na + -K + - ATPase in basolateral membrane whose expression is stimulated by aldosterone Intercalated cells : Type A- Actively secrete H + by H + -K + - ATPase while reabsorb HCO 3 - in acidosis Type B- Secrete HCO 3 - in exchange to Cl - and reabsorb H + in alkalosis 19

20. Fig. Cells in Late DCT and Collecting Tubules 20

21. Bibliography Guyton and Hall Textbook of Medical Physiology 13 th Edition- John E. Hall, PhD Wheater’s Functional Histology, A text and Color Atlas, 6 th Edition- Barbara Young, Geraldine O’ Dowd, Phillip Woodford 21

22. THANK YOU 22