بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

2. Kidney By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology

4. Proximal Tubules

9. Glucose, amino acids, vitamins, protein →100% HCO3- → 90% inorganic phosphate → 80% Na+ & water → 2/3 or 65% K+, Ca2+, Mg2+ & urea → Variable amount Reabsorption

10. Organic solutes as PAH, drugs, various amines and ammonia. Secretion

11. Overall Functions of Proximal Tubules a) Reabsorption of: • All filtered glucose, amino acids, vitamins, protein and Kreb’s cycle intermediates. • About 2/3 of filtered load of Na+ & water. • About 90% of the filtered load of HCO3- . • About 80% of the filtered inorganic phosphate. • Variable amount of K+, Ca2+, Mg2+ & urea. b) Secretion of • Organic solutes as PAH, drugs, various amines and ammonia.

12. Loop of Henle

13. Loop of Henle Descending LH: Starts: • At junction ( ) outer and innerstrips of outer medulla Epithelium: • Very thinendothelial –like cells. • Few microvilli • Few mitochondria • Permeability (high to water, hard to solutes)

14. Outer Strip Inner Strip

16. Loop of Henle Ascending LH: Thin ALH: • Presents only in long loops Epithelium: • Similar to DLH • Permeability • Impermeable to water • Permeable to solutes → allow Na reabsorption, and Urea secretion

17. 1120 = NaCl 80 = Urea 600 = NaCl 600 = Urea

18. Loop of Henle Ascending LH: Thick ALH: Epithelium: • Tall epithelium • Numerous microvilli • Much mitochondria • Basolateral border rich in Na-K pump • Apical border contain Na-K-Cl2 transporter

19. Basolateral border Apical border

20. Tight Junctions

21. Hypotonic fluid + + + TEPD + 5 to +15 mv Na, Ca, Mg

22. Overall Functions of LH 150- 200 mosm/L 30% Ca 65% Mg 10 % K 25% Na (6000-900 meq/day) 15% Water Urea

23. Distal Segment of Nephron

24. Distal Segment of Nephron • a) Distal convoluted tubule (early distal tubules • b) Connecting tubules (late distal tubule) • c) Collecting ducts

25. CT DCT CD

26. Overall Functions of Distal Segment • Final adjustment of urine formation. • Reabsorption of 7-10% of filtered load of Na+. • Reabsorption of 10-15% of filtered lead of water. • Secretion of variable amount of H+ & K+. • Major control site for Na+, K+, Ca2+ & acid-base balance of body. • Many of these functions are controlled by hormones.

27. Distal Convoluted Tubules

29. Characters of DCT • Represent early 2/3 of distal tubules. • Reabsorbs 4% of filtered load of Na+. • NaCl is transported by a Na+ - Cl- transporter located at apical border. • This transporter is inhibited by thiazide diuretics. • The basolateral Na+- K+ ATPase together with that of thick ALH has highest activity of any nephron segment. • The osmolarity of tubular fluid leaving DCT is 100 mOsm/L (i.e. more hypotonic)  so, the diluting segments of the nephron are: thick ALH and early DCT.

31. Connecting Tubules • It is the late 1/3 of distal tubules. • As the collecting duct, its cell types are principal and intercalated cells. • Has variable water permeability according to ADH level. • Its TEPD is negative (about -45 mV).

33. Collecting Ducts • Important site for final adjustment of urine volume, reaction (pH) and composition. • Include: cortical (CCD), outer medullary (MCD) & inner medullary (papillary) (PCD). • Have 2 major cell types: • 1. Principal cells. • 2. Intercalated cells.

34. CCD MCD PCD

36. Na Handling

37. Na Handling

38. Na Reabsorp. in Proximal Tubules General characters • About 2/3 (67%) of the filtered Na+ with the same percentage of water i.e. iso-osmotic reabsorp. • TFNa/ PNa ratio at the end of PT is one as it is iso-osmotic • In early PT, Na+, water, glucose, HCO3, amino acids and organic anions as lactate, pyruvate, and phosphate …. all are absorbed 2ry to Na+. • In the late PT: Na+ is absorbed with chloride mainly.

39. Transcellular and Paracellular Transport Paracellular Transport Transcellular Transport

40. Transcellular Transport • Occurs mostly at early segment of PT a) Carrier –mediated transport Symport Na-K pump Antiport

41. Transcellular Transport b) Channel –mediated transport Na Channels Na-K pump

42. Transcellular Transport Na-K pump Electrogenic symport Electoneutral symport

43. Transcellular Transport Na-K pump Electoneutral antiport

44. Transcellular Transport Cl ions Na-K pump Na channels

45. Paracellular Transport • Occurs mostly at late segment of PT a) Cl- derived Na Reabsorp. Early PT HCO3- Cl = 105 meq/L Cl = 132 meq/L - - - - - Na+ Late PT

46. Paracellular Transport a) Solvent drag Reabsorp. PTC 3-5 mosmol/L Water NaCl

47. Absorptive and Secretory Function in PT Related to Na+ Reabsorption

48. Glucose Reabsorption

49. Glucose Reabsorption • % : 100% of glucose is reabsorbed in PT Na-K ATPase 2ry active transport Facilitated diffusion