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Reabsorption of sodium and water

Reabsorption of sodium and water. S pecific learning objectives. Renal handling of sodium Reabsorption of sodium at different levels of nephron Applied aspects Reabsorption of water Applied aspects. Na + Reabsorption.

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Reabsorption of sodium and water

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  1. Reabsorption of sodium and water

  2. Specific learning objectives • Renal handling of sodium • Reabsorption of sodium at different levels of nephron • Applied aspects • Reabsorption of water • Applied aspects

  3. Na+ Reabsorption • The reabsorption of Na+ and Cl– plays a major role in body electrolyte and water homeostasis. H+ Amino acids Organic acids Glucose Na+ transport Co-transport Phosphate Other electrolytes

  4. 60% 30% 7% 3% ( Aldosterone)

  5. Na+ Reabsorption Passive Transport Active Transport

  6. 1. Facilitated diffusion : Sodium diffuses across the apical membrane into the cell down an electrochemical gradient established by the sodium-potassium ATPase pump on the basolateral side of the membrane. 2. Active transport : Sodium is transported across the basolateral membrane against an electrochemical gradient by the sodium-potassium ATPase pump. 3. Solvent drag :Sodium, water, and other substances are reabsorbed from the interstitial fluid into the peritubular capillaries by ultrafiltration, a passive process driven by the hydrostatic and colloid osmotic pressure gradients.

  7. Regulation of Na+ Excretion • Na+ in the body is a prime determinant of the ECF volume. • Depends on • changes in GFR • changes in tubular reabsorption (primarily in the 3% of filtered Na+ that reaches the collecting ducts).

  8. Regulation of Na+ Excretion • The factors affecting include • Tubuloglomerular feedback • Circulating level of aldosterone and other adrenocortical hormones • The circulating level of ANP and other natriuretic hormones • The rate of tubular secretion of H+ and K+.

  9. Water Reabsorption

  10. Types of water Reabsorption- In nephron, • Obligatory water reabsorption • Facilitatoryor Facultative water reabsorption

  11. Obligatory water reabsorption • “Water reabsorption takes place as a result of solute reabsorption” • Takes place in PCT

  12. Obligatory water reabsorption PCT, epithelial cell membrane is permeable to water; because • Leaky tight junction – solvent drag • Aquoporin-1—water channels of luminal surface • In PCT, 65% solutes are reabsorbed • Hence equal volume of (65%) water reabsorbed

  13. Facilitatory water reabsorption • In CT; reabsorption of water is facilitated (aided) by some external agents; hence called Facilitatory water reabsorption. • Absorption determined by body’s need • Facilitatory agents are –ADH (Vasopressin) & Aldosterone

  14. Mechanism of action of ADH • Water reabsorption aided by ADH: • Water channels in CT is aquoporin-2 • Aquoporin-2 synthesized is stored in vesicles in epithelial cells of CT . • Water channels incorporated into luminal membrane only in the presence of ADH

  15. VASOPRESSIN (ADH) Aquaporin is stored in vesicles in the cytoplasm of principal cells. Vasopressin V2 receptor Cyclic adenosine 5-monophosphate Insertion of these vesicles into the apical membrane of cells. Protein kinase A. Increased permeability of collecting duct to water

  16. Action of ADH (Vasopressin) • ADH  through V2 receptor  increase cAMP  activate protein kinase  remove aquoporin-2 (water channels) molecules from vesicles and incorporates into the luminal epithelial membrane • Incorporation of aquoporin-2 (water channels) into cell membrane increase water permeability and cause water reabsorption

  17. ADH Osmoreceptor- ADH feedback mechanism for regulating extracellular fluid osmolarity

  18. Summary

  19. References • Comprehensive Textbook of Medical physiology (Vol 2, 1stedition) G K Pal • Text book of medical physiology (Vol 2, 6thedition) A K Jain • Essentials of medical physiology (6thedition) K Sembulingam and PremaSembulingam • https://www.drawittoknowit.com/course/physiology/glossary/physiological-process/sodium-reabsorption-in-neprhon • http://www.austincc.edu/apreview/PhysText/Renal.html

  20. THANK YOU

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