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Basic Processes Of Kidney


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Basic Processes Of Kidney

  1. 1. THREE BASIC RENAL PROCESSES <ul><li>Glomerular Filtration: Filtering of blood into tubule forming the primitive urine </li></ul><ul><li>Tubular Reabsorption: Absorption of substances needed by body from tubule to blood </li></ul><ul><li>Tubular Secretion: Secretion of substances to be eliminated from the body into the tubule from the blood </li></ul>04/08/10
  2. 2. BASIC RENAL PROCESSES 04/08/10 GF TR TA Urine Excreted Efferent Arteriole Afferent Arteriole Glomerulus Kidney Tubule Peritubular Capillary
  3. 3. Glomerular Filtration <ul><li>First step in urine formation </li></ul><ul><li>180 liters/day filtered </li></ul><ul><li>Entire plasma volume filtered 65 times/day </li></ul><ul><li>Proteins not filtered </li></ul>04/08/10
  4. 4. Forces Involved in Glomerular Filtration 04/08/10 Glomerular Capillary Blood Pressure + 55 Plasma Colloid Osmotic Pressure - 30 15 10 Bowman’s Capsule Hydrostatic Pressure - Net Filtration Pressure +
  5. 5. Tubular Reabsorption <ul><li>Water: 99% reabsorbed </li></ul><ul><li>Sodium: 99.5% reabsorbed </li></ul><ul><li>Urea: 50% reabsobed </li></ul><ul><li>Phenol: 0% reabsorbed </li></ul>04/08/10
  6. 6. Tubular Reabsorption <ul><li>By passive diffusion </li></ul><ul><li>By primary active transport: Sodium </li></ul><ul><li>By secondary active transport: Sugars and Amino Acids </li></ul>04/08/10
  7. 7. Tubular Reabsorption is a Function of the Epithelial Cells Making up the Tubule 04/08/10 Lumen Plasma Cells
  8. 8. Sodium Reabsorption 04/08/10 Lumen Plasma Cells PUMP: Na/K ATPase Sodium Potassium Chloride Water
  9. 9. Rennin-Angiotensin-Aldosterone System <ul><li>Stimulates Sodium Reabsorption in distal and collecting tubules </li></ul><ul><li>Naturetic peptide inhibits </li></ul><ul><li>In absence of Aldosterone, 20mg of sodium/day may be excreted </li></ul><ul><li>Aldosterone can cause 99.5% retention </li></ul>04/08/10
  10. 10. Rennin-Angiotensin-Aldosterone System 04/08/10 Fall in NaCl, extracellular fluid volume, arterial blood pressure Juxtaglomerular Apparatus Renin Liver Angiotensin + Angiotensin Angiotensin Aldosterone Lungs Converting Enzyme Adrenal Cortex Increased Sodium Reabsorption Helps Correct
  11. 11. DIURETICS <ul><li>ACE Inhibitors (Angiotensin Converting Enzyme): Cause loss of salt---> water follows </li></ul><ul><li>Atrial Naturetic Peptide (ANP) also inhibits sodium reabsorption </li></ul><ul><li>Osmotic diuretics: Are not reabsorbed </li></ul>04/08/10
  12. 12. Glucose and Amino Acids are reabsorbed by secondary active transport <ul><li>They are actively transported across the apical cell membranes of the epithelial cells </li></ul><ul><li>Their active transport depends on the sodium gradient across this membrane </li></ul><ul><li>All other steps are passive </li></ul>04/08/10
  13. 13. GLUCOSE REABSORPTION HAS A TUBULAR MAXIMUM 04/08/10 Renal threshold (300mg/100 ml) Plasma Concentration of Glucose Glucose Reabsorbed mg/min Filtered Excreted Reabsorbed
  14. 14. Tubular Secretion <ul><li>Protons (acid/base balance) </li></ul><ul><li>Potassium </li></ul><ul><li>Organic ions </li></ul>04/08/10
  15. 15. Potassium Secretion 04/08/10 Lumen Plasma Cells PUMP: Na/K ATPase Sodium Potassium Chloride Water
  16. 16. DUAL CONTROL OF ALDOSTERONE SECRETION 04/08/10 Fall in sodium ECF Volume Blood Pressure Increased Plasma Potassium Increased Aldosterone secretion Increased Tubular Potassium Secretion Increased Urinary Potassium Secretion Increased Tubular Sodium Reabsorption Fall in Urinary Sodium Excretion
  17. 17. Reabsorption in Proximal Tubule (Summary) <ul><li>Glucose and Amino Acids </li></ul><ul><li>67% of Filtered Sodium </li></ul><ul><li>Other Electrolytes </li></ul><ul><li>65% of Filtered Water </li></ul><ul><li>50% of Filtered Urea </li></ul><ul><li>All Filtered Potassium </li></ul>04/08/10
  18. 18. Secretion in Proximal Tubule (Summary) <ul><li>Variable Proton secretion for acid/base regulation </li></ul><ul><li>Organic Ion secretion </li></ul>04/08/10
  19. 19. Reabsorption in Distal Tubule (Summary) <ul><li>Variable Sodium controlled by Aldosterone </li></ul><ul><li>Chloride follows passively </li></ul><ul><li>Variable water controlled by vasopressin </li></ul>04/08/10
  20. 20. Secretion in Distal Tubule (Summary) <ul><li>Variable Proton for acid/base regulation </li></ul><ul><li>Variable Potassium controlled by aldosterone </li></ul>04/08/10
  21. 21. Collecting Duct (Summary) <ul><li>Variable water reabsorption controlled by vasopressin </li></ul><ul><li>Variable Proton secretion for acid/base balance </li></ul>04/08/10
  22. 22. REGULATION OF URINE CONCENTRATION <ul><li>Medullary countercurrent system </li></ul><ul><li>Vasopressin </li></ul>04/08/10
  23. 23. Medullary countercurrent system <ul><li>Osmotic gradient established by long loops of Henle </li></ul><ul><li>Descending limb </li></ul><ul><li>Ascending limb </li></ul>04/08/10
  24. 24. Descending limb <ul><li>Highly permeable to water </li></ul><ul><li>No active sodium transport </li></ul>04/08/10
  25. 25. Ascending limb <ul><li>Actively pumps sodium out of tubule to surrounding interstitial fluid </li></ul><ul><li>Impermeable to water </li></ul>04/08/10
  26. 26. COUNTERCURRENT MAKES THE OSMOTIC GRADIENT 04/08/10 300 450 600 750 900 1050 1200 1200 From Proximal Tubule To Distal Tubule Cortex Medulla 300 450 600 750 900 1050 1200 1200 100 250 400 550 700 850 1000 1000 Active Sodium Transport Passive Water Transport Long Loop of Henle
  27. 27. THE OSMOTIC GRADIENT CONCENTRATES THE URINE WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS PRESENT 04/08/10 From Distal Tubule Cortex Medulla 300 450 600 750 900 1050 1200 1200 300 400 550 700 850 1000 1100 1200 Interstitial Fluid Collecting Duct Pores Open Passive Water Flow
  28. 28. WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS ABSENT A DILUTE URINE IS PRODUCE 04/08/10 From Distal Tubule Cortex Medulla 300 450 600 750 900 1050 1200 1200 100 100 100 100 100 100 100 100 Interstitial Fluid Collecting Duct Pores Closed No Water Flow Out of Duct
  29. 29. Renal Failure <ul><li>Acute: Sudden onset, rapid reduction in urine output - usually reversible </li></ul><ul><li>Chronic: Progressive, not reversible </li></ul><ul><li>Up to 75% function can be lost before it is noticeable </li></ul>04/08/10
  30. 30. THE URINARY BLADDER STORES THE URINE <ul><li>Gravity and peristaltic contractions propel the urine along the ureter </li></ul><ul><li>Parasympathetic stimulation contracts the bladder and micturition results if the sphincters (internal and external urethral sphincters) relax </li></ul><ul><li>The external sphincter is under voluntary control </li></ul>04/08/10
  31. 31. Reflex and Voluntary Control of Micturition <ul><li>Bladder filling reflexively contracts the bladder </li></ul><ul><li>Internal Sphincter mechanically opens </li></ul><ul><li>Stretch receptors in bladder send inhibitory impulses to external sphincter </li></ul><ul><li>Voluntary signals from cortex can override the reflex or allow it to take place </li></ul>04/08/10