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Renal structure and function

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Renal structure and function

Renal structure and function

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  • 1. Renal Structure and Function 1
  • 2. Kidneys• Paired• Retroperitoneal• Partially protected by the 11th and 12th ribs• Right slightly lower due to liver• Surrounded by renal capsule• Adipose capsule• Renal fascia 2
  • 3. 3
  • 4. 4
  • 5. Anatomy• Hilum (hilus)• Renal artery and vein• Cortex• Medulla• Renal pyramids and renal papillae• Major and minor calyces• Renal Pelvis• Ureters 5
  • 6. 6
  • 7. • Ureters connect kidneys to urinary bladder• Urethra leads from bladder outside the body 7
  • 8. 8
  • 9. • Kidneys make up 1 % of body mass, but receive about 25% of cardiac output.• Kidney has two major functions: 1. Filtration of blood • Removes metabolic wastes from the body, esp. those containing nitrogen 9
  • 10. 2. Regulation: Blood volume and composition Electrolytes Blood pH Blood pressure 10
  • 11. Nephron• Functional unit of the kidney• Filtration, tubular reabsorption, tubular secretion• Renal corpuscle: – Glomerulus – capillaries – Glomerular or Bowman’s capsule 11
  • 12. • Bowman’s capsule – Receives filtrate• Proximal convoluted tubule – Reabsorption of water and solutes• Nephron loop or Loop of Henle – Regulates concentration of urine• Distal convoluted tubule and Collecting duct • Reabsorption of water and electrolytes – ADH, aldosterone, ANP – Tubular secretion 12
  • 13. 13
  • 14. 14
  • 15. 15
  • 16. 16
  • 17. Filtration• Renal corpuscle• Filtration membrane – Fenestrated endothelium of capillaries – Basement membrane of glomerulus – Slit membrane between pedicels of podocytes 17
  • 18. Forces that influence filtration• Glomerular blood hydrostatic pressure• Opposing forces: – Plasma colloid osmotic pressure – Capsular hydrostatic pressure 18
  • 19. 19
  • 20. Glomerular Filtration Rate• Volume of plasma filtered / unit time• Approx. 180 L /day• Urine output is about 1- 2 L /day• About 99% of filtrate is reabsorbed 20
  • 21. 21
  • 22. GFR influenced by:• Blood pressure and blood flow• Obstruction to urine outflow• Loss of protein-free fluid• Hormonal regulation – Renin – angiotensin – Aldosterone – ADH – ANP 22
  • 23. Juxtaglomerular apparatus• Juxtaglomerular cells lie in the wall of afferent arteriole• Macula densa in final portion of loop of Henle – monitor Na+ and Cl- conc. and water• Control blood flow into the glomerulus• Control glomerular filtration 23
  • 24. 24
  • 25. 25
  • 26. Tubular reabsorption• Water, glucose, amino acids, urea, ions• Sodium diffuses into cell; actively pumped out – drawing water with it 26
  • 27. 27
  • 28. 28
  • 29. • In addition to reabsorption, also have tubular secretion – substances move from peritubular capillaries into tubules – a second chance to remove substances from blood. 29
  • 30. 30
  • 31. • By end of proximal tubule have reabsorbed:• 60- 70% of water and sodium• about 100% of glucose and amino acids• 90 % of K+, bicarb, Ca++, uric acid• Transport maximum – maximum amount of a substance that can be absorbed per unit time• Renal threshold – plasma conc. of a substance at which it exceeds Tm. 31
  • 32. Loop of Henle• Responsible for producing a concentrated urine by forming a concentration gradient within the medulla of kidney.• When ADH is present, water is reabsorbed and urine is concentrated.• Counter-current multiplier 32
  • 33. 33
  • 34. Distal convoluted tubule and collecting ducts• What happens here depends on ADH• Aldosterone affects Na+ and K+• ADH – facultative water reabsorption• Parathyroid hormone – increases Ca++ reabsorption 34
  • 35. 35
  • 36. Distal convoluted tubule and collecting ducts• Tubular secretion to rid body of substances: K+, H+, urea, ammonia, creatinine and certain drugs• Secretion of H+ helps maintain blood pH (can also reabsorb bicarb and generate new bicarb) 36
  • 37. 37
  • 38. Renal diagnostic procedures• Urinalysis is non-invasive and inexpensive• Normal properties are well known and easily measured 38
  • 39. pH• Normally 4.8 – 8.0• Higher in alkalosis, lower in acidosis• Diabetes and starvation ↓ pH• Urinary infections ↑ pH – Proteus and pseudomonas are urea splitters 39
  • 40. Specific gravity• Normal values 1.025 -1.032• High specific gravity can cause precipitation of solutes and formation of kidney stones• When tubules are damaged, urine specific gravity approaches that of glomerular filtrate – 1.010 – remains fixed = 2/3 of nephron mass has been lost 40
  • 41. • Diabetes insipidus = 1.003• Diabetes mellitus = 1. 030• Emesis or fever = 1.040 41
  • 42. Microscopic analysis• Red blood cells – should be few or none – Hematuria – large numbers of rbc’s in urine – Catheterization – Menstruation – Inflamed prostate gland – Cystitis or bladder stones 42
  • 43. • Casts – precipitate from cells lining the renal tubules – Red cells – tubule bleeding – White cells – tubule inflammation – Epithelial cells – degeneration, necrosis of tubule cells 43
  • 44. • Crystals – – Infection – Inflammation – stones 44
  • 45. • White blood cells – Pyuria – Urinary tract infection• Bacteria 45
  • 46. Substances not normally present in urine• Acetone• Bile, bilirubin• Glucose• Protein – albumin – Renal disease involving glomerulus 46
  • 47. Blood Urea Nitrogen BUN• Urea produced by breakdown of amino acids - influenced by diet, dehydration, and hemolysis• Normal range 10-20 mg/ dL• If the GFR decreases due to renal disease or blockage, or decreased blood flow to kidney - BUN increases• General screen for abnormal renal function 47
  • 48. Creatinine clearance• Creatinine is an end product of muscle metabolism• Muscle mass is constant; creatinine is constant• Normal 0.7 – 1.5 mg/ dL in plasma• Can then be compared to creatinine in urine over 24 hour period to determine clearance 48
  • 49. • Creatinine clearance is an indirect measure of GFR and renal blood flow• Creatinine is neither reabsorbed nor secreted, just freely filtered.• Amount excreted = amount filtered• Useful to monitor changes in chronic renal function• Increases with trauma with massive muscle breakdown 49
  • 50. Diagnostic testing• Inulin clearance - not absorbed or secreted = GFR• PAH – para-aminohippuric acid – not absorbed ; actively secreted = renal plasma flow 50