Renal structure and function
- 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
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- 5. Anatomy • Hilum (hilus) • Renal artery and vein • Cortex • Medulla • Renal pyramids and renal papillae • Major and minor calyces • Renal Pelvis • Ureters 5
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- 7. • Ureters connect kidneys to urinary bladder • Urethra leads from bladder outside the body 7
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- 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
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- 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
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- 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
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- 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
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- 26. Tubular reabsorption • Water, glucose, amino acids, urea, ions • Sodium diffuses into cell; actively pumped out – drawing water with it 26
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- 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
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- 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
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- 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
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- 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
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- 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