Kidney function


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Kidney function

  2. 2. FUNCTIONS OF KIDNEYexcretory functionhomeostatic functionendocrine functionmetabolic function
  3. 3. EXCRETORY FUNCTION• This include formation and excretion of urine.• The main step involved are – Glomerular filtration – Tubular reabsorption – Tubular secretion
  4. 4. Filtration• Renal corpuscle• Filtration membrane – Fenestrated endothelium of capillaries – Basement membrane of glomerulus – Slit membrane between pedicels of podocytes 4
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  6. 6. Forces that influence filtration• Glomerular blood hydrostatic pressure• Opposing forces: – Plasma colloid osmotic pressure – Capsular hydrostatic pressure 6
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  8. 8. 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 8
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  10. 10. GFR influenced by:• Blood pressure and blood flow• Obstruction to urine outflow• Loss of protein-free fluid• Hormonal regulation – Renin – angiotensin – Aldosterone – ADH – ANP 10
  11. 11. 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 11
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  14. 14. Tubular reabsorption• Water, glucose, amino acids, urea, ions• Sodium diffuses into cell; actively pumped out – drawing water with it 14
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  17. 17. • In addition to reabsorption, also have tubular secretion – substances move from peritubular capillaries into tubules – a second chance to remove substances from blood. 17
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  19. 19. • 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. 19
  20. 20. 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 20
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  22. 22. 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 22
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  24. 24. 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) 24
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  26. 26. Homeostatic Functions of Urinary System1. Regulate blood volume and blood pressure: – by adjusting volume of water lost in urine – releasing erythropoietin and renin2. Regulate plasma ion concentrations: – sodium, potassium, and chloride ions (by controlling quantities lost in urine) – calcium ion levels
  27. 27. 3. Help stabilize blood pH: – by controlling loss of hydrogen ions and bicarbonate ions in urine4. Conserve valuable nutrients: – by preventing excretion while excreting organic waste products5. Assist liver to detoxify poisons
  28. 28. ENDOCRINE FUNCTIONS… Kidneys have primary endocrine function since they produce hormones In addition, the kidneys are site of degradation for hormones such as insulin and aldosterone. In their primary endocrine function, the kidneys produce erythropoietin, renin and prostaglandin. Erythropoietin is secreted in response to a lowered oxygen content in the blood. It acts on bone marrow, stimulating the production of red blood cells.
  29. 29.  Renin -the primary stimuli for renin release include reduction of renal perfusion pressure and hyponatremia. Renin release is also influenced by angiotension II and ADH. It is a key stimulus of aldosterone release. The effect of aldosterone is predominantly on the distal tubular network, effecting an increase in sodium reabsorption in exchange for potassium. The kidneys are primarily responsible for producing vitamin D3 from dihydroxycholecalciferol
  30. 30. METABOLIC FUNCTION• Kidney perform gluconiogenesis during periods of starvation.
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