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Production of urine by the mammalian kidney

Production of urine by the mammalian kidney. Overview of the urinary system What urine is How it is formed Control of urine formation. nephron. Blood enters and leaves here. Urine leaves here. Why do kidneys produce urine? To regulate blood composition and volume.

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Production of urine by the mammalian kidney

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  1. Production of urine by the mammalian kidney Overview of the urinary system What urine is How it is formed Control of urine formation

  2. nephron Blood enters and leaves here Urine leaves here

  3. Why do kidneys produce urine?To regulate blood composition and volume • Disposal of metabolic waste • Urea, creatinine, ammonium, uric acid • Maintenance of water-salt balance • Sodium, potassium, bicarbonate, etc. • Maintenance of acid-base balance • Blood pH must be approx. 7.4

  4. Urine is formed in nephrons About 1 million nephrons per kidney Each DAY: Approx 1000-2000 liters of blood flow though kidney Approx 180 L of filtrate processed Approx 1.2 L of urine actually excreted the rest is reabsorbed HOW?

  5. Steps in urine formation Filtration- water and small molecules removed from blood Reabsorption- water and essential molecules returned to blood Secretion- wastes and excess salts added from body fluids to filtrate (urine)

  6. Secretion, reabsorption (loop of Henle)

  7. Control of filtration rate Hydrostatic pressure of blood forces it out of capillary and into glomerulus Osmotic pressure of plasma in glomerulus and hydrostatic pressure in glomerulus resists it (Net filtration pressure: the difference)

  8. Filtration rate is affected by: Constriction of afferent or efferent arteriole Colloid pressure (of blood or filtrate) Generally about 180L of urine is formed during the day Kidney damage can occur if blood pressure drops too low

  9. Control of urine production High solute concentration in tissue- helps draw water out of tissue Hormones- regulate water reabsorption, ion secretion or reabsorption affect urine composition and volume Hormones that control blood pressure act on kidney- to retain or lose water

  10. Regulation of filtration rate Rises when body fluid levels are high; decreases when fluids must be conserved Sympathetic nervous system- conserve fluid by constricting afferent arterioles Renin-angiotensin system ANP

  11. Reabsorption All small molecules enter tubule; most are put back Tends to be localized to certain parts of the nephron- differences in permeability Most reabsorption takes place in proximal convoluted tubule amino acids glucose various ions; vitamins; acids

  12. Efficiency of urine formation Component Urine Blood plasma Sodium (mEq/l) 147.5 138.4 Potassium 47.5 4.4 Glucose (mg/dL) 0.009 90 Proteins 0.000 7500 Urea (mg/dL) 1800.00 305 Ammonia 60.00 0.2

  13. Regulation of urine concentration and volume Aldosterone- additional reabsorption of sodium (and therefore water) in distal tubule secretion of potassium ADH acts on distal convoluted tubule and collecting duct, to reabsorb water (if body fluid levels are high, ADH secretion drops)

  14. Tubular secretion Substances are removed from capillaries to renal tubule Waste products Excess ions

  15. Micturition (urination) Bladder is distended as it fills; stretch receptors trigger the micturition reflex Parasympathetic nerves stimulates the detrusor muscle to contract External urethral sphincter is under voluntary control; neurons originate in brain stem and cerebral cortex

  16. Kidney failure is fatal if untreated Dialysis Transplants first successful organ transplant in humans: kidney, 1954 What about transplants?

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