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How does the kidney work? What controls the rate and concentration of urine?. Review nephron in kidney Steps in urine formation and concentration Glomerular filtration Reabsorption Tubular secretion. Nephron is functional unit of kidney. Over 1 million nephrons in human kidney

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how does the kidney work what controls the rate and concentration of urine
How does the kidney work?What controls the rate and concentration of urine?
  • Review nephron in kidney
  • Steps in urine formation and concentration
    • Glomerular filtration
    • Reabsorption
    • Tubular secretion
nephron is functional unit of kidney
Nephron is functional unit of kidney
  • Over 1 million nephrons in human kidney
  • Glomerulus is filtration site in cortex
  • Tubules form loop of Henle, extending a few centimeters into medulla
  • Reabsorption and secretion in tubules
filtration at glomerulus
Filtration at Glomerulus
  • Filtration membrane formed by podocyte cells lets all of plasma components of blood filter out of glomerular capillaries and into proximal convoluted tubule
what happens to filtrate to make urine
What happens to filtrate to make urine?
  • Filtrate contains all non-protein and non-cellular parts of blood
    • Water
    • Dissolved ions
    • Dissolved glucose
    • Amino acids
    • Nitrogenous wastes (nitrites, urea)
    • No proteins
    • No cells
  • Production of urine and thus control of blood chemistry involves three processes
    • Control over glomerular filtration rate (how fast is blood plasma filtering out of blood into tubules of kidney
    • Subsequent movement of fluid and dissolved substances out of filtrate and back into blood by reabsorption
    • Tubular secretion or further removal of certain substances from blood
what controls glomerular filtration rate
What controls glomerular filtration rate?
  • Locally, glomerular filtration depends on
    • Blood pressure in glomerular capillaries
    • “Osmotic pressure” or amount of dissolved substances in blood versus amount of dissolved substances in surrounding glomerular tissues
  • Local changes in kidney arterial pressure (by smooth muscles in walls of vessels vaso-dilating) is main control of glomerular filtration rate
but many external factors can also control glomerular filtration rate
But many external factors can also control glomerular filtration rate

How would caffeine affect glomerular filtration rate?

reabsorption or how to concentrate the filtrate into urine
Reabsorption, or how to concentrate the filtrate into urine

Countercurrent exchange mechanism creates sodium concentration gradient throughout kidney

reabsorption creates concentration gradient
Reabsorption creates concentration gradient
  • Reabsorption of sodium creates concentration gradient
  • Other substances, like glucose are also reabsorbed or pass back into blood across tubule membranes.
  • Urea, uric acid and creatinine, all nitrigenous waste productrs of the body’s metabolism, remain in filtrate
changes in permeability of collecting duct produce concentrated or non concentrated urine
Changes in permeability of collecting duct produce concentrated or non-concentrated urine
tubular secretion
Tubular secretion
  • Tubular secretion allows certain substances to be taken up directly from the blood into the tubules
  • This is especially important for
    • H+ ions (thus maintaining blood pH
    • K+ ions (thus maintaining potassium balance)
    • Certain drugs that are not filtered across glomerulus
final composition of urine depends on
Final composition of urine depends on
  • Glomerular filtration rate gives initial volume
  • Amount of reabsorption of water will affect final urine volume
  • Amount of reabsorption of sodium will affect final salinity or concentration of urine
  • Tubular secretion may add certain other substances to urine
signs of kidney problems
Signs of kidney problems
  • Presence of protein or cells in urine may indicate problems with glomerular filtration
  • Presence of glucose may indicate problems with tubular reabsorption or very high blood sugar levels that present full resabsorption