Reabsorption of Glucose

Glucose and amino acids in the blood are easily filtered by the glomeruli into the renal tubules. These molecules, however, are usually not present in the urine. It can therefore be concluded that filtered glucose and amino acids are normally completely reabsorbed by the nephrons. This occurs in the proximal tubule by secondary active transport, which is mediated by membrane carriers that cotransport glucose and Na+ (see fig. 17.13), or amino acids and Na+.

Carrier-mediated transport displays the property of saturation. This means that when the transported molecule (such as glucose) is present in sufficiently high concentrations, all of the carriers become occupied and the transport rate reaches a maximal value. The concentration of transported molecules needed to just saturate the carriers and achieve the maximal transport rate is called the transport maximum (abbreviated Tm).

Para Aminohippuric Acid Pah

Figure 17.23 The renal clearance of PAH. Some of the para-aminohippuric acid (PAH) in glomerular blood (a) is filtered into the glomerular (Bowman's) capsules (b). The PAH present in the unfiltered blood is secreted from the peritubular capillaries into the nephron (c), so that all of the blood leaving the kidneys is free of PAH (d). The clearance of PAH therefore equals the total renal blood flow.

Figure 17.23 The renal clearance of PAH. Some of the para-aminohippuric acid (PAH) in glomerular blood (a) is filtered into the glomerular (Bowman's) capsules (b). The PAH present in the unfiltered blood is secreted from the peritubular capillaries into the nephron (c), so that all of the blood leaving the kidneys is free of PAH (d). The clearance of PAH therefore equals the total renal blood flow.

The carriers for glucose and amino acids in the renal tubules are not normally saturated and so are able to remove the filtered molecules completely. The Tm for glucose, for example, averages 375 mg per minute, which is well above the normal rate at which glucose is delivered to the tubules. The rate of glucose delivery can be calculated by multiplying the plasma glucose concentration (about 1 mg per ml in the fasting state) by the GFR (about 125 ml per minute). Approximately 125 mg per minute are thus delivered to the tubules, whereas a rate of 375 mg per minute is required to reach saturation.

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Essentials of Human Physiology

Essentials of Human Physiology

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Responses

  • teppo
    Are amino acid completely reabsorbed by nephron?
    8 years ago
  • JULIA MCINTYRE
    What is the renal clearance of glucose per minute?
    8 years ago
  • tuulia
    When does glucose transport reach saturation?
    8 years ago
  • semira
    Why all glucose are reabsorbed?
    7 years ago
  • uta
    What are reabsorption capillaries in the kidney?
    7 years ago
  • Donald
    Where does glocose transport reach saturation?
    7 years ago
  • henrik haapasalo
    Why are glucose and amino acids reabsorbed in the nephron?
    7 years ago
  • Leonie
    Where is glucose reabsorption in a nephron?
    7 years ago
  • Elias
    Where does glucose reabsorption occur?
    7 years ago
  • Maura
    Why glucose reabsorption equal 0?
    6 years ago
  • max
    Where is glucose reabsorbed into the tubules of the nephrons?
    6 years ago
  • Bernd
    How is glucose reabsorbed in the nephron of humans?
    5 years ago
  • aurora uusitalo
    What is the maximum rate of glucose reabsorption by the nephron?
    2 years ago
  • Henna
    What is the maximum rate of glucose reabsoption by the nephron?
    1 year ago

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