• Removes solutes and water from the tubular fluid and returns them to the blood;
  • It reclaims much of the water, ions, and nearly all of the nutrients that are filtered.
  • Moves solutes from the blood and nephron tubule cells into the tubular fluid;
  • Secretion is important for removal of substances that aren’t filtered (such as drugs and metabolites) and for fine-tuning the final urine composition.
  • Vasculature:– Efferent arteriole leaves glomerulus, gives rise to peritubular capillaries.– Peritubular capillaries give rise to vasa recta of juxtamedullary nephrons.

    – Vasa recta drains deoxygenated blood into the interlobular vien.

  • Proximal tubule:
    Reabsorbs:WaterSodiumChloridePotassiumCalciumPhosphateUreaBicarbonateGlucose, amino acids, and other nutrients.

    Secretes:

    HydrogenPAH (para-aminohippurate)Ammonium ionsCertain drugs

    Organic acids and bases (such as creatinine)

  • Nephron loop:Concentrates or dilutes urine.

    Thin limb:

    Water is reabsorbed.
    Thick ascending limb:SodiumPotassiumChlorideCalciumBicarbonateMagnesium

    (no water reabsorption)

  • Distal tubuleReabsorption and secretion are hormonally regulated to fine-tune tubular fluid, to maintain ECF volume and osmolarity homeostasis.

    Early distal tubule, aka, diluting segment:

    SodiumChloridePotassiumCalcium(no water reabsorption).

    Late distal tubule:

    Reabsorbs:WaterSodiumChlorideBicarbonateUrea.

    Secretes:

    Potassium.

  • Collecting duct:
    Secretes OR ReabsorbsPotassiumHydrogenBicarbonate

    Ammonium ions