Updated: 4/11/2019

The Nephron

Review Topic

Proximal Convoluted Tubule
  • The major function of the proximal convoluted tubule (PCT) is
    • isosmotic reabsorption of solutes and water which is imperative for maintaining the extracellular fluid (ECF)
      • this is accomplished by a number of co-transporters such as
        • Na+-glucose co-transporter (SGLT)
          • 100% of the filtered glucose is reabsorbed
        • Na+-amino acid co-transporter
          • 100% of the filtered amino acids are reabsorbed
        • Na+-phosphate co-transporter
        • Na+-H+ exchange
  • Note that the PCT can be divided into an early and late PCT
    • Na+ is reabsorbed in both portions of the PCT but via different mechanisms
      • early PCT
        • Na+ is primarily reabsorbed with HCO3-
          • 85% of the filtered HCO3- is reabsorbed
        • Na+ is also reabsorbed with glucose, amino acids, and other organic solutes (e.g., lactate and citrate)
      • late PCT
        • Na+ is primarily reabsorbed with Cl-
  • There are a number of hormones that act on the PCT and they include
    • parathyroid hormone (PTH)
      • inhibits the Na+-phosphate co-transporter 
    • angiotensin II
      • stimultes the Na+-H+ exchange
  • Medications that act on this portion of the nephrone includes
    • carbonic anhydrase inhibitors (e.g., acetazolamide)
    • osmotic diuretics (e.g., mannitol)
Thin Descending Loop of Henle
  • The thin descending loop of Henle is permeable to water but not ions
    • water moves out of the loop into the interstitium resulting in the tubular fluid becoming more concentrated (hyperosmotic)
Thick Ascending Loop of Henle
  • The major function of the thick ascending loop of Henle is to reabsorb NaCl without water
    • this is accomplished by the Na+-K+-2Cl cotransporter
      • loop diuretics (e.g., furosemide) act on these transporters
      • reabsorption of solutes without water makes the tubular fluid dilute (thus why this is the diluting segment)
  • There is also paracellular reabsorption of Ca2+ and Mg2+
    • this is driven by the lumen-positive potential difference generated by K+ backleak
Distal Convoluted Tubule and Collecting Duct
  • The distal convoluted tubule (DCT) can be divided into an early and late DCT
    • early DCT
      • reabsorbs 5% of the filtered sodium via a Na+-Cl cotransporter
        • this is the site of action of thiazide (e.g., hydrochlorothiazide and metolazone) diuretics
          • thiazides are organic acids that bind to the Cl site of the transporter
      • it is impermeable to water and thus dilutes the tubular fluid (thus called the cortical diluting segment)
    • late DCT and collecting duct
      • both of these segments of the nephron are anatomically and functionally similar
      • there are 2 major cell types
        • principal cells
          • Na+ is reabsorbed via epithelial Na+ channels (ENaC)
            • aldosterone increases Na reabsorption via increased protein synthesis of ENaC and Na+-K+-ATPase
              • aldosterone also stimulates K+ secretion via acting on K+ channels
            • K+-sparing diuretics (e.g., spironolactone, amiloride, and triamterene) impair Na+ reabsorption
              • spironolactone is an aldosterone antagonist
              • amiloride and triamterene act at the level of Na+ channels
          • anti-diuretic hormone (ADH) increases water permeability of the principal cells
            • this is accomplished by binding to V2 receptors and subsequently resulting in increased aquaporin-2 (AQP2) channel expression
          • there is a Ca2+-Na+ exchange in the basolateral membrane of the principle cell
            • PTH increases Ca2+ reabsorption by increase exchange activity
        • α-intercalated cells
          • secretion of H+ is accomplished by 2 active transport mechanisms
            • H+-ATPase
              • this enzyme is stimulated by aldosterone
            • H+-K+ ATPase
              • H+ is secreted in exchange for K+

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Questions (5)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2

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