Updated: 9/21/2017

The Nephron

Topic
Review Topic
0
0
Questions
4
0
0
Evidence
2
0
0
Videos
1
Overview

 
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
    • because water is being reabsorbed in this portion of the nephron, the tubular fluid becomes more 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+
 

Please rate topic.

Average 4.4 of 9 Ratings

Thank you for rating! Please vote below and help us build the most advanced adaptive learning platform in medicine

The complexity of this topic is appropriate for?
How important is this topic for board examinations?
How important is this topic for clinical practice?
Questions (4)
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
Volume  
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
Urine  
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
Calculator

Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
ARTICLES (2)
VIDEOS (1)
Topic COMMENTS (9)
Private Note