Updated: 2/13/2018

Carbon Dioxide Transport

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Forms of Carbon Dioxide (CO2) in the Blood
Dissolved CO2 Bicarbonate (HCO3-) Carbaminohemoglobin
  • ~5-10% of total CO2 content
  • 70% of total CO2 content
  • 20-25% of total CO2 content
  • CO2 bound to N-terminus amino group of hemoglobin (Hb)
  • Stabilizes taut form of Hb → right-shift of O2-Hb dissociation curve (Bohr effect) → favors O2  release
 
  • Transport of CO2 in blood (peripheral tissues → RBC → lungs)
    • peripheral tissues
      • metabolically active tissues produce CO2, which diffuses across the cell membrane and eventually into the RBC at the level of the capllaries
    • RBC
      • carbaminohemoglobin
        • ↑ pCO2 is produced in peripheral tissues
          • this facilitates CO2 binding to Hb, forming carbaminohemoglobin (CO2-Hb)
        • in turn, the Taut (T) state of Hb is stabilized
          • Bohr effect
            • enhanced release of O2 in the presence of low pH or increased pCO2
              • CO2-Hb → ↓ Hb affinity for O2 → ↑ O2 unloading into tissues
                • right shift in the hemoglobin-oxygen (Hb-O2) dissociation curve
              • H+ produced by converting CO2 + H2O to HCO3- + H+ via carbonic anhydrase (CA) which contributes in lowering the pH
              • protonated Hb stabilizes the T state, facilitating O2 release into tissues
                • (oxyhemoglobin) HbO2 + H+ ↔ HbH + O2 (deoxyhemoglobin)
          • Haldane effect
            • at low pO2 levels, the carrying capacity of CO2 increases
              • in other words, there is an increase affinity for CO2 when there is less O2 bound to hemoglobin
      • bicarbonate (HCO3-)
        • CA reversibly catalyzes the formation of HCO3- from the hydration of CO2
        • this reaction is reversible, thus CA is also involved in the dehydration of H2CO3
          • CO2 + H2O H2CO3 H+ + HCO3- 
            • the produced H+ remains in the RBC, where it is buffered by deoxyhemoglobin
            • deoxyhemoglobin is a better H+ buffer than oxyhemoglobin
        • the produced HCO3- is transported into the plasma via a chloride-bicarbonate (Cl-HCO3) exchanger (AE1 or band three protein)
          • this describes the chloride (or Hamburger) shift
    • lung
      • the reactions mentioned above occur in reverse inside the lung
        •  carbaminohemoglobin
          • Bohr effect
            • in lungs (low PCO2), CO2 dissociates from hemoglobin and stabilizes high O2 affinity Relaxed (R) state
              • hemoglobin-oxygen dissociation curve left shifts → ↑ hemoglobin affinity for O2 → ↑ O2 loading
          • Haldane effect
            • O2 loading → ↓ hemoglobin affinity for CO2 → ↑ CO2 unloading
        • bicarbonate
          • HCO3- is exchanged for Cl- (chloride shift) across RBC membranes
            • HCO3- enters RBCs
          • Haldane effect
            • O2 loading → ↓ hemoglobin affinity for H+→ ↑ H+ unloading
            • H+ + HCO3- → H2CO3 → CO2 + H2O
            • ↑ H+ drives equilibrium reactions to right (CO2 formation). 

 
  •  
    •  
      •  
        •  
          • aldane Effect – at low pO2 levels, the carrying capacity of CO2 increases. In other words, there is an increase affinity for CO2 when there is less O2 bound to hemoglobin.
 

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Questions (1)
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
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