How is carbon dioxide transported in the blood?

In this Medmastery Clinical Guide article, learn how carbon dioxide is transported through the blood in its three primary forms. [127]
Last update4th Dec 2020

Carbon dioxide transport in blood occurs primarily in three forms: dissolved (about 5%); as the bicarbonate anion (about 90%); and as carbamino compounds (about 5%).

Bicarbonate

Bicarbonate is created by the reaction of carbon dioxide with water to form carbonic acid, which dissociates into hydrogen and bicarbonate. The reaction of carbon dioxide and water in red blood cells is catalyzed by carbonic anhydrase.

Figure 1. Most of carbon dioxide is transported in the blood as bicarbonate anions, which are formed from the catalysis of carbon dioxide and water by carbonic anhydrase to form carbonic acid.

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Carbamino compounds

Carbamino compounds are formed via the reaction of carbon dioxide with the terminal amino groups of blood proteins, including hemoglobin.

Figure 2. About 5% of carbon dioxide is transported in the blood as carbamino compounds, which are formed from the reaction of carbon dioxide with terminal amino groups of blood proteins.

The carbon dioxide-hemoglobin dissociation curve

The various forms of carbon dioxide in the blood create an equilibrium between dissolved carbon dioxide and chemically-bound carbon dioxide, including that bound to hemoglobin.

Unlike the sigmoid-shaped oxyhemoglobin dissociation curve, the carbon dioxide-hemoglobin dissociation curve is more linear. The amount of carbon dioxide in the blood at any given level of carbon dioxide tension depends on the degree of hemoglobin oxygenation—constituting the Haldane effect. As oxygen is unloaded from hemoglobin in peripheral tissues, the hemoglobin more avidly binds carbon dioxide.

Figure 3. The carbon dioxide-hemoglobin dissociation curve describes the Haldane effect. The amount of carbon dioxide (CO2) in the blood at any given level of carbon dioxide tension (PCO2) is dependent on the amount of hemoglobin oxygenation. More oxygen unloaded into the peripheral tissues means that the hemoglobin will bind more avidly to CO2.

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Recommended reading

  • Grippi, MA. 1995. “Gas exchange in the lung”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Grippi 1995, 137–149)
  • Grippi, MA. 1995. “Clinical presentations: gas exchange and transport”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Grippi 1995, 171–176)
  • Grippi, MA and Tino, G. 2015. “Pulmonary function testing”. In: Fishman's Pulmonary Diseases and Disorders, edited by MA, Grippi (editor-in-chief), JA, Elias, JA, Fishman, RM, Kotloff, AI, Pack, RM, Senior (editors). 5th edition. New York: McGraw-Hill Education. (Grippi and Tino 2015, 502–536)
  • Tino, G and Grippi, MA. 1995. “Gas transport to and from peripheral tissues”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Tino and Grippi 1995, 151–170)
  • Wagner, PD. 2015. The physiologic basis of pulmonary gas exchange: implications for clinical interpretation of arterial blood gases. Eur Respir J45: 227–243. PMID: 25323225

About the author

Michael A. Grippi, MD
Vice Chairman, Department of Medicine | Pulmonary, Allergy, and Critical Care Division, Perelman School of Medicine, University of Pennsylvania, USA.
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