41.Transport of carbon dioxide in the blood. Dissociation curve of carbaminehemoglobin.
Covers the three ways carbon dioxide travels in the blood, with approximate shares: bicarbonate, dissolved gas and carbaminohemoglobin. Walks through bicarbonate formation in systemic capillaries, including the chloride shift, then its reversal in the lungs. Also explains carbaminohemoglobin formation, the Bohr and Haldane effects and how they interact, and closes with the carbaminohemoglobin dissociation curve. Includes recap questions and several figures.
Topic 41 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 3 sections, about 512 words (4 min of reading), with 13 flashcards.
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Transport of carbon dioxide in the blood. Dissociation curve of carbaminehemoglobin.
Forms of CO2 Transport in the Blood:
Recap Questions
Forms of CO2 Transport in the Blood:
Bicarbonate (HCO3-): This is the most abundant form, accounting for about 85-90% of CO2 transport. It also functions as a pH buffer in the blood.
Dissolved CO2: About 5-7% of CO2 is transported in this form. The concentration of dissolved CO2 is determined by Henry's Law, which states that the concentration of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid.
Carbaminohemoglobin (CO2Hb): This form involves CO2 bound to hemoglobin, accounting for approximately 3% of CO2 transport. Importantly, CO2 binds to a different site on hemoglobin than oxygen.
Bicarbonate Formation in Systemic Capillaries:
1. CO2 is produced in tissues during aerobic metabolism.
2. CO2 diffuses from tissues into systemic capillaries and then into red blood cells.
3. Inside red blood cells, the enzyme carbonic anhydrase catalyzes the reaction of CO2 with H2O to form carbonic acid (H2CO3).
4. H2CO3 rapidly dissociates into H+ and HCO3-.
5. H+ ions are buffered by deoxyhemoglobin (HHb) inside the red blood cells. This buffering helps to prevent significant changes in blood pH.
6. HCO3- is transported out of the red blood cell into the plasma in exchange for Cl- (chloride shift or Hamburger's shift). This exchange helps to maintain electrical neutrality.
Bicarbonate in the Lungs:
The processes that occur in the systemic capillaries are reversed in the lungs.
H+ is released from deoxyhemoglobin.
HCO3- enters red blood cells in exchange for Cl-.
H+ and HCO3- combine to form H2CO3.
Carbonic anhydrase in the red blood cells catalyzes the breakdown of H2CO3 into CO2 and H2O.
CO2 and H2O are then expired from the lungs.
Carbaminohemoglobin Formation:
CO2 binds to terminal amino groups on the globin chains of hemoglobin, forming carbaminohemoglobin.
This binding is reversible, and the amount of CO2 bound to hemoglobin is influenced by the PCO2.
Bohr and Haldane Effects:
Bohr Effect: The binding of CO2 to hemoglobin decreases hemoglobin's affinity for oxygen. This effect is enhanced by lower pH and increased temperature, conditions found in metabolically active tissues. The Bohr effect facilitates the release of oxygen to tissues where it is needed most.
Haldane Effect: The binding of oxygen to hemoglobin decreases hemoglobin's affinity for CO2. This effect promotes the uptake of CO2 from tissues into the blood.
Significance: These reciprocal effects, the Bohr and Haldane effects, work together to optimize gas exchange between the lungs and tissues.
Carbaminohemoglobin Dissociation Curve:
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