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Questions and Answers
What is the primary mechanism by which most carbon dioxide is transported in the blood?
What is the primary mechanism by which most carbon dioxide is transported in the blood?
- Dissolved in plasma
- Bound to hemoglobin
- Converted to glucose
- As bicarbonate (correct)
What happens to dissolved carbon dioxide when blood reaches the pulmonary capillaries?
What happens to dissolved carbon dioxide when blood reaches the pulmonary capillaries?
- It is converted into bicarbonate
- It is retained in the blood
- It binds to red blood cells
- It diffuses into alveoli to be exhaled (correct)
Which enzyme facilitates the conversion of carbon dioxide and water into carbonic acid?
Which enzyme facilitates the conversion of carbon dioxide and water into carbonic acid?
- Carbonic anhydrase (correct)
- Carbonic synthetase
- Hemoglobinase
- Bicarbonate dehydratase
What is the role of the chloride shift in erythrocytes?
What is the role of the chloride shift in erythrocytes?
During the reaction that produces bicarbonate in erythrocytes, what is formed alongside bicarbonate (HCO3–)?
During the reaction that produces bicarbonate in erythrocytes, what is formed alongside bicarbonate (HCO3–)?
How much carbon dioxide typically dissolves in blood plasma compared to the total amount transported?
How much carbon dioxide typically dissolves in blood plasma compared to the total amount transported?
What is the main effect of the concentration gradient of bicarbonate in erythrocytes?
What is the main effect of the concentration gradient of bicarbonate in erythrocytes?
What is produced at the pulmonary capillaries from the chemical reaction involving bicarbonate?
What is produced at the pulmonary capillaries from the chemical reaction involving bicarbonate?
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Study Notes
Carbon Dioxide Transport Mechanisms
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Blood plasma: About 7-10% of carbon dioxide dissolves directly into the blood plasma. This dissolved carbon dioxide then travels to the lungs and diffuses into the alveoli for exhalation.
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Bicarbonate (HCO3-): This is the primary mechanism, accounting for about 70% of carbon dioxide transport.
- Formation: In erythrocytes, carbon dioxide reacts with water in the presence of the enzyme carbonic anhydrase (CA) to form carbonic acid (H2CO3). Carbonic acid then dissociates into bicarbonate (HCO3-) and hydrogen (H+) ions.
- Chloride Shift: As bicarbonate accumulates in erythrocytes, it moves out into the plasma in exchange for chloride ions (Cl-) to maintain electrical balance.
- Reversal at Lungs: At the pulmonary capillaries, the reaction reverses, converting bicarbonate back into carbon dioxide and water, which is exhaled.
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Carbaminohemoglobin: Around 20% of carbon dioxide binds to hemoglobin, forming carbaminohemoglobin. This binding occurs on the globin portion of hemoglobin, not to the iron atom where oxygen binds.
- Color: Deoxygenated blood, containing carbaminohemoglobin, has a darker maroon color due to the bluish-purple tone of hemoglobin when not carrying oxygen.
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