Carbon Dioxide Transport Quiz

Carbon Dioxide Transport

• At rest, the body consumes 250 mL of oxygen and produces 200 mL of carbon dioxide per minute. The ratio of carbon dioxide produced to oxygen consumed is called the respiratory quotient (RQ), which in this case is 0.8 (200/250).
• Carbon dioxide is transported from the tissues to the lungs in six different ways: in the red blood cells (RBCs) and in the plasma.
• Plasma transport:
  • Carbamino compound: 1% of CO2 combines with free amino groups in the plasma.
  • Bicarbonate: 5% of CO2 reacts with water to form carbonic acid (H2CO3), which quickly dissociates into bicarbonate (HCO3-) and hydrogen ions (H+).
  • Dissolved CO2: 5% of total dissolved CO2 in the plasma is released to the lungs. This is the portion measured in venous blood.
• Red blood cell transport:
  • Dissolved CO2: 5% of CO2 dissolves in the intracellular fluid of the RBC.
  • CarbaminoHb: 21% of CO2 combines with hemoglobin to form carbaminohemoglobin (HbCO2). The oxygen released from this reaction is available for tissue metabolism.
  • Bicarbonate: 63% of CO2 is transported to the lungs in the form of bicarbonate. The reaction is enhanced by carbonic anhydrase in the RBCs. The formation of bicarbonate causes the RBCs to become saturated with it, leading to excess bicarbonate diffusing out to the plasma, where it combines with sodium (NaCl) and is transported as sodium bicarbonate (NaHCO3) in the venous blood.
• Chloride shift: To maintain neutrality, chloride ions (Cl-) move into the RBCs as bicarbonate ions move out. This is known as the chloride shift or Hamburger phenomenon.
• The ratio of bicarbonate to carbonic acid (HCO3-/H2CO3) in the plasma is 20:1, which helps maintain a pH between 7.35 to 7.45.

Carbon Dioxide Dissociation Curve

• The relationship between partial pressure of carbon dioxide (PCO2) and the amount of carbon dioxide content (CCO2) is almost linear.
• An increase in PCO2 from 40 to 46 mmHg results in a 5% increase in CCO2.
• The same change in partial pressure of oxygen (PO2) produces only a 2% change in the amount of oxygen transported in the blood.
• Haldane effect: Deoxygenated blood enhances CO2 loading by hemoglobin and vice versa. This means that when oxygen is released from hemoglobin, the hemoglobin's affinity for carbon dioxide increases. Conversely, when carbon dioxide is released from hemoglobin, the hemoglobin's affinity for oxygen increases.

Acid-Base Balance

• Electrolytes: Charged ions, such as sodium (Na+), potassium (K+), chloride (Cl-), and bicarbonate (HCO3-).
• Buffer: A substance that neutralizes acids and bases without causing significant changes in pH.
• Acid: Substance that donates hydrogen ions (H+).
• Base: Substance that accepts hydrogen ions (H+).
• pH scale: A quantitative measurement of the hydrogen ion concentration ([H+]) in a solution. The pH scale ranges from 0 to 14, with 7 being neutral. A lower pH indicates higher acidity, while a higher pH indicates higher alkalinity.
• Equation for pH: pH = -log10[H+].

Carbon Dioxide Transport

• At rest, tissue cells consume 250mL of oxygen and produce 200mL of carbon dioxide per minute.
• The respiratory quotient (RQ) is the ratio of carbon dioxide produced to oxygen consumed, which is 0.8 at rest.
• Carbon dioxide is transported from the tissues in six different ways: dissolved in plasma, as carbamino compounds, as bicarbonate, dissolved in red blood cells, as carbaminohemoglobin, and as bicarbonate.

CO2 in Plasma

• 1% of carbon dioxide combines with free amino groups to form carbamino compounds.
• 5% of carbon dioxide ionizes as bicarbonate. Carbon dioxide initially combines with water (hydrolysis) to form carbonic acid (H2CO3) which rapidly converts into HCO3- and H+ ions.
• 5% of total dissolved CO2 is released to the lungs, which is the portion assessed in venous blood.

CO2 in Red Blood Cells

• 5% of CO2 is dissolved in the intracellular fluid of red blood cells.
• 21% of CO2 combines with hemoglobin to form carbaminohemoglobin. The oxygen released from this reaction is available for tissue metabolism.
• 63% of CO2 is transported to the lungs in the form of bicarbonate.
• The same reaction in the plasma is enhanced by carbonic anhydrase.
• The rapid hydrolysis causes red blood cells to become saturated with HCO3-, so excess HCO3- diffuses out to the plasma, combines with Na (NaCl), and is transported as NaHCO3 in the venous blood.

Chloride Shift

• As bicarbonate moves out of the red blood cell, chloride moves into the red blood cell to maintain neutrality. This is known as the chloride shift or Hamburger phenomenon.

CO2 Elimination at the Lungs

• In the lungs, the process reverses. CO2 diffuses from the blood into the alveoli and is exhaled.

CO2 Dissociation Curve

• The CO2 dissociation curve is almost linear.
• There is a strong relationship between partial pressure of carbon dioxide (PCO2) and the amount of CO2 content.
• A PCO2 change from 40 to 46mmHg results in a 5 volume % increase in CO2 content.
• The same PO2 change results in a 2 volume % change.
• The Haldane effect states that deoxygenated blood enhances CO2 loading by hemoglobin, and vice versa.

Acid-Base Balance

• Electrolytes are charged ions.
• A buffer neutralizes acids and bases without causing changes in pH.
• An acid is a substance that donates H+.
• A base is a substance that accepts H+.

pH Scale

• The pH scale is a quantitative measurement of hydrogen ion concentration ([H+]).
• pH = -log10[H+].