Transport of Carbon Dioxide – Lecture Review

A set of question-and-answer flashcards covering the key steps, percentages, chemical reactions, and buffering processes involved in carbon dioxide transport from body tissues to the lungs.

In how many forms is carbon dioxide transported from the tissues to the lungs, and what are they?

Three forms: (1) dissolved in blood plasma, (2) bound to hemoglobin, and (3) as bicarbonate ion in the plasma.

Approximately what percentage of total CO2 is transported dissolved directly in blood plasma?

About 7 % of the total carbon dioxide.

After leaving the tissues, what percentage of CO2 enters red blood cells?

Roughly 93 % of the CO2 diffuses into red blood cells.

What percentage of the CO2 that enters a red blood cell binds to hemoglobin?

Approximately 23 % of the CO2 inside the red blood cell binds to hemoglobin.

When CO2 binds to hemoglobin, does it attach to the heme iron site used by oxygen?

No. CO2 attaches to a separate site on the globin portion of hemoglobin, not the heme iron site used by O2.

What reaction occurs between CO2 and water inside red blood cells?

CO2 reacts with H2O to form carbonic acid (H2CO3), which immediately dissociates into H+ and HCO3⁻ (bicarbonate).

What two ions are produced when carbonic acid dissociates in red blood cells?

A hydrogen ion (H⁺) and a bicarbonate ion (HCO3⁻).

How does hemoglobin function as a chemical buffer inside red blood cells?

It binds the free hydrogen ions produced from carbonic acid dissociation, reducing changes in pH.

What is the chloride shift?

The process in which bicarbonate leaves the RBC in exchange for chloride ions moving into the cell to maintain electrical neutrality.

Why is the influx of chloride ions necessary during the chloride shift?

To balance the positive charge created by bound H⁺ ions and maintain the cell’s electrical neutrality.

What happens to the CO2 dissolved in plasma when blood reaches the lungs?

It diffuses down its partial pressure gradient into the alveoli and is exhaled first.

Why does CO2 unbind from hemoglobin in the pulmonary capillaries?

The lower partial pressure of CO2 in the plasma and alveoli decreases hemoglobin’s affinity for CO2, causing it to diffuse out and be exhaled.

What is the reverse chloride shift?

At the lungs, bicarbonate re-enters the RBC in exchange for chloride leaving, allowing bicarbonate to recombine with H⁺.

What final reaction inside the RBC converts bicarbonate and hydrogen ion back to CO2 for exhalation?

HCO3⁻ + H⁺ → H2CO3 → H2O + CO2, and the CO2 then diffuses into the alveoli to be exhaled.

Name the three major chemical buffers mentioned in the lecture.

Phosphate ions, hemoglobin, and bicarbonate ions.

Why is CO2 considered more soluble in blood plasma than oxygen?

CO2 has a higher solubility coefficient in plasma, allowing it to dissolve more readily than O2 despite both being nonpolar gases.