Exchange and Transport of Gases

topicmedium9 MCQ

Partial pressure gradients, oxygen–haemoglobin dissociation curve and CO2 transport. (Biology › Breathing and Exchange of Gases, NEET UG syllabus.)

What is Exchange and Transport of Gases?

The pressure exerted by an individual gas in a mixture of gases, independent of other gases present.

Key formula / rule: Carbonic Anhydrase Reaction

Explain the mechanism of gas exchange at the alveolar and tissue levels based on partial pressure gradients.
Describe the different modes of transport for oxygen and carbon dioxide in the blood.
Interpret the oxygen-haemoglobin dissociation curve and identify factors that cause its shifts.
Understand and differentiate between the Bohr effect and the Haldane effect.

Confusing the direction of gas diffusion at the alveoli versus the tissues.

Term: Partial Pressure
Meaning: The pressure exerted by an individual gas in a mixture of gases, independent of other gases present.

Term: Oxyhaemoglobin
Meaning: Haemoglobin that is bound to oxygen, formed primarily in the lungs and transported to tissues.

Term: Carbamino-haemoglobin
Meaning: Haemoglobin that is bound to carbon dioxide, formed in tissues and transported to the lungs for exhalation.

Term: Oxygen-Haemoglobin Dissociation Curve
Meaning: A graphical representation showing the relationship between the partial pressure of oxygen (PO2) and the percentage saturation of haemoglobin with oxygen.

Term: Bohr Effect
Meaning: The phenomenon where an increase in carbon dioxide concentration and hydrogen ion concentration (decrease in pH) decreases the affinity of haemoglobin for oxygen, promoting oxygen release to tissues.

Term: Haldane Effect
Meaning: The phenomenon where the binding of oxygen to haemoglobin decreases its affinity for carbon dioxide and hydrogen ions, promoting the release of CO2 from the blood at the lungs.

Term: Chloride Shift (Hamburger phenomenon)
Meaning: The movement of chloride ions into red blood cells to maintain electrical neutrality when bicarbonate ions move out into the plasma, occurring during CO2 transport.

Term: Carbonic Anhydrase
Meaning: An enzyme found in red blood cells that rapidly catalyzes the reversible reaction between carbon dioxide and water to form carbonic acid, which then dissociates into bicarbonate and hydrogen ions.

Explain the mechanism of gas exchange at the alveolar and tissue levels based on partial pressure gradients.
Describe the different modes of transport for oxygen and carbon dioxide in the blood.
Interpret the oxygen-haemoglobin dissociation curve and identify factors that cause its shifts.
Understand and differentiate between the Bohr effect and the Haldane effect.
Explain the roles of carbonic anhydrase and the chloride shift in carbon dioxide transport.

Name: Carbonic Anhydrase Reaction
Note: This reversible reaction is rapidly catalyzed by the enzyme carbonic anhydrase within red blood cells, crucial for carbon dioxide transport.
Expression: CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-

Basic knowledge of the anatomy of the respiratory system (lungs, alveoli, capillaries).
Understanding of blood composition, particularly red blood cells and haemoglobin.
Fundamental concepts of diffusion and partial pressures of gases.

Confusing the direction of gas diffusion at the alveoli versus the tissues.
Incorrectly identifying the primary mode of CO2 transport (it's bicarbonate, not carbamino-haemoglobin).
Misinterpreting the factors that shift the oxygen-haemoglobin dissociation curve to the right (e.g., thinking increased pH shifts it right).
Forgetting the role of carbonic anhydrase in CO2 transport.
Not understanding the significance of the Bohr and Haldane effects in regulating gas exchange.

Which of the following conditions would lead to a left shift in the oxygen-haemoglobin dissociation curve and simultaneously enhance the release of CO2 from the blood into the alveoli?…
hard
The majority of carbon dioxide is transported in the blood in which form?…
easy
What is the approximate partial pressure of oxygen (pO2) in atmospheric air at sea level?…
easy