Question

During oxygen transport the oxyhaemoglobin at the tissue level liberates oxygen to the cells because in tissue (a) \(\mathrm{O}_{2}\) concentration is high and \(\mathrm{CO}_{2}\) is low. (b) \(\mathrm{O}_{2}\) concentration is low and \(\mathrm{CO}_{2}\) is also low. (c) \(\mathrm{O}_{2}\) tension is high and \(\mathrm{CO}_{2}\) tension is low. (d) \(\mathrm{O}_{2}\) tension is low and \(\mathrm{CO}_{2}\) tension is high.

Short answer

The correct answer is (d) \(\mathrm{O}_{2}\) tension is low and \(\mathrm{CO}_{2}\) tension is high.

Step-by-step solution

Understanding the Concepts Involved

Before understanding why this occurs, it is important to understand what is meant by 'oxygen tension' and 'oxygen concentration'. The term 'oxygen tension' refers to the partial pressure of oxygen, while 'oxygen concentration' refers to the amount of oxygen present. The same applies to carbon dioxide.

Explanation of the Oxygen and Carbon Dioxide Tension/Concentration in the Tissues

The partial pressure (or tension) of oxygen in the tissues is low because the oxygen is being used up by the cells for metabolic processes. This also leads to a high partial pressure (or tension) of carbon dioxide in the tissues because carbon dioxide is a waste product of these metabolic processes.

Explanation of the Oxyhaemoglobin Liberation of Oxygen

Oxyhaemoglobin is a compound formed in the red blood cells when oxygen binds to haemoglobin. When the oxygen tension is low in the tissues and the carbon dioxide tension is high, oxyhaemoglobin releases the oxygen it is carrying to be used by the cells. This is due to the Haldane effect, which states that the lower the partial pressure of oxygen (or the higher the partial pressure of carbon dioxide), the more oxygen haemoglobin will deliver to the tissues.

Match the Explanation to the Answer Choices

Given the explanation, the process is that the oxygen tension is low and the carbon dioxide tension is high in the tissues. When these conditions are met, the cells in the tissues receive oxygen from the oxyhaemoglobin. Therefore, the correct answer is (d) \(\mathrm{O}_{2}\) tension is low and \(\mathrm{CO}_{2}\) tension is high.

Key concepts

Oxyhaemoglobin

Oxyhaemoglobin is a critical component in the process of transporting oxygen throughout the body. It forms when oxygen molecules bind to hemoglobin, a protein found in red blood cells. This combination enables the blood to carry oxygen from the lungs, where there is a high concentration of oxygen, to various tissues in the body where it is needed.

Once oxyhaemoglobin reaches tissues where the oxygen concentration or tension is low, it releases the oxygen. This release is essential for providing cells with the oxygen necessary for metabolism and energy production. In essence, oxyhaemoglobin acts as an oxygen ferry, loading up oxygen in high-oxygen areas like the lungs and unloading it where it's low, such as in active tissues.

• Enables efficient oxygen transport
• Binds and releases oxygen depending on tension
• Facilitated by hemoglobin in red blood cells

Oxygen Tension

Oxygen tension, also known as partial pressure of oxygen, is a pivotal factor in oxygen transportation. It refers to the pressure exerted by oxygen molecules in a mixture of gases or in a liquid, like blood. This pressure is a measure of how much oxygen is available to be transported and used by tissues throughout the body.

In tissues where oxygen tension is low, mainly because oxygen is continually being consumed for cellular respiration and other metabolic activities, there is a signal for oxyhaemoglobin to release its oxygen. Understanding oxygen tension helps clarify why oxygen delivery increases in areas of high demand, ensuring that tissues remain well-supplied even during intense activities or when oxygen levels drop.

• Indicates available oxygen pressure
• Guides oxygen delivery based on tissue demands
• Prompts oxygen release from oxyhaemoglobin

Carbon Dioxide Tension

Carbon dioxide tension, akin to oxygen tension, relates to the partial pressure of carbon dioxide in blood. It reflects the concentration of carbon dioxide as a result of cellular metabolism, acting as a waste indicator.

High carbon dioxide tension in tissues signals that there is an accumulation of this byproduct due to metabolism. The increased CO2 levels contribute to lowering the blood's pH, encouraging oxyhaemoglobin to release more oxygen—a vital process for maintaining efficient metabolic actions. Thus, carbon dioxide tension is crucial for the body's regulatory systems that maintain proper oxygen supply and carbon dioxide removal.

• Reflects metabolic activity level
• Higher levels correlate with more carbon dioxide production
• Triggers mechanisms to release oxygen from oxyhaemoglobin

Haldane Effect

The Haldane effect is a physiological phenomenon that describes how the oxygenation of blood influences its capacity to carry carbon dioxide. Specifically, it states that deoxygenated blood can transport more CO2 than oxygenated blood.

In practical terms, when oxyhaemoglobin releases oxygen because of low oxygen tension, it increases its ability to pick up and carry more CO2 from tissues back to the lungs. The Haldane effect complements other gas-exchange processes, such as the Bohr effect, and plays a crucial role in maintaining the acid-base balance in the body. It highlights the dynamic nature of respiratory exchanges and the body's adaptability to changing metabolic demands.

• Enhances CO2 transport back to lungs
• Improves venous blood's capacity for CO2 at low oxygen tension
• Integral for maintaining balance during gas exchange