Question

During one circuit of blood from lungs to the tissues and back through circulatory system, the percentage of haemoglobin giving up its oxygen to tissues is (a) \(25 \%\) (b) \(50 \%\) (c) \(75 \%\) (d) \(100 \%\)

Short answer

The correct answer is (a) 25%

Step-by-step solution

Evaluate the Question

We need to understand what is being asked. Haemoglobin is a protein in red blood cells that carries oxygen. During one circuit of blood from lungs to tissues and back, we need to consider the percentage of haemoglobin that gives up its oxygen to the tissues.

Utilize Biological Knowledge

Oxygen is transported in the blood in two ways: A small amount of oxygen (1.5 percent) is carried in the plasma as a dissolved gas. Most oxygen (98.5 percent) carried in the blood is bound to the protein haemoglobin in red blood cells. A fully saturated oxyhemoglobin (HbO2) has four oxygen molecules attached. However, under normal physiologic conditions, only one-quarter of the oxygen molecules are unloaded (25 %). Thus, the haemoglobin molecule remains 75% saturated with oxygen.

Choose the Correct Answer

Based on the information provided in step 2, the correct answer should be (a) 25%

Key concepts

Oxygen Transport

Oxygen transport is crucial for the survival of all tissues and organs in the body. Our bodies rely on efficient oxygen delivery systems to meet their metabolic needs. Oxygen is picked up from the lungs and transported throughout the circulatory system by red blood cells.
The key player in this process is haemoglobin, a protein that binds oxygen molecules in the red blood cells. Each haemoglobin molecule can carry up to four oxygen molecules. The process of oxygen loading occurs in the lungs, where the concentration of oxygen is high.

• In this high-oxygen environment, haemoglobin becomes saturated with oxygen, forming oxyhaemoglobin (HbO2).
• As the blood travels to tissues, the oxygen pressure decreases, facilitating the release of oxygen molecules from haemoglobin.

This precise release of oxygen ensures that tissues receive the amount they need for energy production. Efficient oxygen transport is, therefore, vital for maintaining cellular respiration and energy production.

Haemoglobin Saturation

Haemoglobin saturation refers to the extent to which haemoglobin in the blood is loaded with oxygen. It reflects the proportion of haemoglobin molecules that are bound to oxygen compared to those that are not. Haemoglobin saturation is a vital measure of the body's oxygen-carrying capacity.
In fully saturated conditions, each haemoglobin molecule in red blood cells is bound to four oxygen molecules. However, as blood travels from lungs through tissues:

• The haemoglobin delivers some of its bound oxygen molecules to supply tissues.
• Under typical physiological situations, approximately 25% of the oxygen is released.
• The remaining 75% stays bound, maintaining a reserve of oxygen.

Monitoring haemoglobin saturation levels can be diagnostic of certain respiratory conditions. For instance, low saturation may suggest issues in oxygen uptake or delivery.

Red Blood Cells

Red blood cells (RBCs) are crucial components of our blood, primarily responsible for oxygen transport. They achieve this through their unique shape and function:

• The biconcave disk shape increases the surface area for oxygen binding.
• This shape also allows RBCs to easily navigate through narrow blood vessels.

Inside these cells, haemoglobin molecules bind oxygen in the lungs.
Completed cells do not have a nucleus or organelles, optimizing space for haemoglobin. As roughly 98.5% of the oxygen in our blood binds to haemoglobin, red blood cells play an indispensable role in the body's oxygen supply system.
They not only deliver oxygen to tissues but also return carbon dioxide, a waste product of metabolism, back to the lungs for exhalation. Hence, red blood cells form a critical part of our respiratory and circulatory systems.