Question

Blood entering the lung is rich in (a) Oxygen (b) Carbon dioxide (c) Urea (d) More RBCs

Short answer

The correct answer is (b) Carbon dioxide.

Step-by-step solution

Review of blood circulation and its components

Blood circulation starts with the right part of the heart pumping deoxygenated blood to the lungs via pulmonary arteries. In the lungs, this deoxygenated blood gets oxygen-rich and then returns to the left part of the heart.

Understanding blood composition

Blood is comprised of several components: red and white blood cells, plasma, and platelets. The red blood cells (RBCs), or erythrocytes, are responsible for carrying oxygen and carbon dioxide. Urea is a waste product, largely removed by the kidneys, and is not particularly associated with lung function.

Analyze the options

Given the choices, we can eliminate (a) Oxygen as the blood entering the lungs is deoxygenated and is yet to get oxygenated. Allow us to eliminate (c) Urea and (d) More RBCs as these are not components that get added or enriched in the blood when it enters the lungs. Hence, we can finalize the answer to be (b) Carbon dioxide as it is the deoxygenated, or CO2-rich, blood that the heart pumps to the lungs for purification.

Key concepts

Deoxygenated Blood

Deoxygenated blood refers to blood that is carrying a lower amount of oxygen and a higher amount of carbon dioxide. This type of blood circulates from the body back into the heart. Specifically, it flows into the right atrium and then into the right ventricle before being pumped into the lungs through the pulmonary arteries.

This blood is rich in carbon dioxide because it has already delivered oxygen to the body's tissues and collected carbon dioxide as a waste product. It signals the need for purification and re-oxygenation.

The lungs play a critical role here as they facilitate the exchange of gases. The carbon dioxide in deoxygenated blood is expelled when we exhale, while oxygen is absorbed during inhalation. This process turns deoxygenated blood into oxygenated blood, ready to supply the body again with vital oxygen.

Pulmonary Arteries

Pulmonary arteries are vital components of the circulatory system. These arteries are responsible for carrying deoxygenated blood away from the heart and into the lungs. This might seem a little unusual, as it's the only artery in the body that carries deoxygenated blood.

The pulmonary arteries originate from the right ventricle of the heart and then branch into the left and right pulmonary arteries, each leading to a lung. Upon arrival, the blood travels through a network of capillaries surrounding the alveoli, tiny air sacs in the lungs, where the exchange of gases takes place.

During this process, the blood releases carbon dioxide and absorbs oxygen. Once oxygenated, the blood leaves the lungs via the pulmonary veins, returning to the left side of the heart. Understanding the unique function of pulmonary arteries is crucial, as it highlights the specialized route that deoxygenated blood takes to become rich in oxygen again.

Erythrocytes

Erythrocytes, commonly known as red blood cells (RBCs), are essential for transporting oxygen to, and carbon dioxide from, the body's tissues. These cells get their distinctive red color from hemoglobin, a protein that binds with oxygen and carbon dioxide.

In the lungs, oxygen molecules attach to the hemoglobin in the erythrocytes, forming oxyhemoglobin. This newly formed compound is then transported to various tissues across the body. As erythrocytes pass through body tissues, they release oxygen for cells to use and pick up carbon dioxide, a waste product of cellular metabolism.

Each erythrocyte is biconcave in shape, which gives it a greater surface area for efficient gas exchange. Moreover, erythrocytes lack a nucleus, allowing more room to carry hemoglobin and thus enhance their primary function of gas transport. By playing a central role in blood circulation and gas exchange, erythrocytes are pivotal in maintaining the body's overall respiratory efficiency.