Question

Pick the correct statement: (a) Contraction of internal intercostals muscles lifts up the ribs and sternum. (b) RBCs transport oxygen only. (c) Thoracic cavity is anatomically an air tight chamber. (d) Healthy man can inspire approximately \(500 \mathrm{~mL}\) of air per minute. (e) During expiration the interpleural pressure is slightly below the surrounding atmospheric pressure.

Short answer

The correct statement is (c) Thoracic cavity is anatomically an air tight chamber.

Step-by-step solution

Analyzing Statement A

Statement A is incorrect. The internal intercostals are muscles that lower the ribs and sternum during forced exhalation, not lift them.

Analyzing Statement B

Statement B is also incorrect. While red blood cells (RBC) do transport oxygen, that is not their only function. They also transport a small amount of carbon dioxide from the body's tissues to the lungs.

Analyzing Statement C

Statement C is correct. The thoracic cavity, which houses the lungs, is designed to be airtight in order to maintain the pressure needed for respiration.

Analyzing Statement D

Statement D is incorrect. A healthy man can inspire approximately \(500 \mathrm{~mL}\) of air per breath, not per minute. The total volume of air breathed in a minute depends on the breathing rate as well.

Analyzing Statement E

Statement E is incorrect. During expiration, the interpleural pressure is slightly above the surrounding atmospheric pressure, as the lungs recoil and expel air.

Key concepts

Thoracic Cavity

The thoracic cavity plays a crucial role in the respiratory system by enclosing and protecting the lungs. It forms an airtight chamber, which is important for maintaining the necessary pressures for breathing.
This cavity is bounded by the ribs, sternum at the front, and the spine at the back, forming a protective barrier around the heart and lungs. It also involves the diaphragm, a major muscle responsible for breathing.

• Being airtight helps to maintain a constant intrathoracic pressure, which is essential for the lungs to expand and contract during breathing.
• This airtight property is vital as any breach, like a puncture, could lead to conditions such as pneumothorax, where air escapes into the pleural space, causing the lung to collapse.

Maintaining the integrity of the thoracic cavity ensures effective breathing, thereby supporting the body’s oxygen and carbon dioxide balance.

Intercostal Muscles

The intercostal muscles are a set of muscles located between the ribs. They play a significant role in the mechanics of breathing. These muscles are divided into two major types: external and internal intercostal muscles, each serving unique functions in respiration.

• The external intercostal muscles are essential during inspiration. They contract to lift the ribs and sternum, increasing the volume of the thoracic cavity so the lungs can expand and fill with air.
• Conversely, the internal intercostal muscles are more active during forced exhalation. They contract to pull the ribs downward, decreasing the thoracic cavity volume and helping expel air from the lungs.

These muscles work in harmony with the diaphragm and other respiratory components, helping maintain efficient respiratory dynamics.

Red Blood Cells (RBC)

Red blood cells (RBCs) are often described as the oxygen carriers of the body, but they do much more. These biconcave cells are packed with a protein called hemoglobin, which not only transports oxygen from the lungs to the tissues but also returns carbon dioxide from the tissues back to the lungs for removal.
Besides gas transport, RBCs help buffer blood pH, contributing to the body’s acid-base balance.

• Oxygen transport: Hemoglobin binds oxygen molecules in the lungs and releases them in tissues needing more oxygen.
• Carbon dioxide removal: While most carbon dioxide is transported dissolved in plasma or as bicarbonate, RBCs also carry a portion of this gas back to the lungs.
• Shape and flexibility: The unique shape of RBCs aids in their passage through tiny capillaries without rupturing.

Having an adequate number of healthy RBCs is crucial for maintaining proper oxygen delivery to tissues and ensuring overall healthy body function.

Interpleural Pressure

Interpleural pressure, also known as intrapleural pressure, refers to the pressure within the pleural cavity, which is the space between the two layers of pleura surrounding the lungs. This pressure is vital for the mechanics of breathing and is generally negative relative to atmospheric pressure.
During inspiration, the interpleural pressure becomes more negative. This drop allows the lungs to expand as air is drawn in. During expiration, though it becomes less negative, it still remains lower than atmospheric pressure, helping expel air as the lungs recoil.
This pressure difference ensures that the lungs remain inflated even after expelling air.

• The negative interpleural pressure keeps the lungs attached to the chest wall, preventing lung collapse.
• Changes in interpleural pressure facilitate efficient air movement in and out of the lungs.
• Any abnormal changes in this pressure, like those resulting from trauma or disease, can adversely affect breathing.

Understanding interpleural pressure dynamics is key to appreciating how efficient and rhythmic breathing is achieved.