Question

Explain what happens when a person inhales. What forces air into the lungs?

Short answer

When a person inhales, the diaphragm contracts and flattens, the rib cage expands, lowering the pressure in the lungs, and causing air to be pushed into the lungs by the higher atmospheric pressure outside.

Step-by-step solution

Understanding Inhalation

Inhalation, also known as inspiration, is the process of taking air into the lungs. It is an active movement that involves the diaphragm, a dome-shaped muscle below the lungs. As the diaphragm contracts, it flattens and moves downward, which creates more space in the chest cavity for the lungs to expand.

Role of the Rib Cage

Simultaneously, the muscles between the ribs, called intercostal muscles, contract to pull the rib cage upwards and outwards. This additional change in the thoracic volume contributes to lowering the air pressure inside the lungs compared to the outside atmosphere.

Air Flow Into the Lungs

Due to the decrease in air pressure within the lungs, air from the outside environment is pushed into the airways by atmospheric pressure which is now greater outside the lungs than inside. This is in accordance with Boyle's Law, which states that the pressure of a given quantity of gas is inversely proportional to its volume, provided the temperature remains constant.

Key concepts

Diaphragm Function

The diaphragm plays a pivotal role in the process of inhalation. It's a large, dome-shaped muscle located right at the base of the lungs and separates the thoracic cavity from the abdominal cavity. When you inhale, the diaphragm contracts and moves downward. This contraction creates more space in the chest cavity, allowing the lungs to expand.

As the lungs expand, air is drawn into them due to the increase of thoracic volume and the consequent decrease in pressure within the lungs. This movement is crucial because it sets the stage for the air to flow naturally into the lungs, driven by the pressure difference between the inside and outside of the body. Without the diaphragm’s function, the act of breathing would be much less efficient, and the vital exchange of gases that our bodies depend upon would be compromised.

Intercostal Muscles

The intercostal muscles, found between the ribs, function in tandem with the diaphragm to facilitate inhalation. These muscles are grouped into two main types: the external intercostal muscles and the internal intercostal muscles. During inhalation, it's the external intercostal muscles that spring into action.

When these muscles contract, they pull the ribcage upwards and outwards, further increasing the volume of the chest cavity. This expansion works together with the diaphragm's movement to lower the air pressure inside the lungs. It's this finely tuned muscular cooperation that enables the lungs to draw in air efficiently. Without the help of the intercostal muscles, the expansion of the lungs would be restricted, hindering effective breathing.

Boyle's Law

Boyle's Law is a fundamental principle of physics that explains the inverse relationship between the volume and pressure of a gas at a constant temperature. Formulated by Robert Boyle in the 17th century, the law states that \( P1 \cdot V1 = P2 \cdot V2 \) where \( P \) is pressure, \( V \) is volume, and the subscripts \( 1 \) and \( 2 \) refer to the initial and final conditions of the gas, respectively.

In the context of inhalation, Boyle's Law elucidates how the air pressure inside the lungs decreases as the volume of the chest cavity increases, owing to the contraction of the diaphragm and the raising of the rib cage by the intercostal muscles. This results in a pressure lower than that of the atmosphere, causing air to rush into the lungs. Understanding Boyle's Law provides insight into the mechanical aspect of breathing and clarifies why our lungs fill with air during inhalation—it's all due to the natural equilibrium-seeking behavior of gases.