Problem 132 - Objective Biology for NEET

Question

Assertion: During inspiration, pressure of air falls in the thorax. Reason: There is a rise in volume of thorax during inspiration.

Step-by-Step Solution

Answer

During inspiration, the thorax's volume increases due to the diaphragm's contraction, creating more room for incoming air. According to Boyle's Law, the increase in volume results in a decrease in internal pressure, causing the pressure of air to fall.

Step 1: Initiate Understanding of Inspiration

Inspiration, or inhaling, is the process where breathing in takes place. This is initiated by the diaphragm, a muscle that contracts and relaxes to facilitate breathing.

Step 2: Connect Thorax Volume Increase to Inspiration

When inspiration happens, the diaphragm contracts and moves downwards, which increases the volume of the thorax (the part of the body between the neck and the diaphragm, not inclusive). This is because the thorax needs to make room for the incoming air.

Step 3: Relate Thorax Volume Increase to Air Pressure Decrease

As the volume of the thorax increases, the pressure inside decreases according to Boyle's Law (a principle in physical chemistry that states the pressure and volume of a gas have an inverse relation when temperature is held constant). This is how the pressure of air falls in the thorax during inspiration.

Key Concepts

Inspiration

Inspiration, commonly known as inhalation, is the process responsible for drawing air into our lungs. This process is vital for the respiratory system to provide oxygen to the bloodstream, which then supplies it throughout the body. When you inhale, the chest cavity enlarges, allowing space for the lungs to expand.

Inspiration involves several physiological changes:

• The diaphragm contracts and moves downward.
• The intercostal muscles between the ribs also contract, pulling the rib cage upward and outward.

These actions increase the volume of the thoracic cavity, reducing the pressure inside as a result.

A decreased pressure in the thorax encourages air to flow from areas where the pressure is higher (atmosphere) to where it is lower (inside the lungs). This simple yet efficient mechanism helps us breathe effortlessly throughout our lives.

Diaphragm

The diaphragm is a muscular dome that plays a crucial role in respiration. Located just below the lungs and heart, it acts as the primary muscle in breathing.

Whenever the body demands air during inspiration, the diaphragm contracts and flattens, creating a vacuum effect in the chest cavity. This action enhances the volume of the thoracic cavity, allowing the lungs to inflate with incoming air.

Apart from managing inspiration, the diaphragm also assists in:

• Expulsion of substances from the abdominal cavity (e.g., vomiting, coughing).
• Influencing the abdominal pressure, critical for bodily functions like defecation and childbirth.

Its automated contractions make it a vital yet often unnoticed part of our respiratory system, ensuring continuous breathing without conscious effort.

Boyle's Law

Boyle's Law is a fundamental principle in physics that explains the behavior of gases. It states that when the temperature is constant, the pressure of a gas is inversely related to its volume.

In the context of breathing, Boyle's Law plays a significant role during inspiration. When the diaphragm contracts and the thoracic cavity expands, the volume within the cavity increases.

According to the law, when the volume of this closed system (thorax) increases, the pressure inside must decrease, leading to:

• The creation of a low-pressure environment compared to atmospheric pressure.
• Air naturally flowing into the lungs to equalize the pressure difference.

This principle of physics provides a scientific explanation for the natural air intake during the respiratory cycle, showcasing how the body harnesses physical laws for vital processes like respiration.