Problem 144 - Objective Biology for NEET

Question

Assertion: Trachea, primary, secondary and tertiary bronchi and terminal bronchioles are non-collapsible. Reason: They all are supported by incomplete cartilaginous ring

Step-by-Step Solution

Answer

The assertion and reason are only partially correct. The trachea and bronchi (primary, secondary, tertiary) are non-collapsible because they are supported by incomplete cartilaginous rings. The terminal bronchioles, though they don't have cartilaginous rings, are kept open by smooth muscle tension, and hence often remain non-collapsible under normal circumstances.

Step 1: Analyze trachea and bronchi structure

The trachea, also referred to as the windpipe, is a tube that connects the pharynx and larynx to the lungs. It's reinforced by c-shaped cartilaginous rings which provide structural support and keeps airway open by preventing it from collapsing. The bronchi are extensions of the trachea that carry air into the lungs. They also have similar cartilaginous rings for support.

Step 2: Analyze bronchioles structure

The bronchioles are smaller extensions of the bronchi. They lead to the alveoli (small sacs of air in the lungs where gas exchange occurs). Unlike the bronchi, bronchioles don't have cartilaginous rings. However, they are lined with smooth muscle that keeps them open.

Step 3: Validate the assertion and reason

The assertion is partially correct. The trachea, primary, secondary, and tertiary bronchi are indeed reinforced by cartilaginous rings and hence are non-collapsible. However, the terminal bronchioles, lacking these rings, are technically collapsible but in practice are kept open by the tension of the surrounding smooth muscle. Therefore, the reason is only partially correct because it does not accurately represent the structure of the terminal bronchioles.

Key Concepts

Trachea Structure

The trachea, commonly known as the windpipe, is an essential part of the respiratory system. It is a tube that connects the pharynx and larynx to the lungs, ensuring that air can pass freely through the respiratory tract. One of the key structural features of the trachea is the presence of c-shaped cartilaginous rings. These rings are made of cartilage, a sturdy and flexible material, providing crucial support.

These cartilaginous rings are incomplete at the back, where the trachea faces the esophagus. This design allows the trachea to maintain its shape without collapsing, even when there is a drop in pressure during inhalation or exhalation. The rigidity offered by these cartilaginous rings is vital for keeping the airway open and unobstructed, allowing for effective breathing.

Bronchioles Function

Bronchioles are small tubular structures branching off from the bronchi, leading to the alveoli, where gas exchange occurs in the lungs. Unlike the bronchi, bronchioles do not contain cartilaginous rings. Instead, they rely on their own structural characteristics to remain open and functional.

The function of bronchioles is to transport air from the bronchi to the alveoli, facilitating the exchange of oxygen and carbon dioxide. The smaller diameter of bronchioles allows them to manage airflow resistance and distribution throughout the lung tissue efficiently. This control over airflow is critical in regulating the amount of air reaching different parts of the lungs, which is essential for optimum respiratory function.

Cartilaginous Rings

Cartilaginous rings are fundamental structural components found in parts of the respiratory tract, including the trachea and bronchi. These rings are typically c-shaped and cover most of the circumference of these tubes, except for a small gap at the back.

The presence of cartilaginous rings provides rigidity and strength, preventing collapse under varying respiratory pressures. By keeping the trachea and bronchi open, they ensure that air can travel to and from the lungs smoothly. The gap in each ring allows for slight compression, which is helpful when swallowing food, preventing the trachea from obstructing the esophagus. This clever design makes cartilaginous rings indispensable for maintaining an efficient and unobstructed airway.

Smooth Muscle in Bronchioles

Smooth muscle plays a pivotal role in maintaining the patency of bronchioles, which lack the cartilaginous rings found in larger respiratory airways. These muscles line the walls of the bronchioles and are crucial for their function.

The primary role of smooth muscle in bronchioles is to regulate airway diameter. This regulation is achieved through contraction and relaxation of the smooth muscle fibers. When the smooth muscle contracts, the airway narrows, reducing airflow - a process called bronchoconstriction. Conversely, relaxation of these muscles leads to bronchodilation, where the airways widen, allowing more air to pass through.

Notably, the tension of smooth muscle fibers helps keep the bronchioles open, even in the absence of supporting cartilaginous rings. This feature is vital for preventing collapse and ensuring that airflow continues to travel to the alveoli for effective gas exchange.