13.4:
Mechanism of Breathing I: Inspiration
The respiratory system comprises the conducting and the respiratory zones.
The conducting zone, including the nasal cavity, trachea, and bronchi, helps filter, clean, warm, and humidify the air as it passes to the lungs.
The respiratory zone consists of the bronchioles, alveolar ducts, and alveoli, which enable the gaseous exchange between air and blood.
The breathing process involves inspiration or inhalation of air through the mouth or nose into the lungs, followed by exhalation of air.
Inspiration occurs when inspiratory muscles—the diaphragm and the external intercostal muscles contract.
The contraction of the diaphragm expands the thoracic and pleural cavities. In contrast, the contraction of the external intercostal muscle elevates the ribs and sternum.
During labored inhalation, the accessory inspiratory muscles, like the sternocleidomastoid, the serratus anterior, the latissimus dorsi, the pectoralis minor and major, and the serratus posterior superior muscles, may also contract.
The forces of inspiratory muscles and the elasticity of the lung tissue cause the lungs to increase their volume.
As a result, the air pressure within alveolar spaces decreases below atmospheric pressure, causing airflow into the lungs.
13.4:
Mechanism of Breathing I: Inspiration
Introduction to Inspiration: The Respiratory System in Action
The respiratory system, an essential network for breathing, comprises the conducting and respiratory zones, each playing a crucial role in the overall process of respiration. Let us explore the detailed mechanism of inspiration, or inhalation, which is the first phase of the respiratory cycle.
Pathway of Air during Inspiration
During inspiration, air enters our body through the nose or mouth and moves through the conducting zone, including the nasal cavity, trachea, and bronchi. These structures are critical in filtering, warming, and humidifying the air, preparing it for its journey to the lungs. Once the air reaches the respiratory zone, it passes through the bronchioles, alveolar ducts, and finally into the alveoli, where gas exchange occurs.
Muscular Mechanics of Inspiration
Inspiration begins with the contraction of the primary inspiratory muscles—the diaphragm and external intercostal muscles:
- • Diaphragm: As the diaphragm contracts, it flattens and moves downward, expanding the thoracic cavity vertically.
- • External Intercostal Muscles: These muscles assist by elevating the ribs and sternum, further expanding the chest cavity and reducing intra-thoracic pressure.
In more strenuous breathing scenarios, such as during exercise or respiratory distress, accessory inspiratory muscles are recruited to enhance the thoracic cavity's expansion. These muscles include:
- • Sternocleidomastoid
- • Serratus Anterior
- • Latissimus Dorsi
- • Pectoralis Minor and Major
- • Serratus Posterior Superior
Dynamics of Lung Expansion
The coordinated contraction of these muscles increases the volume of the lungs. This expansion decreases the pressure within the alveoli to below atmospheric pressure, creating a pressure gradient that drives air into the lungs. The elasticity of the lung tissue aids this volume change, ensuring efficient airflow into the alveolar spaces.
Conclusion
Understanding the dynamic interplay of muscles and the anatomical structure involved in inspiration is crucial for grasping how breathing supports life. The process involves simple air intake and a sophisticated physiological mechanism that ensures efficient gas exchange, essential for maintaining vital cellular functions.