Breathing is a critical function of living, which is carried out by the respiratory system. The primary function of the respiratory system is exchanging carbon dioxide, a waste product of cells, with oxygen, which is necessary for cells to work. Breathing involves inspiration (air moving into the lungs) and expiration (air moving out of the lungs).
Ventilatory (Breathing) Pump
The ventilatory (breathing) pump is responsible for inspiration and expiration. Anatomical parts of the ventilatory pump include respiratory muscles, which are located around the rib cage and abdomen and the pleural space, which is located between the lungs and chest wall.
Chest Wall
The chest wall is comprised of the ribs, sternum, spine and intercostal muscles, which are respiratory muscles located between the ribs, according to "Anthony's Textbook of Anatomy and Physiology." During inspiration, the space in the chest wall increases while a decreased space in the chest wall occurs during expiration.
Muscles Involved in Respiration
Primary muscles involved in inspiration include the diaphragm, external intercostal muscles, which are located outside the ribcage. When at rest, expiration typically requires no muscle work, as the process occurs naturally in the lungs. However, the respiratory muscles are greatly needed during exercise to expel air. Muscles of expiration include the internal intercostals muscles, which are located inside the ribcage, and several abdominal muscles, such as transversus abdominis, rectus abdominis and internal and external obliques, as described in "Anthony's Textbook of Anatomy and Physiology."
Pleural Space
The pleural space is an airtight gap lying between the visceral and parietal pleural. The visceral pleural is a membrane layer that covers the lungs and the parietal pleural covers the chest wall and diaphragm, as described in "Human Anatomy and Physiology" by Dr. Marieb and Dr. Hoehm. During inspiration, the visceral and parietal pleura move outward, lowering the pressure inside the pleural space. This lowered pressure allows air to enter the lung. If the pleural space ruptures, such as by injury, air can enter the pleural space, which can cause the lungs to collapse.
Inspiration
Inspiration starts when the respiratory muscles contract and increase the space within the chest wall. The ribs move upward and outward and the diaphragm moves downward. This increased space lowers the pressure in the pleural space relative to that found outside the body. As a result, air is sucked into the nose or mouth, travels down the trachea (or windpipe) and enters the lung until the pressure inside the lung equals the outside pressure, according to "Anthony's Textbook of Anatomy and Physiology."
Expiration
Expiration occurs when the respiratory muscles relax and the space within the chest wall decreases, as described by "Anthony's Textbook of Anatomy and Physiology." The ribs move downward and inward and the diaphragm moves upward. This decreased space makes the pressure inside the lung higher than the pressure outside of the body, which causes air to leave the lungs.
References
- Anthony's Textbook of Anatomy and Physiology; Gary Thibodeau and Kevin Patton; 1999
- Human Anatomy and Physiology; Elaine Marieb and Katja Hoehm; 2007
