Concept Map: Mechanics of Breathing diaphragm and external intercostals expiration inspiration intrapleural pressure intrapulmonary pressure lungs pulmonary ventilation transpulmonary pressure decrease(s) lung volume and increase(s) include(s) a phase when air enters lungs, called include(s) a phase when air exits lungs, called increase(s) lung volume and decrease(s) is/are always about 4 mmHg greater than minus intrapleural pressure give(s) must be negative to prevent collapse of occur(s) when contracting occur(s) when relaxing
The Correct Answer and Explanation is:
Here is the completed concept map for “Mechanics of Breathing”:
- Diaphragm and external intercostals →
occur(s) when contracting - Expiration →
occur(s) when relaxing - Inspiration →
include(s) a phase when air enters lungs, called - Intrapleural pressure →
must be negative to prevent collapse of → lungs - Intrapulmonary pressure →
is/are always about 4 mmHg greater than → intrapleural pressure - Lungs →
increase(s) lung volume and decrease(s) (intrapulmonary pressure) - Pulmonary ventilation →
include(s) a phase when air exits lungs, called → expiration - Transpulmonary pressure →
minus intrapleural pressure give(s)
Explanation
Breathing, or pulmonary ventilation, involves the mechanical processes that move air into and out of the lungs. It is primarily driven by changes in pressure and volume within the thoracic cavity.
The diaphragm and external intercostal muscles are the main muscles responsible for breathing. When these muscles contract, the thoracic cavity expands, causing inspiration—the phase when air enters the lungs. Conversely, when these muscles relax, the cavity volume decreases, resulting in expiration—the phase when air exits the lungs.
Intrapulmonary pressure, the pressure within the alveoli, fluctuates with breathing but is always higher than intrapleural pressure—the pressure within the pleural cavity—to keep the lungs inflated. The difference between these two pressures is known as transpulmonary pressure, and this must remain positive to prevent lung collapse.
During inspiration, lung volume increases, which causes a drop in intrapulmonary pressure, allowing air to flow in. During expiration, lung volume decreases, intrapulmonary pressure rises, and air is pushed out.
Intrapleural pressure must stay negative relative to atmospheric pressure and intrapulmonary pressure; otherwise, the lungs could collapse due to elastic recoil. This negative pressure is maintained by the opposing forces between the chest wall and lung recoil.
Overall, pulmonary ventilation is the combination of inspiration and expiration processes, governed by pressure gradients. Understanding this mechanical relationship helps explain normal breathing as well as pathological conditions such as pneumothorax, where intrapleural pressure becomes positive, leading to lung collapse.
