MECANICA RESPIRATÓRIA

Summary

This video discusses the physiological mechanisms behind respiratory mechanics, focusing on the cycle of inspiration and expiration in normal breathing. It explains the roles of various muscles involved, including the diaphragm, external intercostals, and scalene muscles, in expanding the thoracic cavity and facilitating airflow. The script also explores the concept of passive expiration, the pressure dynamics (pleural, alveolar, and transpulmonary pressures), and how these contribute to lung expansion and retraction. The video emphasizes the importance of understanding these pressures to prevent lung collapse and ensure proper breathing function.

Takeaways

• 😀 The respiratory cycle consists of two phases: inspiration (inhalation) and expiration (exhalation).
• 😀 Inspiration is an active process involving muscles, while expiration is generally passive, requiring muscle relaxation.
• 😀 The diaphragm is the primary muscle responsible for inspiration, aided by external intercostal muscles and, to a lesser extent, the scalenes.
• 😀 The lungs do not have contractile properties; their expansion and contraction rely on muscle actions and pressure changes.
• 😀 Inspiration begins with signals from the brainstem, particularly the medulla, which activate inspiratory muscles.
• 😀 Forced respiration involves additional muscles such as the sternocleidomastoid, which are not required for quiet breathing.
• 😀 Expiration during quiet breathing occurs passively through the relaxation of inspiratory muscles and lung elastic recoil.
• 😀 The lungs are elastic structures that tend to collapse unless maintained by specific pressures during breathing.
• 😀 The pleural pressure, which is negative, plays a crucial role in keeping the lungs expanded and preventing collapse.
• 😀 Three main pressures are involved in respiration: pleural pressure, alveolar pressure, and transpulmonary pressure.
• 😀 The pleural space between the visceral and parietal pleura contains fluid that generates negative pleural pressure, aiding lung expansion.
• 😀 During inspiration, the alveolar pressure becomes subatmospheric, allowing air to flow into the lungs, while during expiration, it becomes supra-atmospheric, pushing air out.

Q & A

What are the two phases of the respiratory cycle?

The two phases of the respiratory cycle are inspiration and expiration. Inspiration is when air is drawn into the lungs, and expiration is when air is expelled from the lungs.

Why are the lungs not capable of contraction and relaxation during respiration?

The lungs do not have contractile properties because they are not made of muscle tissue. They consist of elastic tissue, which allows them to expand and contract passively due to pressure changes, rather than actively contracting and relaxing.

Which muscles are primarily responsible for the process of inspiration?

The primary muscles responsible for inspiration are the diaphragm and the external intercostal muscles. The scalenes and sternocleidomastoid muscles can also contribute, especially during forced inspiration.

What role does the diaphragm play in the respiratory cycle?

The diaphragm plays a crucial role in inspiration by contracting and moving downward. This increases the vertical diameter of the thoracic cavity, allowing the lungs to expand and air to be drawn in.

How do the external intercostal muscles contribute to the respiratory cycle?

The external intercostal muscles contract during inspiration, pulling the ribs upwards and outwards. This increases the anteroposterior diameter of the thoracic cavity, aiding in lung expansion.

What is the difference between forced and quiet (or passive) expiration?

Forced expiration involves the active contraction of muscles such as the internal intercostals and abdominal muscles to expel air rapidly, while quiet expiration is a passive process that relies on the relaxation of the inspiratory muscles and the elastic recoil of the lungs.

What is the role of pleural pressure in the respiratory cycle?

Pleural pressure maintains the expansion of the lungs. It is negative relative to atmospheric pressure and helps prevent lung collapse by keeping the lungs adhered to the chest wall and diaphragm.

What are the three key pressures involved in lung mechanics?

The three key pressures are pleural pressure, alveolar pressure, and transpulmonary pressure. Pleural pressure helps maintain lung expansion, alveolar pressure controls airflow, and transpulmonary pressure is the difference between alveolar and pleural pressures, influencing lung expansion and recoil.

How does the alveolar pressure change during the respiratory cycle?

During inspiration, the alveolar pressure becomes subatmospheric (lower than atmospheric pressure), drawing air into the lungs. During expiration, the alveolar pressure becomes supra-atmospheric (higher than atmospheric pressure), forcing air out of the lungs.

What is the significance of the transpulmonary pressure?

Transpulmonary pressure is the difference between alveolar pressure and pleural pressure. It is important for lung expansion, as it counteracts the elastic forces of the lungs that tend to collapse them. A higher transpulmonary pressure allows for greater lung inflation.