The HICS Physiology blog

    RESPIRATORY MECHANICS DURING SPONTANEOUS BREATHING Contributed by Emy Ambooken, Thrissur INTRODUCTION: Respiratory mechanics refers to the expression of lung function through measures of pressure and flow. Pressure difference between the atmosphere and inside the lungs acts as a driving force to accomplish spontaneous breathing. WHAT HAPPENS DURING SPONTANEOUS BREATHING? During inspiration : The Diaphragm descends, increasing longitudinal length of the thoracic cavity and external intercostal muscles raise the ribs, thereby increasing the circumference of the thorax. Contraction of the diaphragm and external intercostal muscles provides the energy necessary to drive airflow and overcome the impedance offered by the lungs and chest wall. Accessory muscles of inspiration are also used during maximal inspiration. During expiration : Inspiratory muscles relax, diaphragm moves upward, and the ribs return to their resting position. This reduces volume of the thoracic...

    Principles of Gas Exchange Contributed by Shivali Sandal, Mandi Principles of Gas Exchange Gas exchange is the core function of the respiratory system: delivering oxygen to tissues and removing carbon dioxide. It occurs in two settings: 1.   External respiration — alveoli ↔ pulmonary capillaries. 2.   Internal respiration — systemic capillaries ↔ tissues. The process is entirely passive, driven by pressure gradients, requiring no energy. Anatomy and site of gas exchange The lungs are designed to maximise efficiency. The lungs contain nearly 300 million alveoli , providing a vast surface area of ~70 m² in adults¹. Each alveolus is enveloped by a dense pulmonary capillary network, forming the alveolo-capillary (respiratory) membrane, the site of gas exchange. Normally, it is just 0.5–1 µm , allowing rapid diffusion. The transit time of blood in alveolar capillaries under normal conditions is around 0.75 -1 seconds, though as little as 0.25 s i...