In humans, respiration encompasses breathing, gaseous exchange, and cellular respiration. Our respiratory surface, the alveoli, is located within paired lung organs inside the body.
Our respiratory system consists of paired lungs located inside the thoracic (chest) cavity and Air passage ways.
Lungs, enclosed in pleural membranes, aid breathing with lubricating fluid. Protected by the ribcage and diaphragm, they house millions of alveoli, microscopic sacs for gas exchange with surrounding capillaries. The airway, starting from nostrils to bronchioles, is lined with ciliated cells and mucous for filtration. This ensures clean air reaches the delicate respiratory surfaces, enabling efficient oxygen exchange and carbon dioxide removal essential for human respiration.
The trachea, a long tube, connects to the nasal sacs and contains the vocal cords in the larynx. The glottis, its opening, is guarded by the epiglottis, preventing food entry during swallowing. C-shaped cartilaginous rings support the trachea, preventing collapse.
The trachea divides into two bronchi in the thorax, each with C-shaped cartilaginous rings. These bronchi further branch into smaller bronchioles within their respective lungs.
Each bronchiole is very thin tube that opens into air sacs or alveoli.
The exchange of gases within the lungs relies on the process of breathing or ventilation, as the respiratory surfaces are deep within the lungs. Breathing consists of two phases: inspiration, where air is drawn into the lungs, and expiration, where air is expelled from the lungs.
During inspiration, the diaphragm and intercostal muscles contract, expanding the chest cavity and lowering lung pressure, allowing external air to rush in, expanding the lungs.
In contrast to inspiration, expiration is the process of air moving out from the lungs. It occurs when both intercostal muscles and the diaphragm relax, causing the ribs to move inward and the diaphragm to flatten. This compresses the chest cavity, increasing pressure in the lungs, and forcing air out of the body.