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# IV. Respiratory System ## External Respiration * **Lung Ventilation:** Gas exchange between lungs and the external environment. * **Gas exchange:** Gas exchange between lungs and the surroundings. * **Breathing:** Movement of air into and out of the lungs. * **Lungs:** Organs where gas exchange...

# IV. Respiratory System ## External Respiration * **Lung Ventilation:** Gas exchange between lungs and the external environment. * **Gas exchange:** Gas exchange between lungs and the surroundings. * **Breathing:** Movement of air into and out of the lungs. * **Lungs:** Organs where gas exchange occurs. ## Internal Respiration * **Gas Exchange:** Gas exchange between blood and tissues. * **Cellular Respiration:** Metabolic processes where oxygen is used to release energy. * **CO2 production:** Carbon dioxide is a byproduct of cellular respiration. ## Respiratory Tract ### Upper Respiratory Tract * **Nasal Cavity:** Airway, which warms, filters, and humidifies air. * **Associated Structures:** Paranasal sinuses that contribute to sound resonance, cleansing, and humidifying inhaled air, and the Eustachian tube that connects the middle ear to the nasopharynx. ### Lower Respiratory Tract * **Larynx:** Voice box. * **Trachea:** Windpipe; reinforced with cartilaginous rings. * **Bronchi:** Branches of the trachea that enter the lungs, branching into bronchioles. * **Bronchioles:** Smaller air passages within the lungs. * **Lungs:** The main organs of respiration. ## Lungs * **Location:** Located within the thoracic cavity. * **Pleura:** Thin membranes surrounding the lungs. * **Pleural Fluid:** Fills the space between the membranes and reduces friction during breathing. * **Alveoli:** Tiny air sacs in the lungs; the site of gas exchange. * **Structure:** Composed of millions of alveoli, providing a vast surface area for diffusion. * **Size and Shape:** Right lung has 3 lobes, and the left lung has 2 lobes. The structure of the lungs is complex.