Respiration

Pulmonary Ventilation refers to the movement of air in and out of the alveoli of the lungs. External Respiration refers to the transfer of gases within the lungs: oxygen diffuses from the alveoli to the blood, and carbon dioxide diffuses from the blood to the alveoli. Transport: Oxygen and carbon dioxide are then transported by the cardiovascular system to and from the tissues and lungs. Internal Respiration occurs in the body tissues: oxygen diffuses from the blood to the tissues, and carbon dioxide diffuses from the tissues to the blood. In both external and internal respiration, the gases move along concentration gradients; we'll learn more about this in a separate tutorial. Nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles. These structures have cartilaginous supports in their walls, which maintains an open airway. They are lined by mucus-secreting and ciliated cells; these features trap particles that are inhaled and move them "upwards" and away from the lungs to help prevent infection. The walls of conducting structures comprise smooth muscle, which can contract or dilate to alter the size of the airways and regulate air flow. The respiratory bronchioles are transitional structures; these tiny passages give rise to the alveoli, which is where gases are exchanged. Respiratory bronchioles have ciliated cells in their linings and smooth muscles in their walls; however, they do not have cartilage to keep them open. Click to review Respiratory Histology The alveoli are tiny sacs comprised of a single layer of epithelial cells. Type I alveolar cells are flat epithelial cells that provide the surfaces for gas exchange. Type II alveolar cells are cuboidal epithelial cells with many roles, including: production of surfactant, which contributes to the surface tension that holds the alveoli open; epithelial regeneration, which is vital for lung tissue health, and immune responses. Alveoli are covered in networks of pulmonary capillaries, which bring blood in close contact with the alveoli for external respiration. Finally, let's show how the alveoli and pulmonary capillaries give rise to the respiratory membrane, the site at which gas exchange occurs in the lungs (aka, external respiration). Type I cells make of the majority of the alveolus. Type II cells support the alveolar functions. Alveolar macrophages participate in the innate immune response of the lungs. Now, draw a capillary running along the surface of the alveolus; highlight that, where the two meet, the respiratory membrane is created. Deoxygenated blood from the pulmonary artery passes through the capillary and travels along the alveolar wall; as it does so, oxygen diffuses from the alveolus to the blood, and carbon dioxide diffuses from the blood to the alveolus. Lastly, show that the re-oxygenated blood travels in the pulmonary vein to the heart, where it will be pumped into the systemic circulation. Ventilation/Perfusion Mismatch