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Biology 12 11.1 The Respiratory System The main function of the respiratory system is to allow oxygen from the air to enter the blood and carbon dioxide from the blood to exit into the air. Ventilation, another term for breathing, includes both inspiration (inhalation) and expiration (exhalation). • Air is conducted toward or away from the lungs by a series of cavities, tubes, and openings The respiratory system works with the circulatory system in the following homeostatic functions: • External respiration: exchange of gases (oxygen and carbon dioxide) between the air and blood • Transport of gases to and from the lungs and tissues • Internal respiration: exchange of gases between the blood and tissue fluid The Respiratory Tract Inspiration: air is filtered, warmed, and moistened as it moves along the respiratory tract • Filtered by hairs in the nostrils, and by cilia in the mucus of nasal cavities and airways • Warmed by heat given off by blood vessels close to the lining of the airways • Moistened by the wet surface of airways Expiration: air cools and loses its moisture as it moves out of the respiratory tract • Deposits moisture on the lining of the trachea and nose The Nose The nose is the only external portion of the respiratory system. • Air enters the nose through the nostrils • Air is moistened and warmed in two nasal cavities that are lined with mucous membranes • Nasal cavities are separated from the mouth by the palate, which is composed of the hard palate and soft palate Biology 12 The Pharynx The pharynx is also known as the “throat.” • Connects the nasal and oral cavities to the larynx • Contains lymphatic tissues called tonsils that contain lymphocytes that protect against pathogens • Allows for the passage of air and food The Larynx The larynx is called the voice box since it contains the vocal cords. • Connects the pharynx to the trachea • Composed of cartilage and dense connective tissue • Allows for the passage of air (the glottis allows air into the larynx) • A flap of tissue above the larynx, the epiglottis, prevents passage of food into lower respiratory tract The Trachea The trachea is commonly called the windpipe. • Connects larynx with bronchi • Composed of C-shaped cartilaginous rings • Allows for the passage of air to bronchi • Cleans, warms, and moistens air • Mucous membrane lining contains goblet cells (produce mucus) and ciliated cells (sweep mucus and debris toward the pharynx) Biology 12 The Bronchial Tree The trachea divides into the bronchi, which lead into the lungs. • The bronchi branch into secondary bronchi that lead to bronchioles • Each bronchiole leads to thin-walled air sacs called alveoli (site of gas exchange between air and blood) • The components of the bronchial tree beyond the primary bronchi make up the lungs The Lungs The lungs are paired, cone-shaped organs that contain alveoli, airways, and blood vessels. • At the base of the lungs is the diaphragm, a muscle involved in inspiration and expiration • Each lung is covered with a thin membrane called a pleura o Secretes fluid so that it can slide freely against the pleura of the chest wall and diaphragm during inspiration and expiration • During inhalation, air enters the lungs by way of the bronchial tree and moves to the alveoli • Gas exchange occurs between the air in an alveolus and the blood in the capillaries Biology 12 o Alveoli are covered with pulmonary surfactant, a film of lipoprotein that prevents the alveoli from closing so that inhaled air can enter