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Chapter 15: Respiratory System 15-1 The Respiratory System The respiratory system works with the cardiovascular system to exchange gases between the alveoli and blood (external respiration) and between blood and tissue fluids (internal respiration). Inspiration and expiration move air in and out of the lungs during breathing. Cellular respiration is the final destination where ATP is produced in cells. 15-2 The respiratory tract 15-3 The Respiratory Tract Air is cleansed, warmed, and moistened as it passes the cilia and mucus in the nostrils and nasal cavity. In the nose, the hairs and the cilia act as a screening device. In the trachea, the cilia beat upward, carrying dust and mucus into the pharynx. Exhaled air carries out heat and moisture. 15-4 The Nose The two nasal cavities are divided by a septum. They contain olfactory cells, receive tear ducts from eyes, and communicate with sinuses. The nasal cavities empty into the nasopharynx. 15-5 The path of air 15-6 The Pharynx The pharynx (throat) is a passageway from the nasal cavities to oral cavities and to the larynx. The pharynx contains the tonsils; the respiratory tract assists the immune system in maintaining homeostasis. The pharynx takes air from the nose to the larynx and takes food from the oral cavity to the esophagus. 15-7 The Larynx The larynx is a cartilaginous structure lying between the pharynx and the trachea. The larynx houses the vocal cords. A flap of tissue called the epiglottis covers the glottis, an opening to the larynx. In young men, rapid growth of the larynx and vocal cords changes the voice. 15-8 Placement of the vocal cords 15-9 The Trachea The trachea, supported by C-shaped cartilaginous rings, is lined by ciliated cells, which sweep impurities up toward the pharynx. Smoking destroys the cilia. The trachea takes air to the bronchial tree. Blockage of the trachea requires an operation called a tracheostomy to form an opening. 15-10 Cilia in the trachea 15-11 The Bronchial Tree The trachea divides into right and left primary bronchi which lead into the right and left lungs. The right and left primary bronchi divide into ever smaller bronchioles to conduct air to the alveoli. An asthma attack occurs when smooth muscles in the bronchioles constrict and cause wheezing. 15-12 The Lungs Lungs are paired, cone-shaped organs that lie on either side of the heart and within the thoracic cavity. The right lung has three lobes, and the left lung has two lobes, allowing for the space occupied by the heart. The lungs are bounded by the ribs and diaphragm. 15-13 The Alveoli Alveoli are the tiny air sacs of the lungs made up of squamous epithelium and surrounded by blood capillaries. Alveoli function in gas exchange, oxygen diffusing into the bloodstream and carbon dioxide diffusing out. Infant respiratory distress syndrome occurs in premature infants where underdeveloped lungs lack surfactant (thin film of lipoprotein) and collapse. 15-14 Gas exchange in the lungs 15-15 Mechanism of Breathing During breathing, air moves into the lungs during inspiration (inhalation) from the nose or mouth, then moves out again during expiration (exhalation). 15-16 Inspiration and Expiration There is a continuous column of air from the pharynx to the alveoli, and the lungs lie within the sealed-off thoracic cavity. The thoracic cavity is bounded by the rib cage and diaphragm. Pleural membranes line the thoracic cavity and lungs and the intrapleural pressure is lower than atmospheric pressure, keeping the lobules of the lungs from collapsing. 15-17 Inspiration When we inhale (inspiration) impulses from the respiratory center in the medulla oblongata cause the rib cage to rise and the diaphragm to lower, causing the thoracic cavity to expand. The negative pressure or partial vacuum in the alveoli causes the air to come in. Changing amounts of blood of CO2 and H+ increase breathing rate. 15-18 Nervous control of breathing 15-19 Inspiration 15-20 Expiration When we exhale (expiration), lack of impulses from the respiratory center allow the rib cage to lower and diaphragm to resume dome shape. Expiration is passive, while inspiration is active. The elastic recoil of the lungs causes expiration. A deep breath causes alveoli to stretch; stretch receptors then inhibit the respiratory center. 15-21 Expiration 15-22 Gas Exchanges in the Body External Respiration Individual gases exert pressure proportional to their portion of the total in a mixture of gases; this is called “partial pressure”. External respiration is the diffusion of CO2 from pulmonary capillaries into alveolar sacs and O2 from alveolar sacs into pulmonary capillaries. 15-23 In both cases, diffusion occurs because the partial pressures are higher causing diffusion (from higher to lower concentrations) across the capillary wall. Most CO2 is carried as bicarbonate ions. The enzyme carbonic anhydrase, in red blood cells, speeds up the conversion of bicarbonate and H+ to H2O and CO2; CO2 enters alveoli and is exhaled. Hemoglobin (Hb) takes up oxygen from alveoli and becomes oxyhemoglobin (HbO2). 15-24 Internal Respiration Internal respiration is the diffusion of O2 from systemic capillaries into tissues and CO2 from tissue fluid into systemic capillaries. Oxyhemoglobin gives up O2, which diffuses out of the blood and into the tissues because the partial pressure of O2 of tissues fluid is lower than that of the blood. 15-25 After CO2 diffuses from tissue cells into the blood, it enters red blood cells where a small amount is taken up by hemoglobin, forming carbaminohemoglobin. Most of the CO2 combines with water to form carbonic acid (H2CO3), which dissociates to release hydrogen ions (H+) and bicarbonate ions (HCO3-); the enzyme carbonic anhydrase speeds this reaction. 15-26 The globin portion of hemoglobin combines with excess hydrogen ions to become reduced hemoglobin or HHb; this helps maintain a normal blood pH. Blood leaving capillaries is a dark maroon color because red blood cells contain reduced hemoglobin. 15-27 External and internal respiration 15-28 Binding Capacity of Hemoglobin The partial pressure of gases, temperature, and pH affect binding capacity of hemoglobin. The high pressure of oxygen, the low temperature and low pH aid the binding of oxygen to hemoglobin in the lungs; the opposite is true in the tissues. In both cases, environmental conditions are favorable to the uptake of the appropriate gases. 15-29 Saturation of Hb relative to temperature 15-30 Saturation of Hb relative to pH 15-31 15-32