A&P ch. 19 respiratory system PDF

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Chapter Summary 19.1 General Characteristics of the Respiratory System The respiratory system includes the passages that transport air to and from the lungs and the air sacs in which gas exchanges occur. 1. Respiration is the entire process by which gases are exchanged between the atmosphere

and the body cells. 2. Respiration is necessary because cells require oxygen to extract maximal energy from nutrient molecules and release carbon dioxide, a metabolic waste. 19.2 Organs of the Respiratory System The respiratory system is divided into two tracts. The upper respiratory tract includes the nose, nasal cavity, sinuses, pharynx, and larynx; the lower respiratory tract includes the trachea, bronchial tree, and lungs. 1) Nose a) Bone and cartilage support the nose. b) Nostrils provide entrances for air. 2) Nasal cavity a) The nasal cavity is a space posterior to the nose. b) The nasal septum divides it medially. c) Nasal conchae divide the cavity into passageways and help increase the surface area of the mucous membrane. d) Mucous membrane cleans, warms, and moistens incoming air. e) Particles trapped in the mucus are carried to the pharynx by ciliary action and are swallowed. 3) Sinuses a) Sinuses are spaces in the bones of the skull that open into the nasal cavity. b) They are lined with mucous membrane that is continuous with the lining of the nasal cavity. 4) Pharynx a) The pharynx is posterior to the mouth, between the nasal cavity and the larynx. b) It provides a common passage for air and food. c) It aids in creating vocal sounds. 5) Larynx a) The larynx is an enlargement at the top of the trachea. b) It is a passageway for air and helps prevent foreign objects from entering the trachea. c) It is composed of muscles and cartilages; some of these cartilages are single, whereas others are paired. d) It contains the vocal cords, which produce sounds by vibrating as air passes over them. i) The pitch of a sound is related to the tension on the cords.

ii) The intensity of a sound is related to the force of the air passing over the cords. e) The epiglottis helps prevent food and liquid from entering the trachea. 6) Trachea a) The trachea extends into the thoracic cavity anterior to the esophagus. b) It divides into the right and left main bronchi. c) The mucous lining continues to clean incoming air. d) Incomplete cartilaginous rings support the wall. 7) Bronchial tree a) The bronchial tree consists of branched air passages that connect the trachea to the air sacs. b) The branches of the bronchial tree include main bronchi, lobar bronchi, segmental bronchi, intralobular bronchioles, terminal bronchioles, respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. c) Structure of the respiratory tubes i) As tubes branch, the amount of cartilage in the walls decreases, and the muscular layer persists to the ends of the respiratory bronchioles. ii) Elastic fibers in the walls aid breathing. iii) The epithelial lining changes from pseudostratified and ciliated to cuboidal and then to simple squamous as the tubes become progressively smaller. d) Functions of the respiratory tubes and alveoli include distribution of air and exchange of gases between the alveolar air and the blood. 8) Lungs a) The left and right lungs are separated by the mediastinum and are enclosed by the diaphragm and the thoracic cage. b) The visceral pleura is attached to the surface of the lungs; parietal pleura lines the thoracic cavity. c) The right lung has three lobes, and the left lung has two. d) Each lobe is composed of lobules that contain alveolar ducts, alveolar sacs, alveoli, nerves, blood vessels, lymphatic vessels, and connective tissues. 19.3 Breathing Mechanism Inspiration and expiration movements are accompanied by changes in the size of the thoracic cavity. One inspiration followed by one expiration is a respiratory cycle. 1) Inspiration a) Atmospheric pressure forces air into the lungs. b) Inspiration occurs when the intra-alveolar pressure is reduced. c) The intra-alveolar pressure is reduced when the diaphragm moves downward and the thoracic cage moves upward and outward. d) Surface tension holding the pleural membranes together aids lung expansion. e) Surfactant reduces surface tension in the alveoli. 2) Expiration

a) The forces of expiration come from the elastic recoil of tissues and from surface tension in the alveoli. b) Expiration can be aided by thoracic and abdominal wall muscles that pull the thoracic cage downward and inward and compress the abdominal organs inward and upward. 3) Respiratory volumes and capacities a) The amount of air that moves in or out during a respiratory cycle is the tidal volume. b) Additional air that can be inhaled is the inspiratory reserve volume; additional air that can be exhaled is the expiratory reserve volume. c) Residual air remains in the lungs and is mixed with newly inhaled air. d) The residual volume is difficult to measure. e) The vital capacity is the maximum amount of air a person can exhale after taking the deepest breath possible. f) The inspiratory capacity is the maximum volume of air a person can inhale following exhalation of the tidal volume. g) The functional residual capacity is the volume of air that remains in the lungs following the exhalation of the tidal volume. h) The total lung capacity is equal to the vital capacity plus the residual volume. i) Air in the anatomic and alveolar dead spaces is not available for gas exchange. 4) Alveolar ventilation a) Minute ventilation is tidal volume multiplied by breathing rate. b) Alveolar ventilation rate is the physiologic dead space subtracted from the tidal volume multiplied by breathing rate. c) The alveolar ventilation rate is a major factor affecting gas exchange between the alveolar air and the blood. 5) Nonrespiratory air movements a) Nonrespiratory air movements are air movements other than breathing. b) They include coughing, sneezing, laughing, crying, hiccupping, and yawning. 19.4 Control of Breathing Normal breathing is rhythmic and involuntary, although the respiratory muscles can be controlled voluntarily. 1) Respiratory areas a) The respiratory areas are in the brainstem and include parts of the medulla oblongata and pons. b) The medullary respiratory center includes two groups of neurons. i) The ventral respiratory group provides the basic rhythm of breathing. ii) The dorsal respiratory group stimulates inspiratory muscles and processes sensory information regarding the respiratory system. It then modifies the activity of the ventral respiratory group. c) The pontine respiratory group may contribute to the rhythm of breathing by limiting inspiration.

2) Partial pressure a) The partial pressure of a gas is determined by the concentration of that gas in a mixture of gases or the concentration of gas dissolved in a liquid. b) The partial pressure of a gas dissolved in a liquid equals the partial pressure of that gas in the air with which the liquid has equilibrated. 3) Factors affecting breathing. a) Chemicals, lung tissue stretching, and emotional state affect breathing. b) Chemosensitive areas (central chemoreceptors) are associated with the respiratory center. i) CO2CO2 combines with water to form carbonic acid, which, in turn, releases hydrogen ions in the CSF. ii) Stimulation of these areas increases alveolar ventilation. c) Peripheral chemoreceptors are in the carotid bodies and aortic bodies of certain arteries. i) These chemoreceptors sense low oxygen levels as well as excess hydrogen ions. ii) When oxygen levels are low or blood pH drops, alveolar ventilation increases. d) Stretching the lung tissues triggers an inflation reflex. i) This reflex reduces the duration of inspiratory movements. ii) This prevents overinflation of the lungs during forceful breathing. e) Hyperventilation decreases CO2CO2 levels below normal, but this is dangerous when associated with breath holding during underwater swimming. 19.5 Alveolar Gas Exchanges Gas exchange between the air and the blood occurs in the alveoli. 1) Alveoli a) The alveoli are tiny sacs clustered at the distal ends of the alveolar ducts. b) Some alveoli open into adjacent air sacs through alveolar pores that provide alternate pathways for air when passages are obstructed. 2) Respiratory membrane a) The respiratory membrane consists of the alveolar and capillary walls and their joined basement membranes. b) Gas exchange takes place through these walls. 3) Diffusion through the respiratory membrane a) Gases diffuse from regions of higher partial pressure toward regions of lower partial pressure. b) Oxygen diffuses from the alveolar air into the blood; CO2CO2 diffuses from the blood into the alveolar air. 19.6 Gas Transport Blood carries gases between the lungs and the body cells. 1) Oxygen transport

a) Oxygen is mainly transported bound to hemoglobin molecules. b) The resulting oxyhemoglobin is unstable and releases its oxygen in regions where the PO2PO2 is low. c) More oxygen is released as the plasma PCO2PCO2 increases, as the blood becomes more acidic, and as the blood temperature increases. 2) Carbon dioxide transport a) CO2CO2 may be carried either as dissolved CO2CO2 in the plasma, CO2CO2 bound to hemoglobin, or as a bicarbonate ion. b) Most CO2CO2 is transported as part of bicarbonate ions in the plasma. c) Carbonic anhydrase in red blood cells speeds the reaction between CO2CO2 and water to form carbonic acid as well as the reverse reaction to breakdown carbonic acid into CO2CO2 and water. d) Carbonic acid dissociates to release hydrogen ions and bicarbonate ions. 19.7 Life-Span Changes The lungs, respiratory passageways, and alveoli undergo aging-associated changes exacerbated by exposure to polluted air. However, the increased work required to breathe with age is typically not noticeable unless one engages in vigorous exercise. 1. Exposure to pollutants, smoke, and other particulates raises the risk of developing diseases of the respiratory system. 2. Loss of cilia, thickening of mucus, and impaired macrophages raise the risk of infection. 3. Calcified cartilage, skeletal changes, altered posture, and replacement of smooth muscle with fibrous connective tissue in bronchioles make breathing more difficult. Vital capacity diminishes. 4. Physiologic dead space increases. 5. Alveoli coalesce, decreasing the surface area available for gas exchange....