Copyright © 2016 by Elsevier Inc. All rights reserved.

Learning Objectives Lesson 15.1: Respiratory System
Discuss the major functions of the respiratory system. List the major organs of the respiratory system and describe the functions of each. Compare, contrast, and explain the mechanism responsible for the exchange of gases that occurs during external and internal respiration. Copyright © 2016 by Elsevier Inc. All rights reserved.

Learning Objectives Lesson 15.1: Respiratory System (Cont.)
List and discuss the volumes of air exchanged during pulmonary ventilation. Identify and discuss the mechanisms that regulate respiration. Copyright © 2016 by Elsevier Inc. All rights reserved.

Structural Plan Overview Basic plan of respiratory system would be similar to an inverted tree if it were hollow; leaves of the tree would be comparable to alveoli, with the microscopic sacs enclosed by networks of capillaries (Figure 15-1) Passive transport process of diffusion is responsible for the exchange of gases that occur during respiration Respiratory organs include the nose, pharynx, larynx, trachea, bronchi, and lungs. Think of the air distribution system as an “upside-down tree.” Copyright © 2016 by Elsevier Inc. All rights reserved.

Structural Plan of the Respiratory System
Figure 15-1: Inset shows the alveolar sacs where the exchange of oxygen and carbon dioxide takes place through the walls of the grapelike alveoli. Capillaries surround the alveoli. Courtesy Barbara Cousins. Copyright © 2016 by Elsevier Inc. All rights reserved.

Structural Plan (Cont.)
Respiratory tract Upper respiratory tract Nose Pharynx Larynx Lower respiratory tract Trachea Bronchial tree Lungs The respiratory tract is the pathway of the airflow. The organs of the upper respiratory tract are located outside of the thorax. The organs of the lower respiratory tract are located almost entirely within the thorax. Copyright © 2016 by Elsevier Inc. All rights reserved.

Respiratory mucosa Structure Specialized membrane that lines the air distribution tubes in the respiratory tree (Figure 15-2) More than 125 mL of mucus produced each day forms a “mucous blanket” over much of the respiratory mucosa Mucus serves as an air purification mechanism by trapping inspired irritants such as dust and pollen Respiratory mucosa is typically ciliated pseudostratified epithelium. Goblet cells produce and release huge amounts of mucosa. Copyright © 2016 by Elsevier Inc. All rights reserved.

Respiratory mucosa Function Cilia on mucosal cells beat in only one direction, moving mucus upward to pharynx for removal Cigarette smoke and other irritants are detected by the cilia. Copyright © 2016 by Elsevier Inc. All rights reserved.

Respiratory Mucosa Figure 15-2, A, shows a light micrograph, and B shows a scanning electron micrograph of the ciliated pseudostratified epithelium typical of the respiratory lining. Copyright © 2016 by Elsevier Inc. All rights reserved.

Upper Respiratory Tract
Nose Structure Nasal septum separates interior of nose into two cavities Mucous membrane lines nose Frontal, maxillary, sphenoidal, and ethmoidal sinuses drain into nose (Figure 15-3) Function Warms and moistens inhaled air Contains sense organs of smell Symptoms of sinusitis include pressure, pain, headache, external tenderness, swelling, and redness. Three shelflike structures called conchae protrude into the nasal cavity on each side. Copyright © 2016 by Elsevier Inc. All rights reserved.

The Paranasal Sinuses Figure 15-3, A, is a lateral view of the position of the sinuses. Figure 15-3, B, is the anterior view that shows the anatomical relationship of the paranasal sinuses to each other and to the nasal cavity. A B Copyright © 2016 by Elsevier Inc. All rights reserved.

Upper Respiratory Tract (Cont.)
Pharynx Structure (Figure 15-4) About 12.5 cm (5 inches) long Divided into nasopharynx, oropharynx, and laryngopharynx Two nasal cavities, mouth, esophagus, larynx, and auditory tubes all have openings into pharynx Pharyngeal tonsils and openings of auditory tubes open into nasopharynx; tonsils found in oropharynx Mucous membrane lines pharynx Function Passageway for food and liquids Air distribution; passageway for air The right and left auditory tubes are called eustachian tubes. The lingual tonsils and the palatine tonsils are located in the oropharynx and the pharyngeal tonsils (adenoids) are in the nasopharynx. Copyright © 2016 by Elsevier Inc. All rights reserved.

Sagittal Section of the Head and Neck
Figure 15-4: The nasal septum has been removed, exposing the right lateral wall of the nasal cavity so that the nasal conchae can be seen. Copyright © 2016 by Elsevier Inc. All rights reserved.

Upper Respiratory Tract (Cont.)
Larynx Structure (Figure 15-5) Several pieces of cartilage form framework Thyroid cartilage (Adam’s apple) is largest Epiglottis partially covers opening into larynx Mucous lining Vocal cords stretch across interior of larynx Function Air distribution; passageway for air to move to and from lungs Voice production The larynx is located just below the pharynx. The larynx is composed of nine pieces of cartilage. The epiglottis partially covers the opening of the larynx. Copyright © 2016 by Elsevier Inc. All rights reserved.

The Larynx Figure 15-5, A, shows the sagittal section of the larynx. B shows the superior view of the larynx. C shows a photograph of the larynx taken with an endoscope through the mouth and pharynx. From Cox JD: Radiation oncology, ed 9, Philadelphia, 2010, Mosby. Copyright © 2016 by Elsevier Inc. All rights reserved.

Lower Respiratory Tract
Trachea Structure (Figure 15-6) Tube about 11 cm (4.5 inches) long that extends from larynx into the thoracic cavity Mucous lining C-shaped rings of cartilage hold trachea open Function Passageway for air to move to and from lungs Obstruction Blockage of trachea occludes the airway, and if blockage is complete, causes death in minutes Tracheal obstruction causes more than 4000 deaths annually in the United States The trachea is also known as the windpipe. By pushing your fingers against your throat about an inch above sternum, you can feel the shape of your trachea. Copyright © 2016 by Elsevier Inc. All rights reserved.

Cross Section of the Trachea
Figure 15-6, A, shows the structure of the trachea. B shows incomplete cartilage rings and elasticity of posterior tracheal wall, which allow the esophagus to expand during swallowing. Copyright © 2016 by Elsevier Inc. All rights reserved.

Lower Respiratory Tract (Cont.)
Bronchial tree Structure Trachea branches into right and left bronchi Each bronchus branches into smaller and smaller tubes eventually leading to bronchioles Bronchioles end in clusters of microscopic alveolar sacs, the walls of which are made up of alveoli (Figure 15-7) Function Air distribution Passageway for air to move to and from alveoli Alveoli Exchange of gases between air and blood (Figure 15-8) The trachea is the main trunk of this “upside-down tree.” Each alveolar duct ends in several alveolar sacs, which resemble a cluster of grapes. The surface of the respiratory membrane inside each alveolus is covered by surfactant. Copyright © 2016 by Elsevier Inc. All rights reserved.

Bronchioles and Alveoli
Figure 15-7 shows the bronchioles and the alveoli and how the bronchioles subdivide to form tiny tubes called alveolar ducts. Courtesy Network Graphics. Copyright © 2016 by Elsevier Inc. All rights reserved.

Alveolus and Respiratory Membrane
Figure 15-8 shows the alveolus and respiratory membrane. Each alveolus is continually ventilated with fresh air. Copyright © 2016 by Elsevier Inc. All rights reserved.

Lower Respiratory Tract (Cont.)
Lungs Structure (Figure 15-9) Size: Large enough to fill the chest cavity, except for middle space occupied by heart and large blood vessels Apex: Narrow upper part of each lung, under collarbone Base: Broad lower part of each lung; rests on diaphragm Pleura: Moist, smooth, slippery membrane that lines chest cavity and covers outer surface of lungs; reduces friction between the lungs and chest wall during breathing (Figure 15-10) Function Breathing (pulmonary ventilation) Deep grooves called fissures subdivide each lung into lobes. Pneumothorax is the presence of air in the intrapleural space on one side of the chest. Copyright © 2016 by Elsevier Inc. All rights reserved.

Lungs Figure 15-9 shows the lungs and how the trachea is an airway that branches to form an inverted tree of bronchi and bronchioles. Note that the right lung has three lobes and the left lung has two lobes. Copyright © 2016 by Elsevier Inc. All rights reserved.

Respiration Respiration means exchange of gases between a living organism and its environment (Figure 15-11) External respiration: Pulmonary ventilation (breathing) and pulmonary gas exchange Internal respiration: Systemic gas exchange and cellular respiration If the organism consists of only one cell, gases can move directly between it and the environment. If the organism consists of billions of cells (like our bodies), most of the cells are too far from the air for a direct exchange of gas and the lungs provide a place for the exchange. Copyright © 2016 by Elsevier Inc. All rights reserved.

Respiration (Cont.) Figure shows an overview of respiratory physiology. This chapter is organized around the principle that respiratory function includes external respiration (ventilation and pulmonary gas exchange), transport of gases by blood, and internal respiration (systemic tissue gas exchange and cellular respiration). Cellular respiration is discussed separately (see Chapter 17). Regulatory mechanisms centered in the brainstem use feedback from blood gas sensors to regulate ventilation. Copyright © 2016 by Elsevier Inc. All rights reserved.

Pulmonary Ventilation
Mechanics of breathing (Figure 15-12) Inspiration (movement of air into lungs) Active process: Air moves into lungs Inspiratory muscles include diaphragm and external intercostals Diaphragm flattens during inspiration: Increases top-to-bottom length of thorax External intercostals contraction elevates the ribs: Increases the size of the thorax from the front to the back and from side to side Increase in the size of the chest cavity reduces pressure within it; air then enters the lungs Inspiration occurs when the chest cavity enlarges. Volume and pressure of a gas are inversely proportional. Copyright © 2016 by Elsevier Inc. All rights reserved.

Pulmonary Ventilation (Cont.)
Mechanics of breathing Expiration (movement of air out of lungs) Quiet expiration is ordinarily a passive process During expiration, thorax returns to its resting size and shape Elastic recoil of lung tissues aids in expiration Expiratory muscles used in forceful expiration are internal intercostals and abdominal muscles Internal intercostals: Contraction depresses the rib cage and decreases the size of the thorax from the front to back Contraction of abdominal muscles elevates the diaphragm, thus decreasing size of the thoracic cavity from the top to bottom Reduction in the size of the thoracic cavity increases its pressure and air leaves the lungs When we speak, sing, or do heavy work, we may need more forceful expiration. Copyright © 2016 by Elsevier Inc. All rights reserved.

Pulmonary volumes (Figure 15-13) Spirometer measures amount of air exchanged in breathing Tidal volume We take 500 mL of air into our lungs with each normal inspiration and expel it with expiration Vital capacity The largest amount of air that we can inhale deeply and exhale fully Tidal volume and vital capacity are frequently measured in patients with lung disease such as emphysema or heart problems, conditions that often lead to abnormally low volumes of air being moved in and out of the lungs. Copyright © 2016 by Elsevier Inc. All rights reserved.

Pulmonary volumes Expiratory reserve volume (ERV) Amount of air that can be forcibly exhaled after expiring the tidal volume Inspiratory reserve volume (IRV) Amount of air that can be forcibly inspired over and above the normal inspiration As the tidal volume increases, the ERV and IRV decreases. Residual volume (RV) is the air that remains in the lungs after the most forceful expiration. Copyright © 2016 by Elsevier Inc. All rights reserved.

Regulation of ventilation (Figure 15-14) Homeostasis of blood gases Permits the body to adjust to varying demands for oxygen supply and carbon dioxide removal Brainstem control of respiration Most important central regulatory centers in medulla are called respiratory control centers (inspiratory and expiratory centers) Under resting conditions, nervous activity in the respiratory control centers produces a normal rate and depth of respirations (12 to 18 breaths a minute) The depth and rate of respiration can be influenced by many “inputs” to the brainstem’s respiratory control centers from other areas of the brain or sensory receptors. Copyright © 2016 by Elsevier Inc. All rights reserved.

Regulation of ventilation Cerebral cortex control of respiration Voluntary (but limited) control of respiratory activity Respiratory reflexes Chemoreceptors respond to changes in carbon dioxide, oxygen, and blood acid levels: Located in carotid and aortic bodies Pulmonary stretch reflexes: Respond to the stretch in lungs Pulmonary stretch reflexes protect respiratory organs from overinflation. Copyright © 2016 by Elsevier Inc. All rights reserved.

Regulation of Respiration
Figure shows the respiratory control centers in the brainstem that control the basic rate and depth of breathing. Clinical Application (Keeping the Trachea Open), Research, Issues, and Trends Box (Lung Volume Reduction Surgery), Courtesy Andrew P Evan, University of Indiana. Copyright © 2016 by Elsevier Inc. All rights reserved.

Breathing Patterns Various breathing patterns Eupnea Normal breathing Hyperventilation Rapid and deep respirations Hypoventilation Slow and shallow respirations Dyspnea Labored or difficult respirations Apnea Stopped respiration Respiratory arrest Failure to resume breathing after a period of apnea A series of alternating apnea and hyperventilation is called Cheyne-Stokes respiration (CSR). Copyright © 2016 by Elsevier Inc. All rights reserved.

Gas Exchange and Transport
Pulmonary gas exchange (Figure 15-15) Carbaminohemoglobin breaks down into carbon dioxide and hemoglobin Carbon dioxide moves out of lung capillary blood into alveolar air and out of body in expired air Oxygen moves from alveoli into lung capillaries Hemoglobin combines with oxygen, producing oxyhemoglobin Respiratory physiologists state that blood gas particles diffuse from an area of high partial pressure to an area of lower partial pressure. Oxygen is continually removed from the blood and used by body cells. Copyright © 2016 by Elsevier Inc. All rights reserved.

Gas Exchange and Transport (Cont.)
Systemic gas exchange Oxyhemoglobin breaks down into oxygen and hemoglobin Oxygen moves out of tissue capillary blood into tissue cells Carbon dioxide moves from tissue cells into tissue capillary blood Hemoglobin combines with carbon dioxide, forming carbaminohemoglobin Blood transportation of gases Transport of oxygen Transport of carbon dioxide Only small amounts of oxygen can be dissolved in the blood. Copyright © 2016 by Elsevier Inc. All rights reserved.

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