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Respiratory System
Chapter 17
Respiration
Respiration means exchange of gases (oxygen and carbon dioxide) between a living organism and its environment. The respiratory system performs two basic functions; they serve as an air distributor and as a gas exchanger for the body. The respiratory system ensures that oxygen is supplied to and carbon dioxide is removed from the body's cells. In addition to air distribution and gas exchange, the respiratory system effectively filters, warms, and humidifies the air we breathe. The sinuses also help produce speech or other sounds, help in sense of smell, or olfaction and maintains the pH balance of the body.
Structures of Respiratory System
Respiratory organs include the nose, pharynx, larynx, trachea, bronchi, and lungs which contains millions of sacs like structures called alveoli. A network of capillaries fits like a hairnet around each microscopic alveolus. Two characteristics about the structure of alveoli assist in diffusion and make them able to perform exchange of
gases: o First, the wall of each alveolus is made up of a single layer of cells and so are the thin walls of the capillaries around it. This means that between the blood in the capillaries and the air in the alveolus, there is a barrier probably less than 1 micron thick. This extremely thin barrier is called the respiratory membrane. o Second, there are millions of alveoli and together they make an enormous surface (approximately 100 square meters, an area many times larger than the surface of the entire body) where large amounts of oxygen and carbon dioxide can rapidly be exchanged. Respiratory Tracts The respiratory system is often divided into upper and lower tracts or divisions. The organs of the upper respiratory tract are located outside of the thorax or chest cavity, whereas those in the lower tract, or division, are located almost entirely within it. o The upper respiratory tract is composed of the nose, pharynx, and larynx. o The lower respiratory tract, or division, consists of the trachea, all segments of the bronchial tree, and the lungs. Respiratory Mucosa o Mucous membrane that lines the air distribution tubes in the respiratory tree. More than 125 ml of mucus produced each day by goblet cells forms a "mucus blanket" over much of the respiratory mucosa o Mucus serves as an air purification mechanism by trapping inspired irritants such as dust and pollen, bacterial organisms, and even insects o Cilia on mucosal cells beat in only one direction, moving mucus upward to pharynx for removal. o Cigarette smoke and other chronic irritants both increase production of mucus and paralyze cilia, thus causing accumulations of contaminated mucus to build up and remain in the respiratory passageways for longer periods of time. The result is a typical smoker's cough, which is the body's effort to clear the secretions
Nose
o Air enters the respiratory tract through the external nares, or nostrils. It then flows into the right and left nasal cavities, which are lined by respiratory mucosa. A partition called the nasal septum separates these two cavities. o The surface of the nasal cavities is moist from mucus and warm from blood flowing just under it.
Two nasal cavities, mouth, esophagus, larynx, and auditory tubes all have openings into pharynx. Air and food pass through the pharynx on their way to the lungs and the stomach, respectively. Air enters the pharynx from the two nasal cavities and leaves it by way of the larynx; food enters it from the mouth and leaves it by way of the esophagus. The right and left auditory, or Eustachian tubes open into the nasopharynx. They connect middle ear with nasopharynx which permits equalization of air pressure between the middle ear and the exterior ear.
Masses of lymphatic tissue called tonsils are embedded in the mucous membrane of the pharynx. The palatine tonsils and ligual tonsils are located in the oropharynx and the pharyngeal also called the adenoids , are located in the nasopharynx.
Larynx
o The larynx, or voice box, is located just below the pharynx. It is composed of several pieces of cartilage. Largest of these (the thyroid cartilage) as the "Adam's apple" o Two short fibrous bands, the vocal cords, stretch across the interior of the larynx. o The space between the vocal cords is the glottis. o Another piece of cartilage, the epiglottis, partially covers the opening of the larynx. The epiglottis acts like a trapdoor, closing off the larynx during swallowing and preventing food from entering the trachea.
Disorders of the Upper Respiratory Tract
Upper respiratory infection (URI)- Any infection localized in the mucosa of the upper respiratory tract (nose, pharynx, and larynx) can be called an upper respiratory infection (URI). o Rhinitis —nasal inflammation, as in a cold, influenza, or allergy. Most cases of infectious rhinitis are caused by viruses responsible for the common cold (rhinoviruses) or the flu (influenza viruses). The term allergic rhinitis, or "hay fever," is used to describe sensitivity-type reactions to many types of nasal irritants and airborne allergens including animal dander and plant pollens. o Pharyngitis (sore throat)—inflammation or infection of the pharynx. Pharyngitis may be caused by any of several pathogens, including the streptococcal bacteria that cause "strep throat" o Laryngitis —inflammation of the larynx resulting from infection or irritation. The condition may be caused by bacteria, viruses, exposure to allergens, or by overuse of the voice, smoking, and other factors. Even a moderate amount of laryngeal swelling or edema, especially in a young child, can obstruct air flow and result in asphyxiation. o Epiglottitis — Epiglottitis is a life-threatening condition caused by Haemophilus influenzae type B (Hib) infection. Hib often struck children between 3 and 7 years of age a generation ago but with the introduction of Hib vaccines at the end of the twentieth century produced a 99% drop in the incidence of this infection. o Croup —The term croup is used to describe a non-life-threatening type of laryngitis generally seen in children younger than age 3. It is caused by the parainfluenza viruses. Symptoms include a harsh bark-like cough and labored inspiration.
o The bronchioles subdivide into microscopic tubes called alveolar ducts. Each alveolar duct ends in several alveolar sacs, each of which resembles a cluster of grapes, and the wall of each alveolar sac is made up of numerous alveoli, each of which resembles a single grape. o Alveoli are very effective in exchanging gas, firstly because of extremely thin Respiratory Membrane formed by the thin wall of each alveolus and the thin membrane of blood capillary, and secondly there are millions of alveoli in each lung. The surface of the respiratory membrane inside the alveolus is covered by a substance called surfactant. This important substance helps reduce surface tension in the alveoli and keeps them from collapsing as air moves in and out during respiration
Respiratory distress
Respiratory distress results from the body's relative inability to inflate the alveoli of the lungs normally. Respiratory distress syndrome (RDS) is a condition most often caused by absence or impairment of the surfactant in the fluid that lines the alveoli. a. Infant respiratory distress Syndrome (IRDS): a very serious, life-threatening condition that often affects premature infants of less than 37 weeks’ gestation or those who weigh less than 2.2 kg (5 lb) at birth. The disease, characterized by a lack of surfactant in the alveolar air sacs. In newborn infants who are unable to manufacture surfactant, many air sacs collapse during expiration because of the increased surface tension. The baby soon develops labored breathing, and symptoms of respiratory distress appear shortly after birth. Current treatment of IRDS usually involves delivering air under pressure and applying prepared surfactant directly into the baby’s airways by means of a tube. b. Adult respiratory distress syndrome (ARDS) is caused by impairment or removal of surfactant in the alveoli. For example, accidental inhalation of foreign substances such as water, vomit, smoke, or chemical fumes can cause ARDS. Edema of the alveolar tissue can impair surfactant and reduce the alveoli's ability to stretch, causing respiratory distress.
Lungs and Pleura
The lungs are fairly large organs, large enough to fill the chest cavity, except for middle space (mediastinum)
occupied by heart and large blood vessels The right lung has three lobes, and the left lung has two. The narrow, superior position of each lung, up under the collarbone, is the apex; the broad, inferior portion resting on the diaphragm is the base. Each lung is made up of all the elements of the bronchial tree, alveoli, and pulmonary blood vessels—along with connective tissues, lymphatic vessels, and nerves. o
Disorders of the Lower Respiratory Tract
Lower respiratory infection Acute bronchitis, or tracheobronchitis —inflammation of the bronchi or bronchi and trachea caused by infection (usually resulting from the spread of a URI). Acute bronchitis often starts with a nonproductive cough that progresses to a deep cough that produces sputum containing mucus and pus. Pneumonia —Pneumonia is an acute inflammation of the lungs in which the alveoli and bronchi become plugged with thick fluid (exudate). The vast majority of pneumonia cases result from infection by Streptococcus pneumoniae bacteria, but can be caused by several other bacteria, viruses, and fungi. Pneumonia is characterized by a high fever, severe chills, headache, cough, and chest pain. Aspiration pneumonia describes lung infections caused by inhalation of vomit or other infective material. It is common in acute alcohol intoxication and as a result of anesthesia. Tuberculosis (TB )— Tuberculosis (TB) is a chronic bacillus infection caused by Mycobacterium tuberculosis. TB is a highly contagious disease transmitted through inhalation or swallowing of droplets contaminated with the TB bacillus. It usually affects the lungs and surrounding tissues but can invade any other tissue or organ as well. Early stages of TB are characterized by fatigue, chest pain, pleurisy, weight loss, and fever. As the disease progresses, lung hemorrhage and dyspnea may develop. Successful treatment requires a combination of drugs and other therapies for an extended period—usually longer than a year. Restrictive pulmonary disorders reduce the ability of lung tissues to stretch (as during inspiration) caused by exposure to asbestos, coal, or silicon dust can reduce compliance and thus restrict alveoli. Restriction of breathing also can be caused by the pain that accompanies pleurisy or mechanical injuries, such as rib fractures. Another type of restrictive disorder is cystic fibrosis (CF), which is characterized by thickened fluids in the lungs, which restricts compliance.
Obstructive Pulmonary Disorders
COPD (chronic obstructive pulmonary disease) o A number of different conditions may cause obstruction of the airways. For example, exposure to cigarette smoke and other common air pollutants can trigger a reflexive constriction of bronchial airways. o In obstructive disorders, the total lung capacity may be normal, or even high, but the time it takes to inhale or exhale maximally is significantly increased. o The major disorders observed in people with COPD are chronic bronchitis and emphysema. o In North America, tobacco use is the primary cause of COPD, but air pollution, asthma, and respiratory infections also play a role. o Acute respiratory failure can occur when any of the disorders that produce COPD become intense. o Bronchodilators and corticosteroids have been used to relieve some of the airway obstruction involved in COPD. Chronic bronchitis is a chronic inflammation of the bronchi and bronchioles. It is characterized by edema and excessive mucus production, which block air passages. People with chronic bronchitis have difficulty with
exhaling and often cough deeply as they try to dislodge the accumulating mucus. The major cause of chronic bronchitis is cigarette smoking or exposure to cigarette smoke. Exposure to other air pollutants also may cause chronic bronchitis. Emphysema result from the progression of chronic bronchitis or other conditions as air becomes trapped within alveoli and causes them to enlarge. As the alveoli enlarge, their walls rupture and then fuse into large irregular spaces. The rupture of alveoli reduces the total surface area of the lung, making breathing difficult. Emphysema victims often develop hypoxia, or oxygen deficiency, in the internal environment. Asthma is an obstructive disorder characterized by recurring spasms of the smooth muscle in the walls of the bronchial air passages. The muscle contractions narrow the airways, making breathing difficult. Inflammation (edema and excessive mucus production) usually accompanies the spasms, further obstructing the airways. Asthma can be triggered by stress, heavy exercise, infection, or inhaling allergens or other irritants. Lung cancer— The most common predisposing condition associated with lung cancer is cigarette smoking (accounting for about 75% of lung cancer cases). Other factors thought to cause lung cancer include exposure to "second-hand" cigarette smoke, asbestos, chromium, coal products, petroleum products, rust, and ionizing radiation (as in radon gas).
Respiration
Respiration means exchange of gases (oxygen and carbon dioxide) between a living organism and its environment. Two types of respiration: o External Respiration : Exchange of gases between lungs and environment. It is also known as breathing, or pulmonary ventilation which makes possible the exchange of gases between air in the lungs and in the blood. o Internal Respiration: Exchange of gases occurs between the blood and the cells of the body Cellular respiration refers to the actual use of oxygen by cells in the process of metabolism.
Vital capacity (VC) is the total of tidal volume, inspiratory reserve volume and expiratory reserve volume—or expressed in another way: VC = TV + IRV + ERV. Residual volume (RV) is simply the air that remains in the lungs after the most forceful expiration.
Regulation of Pulmonary Ventilation
Normal respiration depends on proper functioning of the muscles of respiration which are stimulated by nervous impulses that originate in respiratory control centers located in the brainstem. The brainstem centers are influenced by input from a number of sensory receptors located in different areas of the body. These receptors can sense the need for changing the rate or depth of respirations to maintain homeostasis. Certain receptors sense carbon dioxide or oxygen levels, whereas others sense blood acid levels or the amount of stretch in lung tissues Central regulatory centers in the brainstem are called respiratory control center. o Medullary centers —under resting conditions the medullary rhythmicity area produces a normal rate and depth of respirations (12 to 18 per minute) o Pontine centers —as conditions in the body vary, these centers in the pons can alter the activity of the medullary rhythmicity area, thus adjusting breathing rhythm o Brainstem centers are influenced by information from other parts of the brain and from sensory receptors located in other body areas Cerebral cortex —voluntary (but limited) control of respiratory activity Receptors influencing respiration
- Chemoreceptors —respond to changes in carbon dioxide, oxygen, and blood acid levels—located in carotid and aortic bodies
- Pulmonary stretch receptors —respond to the stretch in lungs, thus protecting respiratory organs from over inflation
Breathing Patterns
o Eupnea—normal breathing. o Hyperventilation—rapid and deep respirations o Hypoventilation—slow and shallow respirations o Dyspnea—labored or difficult respirations o Orthopnea—dyspnea relieved by moving into an upright or sitting position o Apnea—stopped respiration o Cheyne-Stokes respiration (CSR)— A series of cycles of alternating apnea and hyperventilation is called Cheyne-Stokes (chain-stokes) respiration (CSR). CSR occurs in critical diseases such as congestive heart failure, brain injuries, or brain tumors. CSR also may occur in the case of a drug overdose. o Respiratory arrest—failure to resume breathing after a period of apnea
Gas Exchange and Transport
Pulmonary Gas Exchange
o External respiration or the exchange of gases between the blood and alveolar air occurs by diffusion. During diffusion, substances move from an area of high concentration to an area of low concentration. o Diffusion of Oxygen (O 2 )- Blood flowing into lung capillaries is low in oxygen. Because alveolar air in lungs is rich in oxygen, diffusion causes movement of oxygen from the area of high concentration (lung) to the area of low concentration (capillary blood). o Diffusion of carbon dioxide (CO 2 )- Blood flowing through the lung capillaries is high in carbon dioxide. Diffusion of carbon dioxide results in its movement from an area of high concentration in the pulmonary capillaries to an area of low concentration in alveolar air. Then from the alveoli, carbon dioxide leaves the lung to the environment.
Exchange of Gases in Tissues
o The exchange of gases that occurs between blood in tissue capillaries and the body cells is called internal
respiration. o Diffusion of Oxygen (O 2 )- Blood flowing into tissue capillaries is high in oxygen Oxyhemoglobin breaks down into oxygen and hemoglobin in the tissue capillaries. Oxygen molecules move rapidly out of the blood through the tissue capillary membrane into the interstitial fluid and on into the cells. o Diffusion of carbon dioxide (CO 2 )- While oxygen is moving down its concentration gradient, carbon dioxide molecules leave the cells from its high concentration area, entering the tissue capillaries where CO 2 is less in concentration..
Blood Transportation of Gases
Transport of Oxygen Oxygen is transported in the blood circulation in two forms: as simply dissolved O 2 in the plasma and as a combination of O 2 and hemoglobin (oxyhemoglobin). Of these two forms of transport, oxyhemoglobin is the carrier of the vast majority of the total oxygen transported by the blood. Transport of Carbon Dioxide CO 2 is transported in the blood to the lungs in one of three forms: As dissolved carbon dioxide (CO 2 )- 10% of the total amount of carbon dioxide is carried in the dissolved form. As carbaminohemoglobin- About 20% of the total CO 2 transported in the blood is in the form of carbaminohemoglobin. It is formed by the union of carbon dioxide, hemoglobin, and certain other plasma proteins. Bicarbonate ions (HCO 3 ~). About 70% of the total CO 2 transported in the blood is carried in the form of bicarbonate ions. When CO 2 dissolves in water (as in blood plasma), some of the CO 2 molecules associate with water to form carbonic acid (H 2 CO 3 ). Once formed, some of the H 2 CO 3 molecules dissociated to form hydrogen (H+) and bicarbonate (HCO 3 ~) ions.
