1. Chapter 23 The Respiratory System

2. Copyright John Wiley & Sons, Inc. All rights reserved. Upper respiratory tract Lower respiratory tract Respiratory System Anatomy Structurally, the respiratory system is divided into upper and lower divisions or tracts. The upper respiratory tract consists of the nose, pharynx and associated structures. The lower respiratory tract consists of the larynx, trachea, bronchi and lungs. 3. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy Functionally, the respiratory system is divided into the conducting zone and the respiratory zone. The conducting zone is involved with bringing air to the site of external respiration. The respiratory zone is the main site of gas exchange and consists of the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. 4. Copyright John Wiley & Sons, Inc. All rights reserved. Air passing through the respiratory tract traverses the: Nasal cavity Pharynx Larynx Trachea Primary (1o ) bronchi Secondary (2o ) bronchi Tertiary (3o ) bronchi Bronchioles Alveoli (150 million/lung) Respiratory System Anatomy 5. Copyright John Wiley & Sons, Inc. All rights reserved. The external nose is visible on the face. The internal nose is a large cavity beyond the nasal vestibule. Respiratory System Anatomy 6. Copyright John Wiley & Sons, Inc. All rights reserved. Three nasal conchae (or turbinates) protrude from each lateral wall into the breathing passages. Respiratory System Anatomy 7. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The pharynx is a hollow tube that starts posterior to the internal nares and descends to the opening of the larynx in the neck. It is formed by a complex arrangement of skeletal muscles that assist in deglutition. It functions as: o a passageway for air and food o a resonating chamber o a housing for the tonsils 8. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The pharynx has 3 anatomical regions: The nasopharynx; oropharynx; and laryngopharynx 9. Copyright John Wiley & Sons, Inc. All rights reserved. The nasopharynx lies behind the internal nares. It contains the pharyngeal tonsils (adenoids) and the openings of the Eustachian tubes (auditory tubes) which come off of it and travels to the middle ear cavity. Respiratory System Anatomy 10. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The oropharynx lies behind the mouth and participates in both respiratory and digestive functions. The main palatine tonsils (those usually taken in a tonsillectomy) and small lingual tonsil are housed here. The laryngopharynx lies inferiorly and opens into the larynx (voice box) and the esophagus. It participates in both respiratory and digestive functions. 11. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy 12. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The larynx, composed of 9 pieces of cartilage, forms a short passageway connecting the laryngopharynx with the trachea (the windpipe). Cartilages include thyroid, Cricoid and epiglottis. Anterior view of the larynx 13. Copyright John Wiley & Sons, Inc. All rights reserved. The epiglottis is a flap of elastic cartilage covered with a mucus membrane, attached to the root of the tongue. The epiglottis guards the entrance of the glottis, the opening between the vocal folds. o For breathing, it is held anteriorly, then pulled back- ward to close off the glottic opening during swallowing. Respiratory System Anatomy 14. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The rima glottidis (glottic opening) is formed by a pair of mucous membrane vocal folds (the true vocal cords). The vocal folds are situated high in the larynx just below where the larynx and the esophagus split off from the pharynx. 15. Copyright John Wiley & Sons, Inc. All rights reserved. Cilia in the upper respiratory tract move mucous and trapped particles down toward the pharynx. Cilia in the lower respiratory tract move them up toward the larynx. Respiratory System Anatomy 16. Copyright John Wiley & Sons, Inc. All rights reserved. Upper respiratory tract Lower respiratory tract Respiratory System Anatomy As air passes from the laryngopharynx into the larynx, it leaves the upper respiratory tract and enters the lower respiratory tract. Air passing through the respiratory tract Nasal cavity Pharynx Larynx Trachea Primary bronchi Secondary bronchi Tertiary bronchi Bronchioles Alveoli (150 million/lung) 17. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The trachea is a semi-rigid pipe made of semi-circular cartilaginous rings, and located anterior to the esophagus. It is about 12 cm long and extends from the inferior portion of the larynx into the mediastinum where it divides into right and left primary (1o , mainstem) bronchi. It is composed of 4 layers: a mucous secreting epithelium called the mucosa, and three layers of CT (submucosa, hyaline cartilage, and adventitia). 18. Copyright John Wiley & Sons, Inc. All rights reserved. The tracheal cartilage rings are incomplete posteriorly, facing the esophagus. Esophageal masses can press into this soft part of the trachea and make it difficult to breath, or even totally obstruct the airway. Respiratory System Anatomy 19. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The right and left primary (1o or mainstem) bronchi emerge from the inferior trachea to go to the lungs, situated in the right and left pleural cavities. The carina is an internal ridge located at the junction of the two mainstem bronchi a very sensitive area for triggering the cough reflex. 20. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The 1o bronchi divide to form 2o and 3o bronchi which respectively supply the lobes and segments of each lung. 3o bronchi divide into bronchioles which in turn branch through about 22 more divisions (generations). o The smallest are the terminal bronchioles. 21. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The bronchi and bronchioles go through structural changes as they branch and become smaller. The mucous membrane changes and then disappears. The cartilaginous rings become more sparse, and eventually disappear altogether. As cartilage decreases, smooth muscle (under the control of the Autonomic Nervous System) increases. o Sympathetic stimulation causes airway dilation, while parasympathetic stimulation causes airway constriction. 22. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy All the branches from the trachea to the terminal bronchioles are conducting airways they do not participate in gas exchange. 23. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy The cup-shaped outpouchings which participate in gas exchange are called alveoli. The first alveoli dont appear until the respiratory bronchioles where they are rudimentary and mostly nonfunctioning. 24. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy Respiratory bronchioles give way to alveolar ducts, and the epithelium (simple cuboidal) changes to simple squamous, which comprises the alveolar ducts, alveolar sacs, and alveoli. 25. Copyright John Wiley & Sons, Inc. All rights reserved. Taken together, these structures form the functional unit of the lung, which is the pulmonary lobule. Wrapped in elastic C.T., each pulmonary lobule contains a lymphatic vessel, an arteriole, a venule and a terminal bronchiole. The pulmonary lobule Respiratory System Anatomy 26. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy As part of the pulmonary lobule, alveoli are delicate structures composed chiefly of type I alveolar cells, which allow for exchange of gases with the pulmonary capillaries. Alveoli make up a large surface area (750 ft2). Type II cells secrete a substance called surfactant that prevents collapse of the alveoli during exhalation. 27. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy Alveoli macrophages (also called dust cells) scavenge the alveolar surface to engulf and remove microscopic debris that has made it past the mucociliary blanket that traps most foreign particles higher in the respiratory tract. The alveoli (in close proximity to the capillaries) form the alveolar-capillary membrane (AC membrane). 28. Copyright John Wiley & Sons, Inc. All rights reserved. Blood Supply to the Lungs The lungs receive blood via two sets of arteries Pulmonary arteries carry deoxygenated blood from the right heart to the lungs for oxygenation Bronchial arteries branch from the aorta and deliver oxygenated blood to the lungs primarily perfusing the muscular walls of the bronchi and bronchioles 29. Copyright John Wiley & Sons, Inc. All rights reserved. Ventilation-Perfusion Coupling Ventilation-perfusion coupling is the coupling of perfusion (blood flow) to each area of he lungs to match the extent of ventilation (airflow) to alveoli in that area In the lungs, vasoconstriction in response to hypoxia diverts pulmonary blood from poorly ventilated areas of the lungs to well-ventilated regions In all other body tissues, hypoxia causes dilation of blood vessels to increase blood flow 30. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy 31. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy 32. Copyright John Wiley & Sons, Inc. All rights reserved. Respiratory System Anatomy 33. Copyright John Wiley & Sons, Inc. All rights reserved. Understanding Gases The respiratory system depends on the medium of the earths atmosphere to extract the oxygen necessary for life. The atmosphere is composed of these gases: Nitrogen (N2) 78% Oxygen (O2) 21% Carbon Dioxide (CO2) 0.04% Water Vapor variable, but on average around 1% 34. Copyright John Wiley & Sons, Inc. All rights reserved. Understanding Gases The gases of the atmosphere have a mass and a weight (5 x 1018 kg, most within 11 km of the surface). Consequently, the atmosphere exerts a significant force on every object on the planet (recall that pressure is measured as force applied per unit area, P = F/A.) We are accustomed to the tremendous force pressing down on every square inch of our body. 35. Copyright John Wiley & Sons, Inc. All rights reserved. Understanding Gases A barometer is an instrument that measures atmospheric pressure. Baro = pressure or weight Meter = measure Air pressure varies greatly depending on the altitude and the temperature. 36. Copyright John Wiley & Sons, Inc. All rights reserved. Understanding Gases There are many different units used to measure atmospheric pressure. At sea level, the air pressure is: 14.7 lb/in2 = 1 atmosphere 760 mmHg = 1 atmosphere 76 cmHg = 1 atmosphere 29.9 inHg = 1 atmosphere At high altitudes, the atmospheric pressure is less; descending to sea level, atmospheric pressure is greater. 37. Copyright John Wiley & Sons, Inc. All rights reserved. Understanding Gases Gases obey laws of physics called the gas laws. These laws apply equally to the gases of the atmosphere, the gases in our lungs, the gases dissolved in the blood, and the gases diffusing into and out of the cells of our body. To understand the mechanics of ventilation and respiration, we need to have a basic understanding of 3 of the 5 common gas laws. 38. Copyright John Wiley & Sons, Inc. All rights reserved. Understanding Gases Boyles law applies to containers with flexible walls like our thoracic cage. It says that volume and pressure are inversely related. o If there is a decrease in volume there will be an increase in pressure. o V 1/P 39. Copyright John Wiley & Sons, Inc. All rights reserved. Understanding Gases Daltons law applies to a mixture of gases. It says that the pressure of each gas is directly proportional to the percentage of that gas in the total mixture: PTotal = P1 + P2 + P3 Since O2 = 21% of atmosphere, the partial pressure exerted by the contribution of just O2 (written pO2 or PAO2) = 0.21 x 760 mmHg = 159.6 mmHg at sea level. 40. Copyright John Wiley & Sons, Inc. All rights reserved. Understanding Gases Henrys law deals with gases and solutions. It says that increasing the partial pressure of a gas over (in contact with) a solution will result in more of the gas dissolving into the solution. The patient in this picture is getting more O2 in contact with his blood - consequently, more oxygen goes into his blood. Medicimage/Phototake 41. Copyright John Wiley & Sons, Inc. All rights reserved. Ventilation and Respiration Pulmonary ventilation is the movement of air between the atmosphere and the alveoli, and consists of inhalation and exhalation. Ventilation, or breathing, is made possible by changes in the intrathoracic volume. 42. Copyright John Wiley & Sons, Inc. All rights reserved. Ventilation and Respiration In contrast to ventilation, respiration is the exchange of gases. External respiration (pulmonary) is gas exchange between the alveoli and the blood. Internal respiration (tissue) is gas exchange between the systemic capillaries and the tissues of the body. 43. Copyright John Wiley & Sons, Inc. All rights reserved. Ventilation and Respiration Certain thoracic muscles participate in inhalation; others aid exhalation. The diaphragm is the primary muscle of respiration all the others are accessory. 44. Copyright John Wiley & Sons, Inc. All rights reserved. Measuring Ventilation Ventilation can be measured using spirometry. Tidal Volume (VT) is the volume of air inspired (or expired) during normal quiet breathing (500 ml). Inspiratory Reserve Volume (IRV) is the volume inspired during a very deep inhalation (3100 ml height and gender dependent). Expiratory Reserve Volume (ERV) is the volume expired during a forced exhalation (1200 ml). 45. Copyright John Wiley & Sons, Inc. All rights reserved. Measuring Ventilation Spirometry continued Vital Capacity (VC) is all the air that can be exhaled after maximum inspiration. o It is the sum of the inspiratory reserve + tidal volume + expiratory reserve (4800 ml). Residual Volume (RV) is the air still present in the lungs after a force exhalation (1200 ml). o The RV is a reserve for mixing of gases but is not available to move in or out of the lungs. 46. Copyright John Wiley & Sons, Inc. All rights reserved. Measuring Ventilation Old and new spirometers used to measure ventilation. 47. Copyright John Wiley & Sons, Inc. All rights reserved. Measuring Ventilation A graph of spirometer volumes and capacities 48. Copyright John Wiley & Sons, Inc. All rights reserved. Measuring Ventilation Only about 70% of the tidal volume reaches the respiratory zone the other 30% remains in the conducting zone (called the anatomic dead space). If a single VT breath = 500 ml, only 350 ml will exchange gases at the alveoli. o In this example, with a respiratory rate of 12, the minute ventilation = 12 x 500 = 6000 ml. o The alveolar ventilation (volume of air/min that actually reaches the alveoli) = 12 x 350 = 4200ml. 49. Copyright John Wiley & Sons, Inc. All rights reserved. Exchange of O2 and CO2 Using the gas laws and understanding the principals of ventilation and respiration, we can calculate the amount of oxygen and carbon dioxide exchanged between the lungs and the blood. 50. Copyright John Wiley & Sons, Inc. All rights reserved. Exchange of O2 and CO2 Daltons Law states that each gas in a mixture of gases exerts its own pressure as if no other gases were present. The pressure of a specific gas is the partial pressure Pp. Total pressure is the sum of all the partial pressures. Atmospheric pressure (760 mmHg) = PN2 + PO2 + PH2O + PCO2 + Pother gases o Since O2 is 21% of the atmosphere, the PO2 is 760 x 0.21 = 159.6 mmHg. 51. Copyright John Wiley & Sons, Inc. All rights reserved. Exchange of O2 and CO2 Each gas diffuses across a permeable membrane (like the AC membrane) from the side where its partial pressure is greater to the side where its partial pressure is less. The greater the difference, the faster the rate of diffusion. Since there is a higher PO2 on the lung side of the AC membrane, O2 moves from the alveoli into the blood. Since there is a higher PCO2 on the blood side of the AC membrane, CO2 moves into the lungs. 52. Copyright John Wiley & Sons, Inc. All rights reserved. Exchange of O2 and CO2 PN2 = 0.786 x 760 mmHg = 597.4 mmHg PO2 = 0.209 x 760 mmHg = 158.8 mmHg PH2O = 0.004 x 760 mmHg = 3.0 mmHg PCO2 = 0.0004 x 760 mmHg = 0.3 mmHg Pother gases = 0.0006 x 760 mmHg = 0.5 mmHg Total = 760.0 mmHg Partial pressures of gases in inhaled air for sea level 53. Copyright John Wiley & Sons, Inc. All rights reserved. Transport of O2 and CO2 In the blood, some O2 is dissolved in the plasma as a gas (about 1.5%, not enough to stay alive not by a long shot!). Most O2 (about 98.5%) is carried attached to Hb. Oxygenated Hb is called oxyhemoglobin. 54. Copyright John Wiley & Sons, Inc. All rights reserved. Transport of O2 and CO2 CO2 is transported in the blood in three different forms: 1. 7% is dissolved in the plasma, as a gas. 2. 70% is converted into carbonic acid through the action of an enzyme called carbonic anhydrase. o CO2 + H2O H2CO3 H+ + HCO3 - 3. 23% is attached to Hb (but not at the same binding sites as oxygen). 55. Copyright John Wiley & Sons, Inc. All rights reserved. Transport of O2 and CO2 The amount of Hb saturated with O2 is called the SaO2. Each Hb molecule can carry 1, 2, 3, or 4 molecules of O2. Blood leaving the lungs has Hb that is fully saturated (carrying 4 molecules of O2 oxyhemoglobin). o The SaO2 is close to 95-98% . When it returns, it still has 3 of the 4 O2 binding sites occupied. o SaO2 = 75% 56. Copyright John Wiley & Sons, Inc. All rights reserved. Transport of O2 and CO2 Measuring SaO2 has become as commonplace in clinical practice as taking a blood pressure. Pulse oximeters which used to cost $5,000 can now be purchased at your local pharmacy. 3660 Group, Inc/NewsCom 57. Copyright John Wiley & Sons, Inc. All rights reserved. Transport of O2 and CO2 Although PO2 is the most important determinant of SaO2, several other factors influence the affinity with which Hb binds O2 . Acidity (pH), PCO2 and blood temperature shift the entire O2 Hb saturation curve either to the left (higher affinity for O2), or to the right (lower affinity for O2). 58. Copyright John Wiley & Sons, Inc. All rights reserved. Transport of O2 and CO2 59. Copyright John Wiley & Sons, Inc. All rights reserved. Fetal and Maternal Hemoglobin Fetal hemoglobin (Hb-F) has a higher affinity for oxygen (it is shifted to the left) than adult hemoglobin A, so it binds O2 more strongly. The fetus is thus able to attract oxygen across the placenta and support life, without lungs. 60. Copyright John Wiley & Sons, Inc. All rights reserved. Initial Response Mucous layer thickens. Goblet cells over-secrete mucous. Basal cells proliferate. Advanced Response to Irritation Mucous layer and goblet cells disappear. Basal cells become malignant & invade deeper tissue. Normal columnar epithelium in the respiratory tract Response to Pollutants 61. Copyright John Wiley & Sons, Inc. All rights reserved. Diseases and Disorders Asthma is a disease of hyper-reactive airways (the major abnormality is constriction of smooth muscle in the bronchioles, and inflammation.) It presents as attacks of wheezing, coughing, and excess mucus production. It typically occurs in response to allergens; less often to emotion. Bronchodilators and anti- inflammatory corticosteroids are mainstays of treatment. Pulse Picture Library/CMP mages /Phototake 62. Copyright John Wiley & Sons, Inc. All rights reserved. Diseases and Disorders Chronic bronchitis and emphysema are caused by chronic irritation and inflammation leading to lung destruction. Patients may cough up green-yellow sputum due to infection and increased mucous secretion (productive cough). They are almost exclusively diseases of cigarette smoking. 63. Copyright John Wiley & Sons, Inc. All rights reserved. Diseases and Disorders Pneumonia is an acute infection of the lowest parts of the respiratory tract. The small bronchioles and alveoli become filled with an inflammatory fluid exudate. o It is typically caused by infectious agents such as bacteria, viruses, or fungi. 64. Copyright John Wiley & Sons, Inc. All rights reserved. Diseases and Disorders Normal Lungs Pneumonia Patient Du Cane Medical Imaging, Ltd./Photo Researchers, Inc