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1. 22 The Respiratory System:Part A

2. Respiration = Respiratory & Circulatory • Pulmonary ventilation (breathing):movement of air into and outof the lungs • External respiration: O2 and CO2exchange between the lungsand the blood • Transport: O2 and CO2in the blood • Internal respiration: O2 and CO2exchange between systemic bloodvessels and tissues Respiratory system Circulatory system

3. Cellular Respiration • Oxygen (O2) is used by the cells • O2 needed in conversion of glucose to cellular energy (ATP) • All body cells • Carbon dioxide (CO2) is produced as a waste product • The body’s cells die if either the respiratory or cardiovascular system fails

4. The Respiratory Organs Conducting zone • Respiratory passages that carry air to the site of gas exchange • Filters, humidifies and warms air Respiratory zone • Site of gas exchange • Composed of • Respiratory bronchioles • Alveolar ducts • Alveolar sacs Conducting zone labeled

5. Conducting zone will be covered first The Nose • Provides an airway for respiration • Moistens and warms the entering air • Filters and cleans inspired air • Serves as a resonating chamber for speech • Houses olfactory receptors

6. Nasal Cavity • Respiratory mucosa • Pseudostratified ciliated columnar epithelium • Mucous and serous secretions contain lysozyme and defensins • Cilia move contaminated mucus posteriorly to throat • Inspired air is warmed by plexuses of capillaries and veins • Sensory nerve endings triggers sneezing

7. Functions of the Nasal Mucosa and Conchae • During inhalation, the conchae and nasal mucosa • Filter, heat, & moisten air • During exhalation these structures • Reclaim heat and moisture

8. Pharynx • Muscular tube that connects to the • Nasal cavity and mouth superiorly • Larynx and esophagus inferiorly • Houses tonsils (respond to inhaled antigens) 3 Parts of Pharynx Nasopharynx Oropharynx Laryngopharynx

9. Pharynx • Nasopharynx - Air passageway posterior to the nasal cavity • Soft palate and uvula close off nasopharynx during swallowing so food doesn’t go into nose • Epiglottis – posterior to tongue: keeps food out of airway • Oropharynx and laryngopharynx serve as common passageway for food and air

10. Larynx • Attaches to the hyoid bone and opens into the laryngopharynx • Continuous with the trachea • Functions • Provides a patent airway • Routes air and food into proper channels • closed during swallowing • opened during breathing) • Voice production

11. Larynx • Vocal ligaments - Form core of vocal folds (true vocal cords) • Opening between vocal cords is the glottis • Folds vibrate to produce sound as air rushes up from the lungs

12. Larynx • Vestibular folds (false vocal cords) • Superior to the vocal folds • No part in sound production • Help to close the glottis during swallowing

13. Trachea • Windpipe • Lined in mucosa with cilia that propel debris laden mucus to the pharynx • Destroyed by smoking

14. Posterior open parts of tracheal cartilage abut esophagus • Trachealis muscle can alter diameter of trachea • Relax - Esophagus can expand when food swallowed • Contract - Food can be forcibly expelled (cough reflex)

16. Bronchial tree bifurcation • Right main bronchus • Left main bronchus • Each main or primary bronchus runs into hilus of lung posterior to pulmonary vessels

17. Respiratory Zone • End-point of respiratory tree • Structures that contain air-exchange chambers are called alveoli • Respiratory bronchioles lead into alveolar ducts: walls consist of alveoli • Ducts lead into terminal clusters called alveolar sacs – are microscopic chambers

18. Alveoli • Alveolar ducts, alveolar sacs (clusters of alveoli) • ~300 million alveoli account for most of the lungs’ volume and are the main site for gas exchange

19. This “air-blood barrier” (the respiratory membrane) is where gas exchange occurs • Oxygen diffuses from air in alveolus (singular of alveoli) to blood in capillary • Carbon dioxide diffuses from the blood in the capillary into the air in the alveolus

20. Surfactant • Type II cuboidal epithelial cells are scattered in alveolar walls • Surfactant is a detergent-like substance which is secreted in fluid coating alveolar surfaces – it decreases tension • Without it the walls would stick together during exhalation • Premature babies – problem breathing is largely because lack surfactant

21. Microscopic detail of alveoli • Alveoli surrounded by fine elastic fibers • Alveoli interconnect via alveolar pores • Alveolar macrophages – free floating “dust cells” • Note type I and type II cells and joint membrane

22. Lungs and Pleura Pleural cavity – slit-like potential space filled with pleural fluid • Lungs can slide but separation from pleura is resisted (like film between 2 plates of glass) • Lungs cling to thoracic wall and are forced to expand and recoil as volume of thoracic cavity changes during breathing Around each lung is a flattened sac of serous membrane called pleura Parietal pleura – outer layer Visceral pleura – directly on lung

23. Relationship of organs in thoracic cavity

24. Paired lungs occupy all thoracic cavity lateral to the mediastinum • Mediastinum contains (mainly): heart, great blood vessels, trachea, main bronchi, esophagus

25. Lungs • Each is cone-shaped with anterior, lateral and posterior surfaces contacting ribs • Superior tip is apex, just deep to clavicle • Concave inferior surface resting on diaphragm is the base apex apex base base

26. Blood Supply • Pulmonary arteries bring oxygen-poor blood to the lungs for oxygenation • They branch along with the bronchial tree • The smallest feed into the pulmonary capillary network around the alveoli • Pulmonary veins carry oxygenated blood from the alveoli of the lungs to the heart

27. Blood supply of Lungs • Lungs get their own blood supply from bronchialarteries and veins • Innervation: pulmonary plexus on lung root contains sympathetic, parasympathetic and visceral sensory fibers to each lung • From there, they lie on bronchial tubes and blood vessels within the lungs

28. Blood Supply • Systemic circulation • Bronchial arteries provide oxygenated blood to lung tissue • Arise from aorta and enter the lungs at the hilum • Supply all lung tissue except the alveoli • Bronchial veins anastomose with pulmonary veins • Pulmonary veins carry most venous blood back to the heart

29. Mechanics of Breathing • Pulmonary ventilation (“breathing”) consists of two phases • Inspiration: gases flow into the lungs • Air in • Expiration: gases exit the lungs • Air out

30. Pressure Relationships in the Thoracic Cavity • Atmospheric pressure (Patm) • Pressure exerted by the air surrounding the body • 760 mm Hg at sea level • Respiratory pressures are described relative to Patm • Negative respiratory pressure is less than Patm • Positive respiratory pressure is greater than Patm • Zero respiratory pressure = Patm

31. Intrapulmonary Pressure • Intrapulmonary (intra-alveolar) pressure (Ppul) • Pressure in the alveoli • Fluctuates with breathing • Always eventually equalizes with Patm

32. Intrapleural Pressure • Intrapleural pressure (Pip): • Pressure in the pleural cavity • Fluctuates with breathing • Always a negative pressure (<Patm and <Ppul)

33. Intrapleural Pressure • Negative Pip is caused by opposing forces • Two inward forces promote lung collapse • Elastic recoil of lungs decreases lung size • Surface tension of alveolar fluid reduces alveolar size • One outward force tends to enlarge the lungs • Elasticity of the chest wall pulls the thorax outward

34. Pressure Relationships • If Pip = Ppul the lungs collapse • (Ppul – Pip) = transpulmonary pressure • Keeps the airways open • The greater the transpulmonary pressure, the larger the lungs

35. Atmospheric pressure Parietal pleura Thoracic wall Visceral pleura Pleural cavity Transpulmonary pressure 760 mm Hg –756 mm Hg = 4 mm Hg 756 Intrapleural pressure 756 mm Hg (–4 mm Hg) 760 Intrapulmonary pressure 760 mm Hg (0 mm Hg) Lung Diaphragm Figure 22.12

36. Homeostatic Imbalance • Atelectasis (lung collapse) is due to • Plugged bronchioles  collapse of alveoli • Wound that admits air into pleural cavity (pneumothorax) • Ex: Broken Rib pierce pleural cavity, letting alveolar air into pleural space

37. Pulmonary Ventilation • Inspiration and expiration • Mechanical processes that depend on volume changes in the thoracic cavity • Volume changes  pressure changes • Pressure changes  gases flow to equalize pressure

38. Ventilation • Mechanical forces cause the movement of air • Gases always flow from higher pressure to lower • For air to enter the thorax, the pressure of the air in it has to be lower than atmospheric pressure • Making the volume of the thorax larger means the air inside it is under less pressure (the air has more space for as many gas particles, therefore it is under less pressure) • The diaphragm and intercostal muscles accomplish this

39. Boyle’s Law • The relationship between the pressure and volume of a gas • Pressure (P) varies inversely with volume (V): P1V1 = P2V2

40. Muscles of Inspiration • During inspiration, the dome shaped diaphragm flattens as it contracts • This increases the height of the thoracic cavity • The external intercostalmuscles contract to raise the ribs • This increases the circumference of the thoracic cavity Together:

41. Inspiration continued • Intercostals keep the thorax stiff so sides don’t collapse in with change of diaphragm • During deep or forced inspiration, additional muscles are recruited: • Scalenes • Sternocleidomastoid • Pectoralis minor • Quadratus lumborum on 12th rib • Erector spinae (some of these “accessory muscles” of ventilation are visible to an observer; it usually tells you that there is respiratory distress – working hard to breathe)

42. Inspiration • Review = Active Process • Inspiratory muscles contract • Thoracic volume increases • Lungs are stretched and intrapulmonary volume increases • Intrapulmonary pressure drops (to 1 mm Hg) • Air flows into the lungs, down its pressure gradient, until Ppul = Patm

43. Changes in lateral dimensions (superior view) Changes in anterior- posterior and superior- inferior dimensions Sequence of events 1 Inspiratory muscles contract (diaphragm descends; rib cage rises). Ribs are elevated and sternum flares as external intercostals contract. Thoracic cavity volume increases. 2 External intercostals contract. 3 Lungs are stretched; intrapulmonary volume increases. Intrapulmonary pressure drops (to –1 mm Hg). 4 5 Air (gases) flows into lungs down its pressure gradient until intrapulmonary pressure is 0 (equal to atmospheric pressure). Diaphragm moves inferiorly during contraction. Figure 22.13 (1 of 2)

44. Expiration • Quiet expiration in healthy people is chiefly passive • Inspiratory muscles relax • Rib cage drops under force of gravity • Relaxing diaphragm moves superiorly (up) • Elastic fibers in lung recoil • Volumes of thorax and lungs decrease simultaneously, increasing the pressure • Air is forced out

45. Expiration continued • Forced expiration is active • Contraction of abdominal wall muscles • Oblique and transversus predominantly • Increases intra-abdominal pressure forcing the diaphragm superiorly • Depressing the rib cage, decreases thoracic volume • Some help from internal intercostals and latissimus dorsi (try this on yourself to feel the different muscles acting)

46. Expiration • Review = normally a passive process • Inspiratory muscles relax • Thoracic cavity volume decreases • Elastic lungs recoil and intrapulmonary volume decreases • Ppul rises (to +1 mm Hg) • Air flows out of the lungs down its pressure gradient until Ppul = 0 • Note: forced expiration is an active process: it uses abdominal and internal intercostal muscles

47. Changes in lateral dimensions (superior view) Changes in anterior- posterior and superior- inferior dimensions Sequence of events 1 Inspiratory muscles relax (diaphragm rises; rib cage descends due to recoil of costal cartilages). Ribs and sternum are depressed as external intercostals relax. 2 Thoracic cavity volume decreases. 3 Elastic lungs recoil passively; intrapulmonary volume decreases. External intercostals relax. 4 Intrapulmonary pres- sure rises (to +1 mm Hg). Diaphragm moves superiorly as it relaxes. 5 Air (gases) flows out of lungs down its pressure gradient until intra- pulmonary pressure is 0. Figure 22.13 (2 of 2)

48. Intrapulmonary pressure. Pressure inside lung decreases as lung volume increases during inspiration; pressure increases during expiration. Inspiration Expiration Intrapulmonary pressure Trans- pulmonary pressure Intrapleural pressure. Pleural cavity pressure becomes more negative as chest wall expands during inspiration. Returns to initial value as chest wall recoils. Intrapleural pressure Volume of breath Volume of breath. During each breath, the pressure gradients move 0.5 liter of air into and out of the lungs. 5 seconds elapsed Figure 22.14

49. Physical Factors Influencing Pulmonary Ventilation • Inspiratory muscles consume energy to overcome three factors that hinder air passage and pulmonary ventilation • Airway resistance • Alveolar surface tension • Lung compliance

50. Airway Resistance • Friction is the major nonelastic source of resistance to gas flow • Gas flow changes inversely with resistance