Respiratory System

1. Respiratory System Lecture 1

2. Functions • gas exchange • between air & blood • sound production • sends olfactory sensations to CNS from olfactory epithelium • helps to control blood pH • moves air to & from exchange surfaces • filters air • helps rid some water and heat in exhaled air

3. Structural Anatomy • upperrespiratory system • nose, nasal cavity & pharynx • lower respiratory system • larynx, trachea, bronchi & lungs

4. Functional Anatomy • conducting zone • respiratory paths from nasal cavity through bronchioles • consists of rigid conduits for air to reach sites of gas exchange • respiratory zone • actual site of gas exchange • includes respiratory bronchioles, alveolar ducts & alveoli

5. Epithelium • changes along tract • pharynx-stratifed squamous • lower-pseudostratified ciliated columnar • bronchioles-cuboidal • exchange surfaces-simple squamous

6. Respiratory Mucosa • conducting path lined with respiratory mucosa • conditions air • by time air reaches alveoli, foreign particles & pathogens have been removed • humidity & temperature are acceptable limits • pseudostratified ciliated columnar epithelium, goblet cells & underlying alveolar tissue • Goblet cells • secrete mucous containing lyzozymes-antibacterial enzymes & defensins-antibodies that help rid body of microbes • Mucous • intercepts & excludes solid matter in air such as dust, pollen, bacteria & viruses • particles hit side wall-trapped in mucus • once particles are sidelined by mucus • carried out by cilia • tiny hair-like structures which undulate 1200 movements/minute • undulation keeps mucous moving either up toward pharynx or down toward stomach • upward & downward movement is termed- mucociliary escalator

7. Respiratory System Anatomy • nose • primary passage for air to enter through external nares-nostrils • warms, cleanses & humidify inhaled air • extends from external nares to posterior or internal nares • nose empties into nasal cavityvestibule • space just inside nose containing hair follicles-vibrissae • filters particles out of air • nasal cavity is divided by nasal septum • Roof • made of ethmoid & sphenoid bones • Floor • palate • in each bone surrounding nasal cavity there are holes-paranasal sinuses • lighten skull

8. Pharynx • nasal cavity leads into pharynx • consists of 3 regions • Nasopharynx • posterior to nasal cavity • extends to soft palate • air passage only • Oropharynx • posterior to oral cavity • extends from soft palate to hyoid bone • air & food passage • Laryngopharynx • begins at hyoid opens into esophagus posteriorly & larynx anteriorly • common passage for air & food • air & food passage

10. Larynx • voice box • opens into laryngopharynx • continuous with trachea inferiorly • provides open airway & switching mechanism to route air & food into proper channels • functions in voice production • consists of 9 cartilages

11. Larynx Cartilages • thyroid • large, shield shaped cartilage • fusion-laryngeal prominence • Adam’s Apple • cricoid cartilage • inferior to thyroid cartilage • ring-like • arytenoid • cuneiform • corniculate • epiglottis • flexible elastic cartilage

12. Trachea • below larynx • patent oropen • kept so by rings of C or tracheal cartilages • descends from larynx into mediastium • divides into right & left primary bronchi • enters lungs at hilus • right & left primary bronchi are paired but of unequal length & diameter • right-wider, shorter & more vertical

13. Layers of Trachea Wall

14. Bronchi • primary bronchi subdivide into secondary or lobar bronchi • 3 on right & 2 on left • lobar bronchitertiary or segmental bronchidivide into smaller & smaller bronchioles • air passages<1mm in diameter-bronchioles • smallest<0.5mm-terminal bronchioles • arborizing branching pattern is respiratory or bronchial tree • conducting zone

15. Label the Parts of the Respiratory Tree

16. Alveoli • each terminal bronchiole feeds into respiratory bronchiole • beginning of respiratory division • each respiratory bronchiole divides into 2 to 10 long, thin passages- alveolar ducts • ducts end in spongy, air-filled sacs-alveolar sacs • each cluster-made of alveoli • comprise most of volume of lung • responsible for spongy look • provide tremendous surface area for gas exchange • surrounded by capillaries & elastic tissue • can recoil to help push out air • inhaled O2 passes into alveoli, diffuses through capillaries & then into arterial blood

17. Respiratory Membrane • walls of alveoli are simple squamous-type I alveolar cells • main sites of gas exchange • type II alveolar cells-Septal cells • secrete pulmonary surfactant • alveolar macrophages-dust cells • phagocytize dust & other particles. • external surface of each alveolus is covered with capillaries • barrier between alveolar air & blood-respiratory membrane consists of only squamous alveolar cells, squamous endothelial cells of capillary walls and shared basement membrane • gas on one side • blood on other • gas exchange occurs by simple diffusion- from higher to lower concentration • diffusion is rapid because: • distances are small • O2 & CO2 are lipid soluble • canpass through surfactant layer Type II Type I Capillary O2 CO2 Alveolus Macrophage

18. Surfactant • mixture of phospholipids & lipoproteins • prevents alveoli from collapsing • detergent like properties • coats alveolar surfacesreduces surface tension • attraction between water molecules at air-water boundary. • molecules of liquids are more strongly attached to each other than gasproduces tension at surface • creates barrier keeping small objects from entering & causes small bubbles to collapse • interferes with cohesiveness of water moleculesreduces surface tension less energy needed to overcome force to expand lungs

19. Respiratory Physiology • gas exchange-respiration has 3 steps • pulmonary ventilation-breathing • external respiration • exchange of gases between blood & lungs • internal respiration • exchange of gases between capillary blood & tissues

20. Breathing • Pulmonary ventilation • physical movement of air into & out of respiratory tract • consists of • inspiration-taking air into lungs • expiration-gas exiting lungs • mechanical

21. Pressure & Volume Changes • air moves into & out of respiratory tract as air in lungs cycles between below atmospheric & above atmospheric pressure • depends on volume changes in thoracic cavity • volume changespressure changesgases flowpressure equalizes • to understand need to understand physical principles of gases-gas laws

22. Boyle’s Law-Ideal Gas Law • relationship between pressure & volume • atconstant temperature pressure of gas varies inversely with its volume • P1V1=P2V2 • P = pressure of gas-mm Hg • V = volume-cubic mm • gases conform to shape of container in which they are contained • always fill container • large volumesgas molecules far apart don’t bump into each other much pressure low • reduced volumes gas molecules compress & bump into each other more often pressure rises • when volume of gas decreases pressure increases • when volume of gas increases pressure decreases • relationship can be stated in formula • P = 1/V

23. Boyle’s Law & Breathing • inhalation & exhalation involve changes in lung volumes creates pressure changes moves air into & out of lungs • think of thoracic cavity as gas filled box with one opening • each lung enclosed in box bounded below by diaphragm • on sides by chest wall & mediastinum

24. Boyle’s Law & Breathing • parietal & visceral pleurae of pleural cavity are separated by thin layer of pleural fluid • allows them to slide past one another but still be held together by fluid between • tension makes surface of lungs stick to inner chest wall & to diaphragm • movement of chest wall or diaphragm changes volume of lungs • breathing makes boxbigger • as rib cage moves updepth & width of thoracic cavity increases • contraction of diaphragmmoves diaphragminferiorlyincreases volume of thoracic cavityalveolar pressure decreases • Pinside <P outsideair rushes in

25. Inhale-Quiet Inspiration • diaphragm & external intercostals contract • ribs lift & pulled outward • diaphragm moves downward chest cavity enlargeslung expands to fill space pressure inside lung lowers air enters respiratory tract • P inside < pressure outside • air moves in until P inside = P outside

26. Exhalation • diaphragm & intercostals relax • thoracic cavity decreases in volume • ribs return to position • P inside decreases air forced out

27. Inhalation & Exhalation

28. Pressure Changes during Inhalation & Exhalation • respiratory pressures are given relative to atmospheric pressure • Atmospheric pressure-Patm • measured in mm Hg • pressure exerted by air surrounding body • sea level = 760mm Hg or 1 atm • pressure in respiratory system • measured in air spaces of lungs-alveolar pressure or intrapulmonary pressure • measured in pleural fluid between parietal & visceral pleurae-intrapleural pressure

29. Inhalation • air continues to flow into alveolipressure increases until thoracic cage stops expanding • air movement continues until pressure inside equalizes with atmospheric pressure • during this time intrapleural pressure drops to -6mm Hg • pressure averages –4mm Hg below atmospheric pressure at all times due to relationship of lungs & body wall

30. Exhalation

31. Intrapleural Pressure • opposing forces at lungs produce negative pressure at all times • alveolar fluid surface tension pulls visceral pleura away from parietal pleura producing strong fluid bond • force keeps pleurae together • opposed by elasticity of chest wall • elastic components gives lung naturaltendency to recoil • cannot overcome fluid bond • elastic fibers stay stretched even after full exhalationpressure remains negative negative intrapleural pressure • amount of fluid in pleural cavity must be minimal to maintain negative pressure • negative pressure is important because anytime intrapleural pressure equalizes with intrapulmonary pressure-lung collapses

32. Muscles of Breathing • air moves due to pressure changes • direct result of volume changes • due to muscle contractions • main muscles-quiet inspiration-diaphragm & external intercostals • diaphragm-responsible for 75% of air flow • external intercostals-25% • deep or forced breathing is aided by • Sternocleidomastoids • Scalenes • Pectoralis minor

33. Mechanics of Expiration • Quiet expiration due to muscle relaxation • passive • muscle contraction is not required • depends on natural elasticity or elastic recoil of lungs • Forced expiration • active process • requires contraction of accessory muscles • transversus abdominus • rectus abdominus

35. Other Factors Influencing Air Flow • surface tension • must be overcome to expand lungs • surfactant • reduces surface tension • compliance of lungs • effort required to stretch lung & chest wall • lower compliancegreater force needed to fill & empty lungs • greater compliancelungs easier to fill & empty • surfactant increases compliance • Decreased mobility of thoracic cagedecreases compliance • airway resistance • resistance to air flow • walls of bronchioles offer some resistance to flow • larger diameters have less resistance • any condition that narrows walls increases resistance

36. Respiratory Cycle • one cycle consists of one inhalation & one exhalation • Tidal volume • amount of air brought into & taken out of lungs in one respiratory cycle • beginning of respiratory cycle intrapulmonary & atmospheric pressures are equalno air movement • Inhalation beginsintrapleural pressure drops due to expansion of thoracic cavity to –6mm Hg-intrapulmonary pressure drops to –1mm Hg • Exhalation • intraplueral & intrapulmonary pressures riseair forced out of lungs • End of respiratory cycle • atmospheric & intrapulmonary pressures become equal again

37. Respiratory Rates • respiratory system adapts to meet O2 demands of body • does so by varying number of breaths per minutes or BPM • number of breaths taken each minute = respiratory rate • 12-18 bpm-normal range

38. Respiratory Rates • MV-minute volume • total volume of air inhaled &exhaled each minute • MV = F (bpm) X VT (tidal volume) • 12 X 500 = 6000ml/minute • may not indicate how much air reaches alveoli • not all air reaches alveoli-remains in conducting airways & does not exchange gases with blood • anatomical dead space-150ml

39. Respiratory Rates • during one inhalation 500 mls of fresh air (tidal volume) is brought into respiratory system • displaces 150ml of stale air in dead spaceleaving 350ml of fresh air to go to alveoli • Tidal Volume – Dead Space = 500ml- 150ml = 350ml • 350 ml of air is involved in alveolar ventilation • Alveolar ventilation rate-VA • amount ofair reaching alveoli each min • VA = f X (TV – VD). 12 breaths/min X (500ml/breath – 150ml/breath) = 4200ml/min or 4.2L/min • better indicator of ventilation because determines rate of O2 delivery to alveoli

40. Respiratory Rates • minute volume can be increased by increasing tidal volume or respiratory rate • O2 demands increaseTV & respiratory rate must increase • rate of breathing or depth of breathing changes alveolar ventilation

41. Respiratory Volumes • total volume of lungs can be divided into volumes & capacities • Volumes: • tidal volume • amount of air moving during quiet inspiration & expiration; 500 mls • inspiratory reserve volume • amount of air that can be inspired beyond tidal inspiration • differs significantly by gender; lungs of males are larger • expiratory reserve volume • amount of air that can be exhaled after normal expiration • residual volume • amount of air left after strenuous expiration • cannot be directly measured • keeps alveoli open & prevents lung collapse • part is minimal volume • volume of air remaining when lung collapse

42. Respiratory Capacities • sum of 2 or more lung volumes • IC-inspiratory capacity • total amount of air that can be inspired after tidal expiration = TV + IRV • FRC-functionalresidual capacity = RV + ERV • amount of air remaining after tidal expiration • VC-vital capacity • total amount of exchangeable air = TV + IRV + ERV • amount of air that can be moved into or out of respiratory system with one breath • TLC-total lung capacity • sum of all lung volumes = VC + RV • FVC-forced vital capacity • amount of gas expelled when deep breath is taken & then forcibly exhaled as maximally as possible