Respiratory System

1. Respiratory System • Anatomy of the Respiratory System • Pulmonary Ventilation • Gas Exchange and Transport • Respiratory Disorders

2. Organs of Respiratory System • Nose • Pharynx • Larynx • Trachea • Bronchi • Lungs

3. General Aspects • Airflow in lungs • bronchi  bronchioles  alveoli • Conducting division = Passages for airflow • Nostrils to bronchioles • Respiratory division = Gas exchange regions • Alveoli • Upper respiratory tract = Parts in the head and neck • Nose through larynx • Lower respiratory tract = Parts in the thorax • Trachea through lungs

4. Nose • Functions • warms, cleanses, humidifies inhaled air • detects odors • resonating chamber that amplifies the voice

5. Upper Respiratory Tract

6. Nasal Cavity- Conchae and Meatuses • Superior, middle and inferior nasal conchae • 3 folds of tissue on lateral wall of nasal fossa • mucous membranes supported by thin scroll-like turbinate bones • Meatuses • narrow air passage beneath each conchae • narrowness and turbulence ensures air contacts mucous membranes

7. Nasal Cavity - Mucosa • Olfactory mucosa • lines roof of nasal fossa • Respiratory mucosa • lines rest of nasal cavity with ciliated pseudostratified epithelium • Defensive role of mucosa • mucus (from goblet cells) traps inhaled particles • bacteria destroyed by lysozyme

8. Nasal Cavity- Cilia and Erectile Tissue • Function of cilia of respiratory epithelium • sweep debris-laden mucus into pharynx to be swallowed • Erectile tissue of inferior concha • venous plexus that rhythmically engorges with blood and shifts flow of air from one side of fossa to the other once or twice an hour to prevent drying • Spontaneous epistaxis (nosebleed) • most common site is inferior concha

9. Nasopharynx • pseudostratified epithelium • posterior to choanae, dorsal to soft palate • receives auditory tubes and contains pharyngeal tonsil • 90 downward turn traps large particles (>10m)

10. Oropharynx • stratifeidsquamous epithelium • space between soft palate and root of tongue, inferiorly as far as hyoid bone, contains palatine and lingual tonsils

11. Laryngopharynx • stratified squamous • hyoid bone to level of cricoid cartilage

12. Glottis – vocal cords and opening between • Epiglottis • flap of tissue that guards glottis • directs food and drink to esophagus

13. Epiglottic cartilage - most superior • Thyroid cartilage – largest; laryngeal prominence • Cricoid cartilage - connects larynx to trachea • Arytenoid cartilages (2) - posterior to thyroid cartilage • Corniculate cartilages (2) - attached to arytenoid cartilages like a pair of little horns • Cuneiform cartilages (2) - support soft tissue between arytenoids and epiglottis

14. Trachea • Rigid tube ~4.5 in. long and ~2.5 in. diameter. • Anterior to esophagus • Supported by 16 to 20 C-shaped cartilaginous rings • opening in rings faces posteriorly towards esophagus • trachealis spans opening in rings, adjusts airflow by expanding or contracting • Larynx and trachea lined with ciliated pseudostratified epithelium which functions as mucociliary escalator

15. Mucociliary Escalator

16. Lung Lobes • Right lung has 3 lobes • Superior • Middle (smallest) • Inferior • Left Lung has 2 lobes • Room for the heart • Carina

17. Bronchial Tree • Primary bronchi (C-shaped rings) • from trachea; after 2-3 cm enter hilum of lungs • right bronchus slightly wider and more vertical (aspiration) • Secondary (lobar) bronchi (overlapping plates) • one for each lobe of lung • Tertiary (segmental) bronchi (overlapping plates) • 10 right, 8 left

18. Bronchial Tree • Bronchioles (lack cartilage) • layer of smooth muscle • pulmonary lobule is the portion ventilated by one bronchiole • divides into 50 - 80 terminal bronchioles • Each divides into 2-10 alveolar ducts; end in alveolar sacs • Alveoli • main site for gas exchange

20. Pleurae and Pleural Fluid • Similar to the pericardium except around the lungs • Visceral (on lungs) and parietal (lines rib cage) pleurae • Pleural cavity - space between pleurae, lubricated with fluid • Functions • reduce friction • compartmentalization

21. Pulmonary Ventilation • Breathing (pulmonary ventilation) – one cycle of inspiration and expiration • quiet respiration – at rest • forced respiration – during exercise • Flow of air in and out of lung requires a pressure difference between air pressure within lungs and outside body

22. Diaphragm

23. Respiratory Muscles • Diaphragm (dome shaped) • contraction flattens diaphragm • Scalenes • hold first pair of ribs stationary • External and internal intercostals • stiffen thoracic cage; increases diameter • Pectoralis minor, sternocleidomastoid and erector spinae muscles • used in forced inspiration • Abdominals and latissimusdorsi • forced expiration (to sing, cough, sneeze)

24. Neural Control of Breathing • Breathing depends on repetitive stimuli from brain • Neurons in medulla oblongata and pons control unconscious breathing • Voluntary control provided by motor cortex • Inspiratory neurons: fire during inspiration • Expiratory neurons: fire during forced expiration • Fibers of phrenic nerve go to diaphragm; intercostal nerves to intercostal muscles

25. Respiratory Control Centers • Respiratory nuclei in medulla • The Dorsal Respiratory Group (formerly called the inspiratory center) • The Ventral Respiratory Group (formerly called the expiratory center ) • Pons • The Pontine Respiratory Center (formerly the pneumotaxic and apneustic centers)

26. Input to Respiratory Centers • From limbic system and hypothalamus • respiratory effects of pain and emotion • From airways and lungs • irritant receptors in respiratory mucosa • stimulate vagal afferents to medulla, results in bronchoconstriction or coughing • stretch receptors in airways - inflation reflex • excessive inflation triggers reflex • stops inspiration • From chemoreceptors • monitor blood pH, CO2 and O2 levels

27. Chemoreceptors(found near baroreceptors) • Peripheral chemoreceptors • found in major blood vessels • aortic bodies • signals medulla by vagus nerves • carotid bodies • signals medulla by glossopharyngeal nerves • Central chemoreceptors • in medulla • primarily monitor pH of CSF

28. Pressure and Flow • Atmospheric pressure drives respiration • 1 atmosphere (atm) = 760 mmHg • Intrapulmonary pressure and lung volume • pressure is inversely proportional to volume • for a given amount of gas, as volume , pressure  and as volume , pressure  • Pressure gradients • difference between atmospheric and intrapulmonary pressure • created by changes in volume thoracic cavity

29. Respiratory Cycle • Atmospheric pressure drives respiration • 1 atmosphere (atm) = 760 mmHg •  intrapulmonary pressure • lungs expand with visceral pleura • 500 ml of air flows with a quiet breath

30. Passive Expiration • During quiet breathing, expiration achieved by elasticity of lungs and thoracic cage • As volume of thoracic cavity , intrapulmonary pressure  and air is expelled • After inspiration, phrenic nerves continue to stimulate diaphragm to produce a braking action to elastic recoil Forced Expiration • Internal intercostal muscles depress the ribs • Contract abdominal muscles •  intra-abdominal pressure forces diaphragm upward •  pressure on thoracic cavity

31. That’s it for today

32. Pneumothorax • Presence of air in pleural cavity • Collapse of lung (or part of lung) is called atelectasis

33. Other causes of Atelectasis • Atelectasis is the decrease or loss of air in all or part of the lung • Tumors obstructing a bronchus • Foreign body (an inhaled marble?) • Serious pneumonia • Lack of surfactant • Smoke inhalation • Post-operative complication

34. Factors that affect resistance to airflow Compliance is reduced by smoking and by fibrotic conditions such as sarcoidosis or lupus • Pulmonary compliance • distensibility of lungs • Bronchiolar diameter • primary control over resistance to airflow • bronchoconstriction • triggered by airborne irritants, cold air, parasympathetic stimulation, histamine • bronchodilation • sympathetic nerves, epinephrine Asthma

35. Alveolar Surface Tension • Thin film of water needed for gas exchange • creates surface tension that acts to collapse alveoli and distal bronchioles • Pulmonary surfactant decreases surface tension • Premature infants that lack surfactant suffer from respiratory distress syndrome

36. Measurements of Ventilation • Spirometer - measures ventilation • Respiratory volumes • tidal volume: volume of air in one quiet breath • inspiratory reserve volume • air in excess of tidal inspiration that can be inhaled with maximum effort • expiratory reserve volume • air in excess of tidal expiration that can be exhaled with maximum effort • residual volume (keeps alveoli inflated) • air remaining in lungs after maximum expiration

37. Respiratory volumes • tidal volume: • inspiratory reserve volume • expiratory reserve volume • residual volume • Vital capacity • total amount of air that can be exhaled with effort after maximum inspiration • assesses strength of thoracic muscles and pulmonary function

38. What influences lung volume and capacity? • Age -  lung compliance, respiratory muscles weaken • Exercise - maintains strength of respiratory muscles • Body size - proportional, big body/large lungs • Restrictive disorders •  compliance and vital capacity • Obstructive disorders • interfere with airflow, expiration requires more effort or less complete

39. Composition of Air • Mixture of gases; each contributes its partial pressure • At sea level 1 atm. of pressure = 760 mmHg • Air is about 79% nitrogen = 597 mmHg • Air is only about 21% oxygen = 159 mmHg • Air has almost no carbon dioxide = 0.3 mmHg • In Denver (or Reno) atmospheric pressure = 625 (to 645) mmHg • Air is about 79% nitrogen = 494 (510) mmHg • Air is only about 21% oxygen = 131 (135) mmHg • Air has almost no carbon dioxide = 0.3 mmHg

40. Alveolar Gas Exchange • Important for gas exchange between air in lungs and blood in capillaries • Gases diffuse down their concentration gradients • Amount of gas that dissolves in water is determined by its solubility in water and its partial pressure in air

41. Alveolar Gas Exchange • Time required for gases to equilibrate = 0.25 sec • RBC transit time at rest = 0.75 sec to pass through alveolar capillary • RBC transit time with vigorous exercise = 0.3 sec What percentage of O2 loading at 0.75 sec transit time is now possible?

42. Factors Affecting Gas Exchange • Membrane thickness - only 0.5 m thick • Membrane surface area - 100 ml blood in alveolar capillaries, spread over 70 m2 • Ventilation-perfusion coupling • areas of good ventilation need good perfusion (vasodilation)

43. Oxygen Transport • Concentration in arterial blood • 20 ml/dl • 98.5% bound to hemoglobin • 1.5% dissolved • Binding to hemoglobin • each heme group of 4 globin chains may bind O2 • oxyhemoglobin (HbO2 ) • deoxyhemoglobin (HHb)

44. Carbon Dioxide Transport • As bicarbonate (and carbonic acid) - 90% • CO2 + H2O  H2CO3  HCO3-+ H+ • As carbaminohemoglobin (HbCO2)- 5% binds to amino groups of Hb (and plasma proteins) • As dissolved gas - 5%

45. Systemic Gas Exchange • CO2 loading • carbonic anhydrase in RBC catalyzes • CO2 + H2O  H2CO3  HCO3-+ H+ • chloride shift • keeps reaction proceeding • exchanges HCO3-for Cl- • (H+ binds to hemoglobin)

46. Systemic Gas Exchange • O2 unloading • H+ binding to HbO2 its affinity for O2 • Hb arrives 97% saturated • Hb leaves 75% saturated • venous reserve

48. Reactions in the alveolus are the reverse of systemic gas exchange

49. Factors Affect O2 Unloading • Active tissues need oxygen! • ambient PO2: active tissue has  PO2 ; O2 is released • temperature: active tissue has  temp; O2 is released

50. Factors Affect O2 Unloading • Active tissues need oxygen! • Bohr effect: active tissue has  CO2, which lowers pH (muscle burn); O2 is released