Respiratory System

1. Respiratory System Chapter 22

2. Role of Respiratory System • Supplies body w/ O2 and disposes of CO2 • Four part process • Pulmonary ventilation • Moving air in and out of lungs • External respiration • Exchange of gases between lungs and blood • Transport of respiratory gases • Moving air to and from tissues via blood • Internal respiration • Exchange of gases between blood and tissues

3. Functional Respiratory System • Conducting zone: carries air • Cleanses, humidifies, and warms air • Nose  terminal bronchioles • Respiratory zone: site of gas exchange • Respiratory bronchioles • Alveolar ducts • Alveoli

4. Nose and Nasal Cavity • Normal air entry, why not mouth? • Moistens, warms, and filters air • Superficial capillary beds • Vibrissae filter particulates • Respiratory epithelium (what is that?) • Mucus traps debris and moves posterior to pharynx • Defensins and lysozymes • Turbinate bones and meatuses enhance • Olfaction • Olfactory epithelia through cribriform plates • Nerve endings irritated = sneezing • Resonation for speech

5. Pharynx • Nasopharynx • Air mov’t only • Closed off by uvula w/ swallowing • Giggling prevents = nose expulsion • Respiratory epithelium (why?) • Pharyngeal tonsil (adenoids) • Oropharynx • Food and air mov’t • Stratified squamous (why?) • Palatine and lingual tonsils • Laryngopharnx • Food and air mov’t • Stratified squamous • Branches to esophagus and larynx http://medical-dictionary.thefreedictionary.com/pharynx

6. Larynx • Keep food and fluid out of lungs • Epiglottis (elastic) covers glottis • Coughing/choking when fails • False vocal cords • Transport air to lungs • Supported by 8 hyaline cartilages • Voice production • True vocal cords (elastic) vibrate as air passes • Pitch from vibration rate (more tension = faster = higher) • Loudness from force of expelled air (whisper = little/no vibration) • Additional structures amplifies, enhances, and resonates • Pseudostratified ciliated columnar again (why?) • Mucus up to pharynx

7. Trachea • Transports air to lungs • Mucosal layer • Respiratory epithelium • Mucus trapped debris to pharynx • Submucosal layer • Mucus glands • Adventita • Connective tissue supported by C-rings of hyaline cartilage

8. Bronchial Tree Table 2:  Divisions of the Bronchial Tree.  Taken from Ross et al., Histology, a text and atlas, 10th edition, p. 589, Table 18.1.

9. The Respiratory Membrane • Walls of the alveoli where actual exchange occurs • Simple squamous cells (type I cells) surrounded by capillaries • Surface tension resists inflation • Cuboidal epithelia (type II cells) produce surfactant to counter • Macrophages patrol • Dead/damage swept to pharynx

10. Lung Anatomy • Paired air exchange organs • Right lung • Superior, middle, and inferiorlobes • Oblique and horizontalfissures • Left lung • Superior and inferiorlobes • Obliquefissure • Cardiacnotch contributes to smaller size • Costal, diaphragmatic, and mediastinalsurfaces • Hilum where 1° bronchi and blood vessels enter

11. Pleura • Serous membrane covering • Parietal pleura • Visceral pleura • Pleural fluid in cavity • Reduces friction w/ breathing • Surface tension binds tightly • Expansion/recoil with thoracic cavity • Creates 3 chambers to limit organ interferences

12. Pressure Relationships Atmosphere Patm • Relative to atmospheric pressure (Patm) • Sea level = 760 mmHg • Intrapulmonary pressure (Ppul): pressure in alveoli • Intrapleural pressure (Pip): pressure in pleural cavity • Always negative to Ppul • Surface tension b/w pleura Chest wall (Patm – Ppul) Pip Ppul (Ppul – Pip) Lung wall Intrapleural fluid

13. Transpulmonary Pressure (Ptp) • Difference b/w intrapulmonary and intrapleural pressure (Ppul – Pip) • Influences lung size (Greater diff. = larger lungs) • Equalization causes collapse • Keeps lungs from collapsing (parietal and visceral separation) • Alveolar surface tension and recoil favor aveoli collapse • Recoil of chest wall pulls thorax out

14. Pulmonary Ventilation • Inspiration and expiration change lung volume • Volume changes cause pressure changes • Gases move to equalize • Boyle’s Law • P1V1 = P2V2 • Increase volume = decrease pressure • Decrease volume = increase pressure Ppul < Patm Ppul > Patm inspiration Patm – Ppul R F = expiration

15. Breathing Cycle Inspiration Expiration Inspiratory muscles relax Thoracic cavity decreases Pip increase  Ptp decrease Lung volume decreases Ppul > Patm Air flows out till Ppul = Patm • Thoracic cavity increases • Pip decrease  Ptp increase • Lung volume increases • Ppul < Patm • Air flows in till Ppul = Patm

16. Influencing Pulmonary Ventilation • Airway resistance • Flow = pressure gradient/ resistance (F = P/R) • Diameter influences, but insignificantly • Mid-sized bronchioles highest (larger = bigger, smaller = more) • Diffusion moves in terminal bronchioles (removes factor) • Alveolar surface tension • Increase H20 cohesion and resists SA increase • Surfactants in alveoli disrupt = less E to oppose • Lung compliance • ‘Stretchiness’ of the lungs • Stretchier lungs = easier to expand

17. Pulmonary Volumes • Tidal volume (TV): air moved in or out w/ one breath • Inspiratory reserve volume (IRV): forcible inhalation over TV • Expiratory reserve volume (ERV):forcible exhalation over TV • Residual volume: air left in lungs after forced exhalation

18. Respiratory Capacities • Inspiratory capacity (IC) • Inspired air after tidal expiration • TV + IRV • Functional residual capacity (FRC) • Air left after tidal expiration • RV + ERV • Vital capacity (VC) • Total exchangeable air • TV + IRV + ERV • Total lung capacity (TLC) • All lung volumes • TV + IRV + ERV + RV

19. Non-Respiratory Air • Dead space • Anatomical:volume of respiratory conducting passages • Alveolar: alveoli not acting in gas exchange • Total:sum of alveolar and anatomical • Reflex movements • Cough: forcible exhalation through mouth • Sneeze: forcible exhalation through nose and mouth • Crying: inspiration and short expirations • Laughing: similar to crying • Hiccups: sudden inspiration from diaphragm spasms • Yawn: deep inspiration into all alveoli

20. Properties of Gases • Dalton’s Law • Pressure exerted by each gas in a mix is independent of others • PN2 ~ 78%, PO2 ~ 21% , PCO2 ~ .04 • Partial pressure (P) for each gas is directly proportional to its concentration • O2 at sea level  760mmHg x .21 = 160mmHg • 10,000 ft above  523mmHg x 0.21 = 110mmHg • Henry’s Law • In contact w/ liquid, gas dissolves proportionately to partial pressure • Higher partial pressure = faster diffusion • Equilibrium once partial pressure is equal • Solubility and temperature can influence too (concentration)

21. External Respiration • Gas exchange • Partial pressure gradients drive • Alveoli w/ higher PO2 and tissues w/ PCO2 • PO2 gradients always steeper that PCO2 • PCO2 more soluble in plasma and alveolar fluid than PO2 • Equal amounts exchanged • Respiratory membrane • Thin to allow mov’t • Moist to prevent desiccation • Large SA for diffusion amounts

22. External Respiration (cont.) • Ventilation and perfusion synchronize to regulate gas exchange • PO2 changes arteriole diameter • Low  vasoconstriction  redirect blood to higher PO2 alveoli • PCO2 changes bronchiole diameter • High  bronchiole dilation  quicker removal of CO2

23. Oxygen Transport • 98% bound to hemoglobin as oxyhemoglobin (HbO2) • Review structure • Deoxyhemoglobin (HHb) once O2 unloaded • Rest dissolved in plasma • Affinity influenced by O2 saturation • 1st and 4th binding enhances • Previous unloading enhances • Hemoglobin reversibly binds O2 • Influenced by PO2, temp., blood pH, PCO2, and [BPG] Lungs HHb + O2 HbO2 + H+ Tissues

24. PO2 Influences on Hemoglobin • Hb near saturation at lungs (PO2~ 100mmHg) and drops ~ 25% at tissues (PO2 ~ 40mmHg) • Hbunloads more O2 at lower PO2 • Beneficial at high altitudes • In lungs, O2 diffuses, Hb picks up = more diffusion • Hb bound O2 doesn’t contribute to PO2

25. Controlling O2 Saturation • Increase in [H+], PCO2, and temp • Decrease Hb affinity for O2 • Enhance O2 unloading from the blood • Areas where O2 unloading needed • Cellular respiration • Bohr effect from low pH and increased PCO2 • Decreases have reverse effects

26. Carbon Dioxide Transport • Small amounts (7 – 10%) dissolved in plasma • As carbaminohemoglobin(~20%) • No competition with O2 b/c of binding location • HHb binds CO2and buffers H+ better than HbO2, called the Haldane effect • Systemically, CO2 stimulates Bohr effect to facilitate • In the lungs, O2 binds Hb releasing H+ to bind HCO3-

27. Carbon Dioxide Transport (cont.) • Primarily (70%) as bicarbonate ions (HCO3-) CO2 + H2O H2CO3 H+ + HCO3- • Hb binds H+ = Bohr effect and little pH change • HCO3- stored as a buffer against pH shifts in blood • Bind or release H+ depending on [H+] • CO2 build up (slow breathing) = H2CO3 up (acidity) • Faster in RBC’s b/c carbonic anhydrase • Fig 22.22

28. Neural Control of Respiration • Medullary respiratory centers • Dorsal respiratory group (DRG) • Integrates peripheral signals • Signals VRG • Ventral respiratory group (VRG) • Rhythm-generating and forced inspiration/expiration • Excites inspiratory muscle to contract • Pontine center • Signals VRG • ‘Fine tunes’ breathing rhythm in sleep, speech, & exercise

29. Regulating Respiration • Chemical factors • Increase in PCO2 increases depth and rate • Detected by central chemoreceptors (brainstem) • CO2 diffuses into CSF to release H+ (no buffering) • Greater when PO2 and pH are lower • Initial decrease in PO2 enhances PCO2 monitoring • Peripheral chemoreceptors in carotid and aortic bodies • Substantial drop to increase rate b/c Hb carrying capacity • Declining arterial pH increases depth and rate • Peripheral chemoreceptors increase CO2 elimination

30. Regulating Respiration (cont.) • Higher brain center influence • Hypothalamic controls • Pain and strong emotion influence rate and depth • Increased temps. increases rate • Cortical controls • Cerebral motor cortex bypasses medulla • Signals voluntary control (overridden by brainstem monitoring) • Pulmonary irritant reflexes • Reflexive constriction of bronchioles • Sneeze or cough in nasal cavity or trachea/bronchi • Inflation reflex • Stretch receptors activated w/inhalation • Inhibits inspiration to allow expiration

31. Homeostatic Imbalances • Sinusitis: inflamed sinuses from nasal cavity infection • Laryngitis: inflammation of vocal cords • Pleurisy: inflammation of pleural membranes, commonly from pneumonia • Atelectasis: lung collapse from clogged bronchioles • Pneumothorax: air in the intrapleural spaces • Dyspnea: difficult or labored breathing • Pneumonia: infectious inflammation of the lungs (viral or bacterial) • Emphysema: permanent enlargement of the alveoli due to destruction • Chronic bronchitis: inhaled irritants causing excessive mucus production • Asthma: bronchoconstriction prevents airflow into alveoli • Tuberculosis: an infectious disease (Mycobacterium tuberculosis) causing fibrous masses in the lungs • Cystic fibrosis: increased mucus production which clogs respiratory passages • Hypoxia: inadequate O2 delivery • Anemic (low RBC’s), ishemic (impaired blood flow), histotoxic (cells can’t use O2), hypoxemic (reduced arterial PO2)