Unformatted text preview: B IO 188 November 25, 2009 1. Please learn the respiratory structures posted in Monday’s notes. You don’t need me to r ecite them. 2. We won’t get to bird lungs until Monday (don’t want to go too fast with a lot of people p robably missing) 3. Today: 1. unsatisfying answer to question about evolution of SA node 2. tidal lungs 1. brief look at functional anatomy 2. 3. gas pressures m echanisms of ventilation What’s the major challenge for gas exchange in a ter restria l vertebrate? 4. Compared to O 2 concentration in H 2O, there’s lots of O 2 i n the air (~ 20%), so what’s the p roblem with breathing air?.. 1. .. breathing a i r requi res a … .. 2. = potentially t remendous source … What’s the most common solution for a i r breathers? W hat’s 5. M ammals, amphibians, most reptiles use t idal ventil ation 1. ventilation like the tide 2. ai r moves into and out of lungs by same path 3. bidi rectional 6. T id al volume = a mount of air that moves in and out per breath 7. Residual volume = a mount of air left in lungs at end of exhalation Residual 1. is never zero!! How does tidal ventil ation reduce water loss? 8. Du r ing inhalation H 2O evaporates from nasal passages, cooling them 9. Du r ing exhalation : wa rm, moist ai r from lungs passes over cool nasal passages → H 2O condenses and is conserved 10. How much H 2O is saved? 1. humans can recover 25% of H 2O i n exhaled a i r r ecover in What do camels, elephant seals and K r ats have that humans don’t? W hat What a re nasal turbinates? W hat 11. Complex bony plates w ithin the nasal chamber 1. covered w ith moist epithelium 2. provide an extensive surface area for exchange of heat and water 12. Animals w ith high r isk of dehydration tend to have highly complex structure of t u rbinates 1. human nasal turbinates are simple What a re disadvantages to having tidal breathing? 13. M ammals have good stuff: 1. huge surface area for gas exchange in alveoli (?) 2. very short diffusion distance across respirato ry membranes 3. bidi rectional tidal ventilation to save H 2O 14. But, tidal ventilation means …. 1. … no countercu r rent exchange 2. … anatomical dead apace in ai r way 3. both factors reduce efficiency of respiratory system How do human lungs work? 15. Ai r enters human lung through the oral cavity or nasal passage via t rachea 16. T r achea branches into two bronchi, then into bronchioles, and then into alveoli 1. alveoli a re the sites of gas exchange a lveoli 2. no gas exchange in rest of ai r way Know these structures in human respir atory system (from 11/23) And these, at higher magnif ication … (from 11/23) What a re alveoli? 17. main site of gas exchange in lungs 18. single layer of cells 19. sur rounded by capilla ries Note alveoli surrounded by capill a r ies and elastic fibers (from 11/23) Single alveolus at higher magnification (f rom 11/23) What does surfactant do? 20. P ulmona ry surfactant is a wetting agent → ↓ surface tension so less force is needed to Pulmona surface inf l ate lungs i nf 21. Lung cannot inflate without surfactant; evolution of tidal lung tied to evolution of surfactant protein surfactant 22. Why is this necessary? 1. fluid lining inner surface of alveoli has ↑ h igh surface tension 2. .. Surface tension makes it hard to expand alveoli du ring inhalation 23. Alveoli also sur rounded by elastic fibers that make it hard to expand lungs 24. Lungs want to collapse! W hat mamma ls l ack surfactant? What Premature babies do not make surfactant. Why is that a problem? P remature . Why is this pleur a l space important? 25. Pleura l “space” is thin, f luid-fi l led potenti al space 26. Fluid reduces f riction, allowing pleurae to slide against each other and … remember, lungs want to coll apse! l ungs 1. .. car r ies a force necessary to expand lungs 2. .. 1. force is negative, l ike a vacuum Stil l haven’t figured out how to breathe. Next topic: Gas pressures and mechanisms of S til ventil at ion ventil What is the pa rt i a l pressure of a gas? 27. P a rti a l p ressure of a gas = pressure exerted by a single gas in a mixtu re Pa 1. for example, P O2 = p artial pressure of O 2 i n a mixtu re of gases ( rel ated t o concent ration) 2. also refer to pa rt ial pressure of gas dissolved in a liquid 3. example: P O2 ( pa rtial pressure of O 2) in blood What is atmospheric pressure? 28. Atmospheric pressure, P atm = sum of par tial pressures of all gases in atmosphere 1. 760 mm Hg at sea level 2. in respirato ry physiology, P atm = 0 m m Hg You need one more important term – alveola r pressure You 29. Concept similar to atmospheric pressure, but refers to total pressure of gases in alveoli 30. What is alveola r pressure, P a lv ? a lveola alv 1. = sum of pa rti a l pressures of a l l gases in alveoli, defined relat ive to P atm 2. slight changes in P alv c auses a i r to move into and out of lungs! Now l isten carefully and use your noggin. How do we expand our lungs and get fresh a i r into lungs? l ungs? 31. I nhalation begins when motor neurons in p hrenic nerve stimulate dome-shaped di aphr agm t o contract (flatten) di 1. → ↑ size thoracic cavity 2. pulls parietal pleura attached to diaphragm away from lung 3. → ↑magnitude of (-) pressure across pleural space → p ull on visceral pleura a ttached to lung → ↑ size alveoli 32. This causes alveola r pressure to drop lower than P atm a lveola 1. ∴ A i r moves down pressure gradient f rom atmosphere to alveoli by bulk flow 2. Boyle’s law in action (for those who’ve had chem) 33. Summa r ize: What is sequence of events in inha l at ion? - M ake your own diagram! After inha l at ion, what happens? A fter 34. Ai r moves into alveoli until what happens to pressures? 1. u ntil … 2. if P alv = P a tm – then a i r doesn’t move in or out t hen atm H ow does exhal ation occur? How 3. .. 4. elasticity of lung and thorax → ↓ size of alveoli 5. this → ↑ P alv 6. when P alv > P atm a i r moves from alveoli to atmosphere 1. until P alv = P atm What is DEAD AIR SPACE? • You tell me… ...
View Full Document
- Spring '08
- parietal pleura, 0 m, common solution, capilla ries