Gas Exchange in Animals: Understanding Respiratory Systems

1. Gas Exchange

2. Animals need a supply of O2 and a means of expelling CO2 They are the reactants and products of cellular respiration Gas Exchange

3. Respiratory medium • Atmosphere has O2 at a partial pressure of ~159 mmHg • Varies with altitude, its about half as much at 18,000 feet above sea level • Water has ~ 1 ml of O2 per 100 ml of H2O at 0o Celsius • Varies with solubility, pressure, salts, and temperature • 0.7 ml of O2 per 100 ml of H2O at 15o Celsius • 0.5 ml of O2 per 100 ml of H2O at 35o Celsius

4. Water Keeps the cells moist Lower oxygen concentration than air Concentration varies more Water is heavier Air Higher conc. of O2 Faster diffusion Needs less ventilation Water is lost by evaporation So lungs have to be interior Water vs. air as a medium

6. Diffusion • Cells are aquatic • O2 has to be dissolved across a respiratory surface to get to cells • O2 can diffuse through a few mm of cells • If a part of your body is more than a few mm thick then you need a way to carry the oxygen • Need a large respiratory surface area

7. Skin breathers • Earthworms • Keep skin moist and exchange gases across their entire surface • Amphibians • Supplement their lungs with gills

8. Form and function • Depends on whether environment is terrestrial or aquatic • Simple animals have nearly every plasma membrane in contact with the outside environment • Protozoans • Sponges • Cnidarians – hydra, anemones • Flat worms

9. Lungs/gills • Highly folded or branched body region • Creates a large surface area for absorption • Gills • External • Problem - losing water due to osmolarity of salt water • Lungs • Internal – prevents drying out of membranes • Allow use of air as a medium • Terrestrial life poses problem of dessication

10. Gills • Invertebrates can have simple gills • Echinodermata: have simple flaps over much of their body • Crustaceans: have regionalized gills • Ventilation: have to keep water moving over the gills, either by paddling water in or staying on the move • This requires energy • Gill slits of fish are believed to be evolutionary ancestors of Eustachian tubes

11. Invertebrate gills

12. Gills •Specialized for gas exchange in water. •Have to be efficient – 10,000X less O2 in water than in air. •O2 and CO2 readily diffuse between blood and water. •Countercurrent Exchange: blood in capillaries flows inopposite direction from the water passing over the gills. Along the capillary, a steep diffusion gradient favors transfer of oxygen into the blood.

13. Countercurrent Flow in Sharks

14. Countercurrent vs. Concurrent Flow

15. Countercurrent exchange • Speeds transfer of O2 to blood • Blood and water move toward each other in gills so as blood is more loaded with O2 it’s running into water with even more O2 dissolved so it can take on the maximum load • Gills can remove 80% of the oxygen from the water passing over it

16. Tracheae • Spiracles are holes all over an insect’s body. • From the spiracles, tubes branch out • Finest branches (0.001mm) reach every cell • Insects still have circulatory system to carry other materials

17. Respiratory Exchange in Insects Spiracles of Two Insects

18. Lungs • Dense networks of capillaries under epithelium forms the respiratory surface • Snails: Internal mantle • Spiders: book lungs • Frogs: balloon like lungs • Vertebrates: highly folded epithelium • humans (~ 100m2 surface area)

19. Lungs • Enclosed by double walled sac whose layers are stuck together by surface tension, allowing them to slide past each other • System of branching ducts • Nasal cavity  pharnyx  open glotis  larynx (voicebox)  trachea (windpipe)  2 bronchi (bronchus)  many bronchioles  cluster of air sacs called alveoli (alveolus)

20. Pulmonary Circulation

21. Alveolar Exchange

22. Ventilating the Lungs • Frogs usepositive pressure breathing: gulp air and push it down • Mammals: negative pressure breathing • Suction pulls air down into a vacuum • During exercise rib muscles pull up ribs increasing lung volume, and lowering pressure • But ribs are only ~ 1/3 of Shallow breathing

23. Diaphragm • Sheet of muscle at bottom of thoracic cavity • During inhalation: it descends • During exhalation: it contracts

24. Volumes • Tidal volume: The volume of air inhaled/exhaled • ~500 ml in humans • Tidal capacity: maximum volume • ~3400 ml for girls 4800ml for boys • Residual volume: air left in alveoli after exhalation

25. Control • Medulla oblongata and pons • negative feedback loop: when stretched too much lungs send message back to brain to exhale • CO2 levels are monitored in the brain • CO2 dissolves in water and forms carbonic acid with sodium carbonate salts • More carbonic acid lowers pH of blood and the medulla responds by increasing depth and rate of breathing

26. Hyperventilating • Trick the brain by purging blood of CO2 so breathing slows

27. Loading/Unloading Gases • Substances diffuse down the Conc. Grad. • In the atm. there’s 760 mmHg of gas • O2 is 21% of this so 0.21 x 760 = 159 mmHg • This is the partial pressure of oxygen PO2 • CO2 partial pressure(PCO2): 0.23 mmHg • Liquids in contact with air have the same partial pressure

28. Gas Exchange at Alveoli • Blood at lung: high PCO2 and low PO2 • At lungs CO2 diffuses out and O2 diffuses in • Now blood has a low PCO2 and high PO2 • In cells doing respiration there is a high PCO2 and low PO2 so the CO2 diffuses into blood and O2 diffuses into the cells

29. Gas Exchange Throughout the Body

30. Respiratory pigments • Colored by metals • Invertebrates have hemocyanin which uses copper making blood blue • Vertebrates: hemoglobin which uses iron to carry the oxygen. Each hemoglobin can carry 4 O2s, each blood cell has many hemoglobins

31. If blood is red why do your veins look blue? • Blood is a bright red in its oxygenated form (i.e., leaving the lungs), when hemoglobin is bound to oxygen to form oxyhemoglobin. It's a dark red in its deoxygenated form (i.e., returning to the lungs), when hemoglobin is bound to carbon dioxide to form carboxyhemoglobin. Veins appear blue because light, penetrating the skin, is absorbed and reflected back to the eye. Since only the higher energy wavelengths can do this (lower energy wavelengths just don't have the *oomph*), only higher energy wavelengths are seen. And higher energy wavelengths are what we call "blue." • From straightdope.com

33. Dissociation curves • Changes in PO2 will cause hemoglobin to pick up or dump oxygen • Lower PO2 means hemoglobin will dump oxygen • Bohr shift: Drops in pH makes hemoglobin dump O2

34. Diving mammals • Weddell seals • Dive 200 – 500 m • 20 min – 1 hr. under water • Compared to us it has ~ 2x as much O2 per kg of weight • 36% of our O2 is in lungs 51% in blood • Seals have 5% and 70% respectively • more blood, huge spleen stores 24L blood • More myoglobin (dark meat) • Slow pulse

35. Liquid Ventilation • Perfluorocarbon liquids – • ~65 mL O2 per 100 mL • Problems with expelling the CO2 • Remember this is a liquid 1.8 times as dense as water so it is hard to breath • Could someday be used for diving, or medical applications (ex: supporting injured lungs, radiology)