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
Burning man 

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 soluability, 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 vs. air as a medium 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 interior

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 Amphibians
Keep moist skin and exchanges gas across its entire surface
Amphibians
Supplement their lungs/gills

8. Form and function Depends on terrestrial/aquatic environment
Simple animals have nearly every plasma membrane in contact with the outside environment
Protozoans
Sponges
Cnidarians
Flat worms

9. Lungs/gills Gills Lungs Highly folded or branched body region
Allow a large surface area
Gills
External
Problem of losing water due to osmolarity
Lungs
Internal
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. Gills in a Tuna head

15. Invertebrate gills

16. 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 its 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

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

20. Giant insects
By flexing they compress and expand the tracheae like a bellows
However insects can’t be too big because the oxygen can’t diffuse far enough
But ancient insects were large. How?

21. 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)

22. 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)

25. Ventilating the Lungs
Frogs use Positive 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

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

28. volumes Tidal volumue: 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

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

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

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

32. 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

34. 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

35. 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

37. 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

38. Diving mammals Weddell seals Dive 200 – 500 m
20 min – 1 hr. under water
Compared to us it has ~ 2xs as much O2 per kg of wieght
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

39. Liquid Breathing 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