Gas Exchange

• Animals need a supply of O2 and a means of expelling CO2

• They are the reactants and products of cellular respiration

Burning man

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

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

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

• Skin breathers

• Earthworms– Keep moist skin and exchanges gas across

its entire surface

• Amphibians– Supplement their lungs/gills

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

• Lungs/gills– 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

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

Gills in a Tuna head

Invertebrate gills

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

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

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?

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)

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)

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

Diaphragm

• Sheet of muscle at bottom of thoracic cavity

• During inhalation: it descends

• During exhalation: it contracts

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

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

Hyperventilating

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

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

• 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

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

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

http://www.worth1000.com/view.asp?entry=229645&display=photoshop

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

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

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