Gas Exchange Animals need a supply of O

Gas Exchange

• Animals need a supply of O 2 and a means of expelling CO 2 • They are the reactants and products of cellular respiration Burning man

Respiratory medium • Atmosphere has O 2 at a partial pressure of ~159 mm. Hg – Varies with altitude, about 1/2 that 18, 000 feet • Water ~ 1 ml of O 2 per 100 ml of H 2 O at 0 o Celsius – Varies with soluability, pressure, salts, and temperature – 0. 7 ml of O 2 per 100 ml of H 2 O at 15 o Celsius – 0. 5 ml of O 2 per 100 ml of H 2 O at 35 o 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 O 2 Faster diffusion Needs less ventilation Water is lost by evaporation • So lungs have to be interior

Diffusion • Cells are aquatic • O 2 has to be dissolved across a respiratory surface to get to cells • O 2 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 O 2 to blood • Blood and water move toward each other in gills so as blood is more loaded with O 2 its running into water with even more O 2 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. 001 mm) 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 (~ 100 m 2 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 volume: The volume of air inhaled/exhaled – ~500 ml in humans • Tidal capacity: maximum volume – ~3400 ml for girls 4800 ml 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 – CO 2 levels are monitored in brain • CO 2 dissolves in water and forms carbonic acid with sodium carbonate salts • More carbonic acid lowers p. H and the medulla responds by increasing depth and rate of breathing

Hyperventilating • Trick the brain by purging blood of CO 2 so breathing slows

Loading/Unloading gases • • • Substances diffuse down the Conc. Grad. In the atmo. There’s 760 mm. Hg of gas O 2 is 21% of this so 0. 21 x 760 = 159 This is the partial pressure of oxygen PO 2 CO 2 partial pressure(PCO 2): 0. 23 Liquids in contact with air have the same partial pressure

• Blood at lung: high PCO 2 and low PO 2 • At lungs CO 2 diffuses out and O 2 diffuses in • Now blood has a low PCO 2 and high PO 2 • In cells doing respiration there is a high PCO 2 and low PO 2 so the CO 2 diffuses into blood and O 2 diffuses into the cells

Respiratory pigments • Colored by metals • Invertebrates have hemocyanin which uses copper making blood blue • Vertebrates: hemoglobin uses iron to carry the oxygen. Each hemoglobin carry 4 O 2 s, each blood cell has many hemoglobins

If blood is red why do your veins look blue? • Blood = red in its oxy’d form (i. e. , leaving the lungs), – hemoglobin is bound to oxygen to form oxyhemoglobin. • dark red in deox’d form (i. e. , returning to the lungs), – 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. • Only higher energy wavelengths are seen. And higher energy wavelengths are what we call "blue. " • From straightdope. com

Dissociation curves • Changes in PO 2 will cause hemoglobin to pick up or dump oxygen • Lower PO 2 means hemoglobin will dump oxygen • Bohr shift: Drops in p. H makes hemoglobin dump O 2

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

Liquid Breathing • Perfluorocarbon liquids • ~65 m. L O 2 per 100 m. L • Problems with expelling the CO 2 • 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