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Gas Exchange in Animals WHY RESPIRE?

Gas Exchange in Animals WHY RESPIRE?

Gas Exchange

CONNECTIONS: Challenges and in Plants and Animals Absorption Transport

Gas Exchange

The villi (projections) that line the intestines of animals Plants transport , Animals pump circulatory in The root hairs of increase the surface minerals, and sugars through vessels. plants increase the available for absorption. through vessels. surface area available Animals for absorption. Gas Exchange

In plants, highly In animals, highly convoluted surfaces, convoluted surfaces, such as the spongy such as the alveoli of mesophyll of . .

Figure 40.22

Organismal WHY RESPIRE? vs.

• External gas exchange: • Mitochondria need Ø environmental / tissues O2 to make ATP. • Internal gas exchange C6H12O6 + O2 è CO2 + H2O + Energy Ø tissues / tissues ATP ¿ q Cell membranes are permeable to simple of dissolved O2 and CO2

• CO2 by-product • Cellular Respiration: using the to drive must be removed ATP production – The more cells (more body mass), the more O2 needed (oxygen demand)

SIZE MATTERS How do animals get enough O2? • Small organisms have high s/v ratios & use v Size matters! cutaneous exchange (protozoans, , cnidarians, ) v So does activity level. • Ciliated epidermal & gastrodermal tissues keep flowing over surface v Larger, faster animals need tricks to speed up exchange of gases between environment & tissues.

• Surfaces must be moist for exchange to occur!

Heyer 1 Gas Exchange

FICKS LAW Adolf Fick, 1858 Diffusion of Dissolved Gases Ficks law of diffusion of a gas across a fluid membrane: Rate of diffusion = KA(P2–P1)/D • FICKS LAW Wherein: • vs. LUNGS § K = a -dependent diffusion constant. • § A = the surface area available for diffusion. • TERRESTRIAL RESPIRATION § (P –P ) = The difference in (partial • RESPIRATORY PIGMENTS 2 1 ) of the gas across the membrane. § D = the distance over which diffusion must take place.

FICKS LAW FICKS LAW Ficks law of diffusion of a gas across a fluid membrane: Ficks law of diffusion of a gas across a fluid membrane: Rate of diffusion = KA(P2–P1)/D Rate of diffusion = KA(P2–P1)/D Therefore, since: Therefore, since: § The diffusion is of dissolved gases across a fluid § K = a temperature-dependent diffusion constant. membrane ØTemperature is important! ØThe respiratory surface must stay wet!

FICKS LAW FICKS LAW Ficks law of diffusion of a gas across a fluid membrane: Rate of diffusion = KA(P2–P1)/D KA(P –P ) Therefore, since: Rate of diffusion = 2 1 /D § (P2-P1) = The difference in concentration () of the gas across the membrane. Therefore, since: ØButContinually since the result replenish of diffusion the respiratory is to eliminate fluid the § A = the surface area available for diffusion. concentration(ventilation difference,system) and how body can fluid the rate (circulatory be § D = the distance over which diffusion must take place. sustained?system) to maintain disequilibrium across the membrane! ØHow can gas exchange rate be increased? outside ØIncrease surface area and decrease thickness membrane inside of respiratory surfaces as much as possible! equilibrium Rate of of Rate diffusion Time

Heyer 2 Gas Exchange

Gas Dissolved Gas Concentrations Concentration of a gas in a mixture measured as partial pressure Still measured as partial pressure = % of total gas x total gas pressure = amount of that gas dissolved in water at equilibrium with a gas having that partial pressure (at STP) Air: composition & partial v cylinder contains Dry air at 1 atm total pressure (sea level) PO =0.2 atm 1 liter water and 2 1 liter air v N2: 78%; PN2= 0.78 atm (total 1 atm at 25C) v O : 21%; P = 0.21 atm 2 O2 v Oxygen diffuses v CO : 0.03%; P = 0.0003 atm between air & 2 CO2 water. v Other gases bring total up to 1 atmosphere

Dissolved Gas Concentrations Still measured as partial pressure = amount of that gas dissolved in water at equilibrium with a gas RESPIRATION having that partial pressure (at STP) v The air & water are • FICKS LAW at equilibrium • GILLS vs. LUNGS PO =0.2 atm 2 \ they have the • AQUATIC RESPIRATION = 210 ml O2 same P • TERRESTRIAL RESPIRATION O2 • RESPIRATORY PIGMENTS v The amount of a gas PO =0.2 atm 2 dissolved in water depends on its = 5.8 ml O2 .

§ ­ temp ® ¯ gas solubility

Respiratory Surfaces GILLS vs. LUNGS Maximizing the respiratory surfaces:

– Evaginations (gills)

– Invaginations (lungs)

ésurface area / êdistance between environment and tissues

Heyer 3 Gas Exchange

Terrestrial vs. Aquatic Respiration Terrestrial vs. Aquatic Respiration — the Trade-offs % •Hence, in low-oxygen environments (i.e., in water), for ventilation 5C 35C need large, wet respiratory surface exposed to the respiratory medium. % O2 in •Gills! air 21% 21% 1% •But, in dry environments (i.e., in air), large, wet respiratory surface would dry out and result in % O2 in excessive water loss. 0.9% 0.5% 20% * •No gills! water •In dry, high-oxygen environments (i.e., in air), contact of the wet respiratory surface with the respiratory O2 in medium can be restricted to protect from drying out. air/water 25x 40x •Lungs! •But, in viscous, low-oxygen environments (i.e., in water), restricted contact provides inadequate gas * Water is ~800x more dense & 50x more viscous than air! exchange. •No lungs!

Aquatic Respiration Structures usually need Animal type Ventillation more oxygen than Fish Pharyngeal gills Buccal pumping ; worm Parapodia Gill movement they have more Aquatic mollusk Ctenidia Cilia gill area than Dermal branchia Cilia most

Crustacean Gills Gill bailer invertebrates.

Horseshoe crab Book gills Gill movement

Buccal pumping Fish ventilation 1-way flow of water across gills

v Fish use energy to pump water across gills (ventilation). v At low speed, buccal pumping is used. v At higher speed, ram ventilation (swimming with mouth & open) is more efficient (but still costs energy).

Heyer 4 Gas Exchange

O2 diffuses from high concentration to low concentration.

Fig. 42.22

If fish used Concurrent Exchange: So fish use .

Equilibrium reached: Equilibrium prevented: No further exchange Exchange continues

c.f., Campbell Fig. 42.22

More active fish have bigger gills. index of relative gill surface area/body mass Aquatic Respiration Structures Animal Gill type Ventillation

Fish Pharyngeal gills Buccal pumping Mackerel: 2551 Polychaete worm Parapodia Gill movement

Aquatic mollusk Ctenidia Cilia

Echinoderm Dermal branchia Cilia

Toadfish: 137 Gills Gill bailer

Horseshoe crab Book gills Gill movement

Heyer 5 Gas Exchange

Counter- exchange in mollusc ctenidia • Flattened filaments attached on alternate sides to a longitudinal axis • Water flow through chamber generated by cilia counter to flow direction of gills

Water flow

Fig. 42.21

Cross-section view & BOOK LUNGS

• . • Page-like structure. • In larger species its supplemented by a tracheal system.

Tracheal Systems of Terrestrial Terrestrial Tracheal System – , millipedes, onycophorans, and big arachnids.

silkworm & tracheae

Spiracle (w/ filters) • Ventilated by air sacs in larger or more active species. (lined w/ taenidia)

Tracheole Tracheole Tracheole Tracheole trachea Fig. 42.23

Heyer 6 Gas Exchange

Flight muscles have very high aerobic demand —Tracheoles end near mitochondria in each cell. gas exchange: vSpiracles can close to limit water loss.

spiracles

silkworm spiracle

Fig. 42.23c & tracheae dung beetle spiracle

Vertebrate Lungs Terrestrial snails & slugs have: • & : – Septate sac w/ Septa • lost their ctenidia from mantle cavity • vascularized mantle cavity acting as lung • : – Complex, w/alveoli

• : – Elaborate flow- through system w/ parabronchi

Lungless Amphibians with lungs

vGas exchange through vFrogs and larger ; blood gets salamanders do gas oxygenated when if exchange through flows near skin. skin and lungs. vSmall, slender bodies. vUsually most O2 is absorbed in the lungs, vThey dry out easily. but most CO2 is vCold bodies; dont use eliminated through much O2. the skin.

Heyer 7 Gas Exchange

Frogs: positive-pressure Reptiles air into lungs v Reptiles have impermeable skin; gas exchange happens in lungs. v Most have fairly low oxygen requirements. Breathing is not continuous. v Body temperature is usually near ambient; this keeps water loss low compared to warm-bodied animals.

Mammalian Lung — 300 Million Alveoli Negative pressure breathing

Fig. 42.24 Human lung: • Surface area = 100 m2 • Only 0.2 µm between air/blood

Fig. 42.27

Negative pressure breathing

O2 & CO2 diffuse from high concentration to low concentration.

§ : 150 ml § (resting): 500 ml § Tidal volume (exercise): 3000 ml Fig. 42.29

Heyer 8 Gas Exchange

Both Positive- & Negative-Pressure Breathing Air Lung of Birds expand & contract rib cage (no diaphragm)

• Parabronchi: continuous, one- way, flow-through exchange

Constant air flow through rigid lungs • Negative pressure ventilation during • Positive pressure ventilation during • Two ventilation cycles needed for inhaled air to be exhaled

Fig. 42.26 http://people.eku.edu/ritchisong/avian_biology.htm

Counter-current exchange

between air and blood capillaries http://tabletopwhale.com/2014/10/24/3-different-ways-to-breathe.html • Parabronchi: continuous, one- way, flow-through exchange

http://people.eku.edu/ritchisong/avian_biology.htm

Blood-gas barrier: lung cross-sections Blood-gas barrier thickness

Bird parabronchi

Mammal alveoli

Heyer 9 Gas Exchange

Terrestrial vs. Aquatic Respiration Diffusion & exchange is of

dissolved O2 only! O2 Level 5°C 35°C % Metab. for Resp.

How much O2 can be carried Air 21% 21% 1% dissolved in blood alone? Water 0.9% 0.5% 20%

O2 in air 25X 40X vs. water

RESPIRATION Respiratory Pigments Carry O2 • with a metal core, giving it color. • FICKS LAW • GILLS vs. LUNGS • E.g., (Hb). • AQUATIC RESPIRATION • TERRESTRIAL RESPIRATION • Pigment • RESPIRATORY PIGMENTS packed in blood cells (RBCs) reduce of high- protein .

Hb affinity for O2 Other Respiratory Pigments shifts w/ blood oxygen content • Hemoglobin has Name Metal Color Animal – high O2 affinity when PO2 is high

Chlorocruorin Iron Green Sedentary – low O2 affinity when PO2 is low

Hemocyanin Copper Blue Arthropods and Molluscs Myoglobin Iron Red Marine Mammals, Waterfowl

Heyer 10 Gas Exchange

Blood temperature & pH also influence O2 -Dissociation Curve for Hb hemoglobins affinity for O2. The Bohr Shift

• CO2 dissolved into blood forms carbonic acid, lowering pH. • Gives O2 up easier when pH is lower at cells (more carbonic and present) • Grabs O2 at alveoli where CO2 levels are lowest due to exhalation

Fig. 42.30a

Myoglobin

v Myoglobin: another O2 carrier, found in muscle. v Single subunit; no cooperativity saturation

c.f., Fig. 42.30b

Fetal hemoglobin The Bohr shift is used elsewhere … for a very different purpose: O2 binding affinity of fetal hemoglobin vs. mothers hemoglobin

Swim Bladder

Oxygen [swim] bladder as a control organ

• épH è bind O2 to Hb è deflate è sink

• êpH è offload O2 from Hb è inflate è rise

Heyer 11

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