Gas Exchange & Circulation

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Randell Johns
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C 6 H 12 O 6 + O 2 Taking up oxygen Diffusion Diffusion is the only way. Molecules spread out by random motion.

1 Why is gas exchange important? Gas Exchange & Circulation Read Ch. 42 start with 42.5: Gas Exchange in Animals Respiration: C 6 H 12 O 6 + O 2! Energy + CO 2 + H 2 O Photosynthesis: Energy + CO 2 + H 2 O! C 6 H 12 O 6 + O 2 Taking up oxygen Diffusion Diffusion is the only way. Molecules spread out by random motion. concentration gradient Random walks in 3 dimensions Taking up oxygen "! For very small organisms, diffusion is fast enough to supply O 2. "! O 2 use is correlated with body mass (or volume), but diffusion rate depends on surface area... 1

surface area/volume ratio Taking up oxygen v For very small organisms, diffusion is

v O 2 use is correlated with body mass (or volume), but diffusion rate depends on

Taking up oxygen v Diffusion alone is enough for animals up to about 1 mm thick.

Taking up oxygen Fick s Law of Diffusion C 1 C 2 Rate of diffusion is proportional to:

2 surface area/volume ratio Taking up oxygen v For very small organisms, diffusion is fast enough to supply O 2. v O 2 use is correlated with body mass (or volume), but diffusion rate depends on surface area... v and larger organisms have lower surface area/volume ratios. Taking up oxygen v Diffusion alone is enough for animals up to about 1 mm thick... Taking up oxygen v Diffusion alone is enough for animals up to about 1 mm thick... v depending on rate of O 2 use. Taking up oxygen Fick s Law of Diffusion C 1 C 2 Rate of diffusion is proportional to: Larger, faster animals need tricks to speed up diffusion. u Surface area u Concentration gradient u Diffusion distance u Diffusion constant 2

O 2 requirements and Diffusion Speeding up Diffusion "! Gases diffuse from higher to lower concentration. "! O 2 concentration must be lower in organism than in environment.

Speeding up diffusion: gills Fish gills compared to invertebrates "! Higher metabolic rate "! Large surface area "!

Gill area is proportional to body size Allometry log gill area, mm 2 Bigger fish have bigger gills.

3 O 2 requirements and Diffusion Speeding up Diffusion "! Gases diffuse from higher to lower concentration. "! O 2 concentration must be lower in organism than in environment. "! Will organism get enough O 2? Depends on rate of O 2 use and diffusion. "! Large, active animals need tricks to speed up diffusion. Speeding up diffusion: gills Fish gills compared to invertebrates "! Higher metabolic rate "! Large surface area "! Short diffusion distance (thin epithelium) "! More O 2 "! Bigger relative gill area Gill size depends on body size and metabolic rate. Gill area is proportional to body size Allometry log gill area, mm 2 Bigger fish have bigger gills... Scaling: the relationship between the size of an organism and the size of any of its parts log body mass, g but not relative to their body size. 3

Gill area vs. body size Faster fish have bigger gills.

137 gill area per unit body mass compared to body mass

Diffusion is extremely slow at larger scales. "!

4 Gill area vs. body size Faster fish have bigger gills. index of relative gill surface area Mackerel: 2551 Toadfish: 137 gill area per unit body mass compared to body mass Diffusion isn t enough: ventilation "! Bony fish: opercular pumping "! Supplements diffusion with convection. How do gas molecules move? "! At very small scales, diffusion is the only way. "! Diffusion is extremely slow at larger scales. "! Convection (bulk flow) is needed. Speeding up diffusion: ventilation Angel sharks: buccal pumping Opercular pumping: one-way water flow "! Many sharks have spiracles: "! modified gill slits for water intake 4

"! At very small scales, diffusion is the only way. "!

fish gills (1) Countercurrent exchange of O 2 in fish gills (2)

5 Speeding up diffusion: ventilation "! At higher speed, ram ventilation is used. How do gas molecules move? "! At very small scales, diffusion is the only way. "! Diffusion is extremely slow at larger scales. "! Convection (bulk flow) is needed. Fish gills: countercurrent exchange Countercurrent exchange of O 2 in fish gills (1) Countercurrent exchange of O 2 in fish gills (2) Countercurrent vs. Concurrent Exchange "!Water & blood flow opposite directions. "!This maximizes the concentration gradient & speeds up diffusion. "!Equilibrium is never reached. 5

6 Fick s Law of Diffusion Rate of diffusion is proportional to: Gas Exchange & C 1 C Circulation 2 u Surface area u Concentration gradient u Diffusion distance u Diffusion constant air vs. water Fick s Law of Diffusion Diffusion between gas & liquid C 1 C 2 How is concentration measured? u moles/liter u gas pressure v Closed cylinder contains 1 liter water and 1 liter air (at 1 atm). v Oxygen diffuses between air & water. Air: composition & partial pressures v N 2 : 78%; P N2 = 0.78 atm v O 2 : 21%; P O2 = 0.21 atm v CO 2 : 0.03%; P CO2 = atm Other gases bring total up to 1 atmosphere. Partial pressure & concentration 210 ml O 2 P O2 =0.2 atm 5.8 ml O 2 P O2 =0.2 atm v The amount of O 2 dissolved in water depends on solubility and pressure. v The air & water are at equilibrium if they have the same P O2. 6

The diving bell spider Problems with breathing water v Osmoregulation (gain or loss of water

1 liter water: 5 ml O 2 1 liter air: 200 ml O 2 Water vs.

1 liter water: 1 kg 1 liter air: 1.2 g v Water has high thermal conductivity & heat capacity.

Air Air s hard tradeoff v Air has plenty of O 2... v But breathing air causes evaporation.

7 The diving bell spider Problems with breathing water v Osmoregulation (gain or loss of water or salt). v Water doesn t hold much O 2. 1 liter water: 5 ml O 2 1 liter air: 200 ml O 2 Water vs. Air Problems with breathing water v Water is dense & viscous. 1 liter water: 1 kg 1 liter air: 1.2 g v Water has high thermal conductivity & heat capacity. Water conducts heat 25x as fast as air. Water vs. Air Air s hard tradeoff v Air has plenty of O 2... v But breathing air causes evaporation. Anything that speeds up gas exchange in air will also speed up evaporation. Water vs. Air Most terrestrial animals have lung-like structures. Gills work well in water, but not in air. Banana slug (phylum mollusca) Lungs are like inside-out gills. 7

cavity. "!They dry out easily. "!Don t pump air through lung.

Animals in dry environments must limit water

Exoskeleton reduces water loss, but also

8 Air-breathing snails "!Gas exchange through skin and lung-like mantle cavity. "!They dry out easily. "!Don t pump air through lung. "!Don t use much O 2. Insect Gas Exchange "!Animals in dry environments must limit water loss through breathing. "!Exoskeleton reduces water loss, but also reduces gas exchange. Insect Gas Exchange: Tracheae "!Large surface area for gas exchange. "!Bring air close to tissues. Insects have tracheae: tubes that carry air close to tissues. Cockroach trachea Insect Gas Exchange: Spiracles Insect Gas Exchange "!Close to limit water loss; open for gas exchange. silkworm spiracle & tracheae dung beetle spiracle spiracles 8

Insect Gas Exchange: Tracheae Insect Gas Exchange: Tracheae

Insect treacheae deliver O 2 directly to tissues. "!

9 Insect Gas Exchange: Tracheae Insect Gas Exchange: Tracheae "!Some insects pump air in & out. "!2-way air flow reduces water loss. Insect Gas Exchange: Size Limits "!Insect treacheae deliver O 2 directly to tissues. "!As size increases, tracheal area must increase even faster... Insect size limited by O 2 "!Maximum size may be limited by the ability to deliver air to tissues. Insect Size Limits Insect Size Limits leg outline trachea outline 250 µm "!Leg tracheae occupy greater percentage of the leg in bigger beetles. "!Leg tracheae occupy greater percentage of the leg in bigger beetles. 9

More O 2, bigger insects "!In paleozoic era ( mya), O 2 level was 30%... "!... and insects were bigger!

"!Cold body; low O 2 use. Amphibians with lungs "!

Usually most O 2 is absorbed in the lungs, but most CO 2 is eliminated

Frogs: positive-pressure breathing forces air into lungs Reptiles Reptiles

Reptiles have impermeable skin; gas exchange happens in lungs. "!

10 More O 2, bigger insects "!In paleozoic era ( mya), O 2 level was 30%... "!... and insects were bigger! Lungless salamanders "!Gas exchange through skin. "!Small, slender body. "!Must stay wet. "!Cold body; low O 2 use. Amphibians with lungs "!Frogs and larger salamanders do gas exchange through skin and lungs. "!Usually most O 2 is absorbed in the lungs, but most CO 2 is eliminated through the skin. Frogs: positive-pressure breathing forces air into lungs Reptiles Reptiles have impermeable skin; gas exchange happens in lungs. Reptiles "!Reptiles have impermeable skin; gas exchange happens in lungs. "!Most have fairly low oxygen requirements. "!Body temperature is usually near ambient; this keeps water loss low compared to warm-blooded animals. 1 0

Mammals: higher metabolic rate; more O 2.

11 Mammals: higher metabolic rate; more O 2. Mammals "!Higher metabolic rate; "!Increased gas exchange. "!Greater lung surface area. "!More control of ventilation. "!More control of the flow of oxygenated blood. "!More water loss. Mammalian lungs amphibian: Human lungs Mammalian alveoli, SEM "!Large surface area: 100 m

Human lungs Mammalian alveoli, SEM v Large

breathing Human breathing v Dead space: 150 ml v

(exercise): 3000 ml Human lungs O 2 & CO 2

12 Human lungs Mammalian alveoli, SEM v Large surface area: 100 m 2. v Minimal diffusion distance: 0.2 µm between blood, air Negative pressure breathing Human breathing v Dead space: 150 ml v Tidal volume (resting): 500 ml v Tidal volume (exercise): 3000 ml Human lungs O 2 & CO 2 diffuse from high concentration to low concentration. v Countercurrent air/ blood flow not possible in alveoli... 12

Human lungs v Countercurrent air/ blood flow not possible in

.. v But countercurrent air flow in nasal passages catches H 2 O

because: Mammals: warm bodies, more v They don t need to breathe

13 Human lungs v Countercurrent air/ blood flow not possible in alveoli... v But countercurrent air flow in nasal passages catches H 2 O vapor. Breathing Air v Air has plenty of O 2... v But it dries you out. Anything that speeds up gas exchange in air will also speed up evaporation. Reptiles don t lose as much water to evaporation as mammals do, because: Mammals: warm bodies, more evaporation. v They don t need to breathe as much v Their bodies are close to ambient temperature Moisture-catching turbinate bones reduce water loss. Birds v Unlike mammals, birds have 1-way air flow through lungs. v Air sacs move the air. v Like mammals, birds have high metabolic rates. 13

Bird lung (cast) Bird lung: parabronchi Birds

Circulation respiratory pigments v O 2 isn t

v Respiratory pigments increase the solubility

14 Bird lung (cast) Bird lung: parabronchi Birds have a water-recycling system analogous to that of mammals. Respiratory Pigments Gas Exchange & Circulation respiratory pigments v O 2 isn t highly soluble in blood or body fluids. v Respiratory pigments increase the solubility of O 2 in blood. No hemoglobin: 0.3 ml O 2 /100 ml blood Hemoglobin: 20 ml O 2 /100 ml blood 14

Respiratory Pigments v Hemoglobin is the main respiratory pigment in mammals; it s carried in erythrocytes.

v Gas exchange systems increase P O2 in tissues.

v Respiratory pigments help blood carry more moles of O 2 at a given P O2.

15 Respiratory Pigments v Hemoglobin is the main respiratory pigment in mammals; it s carried in erythrocytes. v O 2 & CO 2 diffuse from high concentration to low concentration. v Gas exchange systems increase P O2 in tissues. human toad v P O2 is always lower in tissues than in the environment. v Respiratory pigments help blood carry more moles of O 2 at a given P O2. Hemoglobin binds to O 2 in the lungs, then releases O 2 in the tissues. O 2 Binding Affinity of Hemoglobin O 2 unloaded normally Additional O 2 unloaded during exercise Cooperative O 2 Binding v Lower saturation leads to lower binding affinity! Tissues Lungs Tissues Lungs 15

O 2 Binding Affinity of Hemoglobin Not like this! saturation "!

hemoglobin vs. mother s hemoglobin "!Blood also carries CO 2. "!Some CO 2 dissolved in plasma.

16 O 2 Binding Affinity of Hemoglobin Not like this! saturation "!Myoglobin: another O 2 carrier, found in muscle. "!Single subunit; no cooperativity. Tissues Lungs Globin gene evolution O 2 Binding Affinity of Hemoglobin Fetal hemoglobin vs. mother s hemoglobin "!Blood also carries CO 2. "!Some CO 2 dissolved in plasma. "!Some CO 2 carried by hemoglobin. Dissolving CO 2 makes blood more acidic: H 2 O + CO 2 $ H 2 CO 3 $ H + + HCO 3 - The carbonate buffer system 1 6

v Why seals can dive so long (and not die). Why you want to breathe Free diving hazard: Shallow-water blackout v Hyperventilate and dive deep.

17 Bohr Shift ph 7.4 ph 7.2 Gas Exchange & Circulation v Why is gas exchange important? v Diffusion v Animals: Gas exchange in water and in air v Respiratory pigments v Diving Gas Exchange diving v Diving: How to die, with or without SCUBA. v Why seals can dive so long (and not die). Why you want to breathe Free diving hazard: Shallow-water blackout v Hyperventilate and dive deep. v Diving increases P O2 in your lungs, so you exctract more O 2 from air. v With low P CO2 in blood, you don t feel the need to breathe. v Increasing P CO2 decreases ph, stimulating you to breathe. v When you come back to the surface, P O2 in your lungs decreases dramatically. 17

Scuba hazards: Decompression Sickness "!High pressure causes N 2 to dissolve in tissues. "!When pressure decreases, N 2 forms bubbles in tissues, potentially blocking blood flow. "!Decompression stops allow N 2 to diffuse out slowly.

pulmonary barotrauma and air embolism. Diving hazards: Free diving & SCUBA "!Shallow-water blackout P O2 decreases while ascending; free diving only. "!Decompression sickness N 2 comes out of solution while ascending; SCUBA only.

18 Scuba hazards: Decompression Sickness "!High pressure causes N 2 to dissolve in tissues. "!When pressure decreases, N 2 forms bubbles in tissues, potentially blocking blood flow. "!Decompression stops allow N 2 to diffuse out slowly. Scuba hazards: Pulmonary barotrauma "!As you ascend, ambient pressure decreases. "!If you hold your breath, the expanding air in your lungs forces bubbles across the epithelium "!pulmonary barotrauma and air embolism. Diving hazards: Free diving & SCUBA "!Shallow-water blackout P O2 decreases while ascending; free diving only. "!Decompression sickness N 2 comes out of solution while ascending; SCUBA only. "!Pulmonary barotrauma. Air in lungs expands while ascending; SCUBA only. Marine Mammal Diving Physiology California sea lion Why can they dive so much better than us? Elephant Seals Elephant seal dives: Swim 90 km/day 1 8

6% of body volume for all mammals -- including marine mammals. Dives avg.

19 Elephant seal dives: Elephant seal dives: Avg dive 24 min, max 2 hr 2.5 min surface " Underwater 90% of time Elephant seal dives: It s not in the lungs " Lung volume! 4.6% of body volume for all mammals -- including marine mammals. Dives avg meters; max 1500 meters " Marine mammals don t rely on the air in their lungs while underwater. Marine mammals have 2 kinds of tricks: " Use oxygen slowly. " Store a lot of oxygen. Use oxygen slowly: The Diving Reflex: "!Heart rate slows "!Blood pressure decreases "!Peripheral circulation reduced "!Spleen shrinks: more blood into circulation 1 9

20 Store more oxygen "!Large blood volume "!High concentration of erythrocytes "!High hemoglobin concentration per cell "!High myoglobin concentration Deep dives -- no problem? "!Shallow-water blackout "!Decompression sickness "!Pulmonary barotrauma 2 0

Gas Exchange Respiratory Systems

alveoli gills Gas Exchange Respiratory Systems elephant seals 2008-2009 Why do we need a respiratory system? respiration for respiration Need O 2 in for aerobic cellular respiration make ATP Need CO 2