Gas exchange in animals
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GAS EXCHANGE IN ANIMALS. We will be studying the diversity of adaptations for this process in four animal groups:. Fish. Mammals. Birds. Insects. AN OVERVIEW. Cellular respiration requires O 2 and produces CO 2 :. C 6 H 12 O 6 + 6O 2  6CO 2 +6H 2 O.

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GAS EXCHANGE IN ANIMALS

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Gas exchange in animals

GAS EXCHANGE IN ANIMALS

We will be studying the diversity of adaptations for this process in four animal groups:

Fish

Mammals

Birds

Insects


An overview

AN OVERVIEW

  • Cellular respirationrequires O2 and produces CO2 :

C6H12O6+ 6O2 6CO2 +6H2O

glucose + oxygen  carbon dioxide + water

  • Gas exchange provides a means of supplying an organism with O2 and removing the CO2


Gas exchange in animals

Organism level

Cellular level

Gas exchange medium (air or water)

Circulatory system

Gas exchange surface

Fuel molecules

from food

Respiration

O2

ATP

CO2

CO2


The source of oxygen

THE SOURCE OF OXYGEN

Air

  • about 21% oxygen

  • thinner at higher altitudes

  • easy to ventilate

    Water

  • amount of oxygen varies but is always much less than air

  • even lower in warmer water

  • harder to ventilate


Gas exchange surfaces

GAS EXCHANGE SURFACES

Diffusion

Gases move by diffusion.

Diffusion is greater when:

  • the surface area is large

  • the distance travelled is small

  • the concentration gradient is high

    Gas exchange also requires a moistsurface

  • O2 and CO2 must be dissolved in water to diffuse across a membrane


Gas exchange surfaces1

GAS EXCHANGE SURFACES

Therefore, an efficient gas exchange surface will…

  • have a large surface area

  • provide a small distance for gases to diffuse across

  • be moist

    …and will be organised or operate in a way that maintains a favourable concentration gradient for the diffusion of both gases.

A circulatory system may operate in tandem with the gas exchange system to maintain the concentration gradient


Structure of the gas exchange surface

STRUCTURE OF THE GAS EXCHANGE SURFACE

Depends on:

  • the size of the organism

  • where it lives – water or land

  • the metabolic demands of the organism – high, moderate or low


Types of gas exchange surface

TYPES OF GAS EXCHANGE SURFACE


Water as a gas exchange medium

WATER AS A GAS EXCHANGE MEDIUM

No problem in keeping the cell membranes of the gas exchange surface moist

BUT

O2 concentrations in water are low, especially in warmer and/or saltier water

SO

the gas exchange system must be very efficient to get enough oxygen for respiration


Getting oxygen from water fish gills

GETTING OXYGEN FROM WATER: FISH GILLS

  • Gills covered byan operculum (flap)

  • Fish ventilates gills by alternately opening and closing mouth and operculum water flows into mouth over the gills out under the operculum

  • Water difficult to ventilate  gills near surface of body


Getting oxygen from water fish gills1

GETTING OXYGEN FROM WATER: FISH GILLS

  • Each gill made of four bony gill arches.

  • Gill arches lined with hundreds of gill filaments that are very thin and flat.


Getting oxygen from water fish gills2

GETTING OXYGEN FROM WATER: FISH GILLS

  • Gill filaments are have folds called lamellae that contain a network of capillaries.

  • Blood flows through the blood capillaries in the opposite direction to the flow of water.


Enhancing the efficiency of fish gills

ENHANCING THE EFFICIENCY OF FISH GILLS

  • Gills have a very large surface area: four arches with flat filaments with lamellae folds

  • Gills are thin-walled and in close contact with water: short distance for diffusion

  • Gills have a very high blood supply to bring CO2 and carry away O2  dark red colour

  • Gills are moist: fish live in water!


Enhancing the efficiency of fish gills1

ENHANCING THE EFFICIENCY OF FISH GILLS

Fresh water flows over gills in one direction.

COUNTER-CURRENT FLOW: water and blood in the gills flow in opposite directions

 maintains a favourable concentration gradient for diffusion of both gases

Concurrent flow animation

Countercurrent flow animation


Concurrent flow

CONCURRENT FLOW


Counter current flow

COUNTER-CURRENT FLOW


Getting oxygen from air mammals birds insects

GETTING OXYGEN FROM AIR: MAMMALS, BIRDS & INSECTS

As a gas exchange medium, air has many advantages over water:

  • Air has a much higher oxygen concentration than water

  • Diffusion occurs more quickly so less ventilation of the surface is needed

  • Less energy is needed to move air through the respiratory system than water


Getting oxygen from air mammals birds insects1

GETTING OXYGEN FROM AIR: MAMMALS, BIRDS & INSECTS

BUT

as the gas exchange surface must be moist, in terrestrial animals wateris continuously lost from the gas exchange surface by evaporation

SO

the gas exchange surface is folded into the body to reduce water loss.


Warm blooded animals

WARM-BLOODED ANIMALS

Warmth speeds up body’s reactions

 enables faster movement etc

BUT

increases evaporation of water from lungs

AND

increases demand for energy to stay warm

SO

higher demand for gas exchange to provide O2 for and remove CO2 from respiration


Mammal lungs ventilation

MAMMAL LUNGS: VENTILATION

Two lungs ventilated by movement of diaphragm and ribs


Mammal lungs structure

MAMMAL LUNGS: STRUCTURE

System of tubes (held open by rings of cartilage) allow air to flow in and out of lungs

  • Air enters via trachea (windpipe)

  • Trachea branches into two bronchi (one bronchus to each lung)

  • Bronchi branch into bronchioles


Mammal lungs structure1

MAMMAL LUNGS: STRUCTURE

Rubber cast of human lungs


Mammal lungs structure2

MAMMAL LUNGS: STRUCTURE

Healthy lungs

Smoker’s lungs


Mammal lungs structure3

MAMMAL LUNGS: STRUCTURE

Many alveoli at the end of the bronchioles

  • walls made of flat cells; only one cell thick

  • each alveolus lined with moisture

  • surrounded by capillary network carrying blood


Gas exchange in mammals

GAS EXCHANGE IN MAMMALS

Inhaled air: 21% O2 and 0.04% CO2

Blood arriving: low in O2 and high in CO2

O2 in lung air

dissolves in moist lining

diffuses into blood

diffuses into lung air

diffuses into moist lining

CO2 in blood

Exhaled air: 17% O2 and 4% CO2

Blood leaving: high in O2andlow in CO2


Gas exchange in mammals1

GAS EXCHANGE IN MAMMALS

Gas exchange animation


Gas exchange in mammals2

GAS EXCHANGE IN MAMMALS


Gas exchange in animals

ENHANCING THE EFFICIENCY OF MAMMAL LUNGS

Large surface area

  • many tiny alveoli

  • area as big as a tennis court in humans!

Short distance for diffusion

  • alveoli and capillary walls only one cell thick

  • cells are flattened so very thin

  • capillaries pressed against alveoli

Moist

  • wet lining of alveolus

  • system internal to reduce water loss by evaporation


Gas exchange in animals

ENHANCING THE EFFICIENCY OF MAMMAL LUNGS

Maintaining a concentration gradient

  • air (with depleted O2 and excess CO2) is exhaled  replaced with fresh inhaled air

  • blood (having lost CO2 and been enriched with O2) returns to heart to get pumped around body replaced with blood collected from body


Bird lungs

BIRD LUNGS

Birds have a high demand for oxygen:

  • warm-blooded so metabolism is high

  • flight requires a lot of energy

Additional challenge:

  • air at higher altitude is thinner  lower in O2

    …yet some species have been seen flying over Mt Everest!

Birds have a very efficient gas exchange system to cope with low O2 supply & high O2 demand


Bird lungs1

BIRD LUNGS

Birds have lungs and air sacs:

  • air sacs are not sites of gas exchange

  • air sacs enable a one-way flow of air through lungs


Bird lungs ventilation

Passage of air through lungs:

in trachea rear air sacs rear bronchi

parabronchi in lungs

out trachea front air sacs front bronchi

BIRD LUNGS: VENTILATION


Bird lungs2

BIRD LUNGS

Main air tubes through lungs are the parabronchi.

Tiny air capillaries loop away from and back to parabronchi  one way flow of air

Blood capillaries run alongside air capillaries

BUT

blood flows in opposite direction to air flow

 COUNTER-CURRENT EXCHANGE of gases


Enhancing the efficiency of bird lungs

ENHANCING THE EFFICIENCY OF BIRD LUNGS

Large surface area

  • many tiny air capillaries

Short distance for diffusion

  • air and blood capillary walls made of flattened, thin cells

  • air & blood capillaries alongside each other

Moist

  • lining of air capillaries is wet

  • system is internal to conserve moisture


Enhancing the efficiency of bird lungs1

ENHANCING THE EFFICIENCY OF BIRD LUNGS

Maintaining a concentration gradient

  • Air flows in one direction through lungs regardless of whether the bird is inhaling or exhaling

  • One way passage in both parabronchi and air capillaries; other wayin blood capillaries

     COUNTER-CURRENT EXCHANGE


Insect tracheal system

INSECT TRACHEAL SYSTEM

Completely different system!

Air tubules (trachea & tracheoles) throughout the body which open to the environment via spiracles


Insect tracheal system1

INSECT TRACHEAL SYSTEM

  • Trachea kept open by circular bands of chitin

  • Branch to form tracheoles that reach every cell

  • Ends of the tracheoles are moist

  • Oxygen delivered directly to respiring cells – insect blood does not carry oxygen


Gas exchange in animals

ENHANCING THE EFFICIENCY OF INSECT TRACHEAE

  • Oxygen delivered directly to respiring cells

  • Can pump body to move air around in tracheal system

    BUT

  • Size of animal limited by relatively slow diffusion rate


Gas exchange in animals

DIVERSITY

fishgills

birdlungs

mammallungs

insecttracheae


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