Biology 2672a: Comparative Animal

Physiology

Breathing in air

Gas transport in organisms - a combination of convection and diffusion

Tidal convection ventilates lungs

Diffusion into bloodstream

Unidirectional flow (convection) in circulatory system

Diffusion from capillaries into tissues

Concurrent gas exchange

Fig. 21.4a

Countercurrent gas exchange

Concurrent

Fig 21.4b

Countercurrent gas exchange

Concurrent

Fig 21.4b

Cross-current gas exchange

Fig. 21.5

Mammal lungs are inefficient

Fig. 21.19 Fig. 21.3

Breathing AirLots of Oxygen!Not so easy to get

rid of CO2Problems with water

lossLungs

(invaginations)

(Most) Fishes Breathing Air

Electric Eel - Mouth

Plecostomus - Gut

Bowfin – Swim bladder Fig. 23.15

Tracheal system

Fig. 22.29

Construction of the tracheal system A branched series of tubes that are

filled with air (except at the very ends)

Trachea>Tracheoles Terminal tracheoles

Constructed from a single invaginated cell

Distance between lumen & cell = 3 x cell membranes

Fluid-filled

Tracheal systemVery extensive

no cell is more than 2-3 cell diameters from a tracheole

Tissues with high metabolism (e.g. flight muscle) may have at least one terminal tracheole penetrating each cell (!)

On-tap oxygen in every cell!

Gas transport in the tracheal system Diffusion works very well

in gases Some convection

Thorax & abdomen pumping Caused by partial pressure gradients? Tracheal pumping? (see movie on WebCT)

One-way flow systems ‘Ram’ ventilation (draft ventilation)

Mammal lungsTrachea

Bronchus

Terminal Bronchiole

Respiratory bronchiole

Alveolar ductAlveolar duct

Alveoli

Fig. 21.18

Breathing air while flyingEnergetic costs of flying are 2.5-

3 × higher than runningTwo groups of extant flying

vertebrates

Insects -Tracheal system reaches every cell

Ways to maximise O2 uptake

Countercurrent exchangeReduce diffusion distance Increase flow rate Increase absorption of O2

J=KP1-P2

X

Bird lungs – a one-way system

Fig. 22.24

The bird lung - orientation

Beak

Butt

Anterior Air Sacs

Posterior Air Sacs1° bronchus Mesobronchus

Parabro

nchiP

osterio

r 2°

bro

nch

us

An

teri

or

2°

bro

nch

us

Fig. 22.22

Bird lung: Breathe in

Bird lung: Breathe Out

See also Fig 22.22

Bird Lungs: Gas-bloodHighly efficient

>37 % of O2 extracted from the air Mammals: ~25%

Thin blood-gas barriersSurface area : body size ~ same

as mammalsSurface area : lung volume ~2×

mammals

Bird Lungs: Cross-current gas exchange

Fig. 22.23c Fig. 22.5

Ways to maximise O2 uptake

Countercurrent exchangeReduce diffusion distance Increase flow rate Increase absorption of O2

J=KP1-P2

X

Bat lungsMammalian – alveolar dead

space (etc)~Equivalent O2 uptake to birds Heart size, Heart output HaematocritLarge lungs

Surface area pulmonary blood volume thickness of blood-gas barrier

Bats vs birdsLargest birds (~18 kg) much

larger than largest bats (~1.5 kg)

Birds function perfectly well (fly!) at high altitude Geese over Mt Everest Vulture in jet engine at 11.2 km High altitude climbers not plagued

with bats…

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