5. Respiration- The Exchange of Gases

8/3/2019 5. Respiration- The Exchange of Gases

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Respiration:

The Exchange of Gases

Respiration (gas exchange): the interchangebetween an animal and its environment.


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Mechanisms of Gas Exchange

Three phases of gas exchange:

1) Breathing

- gas exchange with environment

2) Gas transport

- circulatory system

- blood vessels

3) Servicing body tissues

- gas exchange with tissues

- O2 uptake - cellular respiration

- CO2 release - waste product


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Respiratory surface - the part of the animal where O2 diffuses

into the animal and CO2 diffuses out to

the environment.

- covered by living cells (single layer, moist)

Outer skin

- skin breathers

- capillaries below skin-small, long, flat organisms

-high surface to volume ratio

e. g. earthworm and hydra


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Most animals require specific adaptations for gas exchange

Gills

- feather-like extensions body surface

- very high surface area- in contact with environment

- must always be moist!!

e.g. fish, amphibians, crabs and

mollusca


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In most terrestrial organisms, the respiratory surfaces areFolded into the body.

Tracheal system

- extensive system of internal tubes

- exchange gases with the cells

- no assistance from the circulatory

system.

e. g. insects


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Most terrestrial organisms have lungs

Lungs

- internal sacs lined with moist

epithelium

- inner surfaces branch extensively

- large surface area!!

- gases carried between lungs and

body cells by the circulation.

e.g. amphibians, reptiles, birds and

mammals.


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Fish Gills

Gills are adapted for gas exchange in aquatic environments

Water - low dissolved O2

Ventilation- mechanism to increase

contact between respiratory

surface (gills or lungs)

and the environment.

- fish ventilate their gills

to maintain the flow of

O2 rich water.


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Fish Gills

Countercurrent flow in gills enhances O2 transfer

Countercurrent exchange

- the transfer of something from a

fluid moving in one direction to

another fluid moving in the

opposite direction.

- opposite flows maintain a diffusion

gradient.

Gills

- water (O2-rich) flows one way

- blood (O2-poor) flows the other way

* can remove 80% of water O2


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Tracheal System

Insect tracheae are tubes that branch throughout the body

air sacs - contraction of muscles around them control air movement

tracheoles - narrowest tubes that extend to the cells; contain fluid


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Lungs - terrestrial vertebrates


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Lungs

The alveoli are the site of gas exchange with the circulation.

Alveoli

- tiny sacs lined with a thin layer

of epithelial cells; the exchange

surface with blood

- each lung contains millions

- O2 dissolves in the film of

moisture lining the epithelialcells and diffuses across to the

blood

- CO2 moves the opposite way


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Lungs - BreathingBreathing - the alternation of inhalation and exhalation.


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Lungs - Breathing

Breathing in birds involves a one-way flow of air rather than

an in-and-out flow in humans.


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Control of Breathing

Breathing is automatically controlled

Breathing control centers

- in brain (pons and medulla)

- nerves from medulla signal diaphragmand rib muscles to contract (inhale)

- pons smooths out rhythm of breathing.

- pH sensing - control of CO2 release

- decrease in pH causes an increase

in breathing rate.

Hyperventilation - deep, rapid breathing.


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Gas TransportBlood transports the respiratory gases

Heart has two divisions:

1) left side handles O2-rich blood from

the lungs (pumps blood to body)

2) right side handles O2-poor blood

from the rest of the body

- pumps blood to alveolar capillaries

(gas exchange)

Partial pressure

- the portion of a mixed gas that a

particular pure gas accounts for

- gradients determine movement


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Gas Transport

Hemoglobin - the molecule in red blood cells that carries O2

- four polypeptide chains and a heme group

containing iron

- can carry up to 4 molecules of O2


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Gas TransportHemoglobin helps transport CO2 and buffer the blood


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Gas TransportThe human fetus exchanges gases with the mothers bloodstream

Fetus

- lungs are full of fluid and

non-functional

- capillaries from the umbilical

cord fan out into the placenta

- gas exchange occurs with the

maternal blood in the placenta

- countercurrent exchange offetal and maternal blood

- fetal hemoglobin has a higher

affinity for O2.


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SUMMARY

- Mechanisms of gas exchange

(skin, gills, tracheal system, lungs)

- Breathing in water

- countercurrent exchange

- Breathing in air

- tracheal system (insects)

- lungs (humans)

- Breathing (control by brain)

- Gas transport (circulation, blood, hemoglobin)

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5. Respiration- The Exchange of Gases