The Importance of a

Respiratory System

Why do we breathe? Aerobic organisms require every cell to obtain oxygen and

remove carbon dioxide to survive Gas Exchange

All organisms share two characteristics:

1. Large respiratory surface

2. Moist environment

3 factors that determine rate of exchange:

1. Area of cell membrane - larger area, more exchange.

2. Concentration difference - more oxygen in air then in lungs,

greater rate of diffusion.

3. Diffusion distance - a very slight increase in distance can greatly

reduce the rate at which a diffusing substance reaches its goal

(2s to travel 10um, 4s to travel 20um, 16s to travel 40um etc.)

Simple Gas Exchange

Single celled organisms rely on diffusion.

To fulfill the moist requirement these organisms must live

in wet, aquatic environments.

Either in the environment or in a host organism.

Some simple multicellular organisms also exchange gas in

this manner.

The key is that they are aquatic as well

Green algae, hydra and planarian worm

Specialized Breathing

The larger the organism the more difficult it is to get

oxygen to every cell in the organism.

1. Diffusion distance needs to be very small

2. As cells become differentiated for other purposes

the amount of surface area devoted to gas

exchange is reduced.

Adaptations have been developed to allow

increased complexity while maintaining gas

exchange at significant levels.

Specialized Breathing

Skin Respiration (p.283, fig.3a)

Phylum Annelida segmented worms

Skin must be kept moist to allow diffusion of oxygen to occur.

Skin is lined with capillaries which allow oxygen to enter the circulatory system and carbon dioxide to exit.

This is an advancement due to the fact that it is in this phylum that circulation starts to play a role in ensuring all cells respire properly.

Diffusion would simply not allow enough exchange of gases.

Specialized Breathing

Gills (p.283, fig.3b & 4)

Whole body is not available for gas exchange due to habitat in

which these organisms live.

Both as defense and maintaining internal environment.

Surface area to allow exchange of gases is decreased however this

is combated in two ways:

1. Where gas exchange does occur the surface area is increased.

2. A mechanism has evolved to allow the organism to ventilate this surface,

that is, to move the oxygen containing medium over the gills to gain fresh

oxygen.

Specialized Breathing

Gills

Feathery tissue in many aquatic species that allow gas exchange across thin gill membranes.

In some organisms (ex. tube worm) the gill is moved through the water while in other organisms (ex. fish and clams) water is ventilated over the gills in usually just one direction.

This reduces the amount of energy the animal must expend to move water over the gills.

Typical Movement

Water moves in through the mouth and over the gills.

Tiny capillaries absorb oxygen and release carbon dioxide.

Counter-current flow in fish

Water flow over gills in one direction

Saves energy since fish does not have to correct flow of

water

As water flows over the gills the most oxygen

depleted blood draws oxygen from the oxygen

depleted water.

Oxygen will diffuse into the blood

As blood flows out of the gill it becomes increasingly

oxygen rich due to the fact that it continues to meet

water that is increasingly oxygen rich.

Countercurrent Exchange in Fish

Why don’t penguins’ feet freeze?

Specialized Breathing

Out of the Water

Moisture retention becomes the main problem.

Breathing is the concept of ventilating a respiratory

surface with air and it relies on a simple law of physics:

Air will move from a region of high pressure to a region of

lower pressure until equilibrium is acquired.

Two main methods of terrestrial breathing have evolved

based on this principle:

Tracheal Respiratory System and Lungs

Specialized Breathing

Tracheal Respiratory System

Insects utilize a series of external pores called spiracles which each

lead to an internal series of tubes called tracheae.

Spiracles are controlled by valves to monitor water loss by the

organism and to facilitate the pressure differential.

Abdomen expands air pressure drops in tracheae 4 anterior paired spiracles

open air rushes into tracheae

Abdomen contracts 4 anterior paired spiracles stay closed but 6 posterior

spiracles open air pressure inside is now high and air flows out

Insects respiratory system and circulatory system are separate from

each other.

Specialized Breathing

The Lung

Characteristic of air-breathing vertebrates is the internal lung.

Internal respiratory surface connected to the air by means of internal passageways.

Main components of lungs:

1. Have a moist respiratory surface.

2. A means of forcibly bringing air into contact with the lung surface.

3. A circulatory system to move the gases around the body.

Frog uses a lung system in conjunction with skin respiration.

Birds

Migratory birds have developed a respiratory advantage to give them enough energy to migrate.

Utilize air sacs that ensure that residual air is never in contact with the lungs.

Air sacs do not allow gas exchange, simply a method of holding air to allow maximum efficiency.

Always an oxygen rich medium in contact with lungs

Birds also have a countercurrent exchange system with respect to their circulatory system