Respiration

Primitive Gas Exchange

• Diffusion is the order of the day!

• Organisms allow gas diffusion to occur across the membrane into the outer environment.

Primitive Gas Exchange

• Larger organisms with a circulatory system but no respiratory system have gas exchange occur at the surface of the animal where capillary’s are plentiful!

The Advent of Gills

• External gills are found on many larvae and some amphibians

The Advent of Gills

Adult fish have internal gills

These are rows of slits or pockets found at the back of the mouth extending to the surface

• Gills are composed of walls of moist, thin vascularized squamous epithelium

• Water flows in one direction: from the mouth, over the gills, and then out

The Advent of Gills

The Advent of Gills

• Capillary action in the gills are running in the opposite direction of the flow of water

• Known as

CountercurrentCountercurrent

flowflow

The Advent of Gills

• As a result the fish is allowed to extract 80 to 90% of the dissolved oxygen from the flowing water

The Advent of Gills• Water is held under the carapace where

the gills are.• As a result, the crawfish can move out of

the water and enjoy life as a terrestrial organism so long as there is enough

dissolved oxygen in his captured

water!

Movement to dry Land

• Water is poor in dissolved oxygen(5 to 10 ml of oxygen per liter of water)

• Air is much more rich inoxygen

(210 ml of oxygen per liter of air)

Movement to dry Land

• Gills did not make the move to land since the expansive surface area of the gills would increase water loss!

• Also, the support of water to hold the gill disks in place would collapse and cause the fish to suffocate!

Movement to dry Land

Two main systems developed to accommodate the internal need for O2

1. development of Trachea with spiracles

2. lungs

Development of Trachea with spiracles

• Spiracles open and close based on levels of CO2 (prevent excessive water loss)

Development of Trachea with spiracles

• Trachea are the network of tiny branched passages that lead to the muscles and other tissues of the body

Development of Trachea with spiracles

• There is no connection between the trachea system and the circulatory system

• Arachnids also incorporate a series of folds in the abdomen called

– book lungsbook lungs

Lungs• Found in some fish, all amphibians,

reptiles, birds and mammals

• Lung fish have tiny lungs as back up … yet still has gills

• Developed as pouches off of the anterior gut wall.

Lungs• Amphibians also use diffusion

through the skin to aid in respiration

• Air is forced in to the lung via movement of the lower floor of the mouth

Lungs• Paired lungs are the dominate means of

respiration in reptiles, birds and mammals.

• Breathing moves air in bulk into and out of the lungs– Simple squamous epithelial must be moist

– One way entrance allows O2 and CO2 to mix

Lungs• Moist mucus rich passage ways act

as filtering agents to clean, moisten, and heat the inspired air.

• Cilia beat upward to pull mucous up and into the esophagus (out of the lungs)

Lungs• Aves breath in two cycles

– 1. air is drawn into the posterior air sacs then is exhaled through the lungs

– 2. air is drawn into the anterior air sacs then exhaled through the trachea

Lungs• Path of air through the lungs is in one

direction and never mixes with CO2!

Lungs• Air flow in lungs is countercurrent to

circulatory flow