Breathing
Ventilation
Air is moved into and out of the lungs, as it is carried to and from the exchange surfaces of the Tiny air sacs in the lungs, where gas is exchanged during breathing..
The A large sheet of muscle that separates the lungs from the abdominal cavity. and The arrangement of bones in the thorax, formed by the ribs, vetebral column and sternum, that encloses the lungs and heart. move to create a lower air pressure in the lungs than that of the air outside the body. Air then rushes into the lungs.
The most important muscle when we The process of breathing in. normally is the diaphragm. The external Sets of muscles between the ribs which raise and lower the rib cage. are the second most important muscles. Breathing is a passive process resulting from pressure changes in the lungs.
Image caption, Breathing in
When we inhale and exhale more forcibly, other muscles are also used
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Question
Which are the main muscles involved in normal breathing?
The diaphragm and (external) intercostal muscles
Gills in fish
Water is capable of holding only low concentrations of oxygen, so fish need a different type of exchange system.
The exchange surfaces in fish are The respiratory organ found in fish and other aquatic animals. Gills have a large surface area, and a good blood supply, for efficient gas exchange to happen in water..
Image caption, Fish gills
Water is taken in through the fish's mouth, passes over the gills, and then out under the operculum
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Exchange of gases in fish is very efficient because of:
- the large surface area of the gills
- the large surface area of the blood capillaries in each gill filament
- the short distance required for diffusion 鈥 the outer layer of the gill filaments and the capillary walls are just one cell thick
- the efficient ventilation of the gills with water - there is a counter current flow of water and blood
The moving blood and ventilated gill surfaces mean that gases exchanged are continually removed 鈥 Gaseous element making up about 20% of the air, which is needed by living organisms for respiration. enters the blood, and A gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis. removed to the water. High The difference in the concentration of a chemical across a membrane. can be maintained.
Gas exchange is more difficult for fish than animals that live on land. The concentration of oxygen in water is dependent on the temperature of the water. The concentration of oxygen in water is only around 1% at 15掳C. This compares with 21% in the air at any temperature. The efficiency of gills has to be - and is - very high - 70 to 80% of the available oxygen is extracted from the water.