Respiratory Systems: Avian (birds) and Amphibians (Frogs)
Avian RespirationBirds have lungs, but they also have air sacs. Depending upon the species, the bird has seven or nine air sacs.
Birds do not have a diaphragm; instead, air is moved in and out of the respiratory system through pressure changes in the air sacs. Muscles in the chest cause the sternum to be pushed outward. This creates a negative pressure in the air sacs, causing air to enter the respiratory system. Expiration is not passive, but requires certain muscles to contract to increase the pressure on the air sacs and push the air out. Because the sternum must move during respiration, it is essential that it is allowed to move freely when a bird is being restrained. Holding a bird "too tight" can easily cause the bird to suffocate. Bird lungs do not expand or contract like the lungs of mammals. In mammalian lungs, the exchange of oxygen and carbon dioxide occurs in microscopic sacs in the lungs, called 'alveoli.' In the avian lung, the gas exchange occurs in the walls of microscopic tubules, called 'air capillaries.' The respiratory system of birds is more efficient than that of mammals, transferring more oxygen with each breath. Respiration in birds requires two respiratory cycles (inspiration, expiration, inspiration, expiration) to move the air through the entire respiratory system. In mammals, only one respiratory cycle is necessary. Q1) Why might birds require a more efficient respiratory system than humans? Q2) How do birds breathe without a diaphragm? |
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Amphibian Respiration
While completely submerged all of the frog's repiration takes place through the skin. The skin is composed of thin membranous tissue that is quite permeable to water and contains a large network of blood vessels. The thin membranous skin is allows the respiratory gases to readily diffuse directly down their gradients between the blood vessels and the surroundings. When the frog is out of the water, mucus glands in the skin keep the frog moist, which helps absorb dissolved oxygen from the air.
A frog may also breathe much like a human, by taking air in through their nostrils and down into their lungs. The mechanism of taking air into the lungs is however slightly different than in humans. Frogs do not have ribs nor a diaphragm, which in humans helps serve in expand the chest and thereby decreasing the pressure in the lungs allowing outside air to flow in. In order to draw air into its mouth:
Frogs also have a respiratory surface on the lining of their mouth on which gas exchange takes place readily. While at rest, this process is their predominate form of breathing, only fills the lungs occasionally. This is because the lungs, which only adults have, are poorly developed Q1) Name all of the sites on the frog where gas exchange occurs?
Q2) Why might the frog have developed several different ways to breathe? Q3) Explain how the frog breathes using its lungs? Q4) Why does the frog need to stay moist out of water? How does the frog do this |
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