Utente:Mikialba/Sandbox2/Polmone
QUESTA PARTE E' ANCORA DA TRADURRE!
Polmone degli uccelli
Molte fonti indicano che gli uccelli devono compiere due cicli respiratori completi per far passare l'aria all'interno di tutto il proprio corpo. Ciò non è possibile perché i polmoni degli uccelli sono essenzialmente di volume fisso.
Questo tipo di polmone non possiede alveoli, ma contiene al proprio interno millioni di piccoli passaggi chiamati parabronchi, connessi alla fine ai dorsobronchi e ai ventrobronchi. L'aria passa per le fessure dei parabranchi e successivamente al'interno dei capillari, dove l'ossigeno e l'anidride carbonica si scambiano.
This complex system of air sacs ensures that the airflow through the avian lung is always travelling in the same direction - posterior to anterior. This is in contrast to the mammalian system, in which the direction of airflow in the lung is tidal, reversing between inhalation and exhalation. By utilizing a unidirectional flow of air, avian lungs are able to extract a greater concentration of oxygen from inhaled air. Birds are thus equipped to fly at altitudes at which mammals would succumb to hypoxia.
Reptilian lungs
Reptilian lungs are typically ventilated by a combination of expansion and contraction of the ribs via axial muscles and buccal pumping. Crocodilians also rely on the hepatic piston method, in which the liver is pulled back by a muscle anchored to the pubic bone (part of the pelvis), which in turn pulls the bottom of the lungs backward, expanding them.
Amphibian lungs
The lungs of most frogs and other amphibians are simple balloon-like structures, with gas exchange limited to the outer surface area of the lung. This is not a very efficient arrangement, but amphibians have low metabolic demands and also frequently supplement their oxygen supply by diffusion across the moist outer skin of their bodies. Unlike mammals, which use a breathing system driven by negative pressure, amphibians employ positive pressure. Note that the majority of salamander species are lungless salamanders and conduct respiration through their skin and the tissues lining their mouth.
Invertebrate lungs
Some invertebrates have "lungs" that serve a similar respiratory purpose but are not evolutionarily related to vertebrate lungs. Some arachnids have structures called "book lungs" used for atmospheric gas exchange. The Coconut crab uses structures called branchiostegal lungs to breathe air and indeed will drown in water, hence it breathes on land and holds its breath underwater. The Pulmonata are an order of snails and slugs that have developed "lungs".