Utente:Mikialba/Sandbox2/Polmone: differenze tra le versioni

Versione delle 14:51, 9 dic 2006

Versione delle 09:43, 10 dic 2006

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==Polmone dei mammiferi==

I polmoni dei mammiferi hanno un rivestimento spugnoso e sono alveolati con [[epitelio]], aventi una larga superficie. I polmoni umani fanno parte di questo tipo di polmoni. L'ambiente del polmone è molto umido e quindi facilmente attaccabile da [[batterio|batteri]]. Molte malattie respiratorie sono proprio dovute ad un'infezione [[Virus (biologia)|virale]] o batterica.

La [[respirazione]] è largamente guidata dal [[diaframma]] il quale si trova in fondo al torace. La contrazione del diaframma espande verticalmente la cavità dove il polmone è semichiuso. Il rilassamento del muscolo ha l'effetto opposto.

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<big>'''''QUESTA PARTE E' ANCORA DA TRADURRE!'''''</big>

==Polmone deidegli mammiferiuccelli==

==Avian lungs==

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.

Many sources state that it takes two complete breathing cycles for air to pass entirely through a bird's respiratory system. This is based on the idea that the bird's lungs store air received from the posterior air sacs in the 'first' exhalation until they can deliver this air to the posterior air sacs in the 'second' inhalation.

Questo tipo di polmone non possiede [[alveolo|alveoli]], ma contiene al proprio interno millioni di piccoli passaggi chiamati [[parabronco|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.

<div id="circlung">This is not possible because bird lungs are essentially sets of fixed volume, open ended tubes. They are like drinking straws. If you blow into one end of a drinking straw then the air comes out the other side. It is not stored, waiting for you to suck it out from the other end some time later. This type of lung construction is called '''[[circulatory lung]]s''' as distinct from the bellows lung possessed by most other animals (see above).</div>

Avian lungs do not have alveoli, as mammalian lungs do, but instead contain millions of tiny passages known as [[parabronchi]], connected at either ends by the dorsobronchi and ventrobronchi. Air flows through the honeycombed walls of the parabronchi and into air capillaries, where oxygen and carbon dioxide are traded with cross-flowing blood capillaries by diffusion, a process of crosscurrent exchange.

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 (medical)|hypoxia]].

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==Invertebrate lungs==

Some invertebrates have "lungs" that serve a similar respiratory purpose but are not evolutionarily related to vertebrate lungs. Some [[arachnid]]s have structures called "[[book lung]]s" 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".

==Origins==

The first lungs, simple sacs that allowed the organism to gulp air under oxygen-poor conditions, evolved into the lungs of today's terrestrial vertebrates and into the [[gas bladder]]s of today's fish. The lungs of [[vertebrate]]s are [[homology (biology)|homologous]] to the [[gas bladder]]s of [[fish]] (but not to their [[gill]]s). The evolutionary origin of both are thought to be outpocketings of the upper intestines. This is reflected by the fact that the lungs of a [[fetus]] also develop from an outpocketing of the upper intestines and in the case of gas bladders, this connection to the gut continues to exist as the [[pneumatic duct]] in more "primitive" [[teleost]]s, and is lost in the higher orders. (This is an instance of correlation between [[ontogeny and phylogeny]].) There are no animals which have both lungs and a gas bladder.