Respiratory System
The respiratory system (or ventilatory system) is the biological system of an organism that introduces respiratory gases to the interior and performs gas exchange.In humans and other mammals, the anatomical features of the respiratory system include airways,lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs. Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skin plays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of leaves known as stomata.
Horses
Horses are obligate
nasal breathers which means that they are different from many other mammals because they do not have the option of breathing through their mouths and must take in oxygen through their noses.
Elephants
The elephant is the only animal known to have no pleural space. Rather, the parietal and visceral pleura are both composed of denseconnective tissue and joined to each other via loose connective tissue. This lack of a pleural space, along with an unusually thickdiaphragm, are thought to be evolutionary adaptations allowing the elephant to remain underwater for long periods of time while breathing through its trunk which emerges as a snorkel.
Birds
The respiratory system of birds differs significantly from that found in mammals, containing unique anatomical features such as
air sacs. The lungs of birds also do not have the capacity to inflate as birds lack a
diaphragm and a
pleural cavity. Gas exchange in birds occurs between air
capillaries and blood capillaries, rather than in alveoli.
Reptiles
The anatomical structure of the lungs is less complex in reptiles than in mammals, with reptiles
lacking the very extensive airway tree structure found in mammalian lungs. Gas exchange in reptiles still occurs in
alveoli however, reptiles do not possess a diaphragm. Thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of intercostal muscles in all reptiles except turtles. In turtles, contraction of specific pairs of
flank muscles governs inspiration or expiration.
Amphibians
Both the lungs and the
skin serve as respiratory organs in amphibians. The skin of these animals is highly vascularized and moist, with moisture maintained via secretion of mucusfrom specialized cells. While the lungs are of primary importance to breathing control, the skin's unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water.
Fish
In most fish respiration takes place through gills. (See also aquatic respiration.) Lungfish, however, do possess one or two lungs. Thelabyrinth fish have developed a special organ that allows them to take advantage of the oxygen of the air.
