Gaseous Exchange in Molluses, Arthropods, Echinodermates and Vertebrates
These animals have developed respiratory organs which help in the exchange of gases. These organs are e.g gills, tracheal tubes, book lungs and lungs. These are described one by one as follows:
They are very effective organs for gaseous exchange in aquatic animals. Gills are in direct contact with the surrounding water. However gills are of different forms (shapes) but basically they share the same fundamental structure. Each gill consists of number of folds of membranes which are called Lamelle (Lamellae is the plural of Lamella). Lamella are richly supplied with blood capillaries. Water enters through the mouth and flows over the gills. During this process oxygen from water diffuses into blood and carbon dioxide diffuses out from the blood capillaries into the water while respiratory pigments help them in diffusion as well as transport of the gases.
These are present in terrestrial insects which are distributed throughout the body and forming a tracheal system. Each trachea has a chitinuous cuticle lining which prevents it from collapsing. Trachea divides into numerous smaller tubes called traceoles in each segment near the cells. Chitinuous lining is not present in tracheoles. These tracheae and tracheoles are filled with a fluid. It allows gaseous exchange to diffuse from the outside air directly to the tissues without the need of transportation by blood. This is much faster than diffusion of oxygen through the tissues and permits high metabolic rates. Spiracles (holes) are present on the side of thoracic and abdominal segments.
The external air enters into the tracheae through spiracles. The oxygen from this air gets dissolved in the fluid present in the tracheoles and then diffuses into the cells. The carbon dioxide from the cell diffuses out of the body through Spiracles. Since the oxygen is transported directly to the body cells, insect’s blood is white i.e without haemoglobin.
These are sac like structures found in some terrestrial arthropods such as scorpions and spiders. Each book lungs consists of a compressed sac like cavity which contains number of membranous folds and are called lamellae.
These are attached to the inner sides of the chamber and these lamellae are arranged like the leaves of a book. Each lamellae is hollow inside where the blood flows, while air is present in the inter lamellar spaces. So that exchange of gases takes place through the thin walls of the lamellae.
In almost all the large terrestrial animals exchange of gases takes place through lungs, these are the most advanced type of respiration organs.
These are found in amphibians, reptiles, birds and mammals and in those aquatic animals which respire through air.
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Gaseous Exchange in Amphibians, Reptiles, Birds and Mammals