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Tuesday, 15 January 2019

January 15, 2019

Tracheal System

 The tracheal system is found in land arthropods, a very successful terrestrial animal phylum. In these animals, air enters the body through small openings called spiracles located along the sides of the body. the spiracles lead into tubes called tracheae, which branch repeatedly within the body tissue. The smaller branches as called tracheoles. The smallest tracheoles contain fluid in which oxygen dissolves before actually reaching the individual body cells. In many flying insects, some of the tracheae expand to form thin walled air sacs. The spiracles, tracheae and tracheoles make up the tracheal system.

    The tracheal system is not linked to the circulatory system. This means that oxygen has to diffuse from the final tracheole to the individual cells. Since diffusion can only occur effectively over very short distances, animals that breathe by tracheae are small (usually with a body that is not more than tow centimeters wide). Generally, arthropods, especially flying insects, are very active as the efficient tracheal system provides them with a plentiful supply of oxygen. (A large amount of energy is needed for flight.).  
January 15, 2019

Simple Gills

 External gills are very simple respiratory structures: just outgrowth of skin which project into the water. They are, however,

 • Highly branched and convoluted, exposing a large gaseous exchange surface to water; and

 • Richly supplied with blood capillaries.

     External gills are found in certain sea slugs and many fish and amphibian larvae. Water only circulates over the gills when these organisms move. Movement, on the other hand, is hampered by the highly branched gills. Thus, external gills are not particularly efficient in obtaining oxygen.

     To function more efficiently, chambers were evolved to enclose gills and circulate water over them. Simple forms of such enclosed gills are seen in aquatic snails and crustaceans. In an aquatic snail, the gills are enclosed in a chamber, the mantle cavity, which opens to the outside. Water is pumped in and out of this cavity exposing the gills to a continuous stream of water. The oxygen uptakes is more efficient in this type of respiratory structures.  
January 15, 2019

Gills in Bony Fishes

 The most complex gills and gill chambers are found in bony fishes. There are two gill chambers (opercular cavities) in a bony fish. They are situated on each other side of the head immediately behind the mouth. Each chamber is covered by a thin bony plate, the gill cover or operculum (plural: opercula) , which has a free edge. Water from outside can enter the body through the mouth, flow into the pharynx and gill chambers, and pass out of the body from under the opercula. Four gills are situated at the entrance of each gill chamber.

          Each gill is a red comb like structure. It is made up if a bony Gill arch bearing

 • Two rows of fine finger like gill filaments on the outer side, and

 • Gill rakers on the inner side.

      The gill filament contains the gaseous exchange surfaces. each filament is made up of a series of transverse plates which is held together along one of the edges. These plates serves to Increase the surface area of the gill filaments a the thus very compact structures with an enormous surface area.

      The gill rakers do not take part in gaseous exchange. They act as food strainers and prevent food from entering the gill chambers.

     Fishes have a very effective mechanism for circulating water over the gills. Thus, the gills of fishes are very efficient, enabling fishes to be active and attain large sizes.  
January 15, 2019

Terrestrial Respiratory Structures

 Land animals exposed to the atmosphere have dry body coverings. Gaseous exchange cannot occur through such surfaces. Instead , these animals evolved respiratory structures to bring dry air in contact with moist surfaces with in their bodies. Unlike gills (which are outgrowths of the body surface), the body surface turned inwards (into the body) to form these respiratory structures. Two such structures are the tracheae and the lungs.  
January 15, 2019

Lung Respiratory System

 Besides arthropods, the terrestrial vertebrates are the other successful group of land animals. These animals use lungs as the gaseous exchange organs. Lungs are closely linked to the circulatory system, so that oxygen can easily be transported over the long distances. This enables vertebrates to attain the sizes seen in many types of mammals.  
January 15, 2019

Multicellular Animals

 Multicellular animals can have larger body surfaces for gaseous exchange than unicellular organisms. However, these organisms too cannot grow beyond a certain size, since the body surface area does not increase as rapidly as body size or volume. Thus, only a few simple multicellular animal carry out gaseous exchange through their body surface es PR skins without using specialized respiratory structures. Such animals are fairly inactive so that their energy requirements and , as a result, their oxygen demands are low.  
January 15, 2019

Aquatic Respiratory Structure: The Gill

 Gills are special respiratory organs used for absorbing dissolved oxygen from an aquatic medium. Basically, they are outgrowths from the body which project in to the external environ. They are very closely linked with the circulatory system.

     Gills range from very simple forms found in certain sea slugs to very complex ones, enclosed in chambers, found in bony fishes.