EXCRETION IN LOWER INVERTEBRATES

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INTRODUCTION

There are thousands of metabolic processes that occur in any animals body. Definitely if they provide energy, and information there are hundreds of useless by product that are also form. This by products which are formed during any metabolic reaction can be toxic for our body if remain for a longer time. Hence there is requirement of any such process and pathway that allow either removal or degradation of this waste products. The process by which this waste is processed and removed from organisms body is refer to as excretion.
Sometimes the waste that is form in our body can be very toxic at that time they are first converted to less toxic product and then allow to eliminate.
Every organism possess different mechanisms, organs and different excretory product. For example porifera and hydra can perform excretion through body surface where as platyhelminthes possess a specialised cells known as flame cells.

Nitrogenous metabolic waste produced in sponges is largely ammonia. No special excretory tissue is present for excreting this to the outer medium. It leaves the body in the outgoing water current by diffusion. Some investigator claim that metabolic wastes are taken up by amoebocytes which discharge them into spongocoel.

Hydra do not have any organ of excretion, which is done individually by Each cell. Due to thinness of body wall and circulation of water in gastrovascular cavity most cell of the body remains freely exposed to the surrounding water there excretion of nitrogenous waste which is mainly ammonia occur directly by the diffusion through the cell membrane to outside world.

The excretory system mainly comprises of large number of flame cells or flame bulb or protonephridia connected with excretory duct of various order.

FLAME CELLS

Flame cells or protonephridia ehich are modified mesenchymal cells are distributed in specific pattern throughout mesenchyme called flame cell pattern. They are irregular in shape and send out pseudopodial processes into the surrounding tissues. Each flame cell has intracellular lumen or cavity in which hang a few long cilia, each arising from basal granules situated in cytoplasm. In living fluke cilia vibrates like a flickering of flame, hence name flame cell.

EXCRETORY DUCT

Lumen of flame cell is continuous with microscopic capillary duct, capillary duct opens into collecting tubules. Several tubules together open into larger twig, which further open into the vessel, vessels anteriorly open into the trunk two dorsal and two ventral unites and open posteriorly into the single longitudinal excretory canal. Excretory canal further opens into excretory pore.

PROCESS OF EXCRETION

There main excretory product is fatty acid, CO2 and ammonia. These substances from mesenchyme diffuses into flame cell. Excretory fluid keep moving by the action of cilia into the tubules and finally removed out through the excretory pore.
Alkaline phosphatase are present in flame cell and collecting tubules can serve as selective transfer of chemical substances.

There is absences of flame cells hence excretory system is quite simple.
The excretory system is tubular and its shape is H shape. It is formed by renette cells. Into cytoplasm of renette cells tunnel like structure forms canal of excretory system. It consist of two lateral longitudinal, canals right and left connect anteriorly, below pharynx by transverse canalicular network. Each longitudinal canal extend poteriorly, along the entire body length through lateral epidermal chord and is closed at the both ends.
Externally their location is marked by two lateral lines. Left canal is slightly wider than right. Anterior limbs of H are reduced. Lumen of canal lacks cilia. There is a short terminal excretory duct which extend from left side of transverse canalicualr network to excretory pore situated mid ventrally a line behind the anterior tip.

PROCESS OF EXCRETION

There excretory product is mainly urea. Excretory canal collects the excretory products from different parts of the body. Pressure from pseudocoelomic body helps in ultrafiltration. Finally excretory products are removed from excretory pores. There is possibility of removal of some ammonia as well as urea

Process of elimination of metabolic wastes is termed as excretion. In any animal main excretory products are carbon dioxide, ammonia, uric acid and urea.
Some organism remove this waste through their body surface such as in hydra there is no such specialized excretory organ is present.
While some organism consist of whole complex system and networks of canals and vessels for excretion as seen in case of Liver fluke. In case of liver fluke main excretory product is fatty acid ammonia and carbon dioxide.
In case of aschelminthes the excretory system is less complex than Liver fluke. Excretory system is simple and form is of H shape. There excretory product is urea. Sometimes, some urea as well as ammonia is also removed from anus.