Regeneration can be defined as the natural process by which damaged or misplaced cells, tissues or organs are restored or replaced. The regeneration process can also restore even the entire parts of the bodies of animals and plants so that they can function completely. The process of regeneration plays an important role in the field of medicinal science in this modern world. Scientists all over the world are studying this process so that this potential method can be used in medicines. Treatment of injuries and diseases can be made possible by this process. This field that is involved in the study of regenerative science is called regenerative medicine.
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If an appendage is capable of regeneration, soon after amputation it develops a blastema from the tissues just behind the level of amputation. Now, these tissues will undergo drastic changes as the cells of these tissues which were once specialized as muscle, bone or cartilage eventually lose their characteristics. These cells start migrating and they begin to migrate beneath the epidermis of the wound and end up forming a blastema. During regeneration, the cells that were present at the nearest tip of the bulge start to multiply. The cells that are placed close to the old tissues of the stump start now differentiating into muscle, cartilage. This development completely depends on the location of the stump. This process of regeneration will continue until all the structures of the regenerated tip are differentiated. All proliferated cells get used up at the end.
Certain requirements should be fulfilled for the regeneration process. A wound is extremely important for the process of regeneration, a source of blastema cells should be present. The blastema cells should be derived from the remnant of the original or the associated structure. Finally, there must be an external force that will stimulate the process of regeneration. Most often the stimuli involved are from the nervous system. For the regeneration of fins in fish and taste barbels and limbs in amphibians, there must be an adequate amount of nerve supply.
Interestingly during the regeneration of tails, the stimulus of the spinal cord becomes extremely important. In salamander eyes, lens regeneration is guided by the presence of the retina. The appendages of arthropods are seen to regenerate in the presence of moulting hormones. The process of regeneration is often triggered by any psychological movement taking place elsewhere in the body. Regeneration process can thus be defined as the process of recovery of certain deficient functions.
It is extremely important to keep the process of regeneration under control. Suppression of excess regeneration is necessary else there is always a threat of excess regeneration in the body.
Almost all living beings show the property of regeneration. Regeneration takes place to a greater extent in lower organisms such as protists and plants. Regeneration is also observed in invertebrates like starfish and earthworms. However, regeneration in higher organisms like mammals is often restricted.
The single-celled green alga, Acetabularia shows the property of regeneration. This living body consists of root-like appendages. The nucleus is important for the regeneration of the umbrella-like cap present in the alga. Similarly, in protozoans, the amputated part which does not have a nucleus fails to survive. Among the invertebrates, many coelenterates, flatworms, and annelids show regeneration. Invertebrates, fishes, amphibians, reptiles, birds also show regeneration.
Throughout the lifetime of an organism, the cells of the organism can regenerate. However, the ability to regenerate gets reduced as ageing takes place. Scientists are focused on the features of regeneration. Researchers have focused their studies on the cells from which the process of regeneration originates. Various genetic techniques help scientists to systematically identify the genes involved in regeneration. The knowledge thus acquired from these researches can provide a foundation for clinical application in near future.
The planarians are found to use organogenesis largely to grow their entire body from an extremely small fragment of a tissue provided that fragment consists of a single neoblast. Interestingly human beings also have the same pathway and genes as used by these planarians.
In many animals like human beings, organs like the liver undergo the process of compensatory hypertrophy. In this process, when a part of the lover is removed, the remaining portion of the liver grows to the size it was before. The liver can now function as it did before. Likewise, our kidney, pancreas, adrenal glands compensate for organ loss but in a limited way.
1. Briefly Explain the Process of Polarity and the Gradient Theory in Regeneration.
Ans. The parts that regenerate show polarity. This means that the regenerating part prefers to grow in the distal direction, In lower organisms however the difference between proximal and distal direction is not distinct. Interestingly it is not difficult to reverse the polarity of the stems in the colonial hydroids. In a hydrant, the stem grows in the proximal end normally. The polarity in this system is determined by the activity gradient in which the hydrant regenerates.
In a planarian(flatworms), the cute parts grow the missing end of the back. With the help of manipulation, fish can regenerate fins in a proximal direction.
2. Write a Note on the Regeneration of Invertebrates.
Ans. When a hydra is cut, the head end of the hydra is regenerated to give a new foot whereas the basal part of the hydra gives rise to mouth and tentacles. The planarian flatworms can regenerate heads and tails from the cut ends. Some of the blastema cells develop into brain tissue in the head and the rest develop into the eyes Among the annelids, the leeches can regenerate and have the ability to replace the lost segments completely. Earthworms and many other marine animals can even regenerate backwards and forward. Insects and crustaceans can easily regenerate their legs, claws and antennas.