How Does Regeneration Occur in Living Organisms?
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.
[Image will be Uploaded Soon]
The Origin and Development of Regeneration Process
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.
Regulation Involved in Regeneration
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.
The Variety in the Range of the Process of Regeneration
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.
Research
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.
Did You Know?
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.
FAQs on Regeneration Process: Definition, Stages & Examples
1. What is the process of regeneration in biology?
Regeneration is the natural biological process where an organism replaces or restores damaged or missing cells, tissues, organs, or even entire body parts. In some organisms, like Planaria, it also serves as a method of asexual reproduction, while in others, like lizards regrowing tails, it is primarily a repair and survival mechanism.
2. What are the basic steps involved in the regeneration process?
The regeneration process generally follows three key steps:
- Wound Healing: The injury is first covered by migrating epidermal cells to protect the underlying tissue and prevent infection.
- Blastema Formation: A mass of undifferentiated cells, known as the blastema, accumulates at the injury site. These cells are similar to stem cells and possess the potential to develop into various new tissues.
- Redifferentiation and Growth: The blastema cells multiply and, guided by genetic signals, differentiate into the specific cell types (e.g., muscle, nerve, skin) required to precisely reconstruct the lost part.
3. How does regeneration occur in simple organisms like Hydra and Planaria?
In simple organisms, regeneration is highly efficient due to specialised cells. In Hydra, totipotent stem cells called interstitial cells migrate to the wound and differentiate to form any missing part. In Planaria (flatworms), regeneration is driven by adult stem cells called neoblasts. When a Planarian is cut, these neoblasts move to the wound surface, proliferate, and then differentiate to perfectly reconstruct all lost tissues and organs, including the brain.
4. What is the main difference between regeneration and fragmentation?
While both can result in new individuals, their core concepts differ. Fragmentation is a method of asexual reproduction where an organism's body intentionally or accidentally breaks into several pieces, and each piece grows into a complete new organism (e.g., Spirogyra). Regeneration is the regrowth of a lost part. While this regrowth can sometimes lead to a new organism (as in Planaria), it can also be just a repair process (like a lizard regrowing its tail). The key distinction is that fragmentation is always about creating new individuals, whereas regeneration is about restoring what was lost.
5. What are the main types of regeneration, such as morphallaxis and epimorphosis?
Biologists classify regeneration into two primary types based on the cellular mechanism involved:
- Morphallaxis: This type involves the reorganisation and repatterning of existing tissues to form the new structure, with minimal new cell growth. The organism essentially remodels its remaining parts. This is characteristic of simple animals like Hydra.
- Epimorphosis: This type involves the dedifferentiation of adult cells to form a blastema (a mass of undifferentiated cells). This blastema then grows and redifferentiates to form the new, complex structure. This is the process seen in salamander limb regeneration and lizard tail regeneration.
6. Why can't complex vertebrates like humans regenerate entire limbs?
Human regenerative capabilities are limited, unlike those of simpler animals, due to several factors:
- Biological Complexity: Human limbs are highly intricate, with specialised nerves, bones, blood vessels, and muscles. Recreating this exact, complex pattern is a significant developmental challenge.
- Immune System Response: The advanced human immune system prioritises rapid wound closure to prevent infection. This leads to the formation of scar tissue, which physically blocks the cellular processes required for regeneration.
- Lack of Blastema Formation: Unlike salamanders, humans do not form a blastema at an amputation site. Our adult stem cells are not mobilised in the same way to initiate large-scale reconstruction.
7. What are some common examples of regeneration in the animal kingdom?
Many animals display remarkable regenerative abilities. Some classic examples include:
- Starfish: Can regrow a lost arm. In certain species, a whole new starfish can develop from a single severed arm if it contains a portion of the central disc.
- Lizards: Can detach and regrow their tails (autotomy) as a defence mechanism to escape from predators.
- Earthworms: Can regenerate lost segments from either the head or tail end.
- Salamanders: Can regenerate entire limbs, jaws, eyes, and even portions of their brain and heart.
