regeneration

the regeneration is to restore missing tissues.The regeneration can be then at the cellular level, tissue, organ, structure and even the whole body.The process of regeneration of missing limbs has been observed in organisms, salamanders, crabs and sea stars and other.

Regeneration in planarians

these bodies are cut by half the half that has regenerated head and half a tailcontaining a regenerated tail head.After cutting a thin layer of epithelium covering the wound, epithelial cells both dorsaland ventral lose their characteristic morphology when covering the wound.

Regeneration in salamanders

The regeneration of limbs in salamanders is given by epimorfosis, cells are able to reconstruct the entire limb if necessary, but can also reconstruct only the missing parts. After the amputation between 6 and 12 hours endodermal cells lining the wound,this layer called the epidermis proliferates forming a wound apical ectodermal cap.During the following days the cells are under the cover dedifferentiate into a mass, theregeneration blastema. Genes expressed in differentiated tissues are negativelyregulated the expression of genes associated with embryonic limb undergoes adramatic increase. These cells continue to spread and eventually metamorphose to form the new structures of the limb.

Regeneration in reptiles

The regeneration process begins with the migration of epithelial cells around the woundto form the apical epidermal layer (or apical cap), just days after elblastema begins to form beneath this layer, generating a conical structure, as in the amphibians. Theblastema consists of undifferentiated mesenchymal cells found in mitosis and that are organized around the ependyma layer (epithelial cells) that give rise to the spinal cord.At first the cells of the blastema begin to differentiate in the proximal part of theamputation, giving rise to fibroblasts, blood vessels, fat cells and cells of the lymphaticsystem. Once these cells are established, other tissues begin to form and buildconnections between them, as the formation of veins and arteries, and then begin toform a mass of cartilage surrounding the ependyma as a continuation of the spinal cord that had not lost.

Regeneration in Mammals

En los mamíferos es posible encontrar regeneración compensatoria del hígado. En este caso las partes faltantes no vuelven a crecer, las partes que quedan se agrandan para compensar la pérdida del tejido faltante. Es decir que el hígado se regenera por la proliferación de tejido existente que no se desdiferencian completamente, cada tipo de célula mantiene su identidad y no hay formación de blastema. Una de las proteínas más importantes en la regeneración del hígado es el factor de crecimiento de hepatocito (HGF por sus iniciales en inglés) este es responsable de la inducción de varias proteínas embrionarias.