**1. Biology of regeneration**

Regeneration means the re-growth of part of the affected or lost organs of the remaining tissue. Animals can regenerate some organs, such as the liver. If a part of the liver is lost due to illness or injury, the liver grows back to its original size, but not in its original form.

**Figure 1.** The amphibian renewal preceding amphibian growth may offer hints to humans. After amputation, the wound heals to form the skin layer, and the underlying tissue undergoes a matrix reshaping, and cells in the region secrete soluble factors. The heterogeneous cell mass, blastema, is formed by the proliferation and migration of cells from neighboring tissues. Next, the blastema leads to the appearance of different new tissues that are spatially plastered to reconstruct the structure of the original limb (credit: Lina et al. [1]).

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Different species have significant capabilities to regenerate parts of the body or whole organism after injury (**Figure 1**), but a thorough understanding of the molecular basis of regeneration mechanisms will require detailed genomic resources.

In all organisms, a *DNA-dependent RNA polymerase* is performing the production of mRNA for protein synthesis or the various non-coding RNA molecules that are used in the cell. *Transcriptional control* is the main method to control what proteins (and nucleic acids) are

Introductory Chapter: Concepts of Tissue Regeneration http://dx.doi.org/10.5772/intechopen.76996 5

Tissues in the human organism are generated, maintained, and repopulated by *stem cells* (**Figure 3**). These are specialized cells capable of cell renewal and can differentiate into different cell types in the human body. Stem cells have several differentiation programs; therefore, they possess information to allow them to become any cell in the body or a restricted cell type with a specialized function. These abilities make stem cells extremely useful for biomedical applications and regenerative medicine and have become the main molecular tool for these purposes. Skeletal muscles have some ability to regenerate and form new muscle tissue, while cardiac muscle cells do not regenerate. However, new research suggests that cardiac stem cells may be coaxed into regenerating cardiac muscles with new medical strategies. Smooth

Questions about how and why tissue regeneration attracts the attention of countless biologists, medical engineers, and doctors. Renewable capacity varies widely across organs and organisms and a range of model systems with different technical features and innovation strategies are studied. Several key issues common to natural regeneration are receiving new attention from improved models and approaches, including identification of innovative

**Figure 3.** Induced pluripotent stem cells (iPSCs) were first created from human cells in 2007. These are adult cells that

have been genetically converted to an embryonic stem cell-like state [3].

produced in the cell, and in what amounts (**Figure 2**).

muscle cells have the greatest ability to regenerate.

**3. Stem cells and regeneration**
