Regeneration and repair processes are critical in healing damages caused by injury, disease, and aging. In regeneration, the damaged tissue is entirely replaced with new growth that restores the original architecture and function. In contrast, tissue repair usually results in a fixed tissue architecture involving scar formation. Scars generally do not reestablish tissue function and may also exhibit structural abnormalities at the injury site.
Regeneration
All animals have varying degrees of...

Regeneration is the process of restoring injured or lost tissues, organs, or body parts. While simpler organisms generally show greater ability to regenerate their whole body, few complex animals show similarly exceptional regeneration. For example, planarian flatworms have a unique regenerative potential making them a popular study organism among biologists to understand the mechanisms of whole body regeneration. Other organisms, such as hydra, also show extreme regeneration potential;...

The skin is divided into epidermis, dermis, and hypodermis, the skin's outermost, middle, and inner layers. The human epidermal layer regularly undergoes renewal, where old, dead cells are replaced by new cells. Epidermal stem cells or EpiSCs divide and differentiate to restore the lost cells. For the renewal process, some EpiSCs continuously self-renew. In contrast, few others differentiate into transit-amplifying cells, which later form prickle or spinous cells, followed by granular...

Replicative cell senescence is a property of cells that allows them to divide a finite number of times throughout the organism's lifespan while preventing excessive proliferation. Replicative senescence is associated with the gradual loss of the telomere — short, repetitive DNA sequences found at the end of the chromosomes. Telomeres are bound by a group of proteins to form a protective cap on the ends of chromosomes. Embryonic stem cells express telomerase — an enzyme that adds...

After cellular or tissue damage, the resident stem cells present in the human body can locally repair and regenerate the damaged tissue or organ. However, even though some tissues do not have stem cells, they can repair and regenerate with the help of pre-existing cells. For example, beta cells of the pancreas and hepatocytes of the liver can divide to renew and regenerate the tissue. Here, both cell division and cell death are well regulated by homeostasis.
However, failure of such a system...

Several body functions deteriorate with age. The external signs of aging are easily identifiable. For example, the skin becomes dry, less elastic, and thins out, forming wrinkles. The skin of the face begins to appear looser due to a decrease in the levels of elastic and collagen fibers in the connective tissue. Additionally, melanin production in the hair follicle decreases with age, resulting in gray hair. Moreover, the senses of sight and hearing decline, so glasses and hearing aids may...