Epithelial and connective tissues replace damaged or dead cells from a supply of adult stem cells. Muscle and nervous tissues undergo either slow regeneration or do not repair at all.
A few types of tissue are composed of cells that have left the cell cycle permanently, and are therefore unable to proliferate. These nondividing tissues (or permanent tissues) include cardiac and skeletal muscle.
Fibrous connective tissues like ligaments and tendons as well as bones, cartilage, and nerves tend to take the longest to heal.
The least capable connective tissue of regeneration would be the cartilage. The cartilage is avascular so it is unable to regenerate, which it regenerates poorly.
Muscle has a rich blood supply, which is why it is the fastest healing tissue listed above. The circulatory system provides all tissues with nutrients and oxygen – both of which enable the tissue to heal. Because muscle gets lots of blood flow, it has a good environment for healing.
Connective tissues such as ligaments, tendons, in- tervertebral discs, and articular cartilage have a limited capacity to heal following structural dam- age1. Nevertheless, bone can heal when injured thanks to the high degree of vascularization and the appropriate cellular environment to promote tissue repair2.
Tissue regeneration comes in as many forms as there are tissues to regenerate (McMinn, 1969), which includes virtually everything except teeth. Some tissues may regenerate better than others, but in all cases it is important not to confuse tissue regeneration with various forms of compensatory growth (Goss, 1978).
Teeth are the ONLY body part that cannot repair themselves. Repairing means either regrowing what was lost or replacing it with scar tissue. Our teeth cannot do that. Our brain for example will not regrow damaged brain cells but can repair an area by laying down other scar-type tissue .
Similar to skeletal muscle tissue, cardiac muscle does not regenerate to a great extent. Dead cardiac muscle tissue is replaced by scar tissue, which cannot contract.
Nerve Cells Do Not Renew Themselves
Yet, nerve cells in your brain, also called neurons, do not renew themselves. They do not divide at all. There are very few exceptions to this rule – only two special places in the brain can give birth to new neurons.
Muscle and nervous tissues undergo either slow regeneration or do not repair at all.
A skin wound that doesn't heal, heals slowly or heals but tends to recur is known as a chronic wound. Some of the many causes of chronic (ongoing) skin wounds can include trauma, burns, skin cancers, infection or underlying medical conditions such as diabetes. Wounds that take a long time to heal need special care.
The collenchyma is living cells, with actively dividing protoplasm. Hence it is not a permanent tissue. Collenchyma is a simple tissue but not permanent.
Cardiac infarcts — cardiac muscle cells do not regenerate and thus are replaced by fibrous connective tissue (scar).
The weakest of all muscle tissues, visceral muscles contract to move substances through the organ, according to The Merck Manual. Because visceral muscle is controlled by the unconscious part of the brain, it is known as involuntary muscle, as it cannot be controlled by the conscious mind.
Tissue regeneration includes regeneration of epithelial tissue, regeneration of fibrous tissue, regeneration of cartilage tissue and bone tissue, regeneration of blood vessels, regeneration of muscle tissue, and regeneration of nerve tissue.
In other organs, once cells become differentiated, they stop being able to divide and proliferate. Without a stem cell reserve or the ability to return to a proliferative state, these tissues have no options for regeneration.
The epidermis constantly renews itself: New cells are made in the lower layers of the epidermis. These move to the surface within four weeks. This constant renewal serves to replace the cells that are lost and fall to the ground as tiny flakes of skin when the skin is rubbed.
Most epithelial tissues self-renew throughout adult life due to the presence of multipotent stem cells and/or unipotent progenitor cells. Epithelial stem cells are specified during development and are controlled by epithelial-mesenchymal interactions.
Bone remodeling, the ultimate stage of bone healing, continue more than a few months. In regeneration, bone regenerates to form and converts condensed, returning to its original form (Dimitriou et al. 2005). Furthermore, blood circulation in the region progresses.
Tissues that have limited ability to regenerate include bone, cartilage, and smooth muscle (such as the muscles around the intestines). Tissues that rarely or never regenerate include the nerves, skeletal muscle, heart muscle, and the lens of the eye. When injured, these tissues are replaced with scar tissue.
However, many mammalian tissues, like cardiac muscle, spinal cord, and major appendages, have strikingly little regenerative capacity.
As collagen is the principal component of the extracellular matrix (ECM), it is vital for the strength, regulation, and regeneration of this tissue (Frantz et al.
The three types of simple permanent tissues are Parenchyma, Collenchyma, and Sclerenchyma.
Permanent tissues do not divide like meristematic tissues since they are dead.