By Konstantina Bilali Panagiotidou - July 23, 2019
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| Regenerating human limbs |
As we mentioned
in the previous article, every human tissue has a different regenerative
potential and that's why they are divided into three catgories.
1) High cellurar turnover & High regenerative
potential :
This category
includes the tissues of blood , skin, epithylium, vascular endothelium and the
mucosa intestine . The time required for this regeneration process is from few
days up to some months. For example, red blood cells, which are produced in the
bone marrow and have as their primary function the transfer of oxygen from the
lungs to all tissues of the body, live for an average of 4 months and then they
regenerate. The same thing happens with the epithelial cells of the stomach
mucosa. Those cells are prone to damage due to the digestion process and are
therefore replaced by new ones in a short period of time. Thanks to this
regenerative capacity of the cells, the mucosa is renewed about every 15 days.
Also, epithelial cells that cover the internal surface of the intestine have a
life span of only a few days.
2) Low cellurar turnover & high regenerative
potential :
This category
includes the tissue of the liver, pancreas, musculature , the cortex of the
adrenal gland, bones and the connective tissue . These tissues, when they get
injured they can regenerate but normaly they have no cell replenishment. Let's
use the example of the bones. Old bones are broken down by cells called
osteoclasts and replaced by new bones that create cells called osteoblasts.
This process happens about every ten years. The new bones do not replace the
older ones , but they are the ones who dominate the state of the skeleton. As the
person becomes older , the regenerating process slows down significantly,
resulting in bones becoming thinner and problems with osteopenia and
osteoporosis.
3) Low cellurar turnover & low regenerative
potential :
This category
includes organs such as : the brain, kidneys, spinal cord, lungs, cartilage ,
retinal and the heart. Tissues such as the nervous system and some cells such
as teeth and the optic nerves, with the exception of the cornea, have no
regenerative potential and no cell replenishment which makes them very
sensitive since the damage cannot be repaired . There is some controversy about
the brain because of the the olfactory bulb, which controlls the sense of
smell, and the hippocampus, associated with memory and learning. These two
regions of the brain can regenerate.
However , if a
deadly accident takes place, such as a traumatic brain injury the regenerating
process is sometimes impossible or extremely slow to progress. This happens
because of the cerebellum, which is a region of the brain located at the
back of the head and the inter alia, which is involved in motion control are
completed a few months after birth and cannot be renewed again. So basically,
some parts of the brain have regenerative potential but the brain as a whole
cannot be renewed.
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