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Why do some internal organs regenerate?


I have been reading about the human liver and zebra fish heart muscle having the ability to regenerate. It seems to me that these organs have very little chance to become damaged or worn out. At the very least their chances of being damaged are comparable to other internal organs. So why those particular organs have the regenerative capability?


It is not really essential that all vital organs should have regenerative potential (for example brain).

The cellular composition of a tissue is a big factor in deciding if the organ/tissue will regenerate or not. Some cells divide while others do not; highly specialized and polarized cells like neurons do not divide perhaps because the act of division itself will compromise their function. That doesn't mean these tissues cannot regenerate; they would need stem cells that can differentiate into the type of cells that died.

So regeneration can happen via:

  • Division of the tissue cells (skin healing, liver regeneration)
  • Differentiation of stem cells (erythropoesis, muscle regeneration)

Organs that do not have non-dividing cells can regenerate by simply proliferating whereas others would need to maintain a stem cell niche- which is not possible in all tissues. Maintenance of stem cells also adds up to the cost of metabolism; so there is some tradeoff.


Why do some internal organs regenerate? - Biology

Your question is interesting and it needs some explanation. Here it is.

Regeneration is the process by which some organisms replace lost body parts and a number of regenerative mechanisms have been evolved by different species.Regeneration is most common in invertebrates, occurring in almost all coelenterates and planarians, most annelids (segmented worms), and many insects.

Autotomy, the spontaneous loss and replacement of a body part, occurs in many insects and crustaceans, and enables them to shed a crippled leg or claw. The new part can be an exact replica of the lost structure, or can be functionally similar but anatomically different from the lost part. Also, sponges have remarkable powers of regeneration. Even if large parts of a sponge's body are lost or damaged, they may be replaced or repaired.

Many starfish can drop off arms as a defensive reaction. They can then regenerate new arms to replace the old ones. If a starfish is cut in two, each of the pieces may regenerate into a new animal.

Among vertebrates, no mammals have the ability to re-grow lost limbs or tails, but some species can regenerate other peripheral appendages, (e.g. a deer's antlers) or internal organs (e.g. the human liver).

In most fishes and salamanders, limited regeneration of limbs occurs, and tail regeneration takes place in larval frogs and toads (but not adults). The whole limb of a Salamander or a Triton will grow again and again after amputation. In reptiles, Chelonians, crocodiles and snakes are unable to regenerate lost parts. But many (not all) kinds of lizards, geckos and Iguanas possess regeneration capacity in a high degree. Usually, it involves dropping a section of their tail and regenerating it as part of a defense mechanism. While escaping a predator, if the predator catches the tail, it will disconnect. The tail lays flopping in the predator's mouth or on the ground. While the predator is occupied or distracted by the wriggling tail, the reptile runs away. The skin, muscles, blood supply, nerves and bone separate at almost any place along the length of the tail (below the reproductive organs). Later, when growing a new tail, it will not include all of the tissues and structures of the original one. Instead of the segmented vertebrae, a long tapering cartilaginous tube develops within which the spinal cord is located and outside of which are segmented muscles. The spinal cord is replaced by an epithelial tube, which gives off no nerves.

Very frequently super-regeneration occurs, the amputated limb or tail being replaced by double or multiple new structures.

While the loss of the tail may be natural, and may save a lizard's life, it isn't without cost. It is stressful to the lizard, especially if that lizard stores critical fat deposits in the tail, such as leopard geckos. Should a lizard be attacked twice, it is advantageous to have a re-grown appendage. However, tail regeneration is energetically expensive and can also result in lowered social status. Still, it is better than being someones dinner.

The less stress the lizard has to deal with, the faster the stump will heal and, if the tail is going to regenerate (they do not always do so), it will do so fairly rapidly.

Most lizards can regenerate more than once. The glass lizard is only able to shed and regenerate the tail once in its lifetime. When the new tail grows back, it will be smaller than the original. Unlike other lizards the monitor's tail does not break off and regenerate.

Regenerating tissues apparently follow a strict polarity, growing back in the proper orientation to the rest of the body. Since the most commonly lost structures are limbs and tails, the pattern of growth is usually outward from the body, suggesting that tissues more proximal than the injury contain all the necessary information to replace the lost part, but not those closer to the main trunk of the body. In some cases, however, as in fish fins, regeneration may occur in both directions. Regeneration is part of developmental biology and involves many unresolved problems. Scientists are trying hard to understand the molecular basis of regeneration.


Adult kidneys constantly grow, remodel themselves, study finds

It was thought that kidney cells didn’t reproduce much once the organ was fully formed, but new research shows that the kidneys are regenerating and repairing themselves throughout life.

Contrary to long-held beliefs, a new study shows that kidneys have the capacity to regenerate themselves.
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Researchers at the Stanford Institute for Stem Cell Biology and Regenerative Medicine and the Sackler School of Medicine in Israel have shown how the kidneys constantly grow and have surprising ability to regenerate themselves, overturning decades of accepted wisdom that such regeneration didn’t happen. It also opens a path toward new ways of repairing and even growing kidneys.

“These are basic findings that have direct implications for kidney disease and kidney regeneration,” said Yuval Rinkevich, PhD, the lead author of the paper and a postdoctoral scholar at the institute.

The findings were published online May 15 in Cell Reports.

It has long been thought that kidney cells didn’t reproduce much once the organ was fully formed. The new research shows that the kidneys are regenerating and repairing themselves throughout life.

“This research tells us that the kidney is in no way a static organ,” said Benjamin Dekel, MD, PhD, a senior author of the paper and associate professor of pediatrics at Sackler, as well as head of the Pediatric Stem Cell Research Institute at the Sheba Medical Center in Israel. “The kidney, incredibly, rejuvenates itself and continues to generate specialized kidney cells all the time.”

Irving Weissman, MD, professor of pathology and of developmental biology and director of the Stanford institute, is the other senior author.

The research, which was done in mice, also shows how the kidney regenerates itself. Instead of a single type of kidney stem cell that can replace any lost or damaged kidney tissue, slightly more specialized stem cells that reside in different segments of the kidney give rise to new cells within each type of kidney tissue.

Like a tree

“It’s like a tree with branches in which each branch takes care of its own growth instead of being dependent on the trunk,” Dekel said.

The scientists also showed that the decision these cells make to grow is made through the activation of a cellular pathway involving a protein called Wnt. Even though populations of kidney epithelial cells look the same, the most robust kidney-forming capacity can be traced back to precursor cells in which Wnt is activated and that can only grow into certain types of specialized kidney tissue, Rinkevich said. “The realization that Wnt signaling is responsible for the growth of new kidney tissue offers a therapeutic target to promote or restore the regenerative capacity of the kidneys,” he said. “We may be able to turn on the Wnt pathway to generate new kidney-forming cells.”

This finding will be important for scientists who attempt to create kidney parts in the lab, the researchers said.

However, they cautioned that such advances are not imminent. “To grow a whole kidney in the laboratory would be complicated because we would need to orchestrate the activities of many different kinds of precursor cells using just the right stimuli,” Dekel said. “It’s not like the blood and immune system, which can be reconstituted from one type of stem cell.”

Other Stanford co-authors of the study are Michael Longaker, MD, MBA, professor of surgery Roeland Nusse, PhD, professor of developmental biology postdoctoral scholars Aaron Newman, PhD, Orit Harari-Steinberg, PhD, Xinhong Lim, PhD, Renee Van-Amerongen, PhD, Angela Bowman, PhD, and Michael Januszyk, MD research assistants Daniel Montoro and Humberto Contreras-Trujillo and graduate student Jonathan Tsai.

This work was supported by the California Institute of Regenerative Medicine, the Smith Family Trust, the Oak Foundation, the Hagey Laboratory for Pediatric Regenerative Medicine, the Israel Scientific Foundation, Israel Cancer Research Fund, the Feldman Family Visiting Professorship at the Stanford medical school, the Human Frontier Science Program Long-Term Fellowship, the Machiah Foundation Fellowship and the Siebel Foundation.


Reverse Engineering Worms

The human roadmap that is contained in our DNA is present in every cell in our bodies, and it should also contain enough information to build or regenerate the body. However, access to that part of the plan is not accessible in humans for some evolutionary reason. One possible reason for this is that regeneration may take too much energy in a large, complex organism like a human. Another could be that our highly developed immune system actually stops the process with responses such as scar formation.

The UW team has been investigating which gene expression patterns take place when regeneration begins in acorn worms. Since regeneration follows precisely the same steps in every worm once it starts, the researchers believe that a “master control” gene may exist. If such a gene is what starts the process, it may be able to trigger regeneration in humans.

They are also attempting to identify which kinds of cells function as the building blocks of regeneration. Stem cells are an obvious possibility, but there may be other types of cells which could be repurposed for regeneration. Eventually, the team hopes to use gene activation or editing to start the process in other animals, including humans.

Ultimately, this would change the face of medicine. Burn victims could regenerate their skin, people would no longer need to wait for organ transplants, and if limbs were lost in an accident, they could be regrown. This technology, if it is possible, is not happening anytime soon. The challenges are complex, and so is the duplication of working human nervous systems, brains, and internal organs that would need to be mastered. Genetically we are in a favorable position, and our progeny may see human regeneration as part of our medical reality in 100 years or so.


Why can skin regenerate, but not other parts of the body?

This may be a silly question, but why can skin (and other organs, like the liver) regenerate, but not, say, bones? And when people get liver transplants, they get a portion of a liver and the rest of it grows, right? Why doesn't this work for other internal organs?

(I guess on a similar note, why do some animals get regenerative abilities, but not mammals?)

Some organs like skin or digestive tract lining or the blood have very active stem cells that are constantly dividing and replacing lost cells and tissue. Cells in the liver I believe can actually switch back into an active dividing stage, which is not seen in other fully differentiated tissues, which is why they can regenerate.

Most other organs in the body however have cells that are differentiated and very specialized and are no longer dividing. They often will have developed into very specific structures that cannot be easily recovered by adding more cells like you can with blood.

While all this is true, OP's question is surprisingly very timely. Whilst what you said is generally accepted, the reasons why other organs don't appear to have regenerative capacity is intriguing. I mean when the liver can regenerate, so should muscles right? Why don't they also have dedifferentiating-redifferentiating potential? Three lines of thought on this:

Regeneration in organisms like the Salamander is amazing, almost any tissue or organ can literally regenerate the lost parts (every organ regenerates itself. If you cut a limb off, the muscles will grow into more muscles while the bones will grow longer from themselves). The most magical of regenerative capabilities happens in planarians. Cut this worm into 252 pieces and all of them will grow into a seperate worm! The more amazing part is that they don't have genes that are very different from those that are found in other organisms. Genes that play vital roles in all other organisms (like beta-catenin) seem to be the drivers of such massive regenerative potential in all these organisms. And even interestingly, such regenerative potential is actually found in almost all major sub-groups of the animal kingdom. This all indicates that all organisms in theory have mechanisms that can lead to regeneration of almost all the organs, just that they are not in use in most of them (probably because of a lack of need and some other side effects like increased incidence of cancer just guessing here).

While it was thought that most differentiated tissues don't have stem cells, I direct you to research on Muse cells. These stem cells seem to be found in almost all tissues (including the freaking heart) and can actually regenerate lost cells but not just as much as weɽ like it to.

It is also recently shown that what we think is differentiated might actually not be so: people managed to change just one gene and remodel a frigging testis into an ovary in mice. God knows what else we could manage to do!


10 Things You Never Knew About the Clitoris

Brace yourselves ladies, there&rsquos a whole lot to know about the clitoris that they didn&rsquot teach us in health class.

Brace yourselves ladies, there&aposs a whole lot to know about the clitoris that they didn&apost teach us in health class. While you&aposve probably heard the many unfortunate nicknames for this body part (including "the bean" who came up with that?), and you definitely know a thing or two about the ahem, functions, of the clitoris, you might not know that it actually gets erect, for example.

Yep, "lady boners" (another very unfortunate nickname, sorry) are real.

To help you become a bit more "cliterate," here are 10 facts about this amazing part of your anatomy.

It's truly unique

When it comes to climaxing, "the clitoris is really, really crucial," says Jim Pfaus, PhD, professor and sex researcher at Concordia University in Montreal. But that&aposs not the only thing that makes it special: the clitoris is actually the only organ in the body with the sole function of providing pleasure.

It's long been a mystery

Until 1998 most textbooks only illustrated the external glans. That&aposs when Helen O&aposConnell, an Australian urologist, revealed through a series of MRI studies that the clitoris is actually a complex, powerful organ system composed of a total of eighteen parts, two thirds of which are interior.

It's much more than meets the eye

When people talk about the clitoris, they&aposre usually just talking about the glans, ”the very sensitive outside part," says Rebecca Chalker, PhD, Professor of Sexology at Pace University and author of The Clitoral Truth ($12, amazon.com). But the bump you can see on the vulva is only the tip of an iceberg.

The internal part is connected to the glans by the corpora cavernosa, two spongey areas of erectile tissue. Farther down, the corpora cavernosa branches off into a pair of wings known as the crura which extend into the body and around the vaginal canal like a wishbone. Then, underneath the crura are the clitoral vestibules, or vestibular bulbs. Like much of the clitoris, these sac-like structures of tissue become engorged with blood when you get aroused.

It's got a lot of nerve

The clitoris is the most nerve-rich part of the vulva, says Debra Herbenick, PhD, a sexual health educator from The Kinsey Institute. The glans contains about 8,000 nerve endings, making it the powerhouse of pleasure. To get some perspective, that&aposs twice as many nerve endings as the penis. And its potential doesn&apost end there. This tiny erogenous zone spreads the feeling to 15,000 other nerves in the pelvis, which explains why it feels like your whole body is being taken over by your O-M-G moment.

Every woman's is different

Women are all unique, so why would clitorises be any different? Every woman needs a different kind of stimulation to feel satisfied, depending on her unique biology. “Just because it&aposs sensitive doesn&apost mean everyone wants it to be stimulated directly," Herbenick says. "Some women prefer touching near the clitoris but not on it.” Pfaus agrees: “If she’s too sensitive with direct stimulation, more of that may make her want to kill you.”

It's the real G-spot

We&aposve all heard about the infamous G-spot: Does it exist? Do all women have one? Yes and yes. That&aposs because the G-spot is actually the clitoris. This notorious pleasure zone became sensationalized back in the 80s which, as Chalker explains, "created this idea that if you could only access the G-spot inside the vagina, it would promote female orgasm." But we&aposve since learned that some women may feel more sensation via the internal shafts of the clitoral complex (hence why some women might like vaginal penetration more than others), while others prefer external touch. One way is not better than another way, Pfaus adds it&aposs really about exploring the possibilities to find out what you like best.

It's very similar to the penis.

The clitoris and the penis are somewhat mirror images of each other, just organized differently, Chalker explains. "In fact, up until two weeks of pregnancy, all embryos appear to be female." It&aposs not until week eight of gestation that testosterone kicks in and the penis starts to form. "None of these parts disappear, they just get rearranged," Chalker says. For example the internal part of the clitoris, also made of erectile tissue, becomes the frame of the penis. With this concept in mind, Chalker points out: "If you consider the clitoris only consisting of the glans, then that&aposs like saying the only part of a penis is the tip."

. It even gets erect

When we talk about erection, we can&apost just talk about the penis, Pfaus says. We have to talk about the clitoris. Sure, it might be less noticeable for women, but it can definitely be observed and felt. This occurs when the vestibular bulbs become engorged with blood during arousal. The blood is then trapped here until released via orgasmic spasms.

Size doesn't matter

Like men, women can get self-conscious about their sexy parts. But guess what? Just like penises, clits come in all shapes and sizes. And size doesn&apost matter for either, Chalker explains. Think of it this way: since the brain is your main sex organ, the genitals are simply the receptors of pleasure. It has to do with visual, tactile, and oral stimulation," Chalker says, "rather that the actual size of the clit. So while glans may vary from woman to woman, this shouldn&apost affect the pleasure-potential." Also worth noting: chances are size doesn&apost (or, at least, shouldn&apost) matter to your partner.

It can grow with age

Although the size of your clitoris doesn&apost impact your sex life, don&apost be surprised if it changes dimensions over your lifetime. According to Chalker, due to a change in hormone levels after menopause, the clit may enlarge for many women. So if you notice some differences in the size of your lady parts over time, don&apost be alarmed.


Why are some people born with a reversal of organs?

When you look in the mirror, you see a transposed image of yourself. Now imagine having supernatural powers or x-ray vision and looking into your mirror image to see your internal organs. This is how your organs may look if you had reversal of organs. When a person's internal organs are reversed, they appear on opposite sides of the body than they typically are. Also called situs inversus, this puzzling and intriguing condition occurs in just 0.01 percent of all people. It's seen equally in males and females [source: eMedicine].

In many cases, reversal of organs won't lower a person's life expectancy or harm his quality of life. That's why some people never know they have this condition. It can be diagnosed by accident -- an incidental finding in an unrelated medical procedure, like an abdominal surgery. Situs inversus and other related disorders can also be diagnosed through x-ray, ultrasound and CT scan. Using ultrasound, doctors can detect reversal of organs while a fetus is still in the womb.

Most of the time, there's no way and no need to treat reversal of organs. Entire organs can't be switched, but accompanying disorders or abnormalities may require treatment.

We still don't know exactly what causes the condition. Scientists only know that a mutation appears in the genes of people whose organs are reversed, but the specific cause of the mutation and its nature are unknown.

Before we explore this medical mystery further, let's cover some related medical terms:

  • Situs solitus: normal arrangement of internal organs
  • Levocardia: normal positioning of the heart on the left side of the body
  • Mesocardia: heart positioned in the center of the chest
  • Dextrocardia: reversal of the position of the heart

Let's look at some examples and variations of this rare birth defect.

Dextrocardia with situs solitus is a congenital condition in which the heart is located on the right side of the chest but all other internal organs are in their normal positions. One slight difference in anatomy is that normally the left lung is smaller than the right lung in order to accommodate the heart. With dextrocardia, the right lung is smaller. People can still live normally and have no symptoms of dextrocardia, although an attentive doctor should notice the position of the heart during a regular physical.

Although some people live with no symptoms of dextrocardia, others may suffer from additional congenital heart abnormalities. One common abnormality is transposition of the great arteries. Normally, the left ventricle, the stronger portion of the heart, pumps blood to the entire body. But in this case, it pumps blood next door to the lungs. Meanwhile, the weaker right ventricle, which normally pumps blood to the lungs, is left to pump blood to the rest of the body. Doctors would notice this as soon as a baby is born because the child's skin color looks bluish. This condition -- known as blue baby -- happens when a baby doesn't have enough oxygen, but it can also happen for reasons other than transposed arteries.

Generally, there are no complications with situs inversus totalis because the organs are just flipped. Like dextrocardia with situs solitus, someone can live without being aware of his condition. But situs inversus totalis is also associated with some other rare conditions. Three percent of people with situs inversus totalis have some form of congenital heart disease [source: Fuster, et al]. Twenty percent of patients with situs inversus totalis also have Kartagener Syndrome [source: Wilhelm]. Not only do people with Kartagener Syndrome suffer from situs inversus totalis, they also suffer from male sterility and abnormalities in the bronchioles of the lungs.

A potentially dangerous form of organ reversal is situs ambiguus (sometimes spelled situs ambiguous). Like dextrocardia with situs solitus, situs ambiguus occurs in one in 20,000 births [source: Fuster, et al]. Usually, the liver and stomach appear on the right and left sides of the body, respectively. But with situs ambiguus, both move toward the center, and the stomach develops behind the liver.

Aside from the liver and stomach, there's the matter of the spleen. Someone with situs ambiguus can also have bilateral rightsidedness or bilateral leftsidedness. With rightsidedness, both sides of the body look how the right side normally looks, causing asplenia -- or no spleen. With leftsidedness, a person has polysplenia -- spleens on both sides of the body. Having no spleen can increase the risk of infection. Polysplenia boosts the chance of rupturing a spleen during an impact or accident causing dangerous internal bleeding. With or without a spleen, 90 percent of situs ambiguus sufferers have congenital heart disease. Some may also have dextrocardia [source: Fuster, et al, Wilhelm].

Reversal of organs is a rare condition that very few doctors and scientists understand. The good news is that many people born with it lead active lives. However, someone whose organs are reversed may also suffer from other complications.

For more information about reversal of organs and other related topics, please see the links on the next page.

Thank you to Dr. Rachel Gutkin and Dr. Gary Gutkin for their assistance with this article.


Invertebrate Animals

Sponges

Hydra

This cnidarian can also regenerate its entire body from cells. The cells that do the job are totipotent stem cells residing in the animal's body.

Planarians

When some species of flatworms (left) are decapitated, they can regenerate a new head. Double-amputees can regenerate both a new head at the anterior surface and a new tail at the posterior surface (right). They do this by the proliferation and differentiation of the pluripotent stem cells (called neoblasts) that it retains in its body throughout its life.

How do the cells know whether to develop into a head or a tail? Thanks to the ease with which individual genes can be knocked out by RNA interference (RNAi), it has been shown that Wnt/&beta-catenin signaling dictates where the head and tail form.

  • Blocking Wnt/&beta-catenin signaling by RNAi causes a head to form where a tail should (producing a two-headed animal) while
  • blocking part of the &beta-catenin degradation complex (thus enhancing the pathway) causes a tail to develop where a head should (producing a two-tailed animal).

Sea Stars (aka "Starfish')

These echinoderms can regenerate the entire organism from just one arm and the central disk.

I have read that at one time oyster fishermen used to dredge up sea stars from their oyster beds, chop them up in the hope of killing them, and then dump the parts back overboard. They soon discovered to their sorrow the remarkable powers of regeneration of these animals.

The photo (courtesy of Dr. Charles Walcott) shows a sea star regenerating an arm.


Tissue Engineering and Regenerative Medicine

A mini bioengineered human liver that can be implanted into mice. Source: Sangeeta Bhatia, MIT

Tissue engineering evolved from the field of biomaterials development and refers to the practice of combining scaffolds, cells, and biologically active molecules into functional tissues. The goal of tissue engineering is to assemble functional constructs that restore, maintain, or improve damaged tissues or whole organs. Artificial skin and cartilage are examples of engineered tissues that have been approved by the FDA however, currently they have limited use in human patients.

Regenerative medicine is a broad field that includes tissue engineering but also incorporates research on self-healing – where the body uses its own systems, sometimes with help foreign biological material to recreate cells and rebuild tissues and organs. The terms “tissue engineering” and “regenerative medicine” have become largely interchangeable, as the field hopes to focus on cures instead of treatments for complex, often chronic, diseases.

This field continues to evolve. In addition to medical applications, non-therapeutic applications include using tissues as biosensors to detect biological or chemical threat agents, and tissue chips that can be used to test the toxicity of an experimental medication.

What is Tissue Engineering? Source: Northwestern University

Cells are the building blocks of tissue, and tissues are the basic unit of function in the body. Generally, groups of cells make and secrete their own support structures, called extra-cellular matrix. This matrix, or scaffold, does more than just support the cells it also acts as a relay station for various signaling molecules. Thus, cells receive messages from many sources that become available from the local environment. Each signal can start a chain of responses that determine what happens to the cell. By understanding how individual cells respond to signals, interact with their environment, and organize into tissues and organisms, researchers have been able to manipulate these processes to mend damaged tissues or even create new ones.

The process often begins with building a scaffold from a wide set of possible sources, from proteins to plastics. Once scaffolds are created, cells with or without a “cocktail” of growth factors can be introduced. If the environment is right, a tissue develops. In some cases, the cells, scaffolds, and growth factors are all mixed together at once, allowing the tissue to “self-assemble.”

Another method to create new tissue uses an existing scaffold. The cells of a donor organ are stripped and the remaining collagen scaffold is used to grow new tissue. This process has been used to bioengineer heart, liver, lung, and kidney tissue. This approach holds great promise for using scaffolding from human tissue discarded during surgery and combining it with a patient’s own cells to make customized organs that would not be rejected by the immune system.

A biomaterial made from pigs' intestines which can be used to heal wounds in humans. When moistened, the material, which is called SIS, is flexible and easy to handle.
Source: Stephen Badylak, University of Pittsburgh.

Currently, tissue engineering plays a relatively small role in patient treatment. Supplemental bladders, small arteries, skin grafts, cartilage, and even a full trachea have been implanted in patients, but the procedures are still experimental and very costly. While more complex organ tissues like heart, lung, and liver tissue have been successfully recreated in the lab, they are a long way from being fully reproducible and ready to implant into a patient. These tissues, however, can be quite useful in research, especially in drug development. Using functioning human tissue to help screen medication candidates could speed up development and provide key tools for facilitating personalized medicine while saving money and reducing the number of animals used for research.

Research supported by NIBIB includes development of new scaffold materials and new tools to fabricate, image, monitor, and preserve engineered tissues. Some examples of research in this area are described below.


What is Tissue Regeneration? (with pictures)

Tissue regeneration is a revolutionary medical approach based on the idea that living tissue can be used to stimulate the natural healing process of the body. On its own, the body can repair and regenerate itself, as seen in the natural healing of wounds, burns and broken bones. Other vertebrates also have this ability, notably certain reptiles that can even regrow amputated limbs. In tissue regeneration, the natural ability of the body to repair and heal is encouraged, mainly by introducing engineered living cells into a diseased or damaged part of the body.

This form of medical healing is also called regenerative medicine and tissue engineering. It is an approach that applies the principles of medicine, biology and engineering. Tissue regeneration is used chiefly to accelerate the healing process, and to promote the healing of diseased tissues and organs that will not heal or mend on their own. Regenerative medicine is especially helpful in healing broken bones, chronic wounds and deep burns, but it also has been shown to help repair damaged nerves and structures of the heart.

Tissue regeneration consists of three main components, which include living cells, the matrix that supports them, and cell communicators. The matrix is the medium within which the living cells thrive, and the cell communicators are the communication or signalling mechanism that stimulates the cells. All three work together to promote regeneration of the living cells and their immediate environment. This results in the growth of new tissues to replace the old, damaged ones.

The living cells used in tissue regeneration are usually the same type of cells found in the diseased tissue or injured organs. The cells can come from the person himself, in which case they are called autologous cells. They can also come from another person, which are called allogeneic cells. It is generally better to use autologous living cells because they are not rejected by the patient’s body. Allogeneic cells don’t always work because the patient’s immune system rejects the foreign cells.

The living cells are artificially multiplied in cell banks, many millions of times over. When they are ready, they are pieced together to form a medicinal construct that is then integrated into the diseased tissues in the patient’s body. Then the construct is left alone to stimulate the natural healing process and hopefully restore the patient to good health. Continuing research and experimentation in tissue regeneration is underway. Doctors and scientists are confident that they will discover even more medical applications for tissue engineering.