Human Body Regeneration- How Body Heals Itself .

Abstract

Regeneration in humans refers to the ability of our bodies to regrow or replace lost or damaged tissues or organs as a response to injury. Biochemically, regeneration in living organisms is the regrowth of lost/destroyed tissues or organs at every moment. Some tissues, such as skin and large organs, especially the liver, regrow quite readily, while others have little or no capacity for regeneration. This process is distinct from wound healing, which is often referred to as partial regeneration, and typically involves the formation of scar tissue to close up the site of injury.

In other words, a trauma response in wound healing resulting from the injury site requires closing up with a scar. Certain tissues and organs in the human body, such as the skin and liver, have a remarkable capacity for regeneration. However, other tissues and organs were previously thought to have little or no regenerative capacity following an injury. Recent advancements in science have challenged this notion, with numerous tissues and organs now known to be capable of induced regeneration. In fact, ongoing research particularly of the heart and lungs, suggests that there is hope for a variety of tissues and organs to eventually become regeneration-capable.

Table of Content

Introduction

History of Human Tissue Regeneration

Where Can Regeneration Take place?

Stem Cells and Regenerative Medicine

Regenerative Techniques

Naturally Regenerating Appendages and Organs

Induced Regeneration in Humans

How Fast Do Cells in the Body Replace Themselves?

How Long Does it Take for the Body to regrow its Cells and Organes from Skin to Skeleton?

Regeneration Across Animal Species

Visible Examples of Body Regeneration

Conclusion

Patient Testimonials

Introduction

The human body has an amazing ability to regenerate itself. Here are some examples:

1. Skin: The body sheds old epithelial cells and replaces them with new ones. The turnover rate is quick; it’s fully regenerated every five to seven days.
2. Liver: The liver is the human body’s detoxifier, purifying a wide variety of contaminants from our systems. It’s aided in the process by a constant blood supply and remains largely immune to damage from these toxins by renewing itself with new cells every 150 to 500 days. (Opfer & Troutner, 2022)
3. Bones: The body regenerates a full bone within ten years. (Laliberte, 2018)
4. Cells: Old cells in our bodies are constantly being replaced with new ones. About 330 billion of those cells are replaced every day — that’s about 1 percent of all our body’s cells. Other cells, like the tiny ones in our gut, renew within a week.
5. Colon: Cells in our colon are replaced every three to five days.
6. Fingertips: Fingertips can regenerate after an injury.
7. Endometrium: The endometrium, or the lining of the uterus, regenerates every month after menstruation. (Laliberte, 2018) (Opfer & Troutner, 2022)

It’s important to note that while many tissues and organs in the body can regenerate, some, like those in our brain, heart, and eyes, are with us our entire lives.

In the realm of regenerative medicine, scientists are exploring the potential of stem cells, which have the ability to differentiate into a variety of cell types, offering possibilities for tissue regeneration. Stem cells could potentially be used to grow new cells in the laboratory that can then be transplanted into patients to replace damaged or destroyed tissues or organs.

In addition to stem cells, certain animals possess remarkable regenerative capabilities that far exceed those of humans. For instance, salamanders and starfish can regenerate entire limbs or even their entire bodies. Researchers are studying these organisms in hopes of understanding the biological mechanisms that allow them to do so.

Moreover, advancements in technology such as 3D bioprinting are opening new avenues in tissue regeneration. In fact, scientists have been able to 3D-print bladders in the lab since 1999. Skin tissue can be regenerated both in vivo (within the body) and in vitro (outside the body in a controlled environment). Other organs and body parts that have been prompted to regenerate include the penis, fats, vagina, brain tissue, thymus, and even a scaled-down human heart. (The Guardian, 2014) This technology can create complex tissues and organs by depositing layers of living cells. In the future, it may be possible to print organs suitable for transplantation.

There are four main techniques that can induce regeneration: regeneration by instrument; regeneration by materials; regeneration by drugs; and regeneration by in vitro 3D printing.

In non-injured tissues, new cells naturally replace expended cells over time. When tissue is injured, however, the body usually responds differently. This emergency response often involves building a degree of scar tissue over a time period longer than a regenerative response.

While the field of regenerative medicine holds great promise, it also presents significant challenges. Ethical considerations, technical hurdles, and the need for further research mean that it may be some time before these therapies become commonplace. Nevertheless, the potential benefits to human health make this an exciting area of scientific research. The ultimate goal of scientists is to induce full regeneration in more human organs. By 2016, regeneration of tissue had been induced and operationalized by science.

History of Human Tissue Regeneration

In living organisms, for example, humans, non-injured tissues are naturally regenerated over time by default. These tissues become new cells available to replace expended cells. For example, the human body has the ability to regenerate a full bone within a ten-year period, while non-injured skin tissue may be regenerated within two weeks. With injured tissue, the body usually has a different response – this emergency response usually involves building a degree of scar tissue over a time period longer than a regenerative response, as has been proven clinically and also through observation. There are various understandings about regeneration processes. For instance, in full-thickness wounds under 2mm, regeneration generally occurs before scarring, whereas in wounds over 3mm, it was found that a wound needed a material inserted in order to induce full tissue regeneration.

There are some human organs and tissues that fully regenerate rather than simply scar as a result of trauma. These include the liver, fingertips, and endometrium. More information is now known regarding the passive replacement of tissues in the human body, as well as the mechanics of stem cells. Advances in research have enabled the induced regeneration of many more tissues and organs than previously thought possible. The aim of these techniques is to use these techniques in the near future for the purpose of regenerating any tissue type in the human body.

Where Can Regeneration Take place?

Regeneration in humans can take place at 3 levels:

1. Molecular Level

The Cell is the most basic functional unit in any system. Cell division is regulated on a molecular level. Inside all of the cells there are hundreds if not thousands of small molecules (proteins, RNA, DNA, carbohydrates, lipids, etc) interacting to drive the everyday processes that the cells must undergo to survive and function.  In the context of regeneration, each cell’s fate is dependent on these molecules and their interactions to drive them to divide, to remain the same, or to die. Cells adjust the rate at which these mechanisms are activated to control growth, replication, and death in response to their environment.

1. Cellular Level

The cell is the body’s most basic functional entity. Cells can be either homogeneous or heterogeneous and almost always bundle together to create a tissue that has a specific structure and function. There are cells, for example, single nerve cells or neurons, that are capable of regeneration.  Neurons consist of a cell body (the head), an axon (the arm), and dendrites (the hands) that work together to receive (dendrites), process (cell body), and deliver (axon) messages all over our body (see image below).  If a neuron is separated at the axon but the cell body remains intact, the axon has the ability to close the wound, generate a new growth place, and begin to regrow another extension to replace the damaged portion which is degraded.

1. Tissue Level

Many tissues in the human body are capable of exhibiting regeneration in response to injury as well as general upkeep of normal tissue, to name a few: blood, skin, bone, skeletal muscle, liver, pancreas, small blood vessels, and kidney epithelium. In a perfect world, these tissues would be able to regenerate under any circumstance, however, the environment within the tissue must be just right. Cells that are able to generate energy, engage in cross-talk, and respond to the ‘regeneration signals’ produced must be present. Additionally, the cells must be able to communicate in a stable and organized fashion so they can be directed to proliferate and differentiate into the appropriate tissue. Finally, those signals that may inhibit regeneration must be modulated to enable an environment for growth and expansion of functional healthy tissue.

Stem Cells and Regenerative Medicine³⁰

Stem cells have a very important role in Regenerative Medicine Research and have many potential applications.

1. First, because of their role in development and their potential to develop into many different cell types, stem cells are vital to the field of developmental biology.  Developmental biologists seek to uncover what genes and pathways are involved in cell differentiation (how cells develop into specific cell types such as liver, skin, or muscle cells) and how these can be manipulated to create new healthy tissues
2. Second, can be applied to drug testing and development.  New drugs that are developed in Pharma could be safely and effectively tested using differentiated stem cells.  As scientists learn more about how stem cells develop to form new tissue they will be able to apply their knowledge in maintaining differentiated cell types that can be used to test particular drugs.
3. Finally, and of most interest to patients and scientists, is the role of human umbilical cord-derived mesenchymal stem cells in Cell-Based Therapy. These therapies will apply the understanding of stem cell development, differentiation, and maintenance to generate new, healthy tissue for diseases needing transplant or replacement of damaged tissue, such as arthritis, autism, Parkinson’s disease, type 1 diabetes, organ failure such as lung, hear, kidney, liver failure, and coronary disease.

Regenerative Techniques

1. Regeneration with drugs:

Lipoatrophy is the localized loss of fat in tissue. It is common in diabetics who use conventional insulin injection treatment. Instead of causing lipoatrophy, a much purer form of insulin has been shown to regenerate the localized loss of fat after injections in to diabetics. In recent years (2016), scientists are believed to have managed to transform a skin cell into any other tissue type via the use of drugs. This technique was noted as safer than genetic reprogramming which was a medical concern. The technique used a cocktail of chemicals and enabled efficient on-site regeneration without any genetic programming.

1. Regeneration by instruments:

A cut by any sharp object generally scars though but a piercing by a needle does not scar. Back in 1976, a 3x3cm scar on a non-diabetic was regenerated by insulin injections and the researchers argued that the insulin was regenerating the tissue. The anecdotal evidence also highlighted that a syringe was one of two variables that helped bring regeneration of the scar. The syringe was injected into the four quadrants three times a day for 82 days. After eighty-two days, with countless injections, the scar was resolved, and it was noted no scar was observable by the human eye. After seven months the area was checked again, and it was once again noted that no scar could be seen.

1. Regeneration by 3D printing:

In 2009, the regeneration of hollow organs and tissues with a long diffusion distance, was a little more challenging. Therefore, to regenerate hollow organs and tissues with a long diffusion distance, the tissue had to be regenerated inside the lab, via the use of a 3D printer. By 2012, thanks to printing tissues, there were four accepted standard levels of regenerative complexity that were acknowledged in various academic institutions:

• Level one, flat tissue-like skin was the simplest to recreate
• Level two, tubular structures such as blood vessels
• Level three, hollow non-tubular structures
• Level four, solid organs, (by far the most complex to recreate due to the vascularity).

1. Regeneration with materials

Generally, humans in vivo, can regenerate injured tissues for limited distances of up to 2mm. The further the wound distance is from 2mm the more the wound regeneration will need inducement. By 2009, via the use of materials, a max-induced regeneration could be achieved inside a 1 cm tissue rupture. Bridging the wound, the material allowed cells to cross the wound gap; the material then degraded. This technology was first used inside a broken urethra in 1996. In 2012, using materials, a full urethra was restored in vivo.

Naturally Regenerating Appendages and Organs

• Heart

Cardiomyocyte necrosis activates an inflammatory response that serves to clear the injured myocardium from dead cells, which stimulates repair but may also extend injury. Research suggests that the cell types involved in the process play an important role. Namely monocyte-derived macrophages tend to induce inflammation while inhibiting cardiac regeneration, while tissue resident macrophages may help restoration of tissue structure and function.

• Kidney

Following an acute injury, the proximal tubule is damaged more, and the injured epithelial cells slough off the basement membrane of the nephron. The surviving epithelial cells, however, undergo migration, dedifferentiation, proliferation, and redifferentiation to replenish the epithelial lining of the proximal tubule after injury.

• Liver

The human liver is particularly known for its ability to regenerate and is capable of doing so from only one quarter of its tissue, due chiefly to the unipotency of hepatocytes. Resection of liver can induce the proliferation of the remaining hepatocytes until the lost mass is restored, where the intensity of the liver’s response is directly proportional to the mass resected. For almost 80 years surgical resection of the liver in rodents has been a very useful model to the study of cell proliferation

• Fingers

Studies have showed that children up to the age of 10 or so who lose fingertips in accidents can regrow the tip of the digit within a month provided their wounds are not sealed up with flaps of skin

• Endometrium

The endometrium after the process of breakdown via the menstruation cycle, re-epithelializes swiftly and regenerates. Though tissues with a non-interrupted morphology, like non-injured soft tissue, completely regenerate consistently, the endometrium is the only human tissue that completely regenerates consistently after a disruption and interruption of the morphology.

• Toes

Toes damaged by gangrene and burns in older people can also regrow with the nail and toe print returning after medical treatment for gangrene.

• Vas Deferens

The vas deferens can grow back together after a vasectomy, thus resulting in vasectomy failure.

Induced Regeneration in Humans

Whereas amphibians regenerate lost appendages spontaneously, mammals generally form scars over the injury site through the process of wound repair. Induced regeneration falls under regenerative medicine which includes the methods and research conducted with the regenerating organs or tissues following disease or trauma. The strategies to regenerative medicine include dedifferentiating injury site cells, transplanting stem cells, implanting lab-grown tissues or organs, and finally implanting bioartificial tissues. Some of the common organs best known to successfully benefit from regenerative medicine include;

• Bladder
• Lungs
• Penis
• Thymus
• Spinal Nerves
• Thymus
• Vagina
• Fat

How Fast Do Cells in the Body Replace Themselves?

Cell renewal is an instinctual daily experience with all living organisms. We all notice that our hair falls out regularly, yet we don’t get bald (at least not everyone). Similarly, we have all had the experience of cutting ourselves only to see how new cells replaced their damaged predecessors. And we donate blood or give blood samples without gradually draining our circulatory system. All of these are examples of the replacement rate of cells, which is characteristic of different tissues and in different conditions. To be more concrete, our skin cells are known to constantly shed and renew.

Red blood cells make their repetitive journey through our bloodstream with a lifetime of about 4 months. There are about 3×10¹³ red blood cells to infer that about 100 million new red blood cells are being formed in our body every minute! Replacement of our cells also occurs in most of the other tissues in our body, though the cells in the lenses of our eyes and most neurons of our central nervous system are thought to be special counterexamples.

Well then, how can the replacement rates of the cells in various tissues in our body be measured? For rapidly renewing tissues common labeling tricks can be useful as with the nucleotide analog BrdU. As for the very slow tissues that can take years or a lifetime, a fascinating example of scientific serendipity, Cold War nuclear tests have come to the aid of scientists as a result of the fact that they changed the atmospheric concentrations of the isotope carbon-14 around the globe. These experiments are effectively pulse-chase experiments but at a global scale. For example, Carbon-14 has a half-life of 5730 years, and thus even though radioactive, the fraction that decays within the lifetime of an individual is negligible and this timescale should not worry us.

The table below shows a collection of the replacement rates of different cells in our body.

How Long Does it Take for the Body to regrow its Cells and Organes from Skin to Skeleton?

Human bodies change and regenerate throughout our lives. That process is easy to see if you watch babies’ limbs grow and their bodies get bigger. It’s also obvious when our toenails grow, or healthy skin emerges after a burn peels away. But less obvious systems of regrowth and rebirth in the body continue throughout adulthood. Dead skin cells constantly rise to the surface of our body, get sloughed off, and then are replaced by new stem cells. Some areas of the body take a long time to refresh themselves; for example, our fat-storage cells shift roughly once per decade, while we get fresh liver cells about once every 300 days.

But of course, your body doesn’t simply throw away an entire liver’s worth of cells on day 300 and create a brand-new set on 301. Instead, it’s more of an organic cycle, since liver cells continue to divide and regenerate continue to divide and regenerate long after they’re mature. Not every body part regenerates or changes, though. While the body’s hairs are in a near-constant state of growth, parts of the human brain and head pretty much finish developing at birth (like the lens of the eye that’s helping you read this).

Eventually, the tips of our DNA begin to fray after years of wear and tear take their toll on the body — part of the natural aging process.

Regeneration Across Animal Species

Regeneration, the ability to restore lost body parts, is a trait that is present in a wide variety of animal species. By comparing the regeneration processes across different animals, we can gain insights into the evolutionary history of this remarkable ability. While recent research has found some similarities in the mechanisms of regeneration, it is crucial to use rigorous comparative methods to determine whether these similarities are due to shared ancestral pathways (homology) or the result of similar evolutionary pressures leading to similar solutions (homoplasy).(Srivastava, 2021)

This review proposes a framework for comparing regeneration across different animal species, with a particular focus on gene regulatory networks (GRNs). GRNs serve as a basis for assessing process homology. For instance, the activation of Wnt signaling in response to injury and the role of adult stem cells in regeneration are areas of ongoing research that allow for comparisons within a GRN framework. (Srivastava, 2021)

By expanding our understanding of GRNs in regeneration and increasing the range of species studied, we can identify common principles in regeneration biology. These findings are not only important for understanding the evolution of regeneration but also have implications for human regenerative medicine. (Srivastava, 2021)

The recent genetic approaches to study the mechanisms of regeneration in different tissues and vertebrates highlights the objectives of regeneration biologists, such as identifying the cellular sources, molecular triggers, and early events of regeneration. (Chen)

It is also important to explore the question of why some animals can regenerate and others cannot. There is the evidence from phylogenetic analyses and experimental manipulations of regeneration in different species. It suggests that mammals may have more regenerative potential than previously thought. (Maden)

Visible Examples of Body Regeneration

Hair

Hair growth after a haircut varies from person to person and is influenced by several factors, including genetics. On average, hair grows about a quarter-inch per month. Some people may experience slightly slower or faster growth. For example, according to a 2016 study:

• Asian hair grows about 0.49 inches per month, or just under 6 inches per year.
• Black hair grows about 0.33 inches per month or just under 4 inches per year.
• White and Latino hair grows about 0.44 inches per month, or 5.3 inches per year. (Cafasso, 2022)

It’s important to note that cutting or trimming your hair does not affect the rate of hair growth. When you cut your hair, you’re only reducing the length of the tips, while the hair follicles, which control the quality of your hair strands, remain intact. (Bunch, 2021)Therefore, regardless of whether you cut it or not, your hair will grow at its natural rate. If you’ve cut your hair to just below your chin, and you want it to grow past your shoulders, it could take approximately 10-12 months. (Does Your Hair Grow Faster If You Cut It? Here’s the Truth, n.d.)

Nail

Nail growth is a fascinating example of the body’s regenerative abilities. Here are some facts about it:

• Fingernails grow at an average rate of 3.47 millimeters (mm) per month, or about a tenth of a millimeter per day. This growth rate can be influenced by several factors, including which hand it is, your age, hormone levels, and overall health.
• If you happen to lose a fingernail, it may take up to six months for that nail to completely grow back.
• The nails on your dominant hand grow faster than the rest, as do the nails on your longer fingers.
• Your fingernails also grow faster during the day and during the summer.
• The rate of growth also depends on which finger the nail is on. A 2007 study found that the fingernail on your little finger grows slower than other fingernails. (Cobb et al., 2018)
• Toenails take a year to a year and a half to grow from cuticle to tip.(Sentry, 2021)

It’s important to note that if you notice a change in your nails or their growth rate, you should see your doctor.

Wound Healing

A hematoma is an area of blood that collects outside of the larger blood vessels. It’s commonly due to injuries or trauma in the area. An injury can cause blood vessel walls to break, allowing blood to make its way into the surrounding tissue. Hematomas may occur in any blood vessel, including veins, arteries, and capillaries. (Sampson, 2019)

The process of skin regeneration after an injury, such as a hematoma, involves several steps:

1. Coagulation: This is the body’s initial response to injury. It involves the clotting of blood to prevent further blood loss. (Kian & Wang, 2020)
2. Inflammation: This is the body’s natural response to injury. It involves the release of various immune cells to the site of injury to fight off any potential infections.
3. Epithelization: This is the process where the skin begins to regenerate. New skin cells are produced and migrate to the site of injury to cover the wound.
4. Fibroplasia: This involves the formation of fibrous tissue, which helps to strengthen the newly formed skin.
5. Maturation: This is the final stage of healing, where the new skin fully establishes itself, restoring the localized properties of the skin. (Crystal, 2018)

It’s important to note that the rate and success of skin regeneration can be influenced by several factors, including the size and location of the hematoma, the individual’s overall health, and the care given to the wound.

The graph below the indicates timeline of how the body regenerates, regrows, and starts anew.

Conclusion

Regeneration in humans is the process of restoring or replacing lost or damaged tissues or organs in response to injury. This process differs from wound healing, which often involves scar tissue formation. Regeneration in humans is limited compared to some animals, such as salamanders and starfish, which can regenerate entire limbs or bodies. Scientists are studying the mechanisms of regeneration in these animals and exploring the potential of stem cells and 3D bioprinting to create new tissues and organs for human patients. Regeneration in humans is a promising field of research that faces many challenges but also offers many benefits for human health.

Patient Testimonials

Michelle Wild, a resident of Houston, Texas, was diagnosed with ameloblastoma, an aggressive type of jaw cancer. She was in constant pain, day and night, to the point where she couldn’t sleep. The pain was so severe that she was prepared to undergo a highly invasive surgery, which involved using a bone from her leg to rebuild her jaw.

However, her sister believed the surgery was too invasive and sought an alternative solution. This led them to Dr. Haque. Michelle’s entire family consulted with Dr. Haque, who confidently assured them that Michelle’s pain would be gone in three days. This was a bold statement that stood out to Michelle.

True to his word, Michelle’s pain disappeared in just four days. She experienced no pain at all, a significant relief from the constant pain she had been enduring. Moreover, her tumor started to shrink, indicating a positive response to the treatment.

Michelle’s experience serves as a testament to the effectiveness of Dr. Haque’s treatment approach. Her story underscores the importance of seeking alternative treatments when conventional methods seem too invasive or ineffective. It also highlights the impact a dedicated healthcare professional can have on a patient’s journey to recovery.

She wrote:

“ I have an ameloblastoma which is a type of aggressive cancer in my jaw and I had been experiencing pain constantly all day, all night, to the point where I couldn’t sleep. I was literally ready to go through surgery which is very invasive; the doctors wanted to take a bone out of my leg to rebuild my jaw, however, my sister said it was too invasive and said she would find another alternative and she found Dr. Haque. My entire family came to Dr. Haque and he said something that stood out to me; he said that the pain I was experiencing would be gone in 3 days. It was great to hear, and in four days I had no pain. No pain at all… The tumor is also starting to shrink!”

• Michelle Wild, Houston, TX, Patient

Rosie Israel, a patient who was diagnosed with stage 4 of small cell lung cancer a few years ago, shares her journey towards recovery. Small cell lung cancer is known for its low survival rate, with only 5% of patients surviving the disease. However, Rosie is now cancer-free, a status she attributes to the valuable advice and guidance she received from Dr. Haque.

Rosie met Dr. Haque over a year ago and has been consulting with him periodically since then. Dr. Haque provided Rosie with valuable advice on nutrition and lifestyle changes, which Rosie believes played a significant role in her recovery. She appreciates Dr. Haque’s passion for helping patients become disease-free and highly recommends his clinic to others.

Rosie’s journey is a testament to the power of medical guidance and lifestyle changes in battling diseases as severe as stage 4 small cell lung cancer. Her story serves as an inspiration for other patients battling similar conditions and highlights the importance of seeking and following professional medical advice. Rosie’s experience with Dr. Haque’s clinic underscores the clinic’s commitment to patient care and disease prevention. Her high recommendation of Dr. Haque and his clinic speaks volumes about their dedication to their patients’ health and well-being. This case study serves as a beacon of hope for patients battling severe diseases and emphasizes the importance of professional medical guidance in disease treatment and prevention.

She wrote:

“I was diagnosed with stage 4 of small cell lung cancer about a few years ago and it’s a cancer that has only 5% survival. Now, thank God, I’m cancer free. I truly appreciate Dr. Haque that I met over a year ago. I have been consulting with him periodically and he gave me some really valuable advice on nutrition and lifestyle that definitely contributed to me being cancer-free today. I highly recommend Dr. Haque and appreciate his passion for trying to get everyone free of disease. I highly recommend his clinic.”

• Rosie Israel, Patient

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Cafasso, J. (2022, February 17). How Long Does It Take for Hair to Grow Back in Various Cases? Healthline. Retrieved December 6, 2023, from https://www.healthline.com/health/how-long-does-it-take-for-hair-to-grow-back

Cobb, C., Adcox, M., & Goodson, A. (2018, April 13). How Fast Do Nails Grow? Rate by Day, Month, Year, Tips, and More. Healthline. Retrieved December 6, 2023, from https://www.healthline.com/health/beauty-skin-care/how-fast-do-nails-grow

Crystal, M. (2018, April 25). How Does Skin Regenerate? Sciencing. Retrieved December 6, 2023, from https://sciencing.com/skin-regenerate-4566222.html

Does Your Hair Grow Faster If You Cut It? Here’s the Truth. (n.d.). TrimmerGuidance.com. Retrieved December 6, 2023, from https://trimmerguidance.com/does-your-hair-grow-faster-if-you-cut-it/

Kian, M., & Wang, Y. (2020, April 10). Skin Regeneration in Wound Healing: The Art of Self Preservation. Saltman Quarterly. Retrieved December 6, 2023, from https://sqonline.ucsd.edu/2020/04/skin-regeneration-in-wound-healing-the-art-of-self-preservation/

Laliberte, M. (2018, March 9). How the Body Heals After Injury (and Every Day). The Healthy. Retrieved December 6, 2023, from https://www.thehealthy.com/immune-system/how-the-body-heals/

Opfer, C., & Troutner, A. (2022, September 22). Does Your Body Really Replace Itself Every Seven Years? Science | HowStuffWorks. Retrieved December 6, 2023, from https://science.howstuffworks.com/life/cellular-microscopic/does-body-really-replace-seven-years.htm

Sampson, S. (2019, March 29). Hematoma: Overview, types, treatment, and pictures. Medical News Today. Retrieved December 6, 2023, from https://www.medicalnewstoday.com/articles/324831

Sentry, S. (2021, February 17). How fast do nails grow? | HowStuffWorks. Health | HowStuffWorks. Retrieved December 6, 2023, from https://health.howstuffworks.com/skin-care/nail-care/health/how-fast-do-nails-grow.htm

The Guardian. (2014, October 4). Penis transplants: the man who gave men their lives back. https://www.theguardian.com/education/2014/oct/04/penis-transplants-anthony-atala-interview

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