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What part of your body never grows back?

On Your Health

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Mind-Blowing Facts About the Human Body You Never Knew

18 January 2021

Posted in

  • General Health
  • Health Across Oklahoma

Your body is amazing. No, really! The human body is a complex structure of interconnected systems and vital organs that work day in and day out to fulfill the functions necessary for everyday living. For example, in order to eat, your mouth, esophagus, stomach, liver, pancreas, and intestines must work together in sync to break down and digest what you eat while extracting the nutrients necessary to keep you healthy.

While most of us understand the basic bodily functions that keep us going, you might not be aware of some of the more incredible functions your body carries out. We’ve gathered up seven facts about the human body and some of its crazier processes that might blow your mind.

Fact No. 1: Your gut is the only organ with its own independent nervous system.

Your gastrointestinal system (commonly called your gut), which is made up of your stomach, pancreas, liver, gallbladder, small intestine, colon and rectum, is often referred to as the «second brain.» It’s the only organ with its own independent nervous system, comprising 100 million neurons embedded in the gut wall. Think of neurons as the messengers of your nervous system. They transmit information to nerve cells, muscles and gland cells throughout your body.

This «second brain» is so robust that it can continue to function even when the primary neural connection between your gastrointestinal system and the brain (called the vagus nerve) is severed. This means that even though your brain wouldn’t be able to communicate with your gut, neurons in your gut wall would still be able to transmit the information necessary for your digestive tract to function on its own.

Fact No. 2: Your veins, capillaries and arteries would stretch for more than 60,000 miles if laid out flat.

When your heart beats, it pumps blood through your circulatory system made up of blood vessels called arteries, capillaries and veins. These blood vessels carry blood to every part of your body: Arteries carry oxygenated blood away from the heart; veins carry blood back to the heart and capillaries connect them together.

If you were to lay out the vast network of blood vessels from an average child end to end, they would stretch for over 60,000 miles! In an average adult, they would stretch for almost 100,000 miles! Your capillaries, which are your smallest blood vessels (measuring only 5 micrometers in diameter), would make up nearly 80 percent of this length.

In comparison, the Earth’s circumference is approximately 25,000 miles. This means the blood vessels from just one person could stretch around the Earth many times!

Fact No. 3: You lose 200 million skin cells every hour, and these dead skin cells can actually decrease air pollution.

Your skin grows fast. Like really fast. During a 24-hour period, you can lose up to 5 billion skin cells (that’s nine zeros!) — about 200 million every hour. Your epidermis (the top layer of your skin) is continuously working to replace these lost skin cells with new ones. In fact, 95 percent of the cells in your epidermis work to make these new skin cells. The other 5 percent produce melanin, which gives skin its color.

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According to the American Chemical Society, these dead skin cells are a significant contributor to house dust and can be beneficial. As your dead skin cells fall off and collect around your home and office, they’re also taking with them skin oils such as cholesterol and squalene. Studies have shown that squalene can reduce levels of ozone – a harmful pollutant that can irritate your eyes, nose and throat and exacerbate asthma symptoms. In fact, the squalene in settled dust can reduce ozone in indoor spaces, reducing indoor pollution levels by up to 15 percent.

Bonus fact: Have you ever wondered how we can lose so many skin cells each day without a break occurring in your skin’s protective barrier? You’re not alone! A study conducted at the Imperial College London in 2016 discovered that our skin cells can maintain a protective barrier thanks to their unique tetrakaidecahedron shape – a 14-sided, 3D shape made from six rectangular and eight hexagonal sides. This shape allows skin cells to form a tight bond with other skin cells around them. The study also discovered that epidermal cells create a protein that acts as temporary glue, binding cells together in what are called «tight junctions.» The unique cell shape and this «glue» allow your skin to keep its integrity despite being thin.

Fact No. 4: Your cornea is unique in that it has no blood vessels.

Your cornea is the transparent part of your eye that covers the pupil (the opening at the center of your eye), the iris (the colored part of your eye) and the anterior chamber (the fluid-filled inside of your eye). The cornea’s transparent nature allows light to pass onto the retina and then to the brain to process what you’re seeing. What’s interesting is that the only reason your cornea is transparent is that it’s only one of two tissues in your body – the other being cartilage – that is entirely free of blood vessels!

Scientists have known for a while the cornea is transparent and free of blood vessels, but they could never explain why until 2006. Researchers at the Harvard Department of Ophthalmology’s Schepens Eye Research Institute and the Massachusetts Eye and Ear Infirmary discovered the unique phenomenon that allows the cornea to be free of blood vessels is tied to the presence of large amounts of a protein called VEGFR-3.

This protein can halt angiogenesis, or the growth of blood vessels. Without these large amounts of VEGFR-3, our vision would be significantly impaired. For instance, when the cornea is clouded by injury, infection or abnormal blood vessel growth, your vision can be severely impacted, and blindness can occur. This discovery is promising for researchers looking to prevent and cure blinding eye diseases and illnesses, such as cancer, because the introduction of the protein can be used therapeutically in other tissues.

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Fact No. 5: Bacteria in your gut can influence your mood.

We already mentioned your gut can do some pretty amazing things, but did you know it can also impact your mental health? You have an immense number of bacteria in your gut that are collectively referred to as your microbiome. This collection of bacteria can impact neural development, brain chemistry, emotional behaviors, pain perception and stress.

Your gut is sterile when you’re born. Over time, your GI tract will develop a diverse colony of bacterial species, which can be influenced by your genetics and the bacteria in the environment you live in. Your microbiome produces hundreds of neurochemicals that your brain uses to regulate learning, memory and even your mood! In fact, your microbiome produces approximately 95 percent of your body’s serotonin, the critical hormone that stabilizes your mood, feelings of well-being and happiness. Serotonin also helps reduce depression, regulate anxiety, maintain bone health and facilitate processes such as sleeping, eating and digestion. And it’s all possible thanks to your gut!

Fact No. 6: Your heart rate and breathing can sync up to the music you’re listening to.

That’s right! The music you listen to can cause physiological changes in your blood pressure, heart rate and respiration. Studies have found that changes in the cardiovascular and respiratory systems that occur when listening to music directly mirror the tempo and intensity of what you’re listening to. For example, songs with crescendos (increases in volume and intensity) can lead to proportional increases in blood pressure, heart rate and breathing. In contrast, decrescendos and silent periods lead to decreases in these vitals. Researchers have also found repeated rhythms in music can cause your cardiovascular system to synchronize with the beat. These findings may lead to new therapies for stroke and other conditions.

These aren’t the only impacts music can have on your cardiovascular system, either. Listening to music, playing an instrument or singing have been found to enable people to exercise longer, help heart rate and blood pressure levels to return to baseline more quickly after physical exertion, improve blood vessel function by relaxing arteries, ease anxiety in heart attack survivors and help people recovering from heart surgery feel less pain and anxiety. These benefits are heightened when you’re familiar with the music you’re hearing, rather than listening to songs you don’t know.

Fact No. 7: Your brain shrinks during pregnancy.

This fact gives an entirely new meaning to the term «pregnancy brain.» A 2017 study published in the journal Nature Neuroscience revealed pregnant women experience reductions in cortical thickness and surface area in sections of the brain called grey matter. This loss of grey matter primarily occurs in the cerebral cortex, specifically in regions that influence social cognition, where we process people’s feelings and nonverbal signals. Rather than having a negative effect, this loss of volume improves the brain’s ability to process social situations more efficiently, especially when interpreting babies’ needs and emotions.

The study found the brain goes through these changes, which are thought to be evolutionary, during pregnancy to enhance emotion and facial recognition, promote mother-infant bonding, facilitate a mother’s ability to recognize the needs of her child and more quickly process social stimuli that may pose a potential threat to her child.

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These grey matter reductions were seen to have endured for at least two years post-pregnancy, offering the first evidence that pregnancy leaves long-lasting changes in a women’s brain.

Hair loss and cancer

Some cancer treatments can cause hair loss. Your doctor will be able to talk to you about your situation. Some people find the condition and growth of their hair changes. Others find their hair falls out completely.

Different treatments will affect your hair differently.


Chemotherapy can cause your hair to fall out, but not all chemotherapy drugs make your hair fall out. It will usually happen within 2 to 3 weeks of starting treatment. Some chemotherapy drugs can make other hair from your body fall out, such as facial hair and pubic hair. Hair usually grows back after treatment finishes.


Radiotherapy can cause your hair to fall out, but only in the area being treated. If you are having radiotherapy to your head, you’ll probably lose hair from your scalp. Hair does not always grow back after radiotherapy. Your doctor will talk to you about this.

Other treatments

Other cancer treatments, such as hormonal therapy or targeted (biological) therapy, can cause changes to your hair.

It can help to know more about how treatment could affect your hair. Your doctor or nurse will be able to answer any questions.

Preventing hair loss

Scalp cooling can reduce hair loss caused by chemotherapy. It works by reducing the amount of chemotherapy drugs reaching the hair follicles. Scalp cooling doesn’t work with all chemotherapy drugs and it’s not always possible to know how effective the treatment will be.

You will need to keep your head cold before, during and after treatment. There are 2 methods of scalp cooling:

  • cold cap – a special cap filled with cold gel
  • refrigerated cooling system – this pumps liquid coolant through a cap

You might feel cold during your treatment, but the chemotherapy staff will try to make you as comfortable as possible. Your hospital may not have the facilities for scalp cooling. Your doctor or nurse can tell you if it’s available and whether it’s suitable for you.

If you don’t lose all your hair, but it thins or becomes dry or brittle, it’s important to treat your hair carefully. This can help to reduce hair loss.

Tips to help you care for your hair and skin during and after treatment

It’s important to look after your hair and skin during and after cancer treatment.

To look after your hair:

  • wash it at least once every 2 days
  • use gentle hair products
  • check with your radiotherapy team if you can use products on the affected area
  • only use conditioner on the middle and ends of long hair
  • blot wet hair with a towel and use a wide-toothed comb
  • wear a soft cap or turban at night
  • eat a balanced diet
  • avoid using hairdryers, straighteners or hot rollers
  • avoid colouring, perming or relaxing
  • try not to tie your hair in a tight band
  • if you lose your hair, it’s important to look after the skin on your head and in other places where you had hair
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To look after your skin:

  • shampoo your scalp every day
  • use an unperfumed moisturiser
  • use pillows made from natural fibres
  • protect your head from the sun and from the cold

Avoid using deodorants, soaps, perfumes and lotions if you’re having radiotherapy. Check which products you can use with your radiotherapy team.

Tips to help you prepare for losing your hair

If it’s likely you will lose your hair during cancer treatment, there are ways you can prepare:

  • eat a well-balanced diet before treatment starts to help your body cope better
  • talk to friends and family about losing your hair
  • buy a hat or other headwear to protect your head
  • talk to other people who have hair loss to share tips on how to cope
  • if you decide to wear a wig, buy one before treatment starts – it’ll be easier to match it to your colour and style, and you can get used to wearing it
  • buy products to help you cope with losing your eyebrows and eyelashes

You could also consider cutting your hair short:

  • you may find it easier to cut it in stages
  • don’t use a blade to shave your head
  • it’s best to cut clean dry hair
  • you could ask a salon that specialises in styling people affected by cancer to cut your hair

What are my options?

There are many ways to cover up hair loss. Hats, scarves and turbans are popular options for men and women.

  • hats – there are many styles to choose from
  • scarves – versatile with many colour and fabric options, lightweight materials such as cotton are best
  • turbans – easy to wear and widely available
  • wigs – you can continue with a familiar style or try something new

Some hats, headbands or bandanas have optional fringe or hair attachments. If you still have some hair, changing your hairstyle can help cover up hair loss. Specialist hairdressers like mynewhair can offer advice.

In certain situations surgery to replace hair (hair transplant) might be an option if your hair loss is permanent. This treatment is not available through the NHS.

You may not want to wear anything on your head. Accessories, clothing and makeup can express your style and draw attention away from hair loss.

After treatment

As your hair grows back after treatment, you may find that it has changed.

Hair usually grows back after chemotherapy. It may be curlier, finer or a different colour. You might find that it grows unevenly or in patches. These changes are rarely permanent.

Hair re-growth after radiotherapy depends on the type and number of treatments you had, and the area of the body that was affected. If your hair grows back, it usually starts 3 to 6 months after treatment. It may be patchy, thinner or a different colour.

Sometimes hair loss can be permanent. If you have hair loss on your head, you may want to wear a wig, hairpiece or another type of headwear.

As your hair grows back:

  • use shampoos and products if they do not irritate your scalp
  • when your hair is long enough to style, you may decide not to cover your head
  • choose a hairdresser who understands your situation – if your hair is finer, you could ask them about using hair extensions
  • you may be able to colour or perm your hair – seek professional advice before doing this
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Axolotl and 4 other creatures that can grow back body parts

Published on

By the CBC Kids team September 04, 2021 | Last Updated April 05, 2022

an axolotl in the water

An axolotl.

Did you know that there are some living things that regenerate parts of their body? Humans can’t, but some creatures can re-grow their limbs or tails or even their brains!

Sometimes, animals even cast off a part of their body on purpose. They might feel threatened, and they can re-grow it later — this is called autotomy.

Check out some of the animals that have this awesome ability!


the strange looking white axolotl on the sandy bottom of the water


The axolotl (say «ax-oh-lot-el») is a Mexican species of salamander. It’s also known as a Mexican walking fish.

It can regenerate, repair or replace its arms, legs, tail, lower jaw, brain and heart. What an awesome ability!

Scientists are very interested in studying how the axolotl is able to do this. Maybe one day they can use what they’ve learned to help people!

If you play video games, you might recognize the axolotl from Minecraft.

Sea stars

orange starfish in a water pond


Sea stars, or starfish, live on the bottom of the sea floor all over the world’s oceans. They are able to grow back all of their limbs if they lose any from an attack.

They can also drop or release an arm when predators grab them. Sea stars usually have five arms but some species can have up to fifty arms!


close-up of deer head with a full rack of antlers


Almost all species of male deer grow antlers. They start growing them from the time they are one year old.

They start as small spikes that they shed like baby teeth. Then they grow a larger, more branch-like rack of antlers by the time they are three years old.

Deer will continue to grow, lose and regrow larger antlers throughout their lives!


an orange bearded lizard looking right at the camera

The bearded dragon can lose its tail when it feels threatened and then grow it back. (Pixabay)

Many species of lizard can release or drop their tails when danger is near. Lizards like the green iguana and bearded dragon can do this.

When they drop their tail, it continues to wiggle and squirm. This confuses the predator while the lizard gets away!

Some lizards will even return later when it’s safe to eat their tails. For some lizards it can take a couple months for the tail to grow back.


close-up of a jumping spider


Spiders don’t have a skeleton like humans do. Their skeleton is on the outside. It’s called an exoskeleton.

Exoskeletons don’t grow. So a spider will create a newer, bigger exoskeleton as it grows. They shed the old one in a process called molting. They have to do this a lot of times until they’re fully grown.

It’s during this molting that they can regrow a missing leg! The new leg will usually be a bit smaller than the other seven.

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