Science Friday: Body Renewal

"Everything old is new again."  You know that old saying? It's especially true of the human body. 

I'm a total geek about health and science - seriously.  And I have no idea where I got that or why.  But I read an article recently on New Scientist (subscriber only, see?  GEEK!) about how fast the cells in your body re-grow and replace themselves - and was totally amazed at how speedy it is.  In fact, in an average adult, the vast majority of their cells is only 7 to 10 years old - so you're not as old as you feel :)

And all this new cell info is incredibly hopeful too.  I mean dang, in  just a few days you can have a totally new intestinal lining.  And you can grow back almost your entire liver, though that's not an excuse to have that extra glass (or five) of wine later.

I did a little more researching and came up with a bit of a list for body parts and how quickly they turn over, just to share with y'all.

Hair

- The hair on your head could be anything up to 6 to 7 years old. 
- Each day your head hairs grow 0.5mm. 
- Body hair grows more slowly, about 0.27mm per day.
 - Your eyebrows renew themselves every 64 days.

Eyes

- The surface of the cornea is covered in a thin layer of cells that is continually

renewed. Complete turnover is every 7 to 10 days. 
- Cells in the retina do not regenerate, which is why vision problems arise with age. However, stem cell treatments are beginning to target degenerating retinas.
- Researchers have managed to regenerate rods, the photoreceptors that capture dim light. But only in a Petri dish, so far.

Skin

- The epidermis or surface of the skin is replaced every couple of weeks. 
- Skin cells regenerate four times faster after a gentle injury, like ripping the top layer with sticky tape.

Nerves

- Damaged nerve cells can regrow to some extent, as long as the nerve cell body is intact. 
- The rate of nerve regeneration after injury is thought to be around 2 to 3mm per day.

Fat

- The average age of a fat cell is 10 years. 
- Each year 10 per cent of your fat cells are replaced.

Liver

- Liver cells turn over every 300 to 500 days.
- The human liver has an amazing capacity to regenerate itself. Remove up to 70 per cent of the organ and it will grow back to its normal healthy size in as little as a couple of months.
- Surgeons have even removed as much as 90 percent of the liver, although recovery is incomplete.

Guts

- The epithelial cells or surface of the gut lining is replaced every 2 to 3 days, some say 5 days, the same as the stomach lining.
- Some cells last longer – those that release antimicrobial fluid last 6 to 8 weeks.
- The average age of the main part of the gut is 16 years.

Nails

- Your fingernails grow almost 3.5mm each month, although the little fingernail grows more slowly than the others.
- Toenails grow at a rate of 1.6mm each month and the big toenail grows fastest.

Heart

- The heart is one of the least regenerative organs of the human body. 
- A 25 year old turns over just 1 per cent of their heart cells ever year, and this figure decreases with age. 
- In the course of a normal lifespan, less than half of your heart cells are replaced.

Mouth

- Your taste buds are replaced every 10 days.

Hands

- Our fingertips can grow back after injury – at least partly. 
- The best results are seen in children, who can regenerate a new fingertip within a few months. But it works for adults too. 
- For this to happen, you need an intact nail bed. The new fingertip has sensation and a fingerprint too.

Lungs

- The lining of the bronchial tubes is replaced every 2-10 days.
- Microscopic air sacs called alveoli last 4 to 5 weeks.

Blood

- Oxygen-carrying red blood cells are replaced every 4 months or 120 days.
- The most common type of white blood cell, neutrophils, only last for a few hours. 
- Another important type called lymphocytes are replaced at a rate of 10,000 cells every second.

Muscle

- The average age of a muscle cell is 15 years, though obviously you build more muscle with exercise.

Bones

- All your bones, the whole skeleton is completely replaced every 10 years.

Brain

The brain is the only part of the body that does not generate new neurons after its structure is complete - except in two specific regions: the olfactory bulb (your sense of smell) and the hippocampus, where initial memories of faces and places are stored.  So your cerebral cortex is the same age as you - we don't get new brains as we age.  Boo.

All really cool stuff, eh?  I'm hoping it inspires me to eat healthier and grow healthier new cells every second that I'm breathing.