[bezoar]

The dermatologists would be proud of you, Militis.

Bezoar

[CookieMan]

That was a great article. Thanks for the read!

Kevin
newbielink:http://www.squidoo.com/easyhumananatomy [nonactive]

[crazzycat]

a lot of what i read i didn't know...thank you   

[Mr. Scientist]

Hello again all,

Well I wanted to answer Jojo's question, but I found a web site that answered it much better than I could've. So the following will be an article from BBCi.
URL- http://www.bbc.co.uk/science/humanbody/body/factfiles/skin/skin.shtml

So here goes, and I quote:

*****************

Largest organ

Your skin is your largest organ. It covers your entire body and has a surface area of around 2 square metres. Its thickness varies from 0.5mm on your eyelids to 4mm or more on the palms of your hands and the soles of your feet. In total, it accounts for around 16 percent of your body weight.

Tough physical barrier

Your skin consists of two main layers: the outer epidermis and the inner dermis.

Cells in the deepest layer of your epidermis divide constantly to make new cells. The new cells are pushed towards the surface of your skin. They eventually die and become filled with keratin, an exceptionally tough protein. Keratin provides your body with a durable overcoat, which protects deeper cells from damage, infection and drying out.

Cells on the surface of your skin rub and flake off steadily and are continuously replaced with new ones. About every 30 days, your body produces a totally new epidermis.

Your inner dermis consists of strong collagen and elastic fibres pierced by blood vessels. It also contains touch, pressure and pain sensors and is packed with hair follicles, sweat and oil glands. The oil glands produce a lubricant that keeps your skin soft and prevents your hair from becoming brittle.

Temperature control

Your skin's blood vessels, sweat glands and hairs play a crucial role in regulating your body temperature. When you need to cool down

Your blood vessels widen and allow heat to escape through your skin
You start sweating, and as your sweat dries, it uses heat from your skin and cools you down
Your hairs lie flat to make sure little warm air doesn't get trapped between your skin and your hairs
When you need to retain heat, the opposite happens – your blood vessels narrow, you produce less sweat and your hairs stand up on end to trap warm air around your body.

Skin colour

Your skin contains specialised cells called melanocytes. They produce melanin, a brown substance, which absorbs some of the Sun's harmful ultraviolet rays. Fair-skinned people only have melanin in the lower layers of their epidermis. People with dark skin have larger amounts of melanin in all layers. Freckles and moles are nothing else but small patches of skin with more melanin than in the surrounding area.

Wrinkles

As you age, the number of collagen and elastic fibres in your dermis decreases. Additionally, you lose fat from the tissue under your skin. As a result, your skin becomes less elastic and begins to sag and wrinkle.

*************

Much more information than necessary, but it's well put.





"I want to know God's thoughts; the rest are details" - Einstein

I take the decrease in collagen and elastic fibres are caused by deteriate free-radicals though?

[stereologist]

The dimensions listed here such as the length of blood vessels and the surface area of our lungs was determined by the science called stereology. The area of the lungs may be a bit off. I'm not sure. That work was done years ago by Ewald Weibel. He worked in conjunction with other scientists using a classical form of stereology.

More recent methods may shed more light on the issue. Also remember that there is a huge difference between individuals. Oneof the more amazing ranges of biological diversity can be seen in the human kidney. At the U of Melbourne in glorious Australia works has shown that some people have as few as 150,000 glomeruli. These are the parts of the kidney that extract waste products from the blood. Other people have 1.25 million. That's a 9X range in humans.

So the next time you read about an interesting fact about the numbers of things in a plant or animal you might want to ask what astounding range is also involved.

[Nizzle]

4. It's NO that enables the male genital to go uppy (by mechanism described in 3.)

[Nizzle]

More than 10% of all our sensory nerves are either in our lips or in our fingertips

[stereologist]

These numbers are really interesting because they are so large. A good question might be how does anyone know that these numbers are correct or even close to their actual values? Do these numbers have any relevance other than to post a value?

How many is one of the basic questions that can be asked. Length is another. Surface area has been posted. What we have not seen here is estimates of volume. Volumes are usually not posted because the numbers are not big. Surface areas can be enormous.

The length of the DNA for instance is an interesting number. It tells us something about the enormous complexity contained in the twisted up chromosomes in our cells.  Not only is there a lot of length, but all of this length is replicated when cells undergo cell division, either mitosis or meiosis. The lung surface area mentioned earlier can decrease over time. Exposure to smoke and other materials can cause the alveolar walls to break down. The walls are quite thin. Loss of a wall removes surface area on each side of the wall. So is a 10 micron by 10 micron piece is lost, then 200 microns squared is lost, not 100 squared microns. Someone suffering from emphysema has a substantially smaller surface area in their lungs than the average human value that was posted here.

[stereologist]

With such a large surface area that has intricate passageways it should be clear to all readers that the values are not measured. Instead the values are estimated. The goal of any estimation technique is to get an unbiased result. This simply means that the average of all samplings should be the same as the right answer. This might seem like an obvious statement, but today most cell number estimates are performed using biased methods. The average of all samplings in a biased study is the wrong answer.

The reason this is done is due to a number of factors including a lack of understanding that the results are biased. Counting is done so often that we forget the difficulties inherent in counting. There is also a belief that counting using a bad method does not matter since the study is only comparing and the bad that is introduced cancels out. When this notion has been tested it has been shown that the 'cancel out' claim fails.

There are machines that can count cells. These machines require that the cells be separated into individual cells and then the cells pass through a very thin pipe where they can be counted. This works for cell cultures, but not for tissues.

[darkuma]

Is it the lifetime of the person or of the red blood cell which is only 120 days?

[Nizzle]

red blood cell of course []

How many days are you alive already darkuma?