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Author Topic: Amazing Human Anatomy Facts  (Read 28333 times)

Offline Nizzle

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« Reply #25 on: 19/10/2009 10:42:51 »
4. It's NO that enables the male genital to go uppy (by mechanism described in 3.)
 

Offline Nizzle

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« Reply #26 on: 19/10/2009 10:43:58 »
More than 10% of all our sensory nerves are either in our lips or in our fingertips
 

Offline stereologist

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« Reply #27 on: 19/10/2009 13:35:59 »
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.
 

Offline stereologist

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« Reply #28 on: 19/10/2009 13:42:58 »
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.
 

Offline darkuma

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« Reply #29 on: 14/12/2009 18:33:14 »
Is it the lifetime of the person or of the red blood cell which is only 120 days?
 

Offline Nizzle

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« Reply #30 on: 15/12/2009 06:15:41 »
red blood cell of course :)

How many days are you alive already darkuma?
 

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« Reply #30 on: 15/12/2009 06:15:41 »

 

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