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Questions tagged [skin]

The skin, part of the integumentary system.

32
votes
2answers
9k views

Why do tattoos persist if body cells are regularly renewed?

I am not quite sure if it is true, but I read somewhere that within 7 years all the body's cells are replaced with new ones. I am not quite sure if it is cells or atoms. If it is then why do tattoos ...
9
votes
1answer
2k views

How can haired mammals synthesize vitamin D?

The human body can synthesize vitamin D in the skin from cholesterol, when sun exposure is adequate. But how can haired mammals do it? Do not they need it?
13
votes
3answers
3k views

Do humans perceive temperature or heat-flux? (or both?)

The general understanding is that when I touch an object, I perceive its (relative) temperature. A metal object at room temperature, however, will often feel cool to the touch. This leads me to ...
4
votes
1answer
1k views

Why are Merkel cells innervated by an axon, and not a dendrite?

Here are two images from Google. Afferent neurons receive input and send it to the central nervous system. Input is received by the neuron's dendritic end and send away centrally via axon terminals ...
12
votes
1answer
1k views

If cells regularly renew, why do we have scars?

Question may sound bit poetic but I have a pretty basic question here: Often we get a minor wound and cells renew and quickly "cover" it. But when we have deeper wounds, often they leave behind scars. ...
8
votes
1answer
820 views

How does skin healing work?

I stacked my bike and split my head right open. About three weeks later the scab falls off and the skin is sealed over, like magic! How does it all work? How does the brain know that part of the ...
7
votes
2answers
12k views

Why doesn't the human skin grow back exactly how it was before being damaged?

Very simple: Why (and how) is regenerated skin different from original ? As we know we lose skin cells that becomes the dust in out homes and it always grows back to full thickness right ? So when I ...
3
votes
1answer
109 views

How can an infection of lower respiratory tract lead to a skin infection? [closed]

I am interested in the multifactorial process about infectious diseases of the lower respiratory system and their progression to a skin infection. Possible agens are zwitterions, viruses, fungi, ...
4
votes
1answer
1k views

Skin color explanation?

I do not understand how skin color in humans work, even after taking a basic genetics course and reading some on wikipedia. From what I understand, skin is color based on multiple genes that control ...
3
votes
1answer
664 views

Why did evolution make people's skin dark?

Why do people living in the equator have dark skin? I know that Melanin acts as a protective biological shield against ultraviolet radiation. But doesn't black absorb all light in a way making the ...
3
votes
1answer
862 views

Why are skin tactile receptors considered to be phasic receptors?

A phasic receptor by definition is one that quickly adapts to change. In terms of neuron firing, this means that it does not trigger another firing because the receptors are used to the stimulus. But ...