The skin, part of the integumentary system.

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28
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2answers
6k 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 ...
11
votes
3answers
1k 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 ...
7
votes
1answer
937 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?
6
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2answers
8k views

How hot can a beverage get without burning the tongue?

What is the maximum temperature that a beverage can be without burning the tongue? I suspect there's a maximum temperature that the surface tissue of a tongue can withstand without being damaged (...
7
votes
1answer
413 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 ...
5
votes
2answers
5k 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 ...
2
votes
1answer
58 views

How can a respiratory infection lead to a skin infection?

Example of a case: 5 children develop a bright red rash on the face and turns violet after a few days and then disappears. Then maculopapular rash appears on the trunk, buttocks and extremities. It ...
3
votes
1answer
194 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 ...
3
votes
1answer
337 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 ...