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john !!
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Report Thread starter 16 years ago
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I've never known this, but how does your hair know when to grow back?

eg.

1. when you shave your eyebrows it takes a while but they will grow back. However if you don't shave them they wouldn't grow more.

2. when my cat had an operation they shaved the area around the operation, and that grew back, but her other hair didn't grow longer...

Is there something in the tip of the hair that gives information to the body to tell it not to grow back? I was thinking like a growing plant has those things the tip makes, so if sun only shines on one half (indicating the plant is growing sideways) then that half of the tip will release more things to stop the growth and that will cause the shoot to curve because the other side grows more.. if you know what I'm tlaking about?
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moojoo
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Report 16 years ago
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I presume there are some kind of mechanoreceptors in the hair follicles that sense when hair had been cut or fallen out. The pressure will feel different with no hair there and hence stimulates the growth of new hair some how, probably a nerve impulse that triggers a release of certain growth regulators.
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Golden Maverick
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(Original post by mik1w)
I've never known this, but how does your hair know when to grow back?

eg.

1. when you shave your eyebrows it takes a while but they will grow back. However if you don't shave them they wouldn't grow more.

2. when my cat had an operation they shaved the area around the operation, and that grew back, but her other hair didn't grow longer...

Is there something in the tip of the hair that gives information to the body to tell it not to grow back? I was thinking like a growing plant has those things the tip makes, so if sun only shines on one half (indicating the plant is growing sideways) then that half of the tip will release more things to stop the growth and that will cause the shoot to curve because the other side grows more.. if you know what I'm tlaking about?
Hair is growing continuously, regardless of where it is on your body. This is why during chemotherapy your hair falls out - chemotherapy stops cells from replicating, and as hair follicle cells replicate quickly they die during the treatment. The reason the other hair does not grow longer is either that the hair is wearing away as fast as it is growing, or because as it grows to a certain length it falls out, allowing a new hair to grow from the follicle.

Hair is dead so there is no communication from the hair to the body. I do know what you're talking about with the root/shoot tips. They either respond to gravity or light. The difference is that in that case the tip is alive and formed of many cells, whereas hair is dead.

Hope that answers your question.
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john !!
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Report Thread starter 16 years ago
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Yes that does!
It all makes sense now
Thanks a lot.
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