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Hair Anatomy

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Jasmine Letson

on 21 June 2011

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Transcript of Hair Anatomy

Anatomy of Hair
By: Jasmine Letson What is hair?
Fine threadlike strands growing from the skin of mammals and other animals. You have more than 1100,000 hairs on your head about 50 to 100 hairs fall out each day What is hair made out of?
Hair is basically a form of skin. It is made up of a protein called keratin and grows everywhere on the body with the exception of the lips, eyelids, palms of the hands and soles of the feet. Each shaft of hair is made of two or threelayers of keratin that grow from a follicle underneath the skin. What is the structure of the hair strand?
Each strand of hair consists of three layers.

-The first layer is called the medulla

-The middle layer called the cortex.

-The outer layer is called the cuticle. The Medulla
The medulla is made of large, loosely connected keratinized cells. The medulla is also called the pith or marrow of the hair. Thick hair usually has a medulla. Fine hair most of the time doesn’t have a medulla and also naturally blonde hair. The purpose of the medulla hasn't been found. The Cortex
The cortex of the hair is made of cells that are bonded tightly together. The cortex contains the pigment for hair color and also responsible for giving the hair its strength. It is about 90% of the total weight of the hair. This is the part of hair that changes when you color, permanently waving, or relax the hair. The Cuticle
The cuticle of the hair is the outermost layer. It is made of a clear single layer of cells that overlap. The reason for the overlapping is to protect the cortex. The cuticle protects the cortex and the medulla. Things you use for your hair that has a high pH causes the cuticle layer to allow liquids to go into the cortex. Things you use for your hair that has a low pH will cause the cuticle to shrink and get harder. What is a dermal papilla?
The dermal papilla is at at the bottom of the hair follicle. Its connected to the bloodstream so that it can nourish the follicle to make new hair. The dermal papilla important to hair growth because it contains androgens. Androgens regulate hair growth. What does hair do for the body?
Each place where there is hair on your body the hair has a different job. The hair on your head keeps your head warm, it also helps us keep our head cool and protect us from UV rays. Eyelashes protect your eyes by keeping dust away, and eyebrows protect your eyes from sweat dripping down from your forehead. What is keratin?
Keratin is a strong protein that’s a major part of hair but also skin, nails and teeth. The amino acids that come together to make keratin. There are"soft" keratins and are "hard" keratins. Soft keratins are in the skin and hard keratins and hair is mostly made from hard keratin proteins. What is the follicular life cycle? (The Growth Cycle)
Hair follicles grow in cycles. And the cycle is broken into three phases:
Anagen - Growth Phase
Catagen - Transitional phase
Telogen - Resting Phase
Each hair goes through the cycle at different times then each other. Anagen - Growth Phase
Anagen is the phase in which the hair…grows. Only about 85% of all hairs are in the growing phase at one time. The Anagen phase can go on from 2 to 6 years. Hair grows about 10cm per year and any single hair is unlikely to grow more than one meter long. Catagen - Transitional phase
At the end of the Anagen phase the hairs enters into a Catagen phase which lasts about 1 or 2 weeks, during the Catagen phase the hair follicle shrinks and separate from the blood supply at the skin level and the hair will stop actively growing. The follicle will be destroyed and the hair is pushed up but doesn’t yet fall out. Telogen - Resting Phase
The resting phase follows the catagen phase and normally lasts about 5-6 weeks. When this phases is happening the hair doesn’t grow but it does stay connected to the follicle while the dermal papilla stays in a resting phase below.

At the end of the Telogen phase the hair follicle goes back into the Anagen phase. The dermal papilla and the follicle come together again and a new hair starts to grow in place. If the old hair has not already been shed yet the new hair pushes the old one out. Why does hair stick up when it’s cold?
The reason your hair sticks up when cold or you get ”Goosebumps” is because when its cold muscles attached to your hair tightens to attempt to keep you warm and when they tighten they pull your hair causing them to stand up. When people become elders why does hair become gray/white?
Each of the hair follicles contains a certain number of pigment cells. These pigment cells make a chemical called melanin which is responsible for your hair color. If your hair is dark or light is determined on how much melanin the hair has. As people age the pigment cells die and when there isn’t many pigment cells the hair starts to become a transparent color. The time when your hair starts to get gray is determined by your genes. From the time that a person sees the first gray hair to the time where the whole entire head is gray can take up to 10 years. Brown and Black Hair
Brown Hair: It is characterized by high levels of eumelanin and low levels of pheomelanin. Brown-haired people have brown eumelanin. They also usually have medium-thick strands of hair.

Black Hair: It has large amounts of eumelanin and is not as dense as other hair colors. Blond and Red Hair
Blond Hair: Blond hair has small amounts of pheomelanin and eumelanin. The more of pheomelanin makes a more golden blond color, and more eumelanin creates an ash blond.

Red hair: It is caused by a variation in the Mc1r gene and recessive. Red hair has the highest amounts of pheomelanin and low levels of eumelanin. It’s the rarest natural human hair color. What makes hair curly or straight?
If your hair is straight or curly depends on the shape of the hair follicle. Straight hair lies flat because it's round and grows out of round follicles. Curly hair bends because its cross-section is an oval. It comes out of oval follicles. Hair is made of protein that contains sulfur atoms. Sulfur atoms that together are called disulfide bonds. When two sulfur atoms bond that aren’t close together in the same protein, then they create a bend in the hair. The curliness is determined by how many disulfide bonds are between the hair proteins. Curly hair has a lot of disulfide bonds and straight hair has fewer disulfide bond. The End
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