Anatomy of Hair

More Fun Hair Facts • All 5 million hair follicles are formed by

week 22 during fetal development. • 100,000 follicles on the scalp. • You have the most follicles when you are

born – as body size decreases with age so does the number of hair follicles – NEVER get any new ones

• Hair is found on all visible body surfaces. • Hair is the only structure that is

completely renewable without scarring • Hair goes about 0.5 inch per month (~ 6

inches per year)

Hair, muscles, and

fingernails are made of

Protein

bundles of helical keratin As hair grows, new helical Keratin is added quickly

Hair is made of tight, closely packed dead cells that are made up of myofibrils or

Hair is extremely STRONG

Try to break a piece apart…

There are 3 layers of skin – the Epidermis,

the Dermis, and the Hypodermis.

Outer layer of skin

Made up of 5 dead layers of keratin packed cells

Epidermis

The hair

follicle sits

in the

dermal

layer

DERMIS

• Directly beneath the epidermis. Packed with

nerve endings and blood vessels

Hair has 3 parts • The bulb

• where hair growth occurs

• The follicle • the part of the

hair underneath the skin

• The shaft • the part of the

hair above the skin

The hair follicle and bulb are located in the dermal layer

Each strand of hair is equipped with an oil gland.

The oil excreted is called “sebum”. The oil is

pushed up the

follicle as the

hair grows.

This keeps

germs from

entering the

body and also

lubricates the

skin.

Pretty nifty!

Each follicle also has a muscle attached to it.

This is how we get “goose bumps”.

The bulb is also called the root of the hair. The follicle is below the skin, and the shaft is above the skin. The sebaceous gland

excretes the oil, called sebum, that forces germs and bacteria up and away from the skin. Sebum also lubricates the skin

Hair growth occurs in the root of the hair only. Blood supply nourishes the root and allows for new cell growth.

Each Follicle contains a

muscle and a sweat gland

Arrector Pili – the

muscle that lifts your hair

on end when you’re cold

or scared

Hair keeps a

record of all

the chemicals

that are in

your blood

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwit5uvvt5zSAhWo7YMKHeucDGcQjRwIBw&url=http://www.madsci.org/posts/archives/2004-01/1073579182.Me.r.html&psig=AFQjCNGF60RauYM-zZlTtRXp-MNnES-Bww&ust=1487602826547506

Image of a

Hair Follicle

Human scalp hair grows about 15 mm, or 1/2 inch per month during its growth phase (anagen) which lasts approximately 1,000 days. After growing, scalp hair remains intact but dormant (catagen) for about 100 more days before falling out (telogen).

Fun Facts - How does hair “know” how long to grow?

• Eyebrow and Eyelash hair – Very slow growing, short life cycle

– 0.16 mm per day, Anagen for about 7 months

• Scalp Hair – Fast growing, long life cycle

– 0.35 mm per day, Anagen for about 2-10 years

• Pubic Hair – Fast growing, short life cycle

– 0.35 mm per day, Anagen for about 4-5 months

• Beard Hair – Fast growing, longer life cycle

– 0.38 mm per day, Anagen for about 11-12 months

• Body Hair – Slower growing, shorter life cycle

– 0.25 mm per day, Anagen for about 6-7 months

Once the hair falls out, growth

starts again in the same follicle

Hair roots

Hair Color Human hair has round pigment granules in

the body of the hair, not on the outside.

Blond Hair

under the

microscope

Black hair

under the

microscope

Hair shape (round or oval) and texture (curly or straight) is influenced heavily by

genes. The physical appearance of hair can be affected by nutritional status and

intentional alteration (heat curling, perms, straightening, etc.).

Sources: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair & http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric1.htm#Index%20(Hairs)

Hair is composed of the protein keratin, which is also the primary component of

finger and toe nails.

Hair is produced from a structure called the hair follicle. Humans develop hair follicles

during fetal development, and no new follicles are produced after birth.

Hair color is mostly the result of pigments, which are chemical compounds that reflect

certain wavelengths of visible light.

The body area (head, arm, leg, back, etc.) from which a hair originated can be

determined by the sample’s length, shape, size, color, and other physical

characteristics.

Summary

In order to test hair evidence for nuclear DNA, the root must be present. The hair may

also be tested using mitochondrial DNA whether or not the root is present.