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
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.