Structure of Hair

Hair Structure

Hair is composed of three principal parts:

The structure of hair has been compared to that of a pencil with the

medulla being the lead, the cortex being the wood and the cuticle

being the paint on the outside.http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair

Cuticle – outer coating composed of overlapping scales

Cortex – protein-rich structure around

the medulla that contains pigment

Medulla – central core

(may be absent)

Structure of Hair

Hair under the microscope

• Basic components: keratin (a protein), melanin (a pigment),

and trace quantities of metallic elements (Cu, Fe, Mn,etc).

• Elements are deposited in hair during growth and absorbed

by the hair from external environment.

Characteristics of the cuticle may be important in distinguishing

between hairs of different species but are often not useful in

distinguishing between different people.

Info: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair Image: http://www.hairdressersus.com/micro/Image5b.jpg

Hair Structure

Cuticle

The cuticle varies in:

• Its scales,How many there are per centimeter,

How much they overlap,

Their overall shape, and

How much they protrude from the surface

• Its thickness, and

• Whether or not it contains pigment.

HAIR SHAFT

Cuticle – First Layer• The cuticle is a translucent outer

layer of the hair shaft consisting of scales that cover the shaft.

• The cuticle scales always point AWAY from the root end - toward the tip of the hair.

• The cuticle is a GOOD WAY to tell species apart

The Cuticle of Human Hair

is rough --- which is why we

use Conditioner

Cuticle under the microscope

Cuticle Scales: Coronal• Scales show crown- shaped pattern• Found in small rodents and bats• Coronal pattern is NEVER seen in human hair

FREE-TAILED

BAT HAIR

CUTICLE SCALES: SPINOUS

• Spinous - petal-like scales are triangular in shape and

protrude from the hair shaft.

• Spinous are found close to the body on mink, and on seals,

sea lions, fox and cats

• Never found in humans.

CUTICLE SCALES: IMBRICATE

• The imbricate (brick-

like) or flattened

scales. Consists of

tightly overlapping

scales with narrow

margins between the

scales.

• Usually only found in

human hair (and some

animal species).

Cortex

Hair Structure

CORTEX

• The area between

the cuticle and the

core of the hair.

• Contains all the

pigment granules,

ovoid bodies and

any moisture

PIGMENT GRANULES• Pigment granules are small, dark, and solid structures

that look like grains of sand

• They contain melanin

• In humans, pigment granules are found in the cortex closest to the cuticle

• Animal hairs have pigment granules only in the medulla.

Human Rat

Medulla

The medulla may vary in:

• Thickness

• Continuity - one continuous structure

or broken into pieces

• Opacity - how much light is able to

pass through it

• It may also be absent in some species.

http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair

Like the cuticle, the medulla can be important for

distinguishing between hairs of different species, but often

does not lend much important information to the

differentiation between hairs from different people.

Hair Structure

http://www.bfro.net/images/whatis/figures/Fig.%203%20with%20caption.jpg

Medulla – in the middle of the hair

• The medulla is a central core

of cells that may be present in

the hair.

• Human hair - the medulla

unorganized, random pattern

• Animal hair - structure is well

defined

• Some medullary patterns: CONTINUOUS

INTERRUPTED

FRAGMENTED

ABSENT

Medulla Patterns

Broken

Intermittent

Continuous

The Medulla of Human

Hair is very thin or is not

present

Continuous Medulla

• Medulla has solid

continuous medulla

through the entire

hair shaft.

• No breaks or gaps

Upper - human hair

Lower - lattice pattern

of a deer

Medulla - Interrupted• Pattern is repeated over and over in the hair shaft at

regular intervals.

• Common in rodent hair (rats, mice, guinea pigs,

ferrets, bats)

Guinea Pig Multiserial ladder (rabbit)

Mouse FE Ferret

FRAGMENTED• Bubbly or cellular medullary area

• Center of hair shaft appears hollow with bubble or cell-like

pattern but can have a few parts visible

• Most common in human hair but can be found in animals

Human

Cow

Absent Medulla• No discernable

medulla visible

• Can be found in

human hair and

animal hairHuman

Silver fox

Human

The structure of hair has been compared to that of a pencil with the medulla

being the lead, the cortex being the wood and the cuticle being the paint on

the outside.

Summary

• The cuticle is a transparent outer layer of the hair shaft. It is made of scales that overlap one another and protect the inner layers of the hair

• the cortex is the largest part of the hair shaft and contains most of the pigment granules (melanin) that give the hair its color.

• The center of the hair is called the medulla. It can be a hollow tube, or filled with cells

Make a foldableFirst page Second Page

End Result

Center of HairVery thick in animalsCan contain patterned cells or be hollow

Med

ula

Cu

ticle

-tr

an

sp

are

nt

Cort

ex

Contains pigments

Spongy layer

Determines shape of hair

Outer scaly layer

Used to determine species

Imbri-cate in humans