Anatomy of Hair - WordPress.com · The structure of hair has been compared to that of a pencil with...
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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
• 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
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
• 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
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