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Hair
• Hair is found in association with thin skin except for the
lips, nipples, and portions of the external reproductive
organs.
• There are three general types of hair:
Lanugo – covers the fetus by the 5th or 6th month of
development. It is delicate and unpigmented.
Vellus – replaces most of lanugo hair. Short fine and
unpigmented.
Terminal – long course and pigmented (scalp,
eyebrows, eyelashes immediately following birth)
• Terminal hair at puberty – for males: arms, chest, legs,
and pubic region (90%); for females: (35%).
Hair Structure
• Two main parts: Shaft and Root
• The base of the root expands to form the
hair bulb.
• The entire hair is composed of columns of
dead keratinized cells arranged in three
concentric layers: the medulla (center), the
cortex, and the cuticle.
Hair
Hair Color
• As with skin, varying amounts of melanin
cause different shades of hair. The
exception is red hair which is caused from
a blend of melanin containing iron.
• With age, melanin in hair fades or
decreases resulting in gray or white hair.
Hair Growth
• Hair is produced in cycles: growth and resting
stages. http://dermatology.about.com/cs/hairanatomy/a/hairbiology_2.htm
• During growth, hair is formed by cells in the
matrix of the hair follicle. Hair grows longer as
cells are added to the base of the root.
• During the resting phase the hair growth stops
and the follicle shortens holding the hair in
place. After resting the hair is released from the
follicle and replaced.
• Different hair has different lengths of each
period. So what happens with alopecia?
Hair Muscles
• Associated with each hair follicle is a smooth
muscle called the arrector pili muscle.
• It extends from the dermal root sheath to the
papillary layer of the dermis.
• At an oblique angle to the surface of the skin.
• Cause of goose bumps, the wrinkled
appearance of the scrotum, and nipples (within
dermis).
Nails
• Functions: protects the ends of the digits,
aids in manipulation and grasping of small
objects, and are used for scratching.
• Consists of proximal nail root and distal
nail body.
Nail Structure
• Root is covered by skin. Lateral and proximal edges
also covered in skin = nail fold. Edges held in place by
nail groove.
• The stratum corneum of the nail fold grow onto the nail
body as the eponychium (what is the common name?).
• Under the free edge of the nail is the hyponychium which
is a thickened region of the stratum corneum.
• The nail root and body are attached to the nail bed, the
proximal portion of which is the matrix.
• The nail matrix produces the nail. The lunula is seen
through the nail body as a white cresent. The matrix is
thicker here.
Glands
• Sweat glands (merocrine): coiled tubular glands
located in the dermis. Pore formed at surface
where duct opens. Aids in temperature
regulation.
• Sweat glands (apocrine): open into hair follicles
found in the axillae and genitalia. Become
active at puberty and are influenced by sex
hormones. Secretion is organic (contain cellular
components) and is metabolized by bacteria
quickly resulting in an odor (BO).
More Glands
• Sebaceous (Holocrine): Located in the
dermis and are simple or compound
alveolar (sac-like structures). Secrete
sebum, an oily white substance rich in
lipids. Prevent drying of hair and skin and
also protection against some forms of
bacteria.