The document discusses the accessory organs of the skin, including hair, nails, and glands. It describes the structure of hair follicles and how they produce hair. It notes the different types of glands in skin like sebaceous glands, which produce oil, and sweat glands, which are either eccrine or apocrine. Eccrine glands produce sweat across most of the body, while apocrine glands are in armpits and genital regions. The skin provides protection, regulates temperature, and acts as a sensory organ.

1. Accessory Organs of the Skin
PART-3

2. 1. Hair
2. Skin glands
3. Nails
Accessory Organs of the Skin

3. Accessory Structures of the Skin
Hair
A characteristic feature of the human skin is the
apparent lack of hair on most of the body
surface. This is actually not quite true. Most of
the skin is haired although the hair in most areas
is short, fine and only lightly pigmented.
Truly hairless are only the palms of hands and
soles of feet, the distal phalanges and sides of
fingers and toes and parts of the external
genitalia.

4. Hair (cont:)
In those parts of the skin which we perceive as "hairy" we find
terminal hairs. The free part of each hair is called the shaft.
The root of each hair is anchored in a tubular invagination of
the epidermis, the hair follicle, which extends down into the
dermis and, usually, a short distance into the hypodermis.
The hair that you groom daily is actually dead keratinized cells.
Each hair follicle has an associated bundle of smooth muscle,
the arrector pili muscle. This muscle inserts with one end to
the papillary layer of the dermis and with the other end to the
dermal sheath of the hair follicle. This makes your hair stand
up on its end.

5. Hair Color and Texture
Hair color is determined by the amount and type of
melanin present.
Melanocytes become less active with age. Gray
hair is a mixture of pigmented and non-pigmented
hairs.
Red hair results from a a modified type of melanin
that contains iron.
The shape of the hair shaft determines texture.
Round shaft – straight hair
Oval shaft – wavy hair
Flat shafts – curly or kinky hair
Perms use chemicals to flatten shafts and makes hair curly.
Alopecia is the term for hair loss.

6. Accessory Structures of the Skin
Nails
Plates of stratified squamous
epithelial cells with hard keratin
Protect distal ends of phalanges
Cells are keratinized in the nail root
Nail growth occurs in the lunula
Cuticle is a fold of stratum
corneum on the proximal end of
nail

7. Exocrine Glands
Sebaceous glands or oil glands are simple branched areolar glands. They
secrete the sebum (seb = oil) an oily product. Sebum is usually secreted into
a hair follicle. Sebum is a natural skin cream: it helps hair from becoming
brittle, prevents excessive evaporation of water from the skin, keeps the skin
soft and contains a bactericidal agent that inhibits the growth of certain
bacteria.
Sebaceous glands are scattered all over the surface of the skin except in the
palms, soles and the side of the feet.
Vernix caseosa - white covering on fetus. Blackhead
Pimple

8. Exocrine Glands
The exocrine gland are:
Sweat glands or sudoriferous glands are simple coiled
tubular glands. They are divided into two principal types:
eccrine and apocrine.

9. Exocrine Glands
Eccrine glands are the most common. Their secretory
portion can be located in the dermis or in the
hypodermis. They produce sweat, a watery mixture of
salts, antibodies and metabolic wastes. Sweat prevents
overheating of the body and thus helps regulate body
temperature.

10. Exocrine Glands
Apocrine glands are found mainly in the skin of the
armpits, of the anogenital areas and of the areola of the
breasts. Their secretory portion can be located in the
dermis or in the hypodermis. Their excretory ducts open
into hair follicles. Their secretion is more viscous than
that of the eccrine glands. They start secreting at puberty
and may be analogous to the sexual scent glands of
other animals.

11. Exocrine Glands
Ceruminous glands (or ear wax glands) and mammary
glands are modified apocrine sweat glands.

12. Physiology of the Skin
Protection - the epidermis provides a barrier to
fluid loss from the body (this protective function is
impaired in patients with burns).
barrier function - intact skin prevents the entry of
micro-organisms into the body. Antimicrobial
proteins are produced by the epidermis - they act
by piercing holes in the outer membranes of
micro-organisms.
Resistance to wear and tear - continuous
replacement of the outer epidermal cells that
wear off - new cells are produced in the deepest
layer of the epidermis and gradually migrate
towards the surface

13. Skin can excrete water, salt, and small amounts of
waste products such as urea.
Vitamin D can be synthesized in skin exposed to
sunlight (vitamin D can also be obtained from the
diet)
The skin provides a barrier to ultraviolet light. The
melanocytes contain melanin, which absorbs UV
radiation, and also distribute the pigment to
neighboring cells. Skin exposed to sunlight
becomes wrinkled and creased. Changes seem to
be due to disruption of collagen and elastin in
dermis, and loss of fibroblasts which make new
proteins.

14. The integumentary system is well-
supplied with receptors for touch,
pain, temperature, vibration and
pressure
Sensory information is relayed to
the central nervous system via
sensory nerves
Social interactions are influenced
by facial expressions, blushing,
touching, etc.

15. Fun Facts
House dust is mainly skin flakes!
If you laid out all your skin on a flat surface, it would have
an area of about 2 square meters.
Skin weighs about 2.5 kilograms - the largest organ in the
body.
What hurts if you pull it, but doesn't hurt if you cut it? Your
hair, of course!
Skin is elastic - it springs back into shape when stretched.
Some medicines (estrogen, nicotine) can pass through the
skin, but others cannot (insulin). Why is that? Because
only fat-soluble substances can enter the skin, not water-
soluble ones.
Your hair stands on end and you develop 'goose bumps'
because there are tiny muscles attached to the hair
follicles and they contract when you are frightened or cold.

16. THANKS