The skin is the largest organ of the body and acts as a protective barrier. It has several layers, including the epidermis and dermis, and contains structures like hair follicles, sweat and sebaceous glands. The skin regulates body temperature, protects against pathogens, and plays a role in sensation and nonverbal communication. Its appendages include hair, nails, and glands that lubricate and protect the skin surface.

2. (skin & its appendages)
The skin covers the entire surface of the
human body. In an adult, the skin has a
surface area of about 1.8 square meters

3. Principal functions:
 Protection, water retention,
thermoregulation, vitamin D synthesis,
sensation, nonverbal communication and has
also limited excretory and absorbing powers.
 The skin (integument) is the largest organ of
the body, and together with its accessory
organs (hair, glands, and nails), it constitutes
the integumentary system

4. In certain areas of the body, it has adaptive
modifications that accommodate
protective or metabolic functions.
In its role as a dynamic interface between
the continually changing external
environment and the body’s internal
environment, the skin helps maintain
homeostasis.

5. Structure of the Skin
 consists of two regions:
the epidermis
the dermis.
 The hypodermis;
a subcutaneous tissue, is found between the skin
and any underlying structures, such as muscle.

6.  But where no muscles are present, the
hypodermis attaches directly to bone or
underlying deep fascia, e.g. there are flexion
creases where the skin attaches directly to the
joints

7.  The epidermis is the outer and thinner region of
the skin.
It is made up of stratified squamous epithelium
divided into several layers;
the deepest layer is the stratum basale,
the most superficial layer is the stratum corneum.
Epidermis

8. Dermis
 The dermis, is a deeper and thicker region
than the epidermis, is composed of dense
irregular connective tissue.
 The upper layer of the dermis has fingerlike
projections called dermal papillae.
 Dermal papillae project into and anchor the
epidermis.

9.  In the overlying epidermis,dermal papillae
cause ridges, resulting in spiral patterns
commonly known as “fingerprints’.
 The function of the epidermal ridges is to
Increase friction to provide a better ‘grip’.
 Because they are unique to each person,
fingerprint and footprints can be used for
identification purposes.

10.  The dermis contains :
collagenous and elastic fibers.
The collagenous fibers are flexible but offer
great resistance to overstretching;
So they prevent the skin from being torn.
elastic fibers stretch to allow movement
of underlying muscles and joints, but they
maintain normal skin tension.

11. The dermis also contains blood vessels that
nourish the skin.
Sometimes, blood flow to a particular area is
restricted in bedridden patients, and
consequently they develop decubitus ulcers
(bedsores).
There are also numerous sensory nerve fibers
in the dermis.

13. The Appendages of the Skin:
The appendages of the skin are:
the nails
the hairs
the sudoriferous (sweat glands) , and
sebaceous glands with their ducts.

14. Sweat Glands;
 A sweat gland is tubular. The tubule is coiled,
particularly at its origin within the dermis.
 These glands become active when a person is under
stress.
 Two types of sweat glands are present:
 Apocrine glands open into hair follicles in the anal
region, groin, and armpits. These glands begin to secrete
at puberty.

15. The anatomical position is described as follows:
 Eccrine glands open onto the surface of the skin.
 They become active when a person is hot, helping
 to lower body temperature as sweat evaporates.
 The sweat (perspiration) produced by these glands
is mostly water, but it also contains salts and some
urea. Therefore, sweat is a form of excretion.
Ears contain modified sweat glands, called Ceruminous
glands, which produce cerumen (earwax).

17. Sebaceous Glands
Most sebaceous glands are associated with a hair
follicle. These glands secrete an oily substance
called sebum that flows into the follicle and then
out onto the skin surface. This secretion lubricates
the hair and skin, and helps waterproof them.

18. Particularly on the face and back, the sebaceous
glands may fail to discharge sebum, and the
secretions collect, forming whiteheads or
blackheads.
If pus-inducing bacteria are also present, a boil
or pimple may result.
Acne vulgaris is the most common form of acne,
is an inflammation of the sebaceous glands
that most often occurs during adolescence.
Hormonal changes during puberty cause the
sebaceous glands to become more active at this
time.

19. Hair and Nails
Hair is found on all body parts except the
palms, soles, lips, nipples, and portions of the
external reproductive organs.
Most of this hair is fine and downy, but the
hair on the head includes stronger types as
well.

20. After puberty, when sex hormones are made in an
enough quantity, there is noticeable hair in the
axillary and pelvic regions of both sexes.
In the male, a beard develops, and other parts of
the body may also become quite hairy.
When women produce more male sex hormone
than usual, they can develop hirsutism.
In males, baldness occurs when the hair on the
head fails to regrow.
Alopecia, meaning hair loss, can have many causes.

21. Hairs project from complex structures called hair
follicles. These hair follicles are formed from
epidermal cells but are located in the dermis of
the skin.
Certain hair follicle cells continually divide,
producing new cells that form a hair.
At first, the cells are nourished by dermal blood
vessels, but as the hair grows up and out of the
follicle, they are pushed farther away from this
source of nutrients, become keratinized and die.

23. The portion of a hair
within the follicle is
called the root,
and the portion that
extends beyond the
skin is called the shaft.

24. Each hair has one or more
sebaceous, glands,
whose ducts empty sebum
into the follicle (oil).
A smooth muscle, the
arrector pili, attaches to
the follicle in such a way
that contraction of the
muscle causes the hair to
stand on end. If a person
has had a scare or is cold,
“goose bumps” develop due
to contraction of these
muscles (gooseflesh).

25. Nails
Nails grow from special epithelial cells
at the base of the nail in a region
called the nail root
(a portion where a nail is implanted to
the skin),
These cells become keratinized as they
grow out over the nail bed.
The visible portion of the
nail is called the nail body,
the distal extremity
the free edge.
The part beneath the body and
root of the nail is called the nail matrix
or .

26. NAMES
The cuticle is a fold of skin hiding
the nail root. Ordinarily, nails
grow only about 1 millimeter
per week (fingernails faster than
toenails).
The pink color of a nail is due to
the vascular dermal tissue
beneath it.
The lunula is the whitish color,
half-moon shaped base of the
nail results from the thicker
germinal layer in this area.

27. Lines of tension:
Lines of tension are
caused by the pull of
elastic and
collagenous fibers
within the dermis of
the skin.
Surgical incisions
made parallel to the
lines of tension heal
more rapidly and
create less scar
tissue than those
made across the lines
of tension.

28. THE END