SKIN
is the surface covering for the body .
It may be considered as the largest organ of the
body
The functions of skin
The most important are protection.
Barrier against fluid loss, bacteria, viruses,
temperature
control
and
providing
an
acceptable personal appearance.
Sensation are received by the nerve endings.
Secretion is either sweat which helps in
regulation of body temper. Milk; from the
mammary glands.
The parts of skin
The superficial part, the epidermis
The deep part, the dermis
The superficial part, the epidermis
a stratified epithelium
On the palms of the hands and the soles of the feet, the
epidermis is extremely thick, to withstand the wear and tear
that occurs in these regions.
on the anterior surface of the arm and forearm, it is thin.
The deep part, the dermis
composed of dense connective tissue containing:
blood vessels
lymphatic vessels
nerves are including specialized nerve endings
concerned with:
touch
Pain
pressure
temperature
dermal papillae:
The junction between the dermis and epidermis is not flat,
being irregular, with the dermis forming numerous upward
projections into the epidermis
The variation in thickness of the dermis
Thinner on the anterior than the posterior
surface
Thinner in women than in men
In the dermis the bundles of collagen fibers are
mostly arranged in parallel rows known as the lines of
cleavage (Langer's lines). At these sites the skin is
thinner than elsewhere and is firmly tethered to
underlying structures by strong bands of fibrous
tissue.
SKIN APPENDAGES
Sweat glands
Sebaceous glands
Hair follicles
Nails.
The nails
keratinized plates on the dorsal surfaces of the tips of the
fingers and toes
The proximal edge of the plate is the root of the nail
The nail is surrounded and overlapped by folds of skin known
as nail folds
The surface of skin covered by the nail is the nail bed
Hairs
grow out of follicles, which are invaginations of the
epidermis into the dermis.
Hair bulbs: is expanded extremities of the follicles,
penetrate to the deeper part of the dermis.
Hair papilla: is vascular
connective tissue present
at the concavity of the
hair bulb.
arrector pili: A band of smooth muscle, connects the
undersurface of the follicle to the superficial part of the
dermis.
The muscle is innervated by sympathetic nerve fibers, and
its contraction causes the hair to move into a more vertical
position; it also compresses the sebaceous gland and
causes it to extrude some of its secretion.
The pull of the muscle also
causes dimpling of the skin
surface, so called gooseflesh.
Hairs are distributed in various numbers over the whole
surface of the body except:
the lips
the palms of the hands
the sides of the fingers
the glans penis and clitoris
the labia minora and the internal surface of the labia
majora
the soles
sides of the feet
the sides of the toes
Sebaceous glands
are modified clusters of epidermal cells that lie adjacent to
hair follicles; pour their oily secretion (sebum) onto the
shafts of the hairs as they pass up through the necks of the
follicles.
The purpose of sebum
is to keep the skin
surface slightly moist; in
so doing the skin and
hair may appear greasy
Sweat glands
are long, spiral, tubular glands
about three million on each body
distributed over the surface of
the body except:
the red margins of the lips
the nail beds
the glans penis
clitoris
Sweat glands are formed from groups of epidermal cells
which have dipped down into the dermis and become
modified to secrete sweat.
These glands extend through the full thickness of the dermis,
and their extremities may lie in the superficial fascia.
FASCIAE
The fascia is the connective tissue deep to the skin.
The fasciae of the body can be divided into two types
Superficial
deep
The superficial fascia, or subcutaneous tissue
is a mixture of loose areolar and adipose tissue that unites
the dermis of the skin to the underlying deep fascia.
It contains numerous bundles of collagen fibers that hold
the skin firmly to the deeper structures at:
the scalp
the back of the neck
the palms of the hands
the soles of the feet
It is devoid of adipose tissue at:
the eyelids
auricle of the ear
penis and scrotum
clitoris
The functions of superficial fascia are:
It binds the skin to the deep fascia but still permits free
skin movement.
Due to its high fat content it serves as: heat insulator, food
and energy
The deep fascia
elastic fibrous membranous layer of connective tissue that
separates the superficial fascia from the deeper structures.
It is absent in :
the face, scalp
anterior abdominal wall.
In the neck it forms well-defined layers that may play an
important role in determining the path taken by pathogenic
organisms during the spread of infection. In the thorax and
abdomen it is merely a thin film of areolar tissue covering the
muscles and aponeuroses.
In the thorax and abdomen it is merely a thin film of areolar
tissue covering the muscles and aponeuroses.
In the limbs it forms a definite sheath around the muscles
and other structures, holding them in place. Fibrous septa
extend from the deep surface of the membrane, between the
groups of muscles, and in many places divide the interior of
the limbs into compartments.
In the joints, the deep fascia may be considerably thickened
to form restraining bands called retinacula.
Their functions are:
It invests the deeper structures and binds them to bones.
This function is especially marked in the limbs.
It gives origins or receive insertions of some muscles.
In certain sites, it is thickened for protection.
It holds underlying tendons in position or to serve as
pulleys around which the tendons may move.
MUCOUS MEMBRANES
the lining of organs or passages that communicate with
the surface of the body
A mucous membrane consists essentially of a layer of
epithelium supported by a layer of connective tissue, the
lamina propria. Smooth muscle, called the muscularis
mucosa, is sometimes present in the connective tissue.
A mucous membrane may or may not secrete mucus on
its surface.
SEROUS MEMBRANES
line the cavities of the trunk and are reflected onto the
mobile viscera lying within these cavities.
They consist of a smooth layer of mesothelium supported
by a thin layer of connective tissue and contains a small
amount of serous liquid (serous exudate).
The serous exudate lubricates the surface of the
membranes and allows the two layers to slide readily on
each other.
The serous membranes acquire different names according
to their sites:
Pericardium: serous sac which surrounds the heart.
Pleura: serous sac which surrounds the lung.
Peritomeum: serous sac which surrounds the abdominal
contents.
Tunica vaginalis: serous sac which surrounds the testis.
Bursae: serous sacs which prevent the friction between
muscles, and bones.
Synovial sheath: serous sacs which envelop the tendons
as they pass under the retinaculae.