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

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 superficial part, the epidermis

The deep part, the dermis composed of dense connective tissue containing:

blood vessels lymphatic vesselsnerves are including specialized nerve endings

concerned with: touchPainpressure 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 over lapped 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 der mis, 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 earpenis 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 mem brane 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.