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 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.