Skin Appegages

SKIN APPENDAGES : The appendages of the skin are the nails, hairs, sebaceous glands, sweat glands, and ceruminous glands.

The NAILS are composed of horny epidermal scales and are found on the dorsal surfaces of the fingers and toes. They protect the many sensitive nerve endings at the ends of these digits. New formation of nail will occur in the epitheliums of the nail bed. As new nail is formed, the whole nail moves forward, becoming longer.

HAIR is an epithelial structure found on almost every part of the surface of the body. Its color depends on the type of melanin present. The hair has two components: the root below the surface and the shaft projecting above the skin. The root is embedded in a pit-like depression called the hair follicle. Hair grows as a result of the division of the cells of the root. A small muscle, the arrector, fastens to the side of the follicle and is responsible for the goose bump appearance of the skin as a reaction to cold or fear. Each hair follicle is associated with two or more sebaceous (oil) glands.

SEBACEOUS GLANDS are found in most parts of the skin except in the soles of the feet and the palms of the hand. Their ducts open most frequently into the hair follicles and secrete an oily substance that lubricates the skin and hair, keeping them soft and pliable and preventing bacterial invasion.

SWEAT GLANDS are found in almost every part of the skin. They are control mechanisms to reduce the body’s heat by evaporation of water from its surface. The perspiration secreted is a combination of water, salts, fatty acids, and urea. Normally, about one liter of this fluid is excreted daily. However, the amount varies with atmospheric temperature and humidity and the amount of exercise taken. When the outside temperature is high, or upon exercise, the glands secrete excessive amounts to cool the body through evaporation. When evaporation cannot handle all the sweat that has been excreted, the sweat collects in beads on the surface of...