Skin is composed of the skin itself and supporting tissue (hypodermis). There are two skin layers: the epidermis is surface layer, one-tenth of a millimeter thick. It is the first barrier preventing invasion of foreign substances. The epidermis is a multilayered keratinized squamous epithelium. Keratinocytes produce keratin, the proteins that form the most exterior skin layer (horny layer). Keratinocytes gradually migrate from deeper layers to the skin surface and are shed.

The dermis below is a complex tissue made of collagen fibers, sweat glands, hair roots, nerve cells, nerve fibers, blood and lymph vessels. Cone-shaped loops of collagen fibers rise as  papillas into the epidermis linking the two layers of skin.  Beneath the dermis is the sub cutis, a layer of loose, chamber-structured connective tissue and fat.

Skin Glands

There are two types of sweat glands, eccrine and apocrine. There are about 3 million eccrine sweat glands that have a tubular shape and are found all over the body. About 3,000 sweat glands per square inch are found in the palm of the hand. The secretory base of the gland lies below the dermis in the subcutaneous tissue. A duct follows a spiral course through the dermis to the skin surface. An adult secretes a minimum of 100 ml sweat each day; heat exposure, and work increase sweat production to a maximum of 10 liters per day. The most important function of sweat production is body cooling. 

Water evaporation requires heat taken from the skin, cooling the skin surface. Sweating under the arms is suppressed by antiperspirants containing aluminum salts.

Hair

Hair is produced in hair follicles by cells at the base of each hair.  Follicular cells are added to the hair fiber and become compressed and molded as the hair root moves up the follicle. The shape of the follicle determines whether the hair will be straight or curly. As more cells are added, the hair fiber is pushed up and out and keratinized.  By the time the hair emerges from the follicle all the cells are dead. The cells layers are a cortex, or core, surrounded by the cuticle. There may be a hollow center or medulla.

All Alpha Nutrition books, formulas and Starter packs are ordered at Alpha Online. eBooks and other digital documents are downloaded from Persona Digital Publications and can be delivered to any destination on the planet.  Physical shipments by the Post Office to all destinations in Canada, Continental USA, Alaska, Hawaii, Puerto Rico, and US Military. Alpha Nutrition ® is a registered trademark and a division of  Environmed Research Inc., Sechelt, British Columbia, Canada. In business since 1984. Online since 1995.