The skin is a dynamic organ that has several functions and numerous important features. It forms a continuous layer covering the body and varying in thickness, colors, amount of hair, glands and nails depending on the region of the body studied. Despite variation, the skin presents a basic structure throughout the body.

II. Anatomy of the skin.
 

 The skin is formed of two distinctive layers:
1. The superficial layer called epidermis: is a stratified epithelium whose cells flattened mature and rise form the underlying dermis. The sole of the hands and feet have extremely thick dermis, possibly to withstand the wear and tear occurring in these areas.
2. The deep layer called dermis: is a thick layer of dense, fibro-elastic connective tissue. It is highly vascular and contains many skin receptors.  The dermis is attached to the underlying layer of tissue by a layer of loose cutaneous tissue high in fat content. This layer, called subcutaneous layer by histologists is termed superficial fascia by anatomists.
 The hair follicles, the sweat glands, the sebaceous glands, and nails are epithelial structures spanning deep into the dermis and the superficial fascia. 

III. Functions of the skin.
 

 The skin has numerous functions:
- protection: the skin protects the deeper tissue from external insults. These insults can be ultraviolet, mechanical, thermal and thermal. It also slows down the process of dehydration and protect against viruses and bacteria
- sensation: the total area of skin in an average man is about 1.8 m2 and weight about 1/6 of the body weight. It contains a great number and variety of receptors for touch, pressure, pain and temperature
- thermoregulation: the skin functions has an organ of thermoregulation by controlling the amount of blood flow through the tissues, therefore controlling sweating and heat loss
- metabolic functions: the skin is a reserve of energy in the form od triglycerides (fat...).  Vitamin D is synthesizedfrom precursor into an active form in the epidermis (by exposure to UV light) to  complements the vitamin D found in food.

IV. The appendages of the skin.
 

 The appendages of the skin are nails, hair follicles, sebaceous and sweat glands. The nails are keratinized plates found on the dorsal surfaces of the tips of the fingers and toes.  The hair grows out of follicles which, as already described span both the epidermis and dermis (see figure 1-4). The part of hair follicle found deep in the dermis is called the hair bulb. The inferior part of the hair bulb has a band of smooth muscle, the arrector pili, which connects the undersurface of the follicle to the superficial part of the dermis. This muscle is innervated by sympathetic fibers. When activated, this band of muscle contracts and move the hair in a more vertical position. It also contracts the sebaceous glands associated to the hair follicle, causing the release of some secretion as well as the pull of the muscle causing dimpling of the skin (gooseflesh). The hair is usually found on the whole body except on the lips, the palms of the hands, the side of the fingers, the glans penis and clitoris, the labia minora and the internal surface majora, the soles of the feet.
 The sebaceous glands release their secretion in the shaft of the hair. The oily secretion is called sebum and helps maintain the flexibility of the growing hair. The sweat glands are long, tubular glands found deeply embedded in the dermis. They secrete a watery substance and are  important in thermoregulation described above.

Note: Quite a few sites are available on the internet describing the microanatomy of the skin. The site created by Loyolla University is among the very best. Visit it at http://www.meddean.luc.edu/lumen/MedEd/medicine/dermatology/melton/skinlsn/sknlsn.htm
 
V. The musculoskeletal system.
The musculoskeletal system will be studied in great details throughout the course. The histophysiology of the musculoskeletal system will described in details during the first lecture of surface anatomy by Steve Janos. The structures covered will be fascia, fat tissue, muscle, deep fascia, tendon, nerve, ligament, cartilae and bones.