1. What is skin ?!

Skin is the largest organ of the integumentary system made up of multiple layers of epithelial tissues that guard underlying organs. As the interface with the surroundings, skin plays the most important role in protecting (the body) against pathogens. Its other main functions are insulation and temperature regulation, sensation, and synthesis of vitamin D.

The skin is a complicated structure, made up of 3 layers : epidermis, dermis, and subcutaneous tissue.

1. Epidermis - is the outer layer of skin. It contains 5 layers. From bottom to top the layers are named: stratum basale, stratum spinosum, stratum granulosum, stratum licidum, and stratum corneum. The thickness of the epidermis varies in different sites and types of skin. The thinnest is on the eyelids (.05 mm) and the thickest is on the palms and soles (1.5 mm). The top layer of the epidermis, the stratum corneum, is made of dead, flat skin cells that shed about every 2 weeks.

2. Dermis - is composed of three types of tissue that are present throughout - not in layers. The types of tissue are: collagen, elastic tissue, and reticular fibers. It also has specialized dermal cells such as hair follicles, sebaceous glands, eccrine (sweat) glands and apocrine (scent) glands.Blood vessels and nerves course through this layer. There are also specialized nerve cells called Meissner's and Vater-Pacini corpuscles that transmit the sensations of touch and pressure.

3. Subcutaneous Tissue - is a layer of fat and connective tissue that houses larger blood vessels and nerves. Its main function is to regulate temperature of the skin itself and the body. The size of this layer varies throughout the body and from person to person.