Skin serves many functions in our body: it forms a protective barrier against diseases and environmental threats, regulates body temperature through homeostasis, perceives sensory information from the environment etc.
Skin is comprised of 3 basic layers: Epidermis, Dermis and Subcutaneous Tissue or Fat:
Ι) Epidermis is the outer, visible layer of the skin. Epidermis is 1mm on average in vertical section and consists at 90% of keratinocytes which help in keratin΄s storage. They mainly form the subsequent layers of the epidermis (stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum), as they grow in the deeper layer of the epidermis, and accumulate in the skin΄s surface as dead cells. Keratinocytes are replaced by new ones with rates that slow down by aging, thus contributing to the constant renewal of the skin. Epidermis also includes:
- Melanocytes, which produce melanin
- Dendritic cells, which have an active role in skin΄s immune system
ΙΙ) Under epidermis lays Dermis, which is thicker than epidermis. Dermis is comprised mainly of Collagen that provides structural support to the skin. Also includes fat, sensors, blood vessels-which nourish the skin as well as the hair follicles included- nerve-fibers, sweat and sebaceous glands. In the dermis lie the roots of hair follicles.
- Blood vessels: they provide nourishment and oxygen to skin and hair follicles
- Sensory organs: Meissner΄s and Pacinian΄s corpuscles
- Nerve-fibers: they transmit the information received by the sensory organs
- Sebaceous glands: they produce sebum, the natural moisturizer of hair and skin
- Sweat glands: by sweat secretion, they regulate the body΄s temperature
- Hair follicles: hair grows in naturally occurring groups of 1-4 hairs, called Hair Follicles or Follicular Units. Hair follicles are complete biological structures that comprise of nerves, blood vessels, sebaceous glands and the small arrector pili: this muscle lies at the base of the hair follicle and in any excitement due to cold or fear, forces shaft to rise. Hair follicles are surrounded by protective, connective collagen tissue and lie everywhere in the body except lips, palms and soles. All hair follicles have a predefined genetic definition.
ΙΙΙ) The third layer of the skin is Subcutaneous layer, which contains fat and connective tissue and helps to preserve body΄s temperature.