Structure and functions of the skin

Skin structure

The skin is the largest organ of the body. It has three main layers, the epidermis, the dermis and the subcutaneous layer.

The epidermis is an elastic layer on the outside that is continually being regenerated. It includes the following:

• Keratinocytes - the main cells of the epidermis formed by cell division at its base. New cells continually move towards the surface. As they move they gradually die and become flattened.
• Corneocytes - the flattened dead keratinocytes that together make up the very outer layer of the epidermis is called the stratum corneum or horny layer. This protective layer is continually worn away or shed.
• Melanocytes – produce the pigment melanin that protects against UV radiation and gives skin its colour.

The dermis is the inner layer that includes the following:

• Sweat glands – produce sweat that travels via sweat ducts to openings in the epidermis called pores. They play a role in temperature regulation.
• Hair follicles – are pits in which hairs grow. Hairs also play a role in temperature regulation.
• Sebaceous glands – produce sebum (an oil) to keep hairs free from dust and bacteria. Sebum and sweat make up the 'surface film'.

The subcutaneous layer under the dermis is made up of connective tissue and fat (a good insulator).

Functions of the skin

• Provides a protective barrier against mechanical, thermal and physical injury and hazardous substances.
• Prevents loss of moisture.
• Reduces harmful effects of UV radiation.
• Acts as a sensory organ (touch, detects temperature).
• Helps regulate temperature.
• An immune organ to detect infections etc.
• Production of vitamin D.