The structure of the skin
The skin is a very important organ. It is a waterproof barrier over the surface of your body, it keeps out infection, it protects the delicate tissues underneath and it can repair itself if it is damaged.
In homeostasis, the skin plays a very important part in maintaining the body temperature within narrow limits. It is important both for losing heat when your core temperature goes up and for conserving heat if your core temperature starts to fall. The structure of the skin is very well adapted to its function in temperature control.
The skin has three main layers - the epidermis, the dermis and the subcutaneous layer.
The epidermis is on the outside. This has a basal layer which is always forming new cells through cell division so the epidermis is made up from layers of cells. The new cells gradually move towards the surface, which takes 1-2 months. As they move up they gradually die, become flattened and develop keratin. The outermost layer of the epidermis is made of flat dead cells which are continually worn away by friction. The keratin and oil from the sebaceous glands help to make the skin waterproof.
The dermis is the middle layer. It contains
- Connective tissue - packs and binds the other structures in the skin.
- Elastic fibres - make the skin stretchy and resilient.
- Capillaries - tiny blood vessels which are supplied by arterioles.
- Hair erector muscles - to move the position of the hairs.
- Sensory cells - these respond to sense touch, pressure, heat, cold and pain.
- Nerve fibres - to activate muscles and glands and relay messages from the sensory cells to the brain.
- Pigment cells which produce melanin - a very dark pigment.
- Sweat glands which open onto the surface as pores.
- Hair follicles - pits in the epidermis which grow hairs.
- Sebaceous glands - produce oil to keep hair follicle free from dust and bacteria, and to help to waterproof the skin.
The subcutaneous layer is the final layer of the skin. This is a layer of fat found in the lower part of the dermis and underneath it. The thickness of this layer varies depending on the place in the body and from person to person. A store of fat is useful to the body as insulation and it can be used for energy when the intake of nutrients is insufficient.
A simple section through the skin