The epidermis functions as the body’s covering. It is the outermost layer of the skin that serves the body’s appearance as well as provides protection against the harsh environment. It also works in sustaining normal body temperatures. The structure of the epidermis is very well designed to serve its purpose. It is made up of several different layers and types.
A number of factors can affect normal epidermis function which may lead to problems of the skin. Epidermal disorders rarely result in life-threatening conditions; however, they can have a huge effect on the physical, psychological and social well-being of the individual. Epidermal diseases usually respond to conservative remedies but severe problems need more intensive and aggressive treatment.
Function of the epidermis
The skin has different layers and each has differing functions. Epidermis functions include:
- Providing protection against the harmful sunrays
The epidermis protects the epidermal cells and collagen found in the inner layer of the skin from getting damaged by the harmful ultraviolet rays from the sun. UV rays cause free radicals to form which damage the skin. With the epidermis, part of UV rays is reflected back at the skin surface, another part is scattered, while a fraction is absorbed by melanin, the substance produced by melanocytes found on the deepest epidermal layer.
- Preventing excessive loss of water
Water gets out of the body through gentle evaporation via the skin. The epidermis works in ensuring that extreme water loss does not occur by absorbing water itself. The outermost layer of the epidermis has 10% to 15% water content. Excessive loss of water can make the skin dry and prone to damage and infection.
- Protecting against infection
Proper epidermis function is important in keeping infections at bay. Epidermal cells work in destroying pathogens that try to enter the body through the skin. Once the epidermal cells detect foreign invaders, they clear them up and bring them to the lymphocytes to neutralize them.
Layers of Epidermis
Effective epidermis function is supported and maintained by its different layers and various cell make up. This outer skin layer is largely composed of scale-like flat squamous cells. Other types of cells are also present, such as:
This type of epidermal cell is responsible in producing melanin which absorbs the UV rays to protect the skin from getting damaged.
- Langerhans cells
Langerhans cells aid in getting rid of pathogens that try to enter the body through the skin. They work with the lymphocytes in fighting foreign invaders.
These epidermal cells create keratin, a type of protein that is responsible for hardening and waterproofing the skin.
- Merkel cells
Merkel cells are the epidermal cells found at the boundary between the epidermis and the dermis.
Aside from the different types of cells found therein, the epidermis also consists of several different layers from the top to bottom.
- Stratum corneum
This is the outermost layer of the epidermis that is made up of keratin and works in keeping the skin hydrated and strong.
- Stratum lucidum
This epidermal layer serves to reduce friction and stop the forces between the stratum granulosum and stratum corneum. The stratum lucidum is made up of several anucleate cell layers and are only found in the palms and soles.
- Stratum granulosum
This is the granular layer of the epidermis which is largely composed of keratohyaline granulesm which are an important component in producing keratin in the outermost layer of the epidermis.
- Stratum spinosum
Stratum spinosum has several cell layers which are active in synthesizing keratin.
- Stratum basale
This is the deepest layer of the epidermis wherein epidermal cell renewal constantly and actively occurs. The stratum basale is made up of a single layer of column-like cells that actively divide, sending some cells for maturation all the way to the skin surface, while the rest of the cells keep on dividing to refill the basal epidermal layer.
Newly-formed epidermal cells are pushed from the stratum basale all the way to the skin surface and are shed after 2 weeks. Another noteworthy aspect of the structure of the epidermis is that its thickness varies on different parts of the body. The epidermis is remarkably thick in areas that receive more physical contact like the soles and palms, at around 1.5mm. In contrast, the epidermis is very thin at 0.05mm on the eyelids.
Factors that affect the function of the epidermis
Any disruption to the effective epidermis function results in skin problem. These problems could involve the cells on different epidermal layers, hormonal imbalance, UV irradiation, overactive sebaceous gland, obstruction of sebaceous canal and allergic reactions to some medication. Some of the common epidermal disorders are:
- Atopic dermatitis
- Seborrhoeic dermatitis
- Pregnancy mask
The most life-threatening, but rather rare, epidermal disease is toxic epidermal necrolysis. It occurs as a result of an allergic reaction to medication which causes the epidermis to separate from the other layers of skin.