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Structure & function of the Skin

Here is a small introduction to the Structure and function of the human skin to give you an understanding of this rather important organ.

Skin is the largest organ of the human body, it covers an area of around 1.7M² and contributes somewhere in the region of 10% to a human beings body mass. The skin is an extremely efficient protector for the body in that it forms a protective barrier for the entire body. It is also capable of ensuring that all of the internal body remains internal. The skin has an excellent self repair system and is contiuously regenerated at an extremly fast rate.

The skin itself is formed of many layers as detailed in the diagram Fig1.

Fig 1 Diagram of a cross section of the skin

The skin is divided into two main layers called the Epidermis and the Dermis.

The epidermis is the outer layers of cells. The dermis is a layer of fibrous tissue which lies between the epidermis and a layer of fat called the subcutaneous tissue. Also situated in the skin are structures called appendages, which include the hair and the follicle, nails, sweat glands and sebaceous glands.

The Epidermis

The epidermis covering most of the body has four layers or strata of cells. With the exception of the palms of hands and soles of feet where there are five layers.

The ability of the cells to constantly reproduce is what forms the structure of the epidermis. This continual reproduction of cells brings about the rising movement of the cells towards the surface. As a consequence of this upward movement the cells in the outermost layer of the epidermis are then replaced continually. In general the time it takes for cells to travel from the bottom of the epidermis layer to the top is around four weeks. Each layer of the epidermis indicates a different stage in the cells progression. This cell reproduction is facilitated by the metabolism of protein by the body from the diet. Some scalp problems are associated with the level of this cell regeneration, with it often being accelerated (see scalp problems).

The Dermis

The dermis is composed of a network of connective tissue, primarily collagen; that provides support, strength and flexibility to the skin. Also present is elastin, giving skin its elasticity. These are surrounded by a gel-like substance called the ground substance; this substance plays a vital role in the hydration and moisture levels within the skin. Cells called fibroblasts produce the ground substance and are the precursors of collagen and elastin. Mast cells produce chemicals such as histamie and serotonin, which are released during allergic and inflammatory responses, invading microorganisms and physical injury. Blood vessels are also found in the dermis. These blood vessels help with thermo-regulation by constricting or dilating in order to conserve or release heat. They also support immune function and provide oxygen and nutrients to the lower layers of the epidermis. Also present in the dermis layer are Lymphatic vessels, sweat glands, sebaceous glands and appendages such as hair follicles.

The main functions of the skin are:

• Protection. The body is protected from external factors such as harmful impact, the environment and infection.
• Preventing excessive water loss from the body.
• Regulating temperature.

The Scalp

The scalp is a term, which refers to the skin found on the head. It is from here that hair grows. The scalp is supplied with an abundance of blood vessels. The scalp is also richly supplied with glands that provide oils to the scalp. These glands are called ‘Sebaceous glands’ and secrete oils onto the scalp. this oil is known as sebum. Even though the skin on the scalp is the same as the skin all over the body, these unique characteristics make it far more vulnerable to certain skin disorders such as fungal infections and parasitic infestations.

There are various problems that can afflict the scalp, and many people suffer from these problems which can range from itching to severe skin diseases. Many of these scalp conditions share similar features such as itching, flaking, inflammation and even hair loss. Accurate diagnosis is vitally important if treatment is to be effective.

To help understand these scalp disorders we have provided some information below on the more frequently occuring conditions including the common descriptions and terms in use.