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Skin (cutis): structure and function

by Josephine Andrews
Published: Last Updated on 274 views

The skin (cutis) is a vital organ that covers the entire outer surface of our body. It is stretchable and elastic, separates the organism from the outside world and protects it from dehydration and harmful influences such as pathogens and sunlight. Read everything important about the layers of the skin, their functions and important diseases of the cutis!

what is the skin

The skin (cutis) is a surface organ, the largest single organ of the body. As the protective shell of our body, it covers an area of ​​one and a half to two square meters in a medium-sized adult. With a thickness of one to two millimeters, the skin organ weighs around three and a half to ten kilograms. Their color changes from person to person – it depends on the amount of blood, the pigment content and the thickness of the epidermis (top layer of the cutis).  

How many layers of skin does a person have?

The skin is made up of three layers. From the outside in, these are:

epidermis

The epidermis mainly consists of a horny layer that sheds outwards and constantly renews itself from below. Read more in the post  Epidermis .

Dermis (dermis, leather)

The dermis is the middle of the three layers of skin. It consists of tight connective tissue and contains, among other things, sebaceous glands. Read more about the dermis in the Dermis  post .

hypodermis (subcutis)

The subcutis consists of loose connective tissue with more or less embedded fatty tissue. You can read more about this in the  Subcutis post .

skin appendages

The skin appendages include hair , nails and glands such as sweat and sebaceous glands. You can read more about the latter in the article  Sebaceous glands .

What is the function of the skin?

The function of the skin is primarily to provide protection to the body. How vital the cutis becomes apparent when larger areas have been destroyed by a burn, for example. Losing as little as 20 percent of the skin can be fatal. In addition to the protective function, the cutis also fulfills other tasks, such as as a sensory organ.

Protective function of the skin to the outside

The outer horny layer (part of the epidermis), which is saturated with fatty substances, protects the organism from excessive water loss through evaporation. On the other hand, an intact skin prevents the penetration of pathogens and harmful substances such as chemicals. To a certain extent, it also offers mechanical protection for internal structures and organs, for example against blows or impacts.

The sweat from the sweat glands and the sebum from the sebaceous glands together form the so-called protective acid mantle of the skin. Its low (acidic) pH has an antimicrobial effect: it inhibits the growth of many bacteria and fungi on the cutis.

Natural sun protection

Another important task of the skin is the reflection and absorption of sunlight by the horny layer and the skin’s surface film. Deeper penetrating rays are almost 100 percent absorbed by the melanin pigment – a black-brown to reddish dye – and converted into heat.

So if someone spends a lot of time in the sun and tans, it simply means that the skin has produced more melanin to better protect itself from UV rays. Incidentally, the increased formation of melanin is stimulated by the UV-B component in sunlight.

Depending on the skin type, everyone naturally has more or less melanin stored in their skin. Dark-skinned people have a particularly large amount of the color pigment. Their skin is therefore less sensitive to light than that of fair-skinned people.

Another protective strategy of the skin against sunlight is the so-called photocallous : repeated exposure to UV-B light causes the top layer of the skin – the cornea – to thicken. Within two to three weeks, a callus develops that lasts for weeks and improves the skin’s own protection: the thickening of the skin reflects, filters and scatters the sunlight.

The UV rays from the sun and solariums can damage the genetic material of the cells. Although the body has repair mechanisms, it cannot always and certainly not completely eliminate the damage. Possible consequences: premature skin aging and skin cancer.

Protective function inside

The inward protective function of the cutis is the formation of antibodies. When the body’s own defense system is mobilized by the Langerhans cells of the epidermis, the body pumps blood and lymph into the affected skin area. The consequences are redness, swelling and wheal formation. Rashes in infectious diseases such as rubella, measles, scarlet fever and reactions to vaccinations are the result of this immunological defense reaction.

thermoregulation

A contraction (pull together) of the cutaneous vessels prevents excessive heat release. “Goosebumps” serve the same purpose: they are caused by contraction of the hair follicle muscles on hairy parts of the body. As a result, the cutis forms small elevations and the fine hairs stand up. This reduces the heat dissipation.

By expanding the vessels, on the other hand, heat is released and heat build-up in the body is prevented.

Sweat is released and evaporated to regulate heat.

sensory perception

The sensory organ skin registers stimuli such as pressure, temperature and pain through specific receptors. This is also referred to as surface sensitivity. You can read more about this in the article  Tactile Perception .

Other tasks of the skin

The Cutis also fulfills other functions. For example, a small proportion of substances that are otherwise only excreted via the kidneys (urinary substances) are secreted via sweat glands (e.g. table salt). Vitamin D is also formed in the epidermis under the influence of sunlight (more precisely: UV-B light) . Its main function is to regulate the calcium and phosphate balance. Both minerals are important for building bones and teeth.

Where is the skin?

The cutis covers the entire body surface. At the body openings (mouth, nose, genital region) it merges into mucous membrane.

Regardless of the three-layer skin structure, there are two different appearances of the cutis on the body:

The skin on the soles of the feet, the palms of the hands and the insides of the fingers runs in fine furrows that are arranged in parallel – like fine ridges. This structure serves to make the cutis rough and grippy, to give it support. Doctors speak of the so-called groin skin. It makes up about four percent of the body surface.

The skin on the rest of the body (about 96 percent of the body surface) consists of rhombic to polygonal folds that are genetically fixed in shape and run in characteristic lines. Hair grows out of the furrows of this field skin, and sweat glands exit the raised areas via a duct to the outside.

What problems can the skin cause?

The cutis can cause numerous problems such as abscesses (encapsulated accumulations of pus), boils (purulent inflammation of hair follicles) or herpes infections (such as cold sores, shingles).

Atopic eczema (neurodermatitis) is a genetically determined chronic skin disease that is associated with inflammatory changes in the cutis and severe itching. It progresses in phases and can be “triggered” by so-called provocation factors. These include, for example, frequent washing, heavy sweating, pollen, animal hair, infections and stress.

Psoriasis is a chronic inflammatory skin disease that leads to scaly, itchy changes in the cutis. Knees, elbows and scalp are particularly affected. In some patients, the joints or nails may also be affected.

In the case of contact dermatitis (also called allergic contact eczema), the skin reacts hypersensitively to contact with certain substances such as fragrances or nickel. Typical symptoms are redness and severe itching.

A weakened immune system can lead to a fungal disease of the skin (dermatomycosis).

Warts (verrucae) are small, sharply demarcated growths on the epidermis. They are generally benign. The human papillomavirus (HPV) is the cause of warts. There are different types of warts such as “common” warts (mainly on the hands and feet) or plantar warts (almost only on the soles of the feet).

A mole (pigment nevus) is caused by an increase in pigment-forming cells (melanocytes) in the epidermis. It is also colloquially referred to as a liver spot. The predisposition to moles is genetic. However, their expression is significantly influenced by sunlight. Birthmarks form primarily on parts of the body that are exposed to the sun.

If the sun is too strong, sunburn can develop – a burn of the cutis by UV light . Some medications can increase the risk of sunburn because they make the cutis more sensitive to light. These include, for example, St. John’s wort and certain antibiotics.

Frequent sunburns (especially in childhood) promote the development of skin cancer. The term describes various malignant tumors of the cutis. The most important are basal cell carcinoma (basalioma), squamous cell carcinoma (sting cell carcinoma, spinalioma) and malignant melanoma.

A common skin disease in young people is acne (acne vulgaris) – a hormone-dependent disease of the sebaceous glands that occurs primarily during puberty.

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