The human skin is a layer of many types of cells, which constitute the complete outer surface of the human body. The surface area of the skin on an adult is between 1.6 and 1.8m². Skin itself weighs approximately 3 kg, 20 kg together with adipose tissue. It is therefore the largest and heaviest organ of the human body. Depending on its location and the person's diet, skin can be between 0.5 and 4mm thick. In places where the skin is exposed to less pressure and stress, such as the eyelids, the skin is thinner, and where there is more wear and tear, such as the soles of the feet, the skin is the thickest. In openings in the body, skin continues in the mucosa.
Parts of the Human Skin
The human skin is comprised of three parts. The first is the epidermis, which is made of many layers of cells. The epidermis does not receive blood flow, rather it is nourished by the deeper layer, called the dermis. In the deeper layers of the epidermis, cells are constantly growing and dividing, causing the older cells to be pushed to the surface. On the way, they flatten and become more compressed, and in the end they die and flake off. All of the skin on a person's body is renewed within 3 to 4 weeks. The bottom layer of the epidermis contains pigment (melanin) which protects the deeper layers of the skin from the harmful effects of UV radiation. Melanin is also responsible for the colour of human skin.
The second layer of the skin is called the dermis. It is a fibrous layer that is made up of a net of collagen and elastic tissue. With the increase of age, these tissues diminish, which is manifested by the skin becoming less elastic and developing wrinkles. Papillae extend toward the epidermis and they contain blood vessels to nourish it, as well as numerous nerve endings, such as sensors of touch, pressure, heat and cold. Papillae also create the characteristic and unique fingerprint of every person.
The deepest layer of the skin is subcutaneous tissue which is made up of fat and connective tissue. This layer serves as a reservoir of energy for the human body. It is in fat cells that vitamins A, D, E and K (fat soluble vitamins) are found.
Derivatives of the Human Skin
The human skin also includes skin derivatives, which are accessory skin organs. Included are the sebaceous and sweat glands, hair and nails. The sebaceous glands are bound to hair, including body hair, and they are mainly found on the face and upper chest. On the other hand, sebaceous glands are not found on the palms of the hand, or on the soles of the feet. These glands secrete sebum, protecting the skin and hair from drying out.
Other derivatives of the skin are sweat glands which we divide into large and small. Large sweat glands are active only once puberty is reached and hormone levels significantly increase. They are found in the armpits, the external area of genital organs and areolas. They are also known as the aromatic sweat glands. Small sweat glands are scattered all over the surface of the body. Most are on the palms of the hands, soles of the feet, and under the arms. Sweat glands secrete sweat, which contains water and ions, mainly sodium and chlorine.
Hair is found on almost every surface of the skin except the palms of the hands, soles of the feet and the penis. Hair can be divided into two categories: long and short. Long hair includes hair on the head, underarm hair, external genitals, facial and body hair. The rest are short hairs such as eyelashes, eyebrows, nose hair and hair in the outer ear canal.
Another derivative of the skin is nails. A nail plate consists of flat compressed cells. The fingernail grows at a rate of approximately 0.1mm per 24 hours, toenails grow slower. This means that a whole nail will regrow within 3 to 4 months.
Function of the Human Skin
The human skin is an organ with a number of functions and has a part in maintaining the internal environment of the body. It creates a protective barrier against the outer environment. The deeper layers of the skin – dermis and subcutaneous tissue, provide protection against mechanical damage and work as thermal and electric insulators. Subcutaneous tissue is a reservoir of water, fat, sugar and ions for the whole body. The skin also contains provitamins that with the effects of UV rays from the sun are converted into vitamin D. It is important to have slightly acidic skin film, which along with undamaged skin provides protection against microbial infection.
Diseases of the HumanSkin
Damaging of the skin barrier leads to disease of this vast organ. Disease can affect only the skin, for example viral illnesses such as warts, or is can affect the accessory organs as well. For example, depigmentation of the skin, a state when the skin does not contain enough melanin, affects the hair and makes it lighter. Other diseases, such as psoriasis, can damage and deform nails as well. It is very important to protect and care for your skin because this barrier is what is supposed to protect us from the harmful effects of the outer environment.