Human Skin Protection and Functions
The human skin is the outer cover of the body that reliably protects organs from damage. It prevents the loss of water and penetration of various bacteria. The surface area of the skin in humans is on average from 1.5 to 2m². Skin thickness varies from 0.5 to 5mm (Jablonski and Chaplin 8962). On the skin surface, there is a unique pattern of triangular and rhombic fields. It is especially clear on the palms, fingers, soles of the feet. This pattern is unique for everyone. Skin not only forms the outer shell of the human body. It is a difficult, efficiently arranged, and impassable barrier for many aggressive environmental factors. The skin is multi-layered and rich in materials and structures that have unique physical and chemical properties. The skin condition is associated with the state of the whole organism, functional activity of its immune, endocrine, nervous, and other systems. The appearance of skin diseases is associated with dysfunction of these systems.
The skin is a complex environment with a strongly pronounced heterogeneity of its physical characteristics. It has three main structural layers – epidermis, dermis, and hypodermis or subcutaneous fat. There are also skin appendages – nails, hair, and glands.
Epidermis is a top, constantly renewed layer of the skin. It consists of five layers of cells. They are different in quantity and shape, as well as functional characteristics. This layer is connected with dermis by the basal membrane, which has the basal layer of prismatic cells that continually divide providing the skin renewal. The basement membrane is formed by root-like outgrowths of the bottom surface of these cells. It serves as a filter that does not transmit large charged molecules. Through the basement membrane, epidermis can influence the cells of the dermis causing them to enhance or retard the synthesis of different substances. Epidermal cells in the border area are constantly divided. They slowly move to the outer surface of the epidermis losing the cell nucleus and gradually undergoing keratinization. Dead cells are exfoliated from the skin surface. The cellular structure of the skin is completely renewed for 3-4 weeks. During the movement from the border area to the surface, cells of the epidermis undergo five stages. In accordance with this, there are five structural layers in the epidermis (Alonso and Fuchs 11830-11832).
The next layer, dermis, has a thickness of 1-4 mm. The fibrous structure of the dermis is a strong lining for the epidermis. Dermis consists of collagen (70-80%), elastin (1-3%) and proteoglycans. Collagen provides resilience, elastin – elasticity, proteoglycans retain water (Jablonski 586). The fibroblast is the main cell of the dermis. It provides the synthesis of collagen, elastin, and proteoglycans. This layer of the skin has receptors, sebaceous, sweat glands, hair follicles, blood, and lymph vessels. The dermis is divided into two layers – papillary and reticular. The dermis provides thermal regulation by changing the magnitude of the blood flow in the vessels of the dermis and sweating by sweat glands. The dermis also provides mechanical protection of subjected structures due to the presence of collagen and hyaluronic acid. The dermis is closely related to subcutaneous fat – hypodermis.
Hypodermis consists of a wide network of fibers, the loops of which are filled with fat cells. Adipose tissue makes the movable attachment of the skin to the underlying tissues. It protects deeper underlying tissues from mechanical damage and retains heat as an energy reserve of the organism. Its thickness varies in different areas from 2 mm to 10 cm or more.
There are also the skin appendages – nails, hair, and glands. There are several types of the skin glands. The most important are sweat and sebaceous glands among excretory glands. The sweat glands are of two types – eccrine, secreting liquid sweat on the surface of the skin, and apocrine, giving concentrated sweat with a characteristic odor. The function of eccrine glands is excessive sweating, as well as the loss of a small part of water in the process of gas exchange through epidermis. There are more eccrine sweat glands than apocrine. However, they are completely absent in some parts of the body. Palms and soles have a great number of eccrine glands. Apocrine glands are larger than eccrine. They are located only in certain places such as armpits, nipples, vulva, and anus.
The skin performs several functions vital for the body. “Among its numerous functions, none are more important than preventing the organism from desiccating protecting it from its environment even while maintaining it in uninterrupted communication with the environment” (Montagna 1). Thus, the first function is protective. Being durable and supple, the skin protects organs from damage caused by pressure, friction, and blows. The skin protects the body from excessive water loss. It protects the organism from UV rays and the penetration of pathogenic bacteria. The skin forms vitamin D from ergosterol under the influence of ultraviolet rays (Obi-Tabot, Quan Tian, Chen and Holick 201). “Sunlight-induced photosynthesis of vitamin D in the skin is essential for the development and maintenance of a healthy skeleton in humans” (Obi-Tabot et al. 201). It participates in thermoregulation by changing the diameter of blood vessels in the skin, as well as the presence of the layer of fat reducing heat transfer. The next function is excretory. Along with sweat, excess water and a quantity of urea and mineral salts are removed from the body. The next function of the skin is respiratory. Through the surface of clean skin up to 1% of gas exchange is implemented (Obi-Tabot et al. 202). The skin is an organ of tactile, pain, and temperature sensitivity. It is organism’s adaptation to changing environmental conditions – tempering.
The skin cancer is a very common disease. It is a disease in which skin cells start developing a malignant tumor formation. The skin cancer is a fairly common form of malignant types of tumors. Both women and men are equally exposed to it. Their age is generally 50 years old or more, although there are cases when young patients suffer from various skin cancer forms. The affected area of the disease is usually parts of skin open to different influences. The skin cancer is observed in 5% of all cases of cancer per se.
Melanoma is one of the most malignant tumor formations relevant to humans. It develops regardless of fitness for a particular age group and, therefore, does not exclude the possibility of its occurrence in young people and older people. It is noteworthy that melanoma develops in women more frequently than in men. Over the past decades, there is a sharp increase in the total number of cases of melanoma. In fact, melanoma may appear in a person belonging to any race and any color of the skin. Melanoma is formed in about 70% of the total number of cases of disease from birthmark pigment stains (Bataille and de Vries 1287). Advantageously, the concentration of malignancy formation is determined in the neck, limbs, or scalp.
When considering the causes that provoke the development of the skin cancer, there are two main types of factors that have a direct bearing on the process. In particular, there are exogenous and endogenous factors. The most important of exogenous factors are ultraviolet radiation and solar rays in particular. The development of melanoma occurs predominantly as a result of periodic severe exposure exerted by sunlight. Moreover, in the latter embodiment, even a single exposure is sufficient. The confirmation of this statement lies in the fact that melanoma occurs mainly within the areas that are hidden with clothing. Moreover, it is established that mostly people who are mainly in the room and only occasionally exposed to ultraviolet light, which implies an ordinary holiday in the sunlight in the open air, can suffer from melanoma. In addition to ultraviolet, an important and quite a frequent factor of an etiological type of the development of melanoma is the injury of pigmented nevi through abrasions and bumps. Pigmented nevi can also be defined as spiloma or birthmark – the formation on the skin surface consisting of pigment (or nevus) cells. There is also the possibility of influencing of lighting – fluorescent lamps, some chemical carcinogens – hair dyes, as well as intensive electromagnetic fields and ionizing radiation (Menzies and Shuster 204-205).
The main signs of melanoma include asymmetry of a nevus when one part is bigger than the other. The edge is uneven or fuzzy. The color in a birthmark is different. The diameter of a nevus exceeds 5 mm, and its growth increases in a short period of time. If to consider prognosis for malignant melanoma, in general, it is quite heavy. It is directly determined based on its timely detection. Most clinics and leading experts acknowledge that a surgical method is considered to be the main method of treatment. This method is still the most popular and effective. In addition to treatment, it is important to take into account nourishment during the disease. Someone might say that with this serious illness, this detail does not influence. However, it is a typical error. One of the treatments is the plastic movement. The first method is a free skin graft. It is applied in cases where the focus is located in the place where the complete change is not possible. The next method is combined transplantation, which includes free and local transplantation.
Taking everything into account, it is important to mention that human skin is a unique organ that performs many functions simultaneously. It acts as a protective cover. Moreover, it protects the human body from drying and also performs other functions. Provided with numerous nerve endings, it represents an important sensory organ. As the organ of discharge, it removes water from the body controlling along with the kidneys the water balance. By varying intensity of the blood flow in the skin and evaporation of sweat from the surface, body temperature is regulated. In the epidermis, under the action of sunlight or artificial ultraviolet radiation, it synthesizes vitamin D. There are several types of the skin cancer. Melanoma is one of them. It is one of the most malignant tumor formations relevant to humans.