The skin is the largest organ of the human body, playing a key role in protecting the body from external factors and maintaining homeostasis. It is a multi-layered structure that not only protects against mechanical injuries and microorganisms, but also participates in thermoregulation and the synthesis of vitamin D. The skin is also the body's sensory interface, allowing the reception of stimuli from the environment. According to research, its surface area in an adult is about 1.5–2 m², and its mass is about 16% of the total body weight (Proksch et al., 2008).
Due to its structure, the skin is divided into three main layers: the epidermis, the dermis, and the subcutaneous tissue. Each of these layers has specific functions and is characterized by a different histological structure. The purpose of this article is to present the structure of human skin and its physiological functions.
Skin layers and their structure
1. Epidermis
The epidermis is the outermost layer of the skin, composed of stratified squamous epithelium. It does not contain blood vessels and is nourished by diffusion of nutrients from the dermis (Baroni et al., 2012). The epidermis consists of several layers:
• The basal layer (stratum basale) – contains stem cells responsible for skin regeneration. It also contains melanocytes that produce melanin, which is responsible for skin pigmentation.
• Spinous layer (stratum spinosum) – consists of several rows of cells connected by desmosomes, which provides the skin with mechanical resistance.
• Granular layer (stratum granulosum) – contains keratohyalin, a protein involved in the keratinization process.
• Stratum lucidum – occurs mainly in thick skin (e.g. on the hands and feet) and is composed of dead, flattened cells.
• Stratum corneum – the final stage of the keratinization process; it consists of dead cells that are gradually exfoliated.
The epidermal renewal process takes about 28 days and is regulated by hormonal factors and the body's repair mechanisms (Madison, 2003).
Dermis
The dermis is located beneath the epidermis and is composed primarily of connective tissue containing collagen and elastin fibers, which are responsible for its strength and elasticity. The dermis is richly vascularized, which allows for thermoregulation and the transport of nutrients (Baumann, 2007).
There are two layers of the dermis:
• Papillary layer (stratum papillare) – made of loose connective tissue, contains dermal papillae, which increase the surface area of contact with the epidermis. It contains numerous blood vessels and nerve endings.
• Reticular layer (stratum reticulare) – more compact, contains thicker collagen and elastin fibers, which provides the skin with mechanical resistance.
The dermis also contains sebaceous glands, sweat glands, and hair follicles.
Subcutaneous tissue (hypodermis)
The subcutaneous tissue, also known as the subcutaneous fat layer, consists mainly of adipose tissue and loose connective tissue. It has a cushioning, insulating and energy-producing function. Its thickness varies depending on the anatomical location and individual predispositions of the organism (Gniadecka et al., 1998).
Skin functions
The skin performs numerous physiological functions that are crucial for the proper functioning of the body:
1. Protection against external factors – the skin protects against microorganisms, UV radiation, chemicals and mechanical injuries. The stratum corneum acts as a hydrolipid barrier, preventing excessive water loss.
2. Thermoregulation – sweat glands and the mechanisms of contraction and relaxation of blood vessels regulate body temperature.
3. Sensory function – the skin contains receptors responsible for the reception of tactile, painful and thermal stimuli.
4. Excretion of toxic substances – through the sweat glands, the body removes metabolic products such as urea and mineral salts.
5. Vitamin D synthesis – under the influence of UV radiation, vitamin D3 is synthesized in the skin, which is necessary for the body's calcium-phosphate metabolism.
Skin care and health
Proper skin care is essential for its protective and aesthetic functions. Key aspects of skin care include:
• Hydration and proper diet – consumption of vitamins A, C, E and omega-3 fatty acids supports skin regeneration (Zouboulis et al., 2014).
• Protection against UV radiation – the use of sunscreens reduces the risk of skin cancer and photoaging.
• Skin hygiene – regular cleansing prevents excessive sebum production and bacterial growth.
• Prevention of skin diseases – acne, eczema or psoriasis require appropriate dermatological treatment
Summary
Human skin is an extremely complex structure that performs many important physiological functions. Its layered structure allows for effective protection of the body, temperature regulation and reception of external stimuli. Proper skin care, a balanced diet and protection from environmental factors are crucial for its health and proper functioning.
Bibliography
1. Baumann, L. (2007). Skin Aging and Therapy . McGraw-Hill.
2. Gniadecka, M., Nielsen, O. F., Wessel, S., & Heidenheim, M. (1998). Dermatology .
3. Madison, K. C. (2003). Barrier Function of the Skin: “La Raison d'Être” of the Epidermis . Journal of Investigative Dermatology.
4. Proksch, E., Brandner, J. M., & Jensen, J. M. (2008). The Skin: An Indispensable Barrier . Experimental Dermatology.
5. Zouboulis, C. C., & Adjaye, J. (2014). Human Skin: From Basic Biology to Clinical Dermatology .
