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Lecture notes, cheat sheets
Dermatovenerology. Structure and functions of the skin (most important)
Directory / Lecture notes, cheat sheets Table of contents (expand) LECTURE No. 1. The structure and functions of the skin Dermatovenereology - a branch of medical science that studies skin diseases, which are a manifestation of the pathology of internal organs and systems, a reflection on the skin of only a part of the lesion of the whole organism. Leather - this is an element of the body's immune system, a protective cover of a person, which has an impact on the functioning of all internal organs and systems. The skin performs a number of vital functions that ensure the normal functioning of all body systems. The main functions of the skin include: protective function (mechanical protection, UV protection, protection against microorganisms, maintaining water balance), thermoregulatory function, metabolic function, receptor function, participation in water-salt metabolism, excretory function (excretion with sweat and sebum metabolic products, medicinal and toxic substances), resorption function (absorption into the systemic circulation of substances that enter the skin by superficial vascular plexuses), immune function (synthesis of interleukins and other cytokines in the epidermis, capture, processing and transport of antigens). The skin consists of three main layers tightly attached to each other: epidermis, dermis and subcutaneous fat. There are two main types of skin: thick and thin. Thick skin (more than 5 mm thick) covers the palms and soles, it is characterized by thicker epidermis and its stratum corneum than in other parts of the body, as well as a relatively thin dermis. Thin skin (1-2 mm thick) covers all other parts of the body, is characterized by the presence of a thin epidermis, as well as a very pronounced dermis. Hair and sebaceous glands are present only in thin skin. Epidermis is a stratified squamous keratinized epithelium of the epidermal type. The bulk of the cells of the epidermal layer are keratinocytes (epidermocytes), there are also dendritic cells. The epidermis consists of the following layers: basal, spiny, granular, shiny (only present in the skin of the palms and soles), and horny. The basal layer is located on the basement membrane. The cells of the basal layer (basal keratinocytes) are arranged in one row and have a cubic or prismatic shape and a large light nucleus. The basal layer is called the cambial layer of the epidermis. In the basal layer, stem cells are located, due to which the layer of the epidermis is constantly replenished as a result of their constant division. The stratum spinosum is represented by 3-15 rows (thick skin contains a larger number of rows) of polygonal cells, which are firmly connected to each other due to interdigitations and desmosomes. A large number of intercellular contacts such as desmosomes around each cell (up to 2000) resemble spines. The cells of the stratum spinosum contain keratinosomes. These are single specific granules. Spicular keratinocytes retain the ability to divide by mitosis, and therefore the basal and spinous layers of the epidermis are collectively called the “germinal layer.” The granular layer is represented by 1-3 rows of spindle-shaped cells with a dark nucleus and inclusions in the cytoplasm (keratohyaline granules). These inclusions contain a protein that ensures the process of keratinization of keratinocytes - filaggrin. Filaggrin promotes aggregation, resulting in the transformation of the cell into a postcellular structure - a horny scale (horny plate). The shiny layer is present only in areas of thick skin. It consists of 1-2 rows of oxyphilic cells with unclear boundaries and poorly defined organelles. When examined under an electron microscope, it is clear that this layer represents the lower rows of the stratum corneum. The stratum corneum is represented by horny scales - postcellular structures, which are sometimes called cornetites. They do not contain nuclei and organelles, but are rich in keratin and constantly exfoliate. The thickness of the stratum corneum of the epidermis depends on the anatomical localization of the skin area. In the epidermis, a dynamic balance is maintained between the number of desquamated horny scales and the proliferation of basal keratinocytes. The protective function of the skin consists in the constant renewal of the epidermis: due to the rejection of horny scales from the surface of the skin, it is cleansed of external pollution and microorganisms. The rate of renewal of the epithelial layer depends on the localization, on average it is about 28 days. In the epidermis, in addition to keratinocytes, there are three types of dendritic cells: melanocytes, Langerhans cells (pigmentless dendrocytes), Merkel cells. Melanocytes (pigmented dendritic cells, pigmented dendrocytes) are localized in the basal layer of the epidermis in white-skinned individuals. In representatives of the Negroid race, as well as in representatives of the Caucasian race, in places of natural pigmentation, these cells are also found in the spinous layer. Langerhans cells (non-pigmented dendritic cells, intraepidermal macrophages) are elements of monocytic origin responsible for antigen capture, processing, antigen presentation and interaction with T-lymphocytes of the dermis. These cells participate in immune reactions, produce lysozyme and interferon. Merkel cells (tactile epitheliocytes) are located in the basal layer of the epidermis and in the epithelium of the hair follicles. These cells are of neuroglial origin and are involved in the formation of tactile sensations on the skin. Dermis. It consists of two layers that are not clearly demarcated from each other: papillary and reticular. The first is adjacent directly to the epidermis and is represented by loose fibrous connective tissue. The papillary dermis defines the pattern of ridges and grooves on the surface of the skin. The pattern of the skin on the palms and soles is strictly individual. The reticular layer of the dermis is formed by dense, irregular fibrous connective tissue. It contains fibrous structures: collagen, elastic and reticular fibers. Subcutaneous fat. This is a continuation of the dermis, consisting of white adipose tissue and layers of loose fibrous connective tissue. The thickness of the dermis depends on location, gender and nutrition. The distribution of subcutaneous fat is regulated by sex hormones. Blood vessels. The blood supply to the skin is carried out by two arterial and venous plexuses - superficial and deep. Lymphatic system of the skin. It is represented by a superficial network, which begins with the papillary sinuses (in the papillae of the dermis), and a deep network (in the hypodermis), between which the efferent vessels are located. Nerve fibers. Innervation of the skin is provided by afferent and efferent fibers, forming the subepidermal and dermal plexuses. Appendages of the skin Sebaceous glands. They belong to simple alveolar glands, consist of terminal sections and excretory ducts and are characterized by a holocrine type of secretion. The vast majority of sebaceous glands are associated with hair follicles, and their ducts open into the mouths of the hair follicles. In the area of the back of the hands, on the red border of the lips, there are few sebaceous glands, and they are small in size. On the skin of the face (on the eyebrows, forehead, nose, chin), scalp, midline of the chest, back, armpits, perianal and perigenital areas, the number of sebaceous glands is large and reaches 400-900 per 1 cm2, and the glands there are large and multilobular . The sebaceous glands secrete a complex secretion called sebum. The composition of sebum includes free and bound (esterified) fatty acids, small amounts of hydrocarbons, polyhydric alcohols, glycerol, cholesterol and its esters, wax esters, squalene, phospholipids, carotene, as well as metabolites of steroid hormones. A special biological role is played by unsaturated fatty acids, which have fungicidal, bactericidal and virusostatic properties. Sebum secretion is regulated mainly by hormonal and, to a lesser extent, neurogenic mechanisms. Androgens increase the secretion of sebum. Sweat glands. They are divided into eccrine (simple tubular) and apocrine (simple tubular-alveolar) glands. Eccrine sweat glands are located on all parts of the skin. They begin to function from the moment of birth and are involved in thermoregulation. They consist of a terminal secretory section and an excretory duct. The terminal section is located in the subcutaneous adipose tissue, contains myoepithelial and secretory (light and dark) cells, the activity of the latter is regulated by cholinergic nerve fibers. The excretory ducts open freely on the surface of the skin and are formed by a two-layer cuboidal epithelium. Apocrine sweat glands are located only in some parts of the body: in the skin of the armpits, areolas of the nipples of the mammary glands, perianal, perigenital areas. Sometimes they are found on the skin around the navel, in the sacrum. These glands begin to function during puberty. Hair. They are keratinized thread-like appendages of the skin. Adults have up to 2 million hairs on the surface of the body, of which there are up to 100 thousand on the head. The structure of hair is genetically determined and largely depends on race. The hair consists of a shaft protruding above the level of the skin, and a root located in the hair follicle, immersed deep in the dermis and subcutaneous fatty tissue. Author: Sitkalieva E.V. >> Forward: Parasitic dermatoses (Scabies. Lice)
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