INTEGUMENTARY SYSTEM: CHARACTERISTICS, FUNCTIONS, PARTS, DISEASES - ANATOMY AND PHYSIOLOGY - 2025

The integumentary or integumentary system is formed by the skin and its annexes, that is, the sweat and sebaceous glands, the hair and the nails. It is the largest organ in the human body, constituting approximately 16% of total body weight.

This organ covers the entire body and continues with the digestive system through the lips and anus, with the respiratory system through the nose, and with the urogenital system. It also covers the external auditory canal and the external surface of the tympanic membrane. In addition, the skin of the eyelids continues with the conjunctiva and covers the anterior part of the orbit.

Layers of skin in areas with and without hair. Madhero88 and M.Komorniczak

The integumentary system represents a protective barrier that protects internal organs, helps maintain hydration and body temperature, is the seat of many sensory receptors that allow the nervous system to acquire information from the external environment.

It also produces several substances of metabolic importance; one of them is vitamin D, essential for calcium metabolism, and the other is melanin, which prevent the excessive penetration of ultraviolet rays from the sun.

Many diseases can cause skin disorders, however, this tissue can also suffer from its own diseases such as warts, carcinomas, infections, etc.

Characteristics of the integumentary system

The integumentary system is composed mainly of the skin and its accessory or attached structures. In an average human being, these tissues represent up to 16% of body weight and can be between 1.5 and 2 square meters in area.

The skin is not a uniform tissue, depending on the region that is observed it can have different thicknesses, textures and distribution of accessory structures. For example, the skin on the soles of the feet and the palms of the hands is thick and has no hairs, but there are abundant sweat glands.

Furthermore, the fingertips and toes contain ridges and grooves called "dermatoglyphs" or "fingerprints", which are genetically determined and develop during fetal life, remaining unchanged for the rest of life.

At the level of the knees, elbows and hands, there are other grooves and folding lines related to physical efforts and regular use. On the eyelids, the skin is soft, very thin, and has fine villi; the skin and hairs of the eyebrows, on the other hand, are much thicker.

Layers of skin

The skin is made up of two layers, which are the epidermis and the dermis, under which is the hypodermis, a loose tissue where variable amounts of fat accumulate (adipose pad) that support the cells of the upper layers.

Roles and importance

The integumentary system is of utmost importance for man and other animals; it works in the protection of the body against irradiation, injury, invasion of pathogenic microorganisms, desiccation or dehydration and also works in the control of body temperature.

Control of body temperature

The function of controlling body temperature is perhaps one of the most important, favoring heat loss due to vasodilation of the blood vessels that irrigate the skin, so that warm blood is distributed to the skin that is colder and dissipates hot.

In addition, the sweat glands, by secreting sweat and this evaporating on the surface of the skin, eliminate heat. When the environment is cold, on the contrary, there is vasoconstriction of the dermal vessels and the blood is "confined" in the hottest areas, protecting the body from heat losses.

How is the integumentary system constituted? (parts)

The integumentary system is made up of the skin and its accessory or attached structures. Next, the description of each of these parts:

- The skin

The skin has two structural components, the outermost is called the epidermis (a superficial epithelium) and the innermost is the dermis (a layer of connective tissue).

The interface between the dermis and the epidermis is formed by "fingerings" of the dermis that are introduced into invaginations present in the epidermis and that together are called the reticular apparatus.

Epidermis

This is the most superficial layer of the skin. Embryologically it is derived from endodermal tissue and its epithelium is squamous, stratified and keratinized. It measures between 0.02 and 0.12 millimeters thick in most of the body, being thickest on the palms of the hands and the soles of the feet, where it can be between 0.8 and 1.4 millimeters.

Continuous pressure and friction in these areas causes continuous increases in the thickness or thickness of the skin.

The epithelium of the epidermis is made up of four types of cells:

- Keratinocytes: these are the most abundant cells, responsible for the production of keratin, a structural fibrous protein.

- Melanocytes: they produce melanin, a substance that gives the skin a dark color.

- Langerhans cells: antigen presenting cells, that is, they have immune functions and are also known as “dendritic cells”.

- Merkel cells: they have functions in mechanoreception, they are very abundant in the oral mucosa, the base of the hair follicles and the fingertips.

Keratinocytes

Keratinocytes are arranged in five well-defined layers or strata that are known, from the inside out, as the stratum basal germinative, stratum spinosum, stratum granulosa, stratum lucid, and stratum corneum.

The basal or germinal stratum is an isolated layer of cuboidal cells with abundant mitotic activity; it is separated from the dermis by a basement membrane. Merkel cells and melanocytes are also scattered in this layer.

The stratum spinosum is the thickest layer of the epidermis and the keratinocytes that belong to it are known as "spiny cells", which are interdigitated with each other, forming intercellular bridges and desmosomes. Langerhans cells also exist in this layer.

The stratum granulosa contains nucleated keratinocytes rich in keratin granules that line its plasma membrane; there may be 3 to 5 layers of cells in this stratum.

The stratum lucid has enucleated keratinocytes lacking other cytosolic organelles. It is a very thin layer that, when stained in histological sections, acquires a very light coloration, which is why it is known as "lucid". Keratinocytes in this stratum possess abundant keratin fibers.

Finally, the stratum corneum is made up of multiple layers of dead, flat, keratinized cells whose fate is "desquamation", as they are continuously eliminated from the skin.

Keratinocyte migration

Keratinocytes in the epidermis are formed in the germ layer or the basal layer, from which they are "pushed" towards the surface, that is, towards the other four upper layers. During this process, these cells degenerate until they die and peel off in the superficial part of the epidermis.

The half-life of a keratinocyte, from when it is produced in the stratum basalis until it reaches the stratum corneum, is approximately 20 or 30 days, which means that the skin is constantly regenerating.

- Dermis

The dermis is the layer of skin that is located immediately below the epidermis. Embryologically it is derived from the mesoderm and is composed of two layers: the lax papillary layer and a deeper layer known as the dense reticular layer.

This layer is actually a dense and irregular collagenous connective tissue, essentially composed of elastic fibers and type I collagen, which support the epidermis and bind the skin to the underlying hypodermis. Its thickness varies from 0.06 mm on the eyelids to 3 mm on the palms of the hands and the soles of the feet.

The dermis in humans is generally thicker on the dorsal surfaces (the back of the body) than on the ventral ones (the front of the body).

Lax papillary layer

This is the most superficial layer of the dermis, it interdigitates with the epidermis, but is separated from it by the basement membrane. It forms the dermal ridges known as papillae and is made up of loose connective tissue.

This layer contains cells such as fibroblasts, plasma cells, primers, macrophages, among others. It has many capillary bundles that extend to the interface between the epidermis and the dermis and nourish the epidermis, which does not have blood vessels.

Some dermal papillae contain so-called Meissner's corpuscles, which are "pear-shaped" structures that have mechanoreceptor functions, capable of responding to deformations of the epidermis, especially in the lips, external genitalia and nipples.

Also in this layer are the terminal bulbs of Kraus, which are other mechanoreceptors.

Dense reticular layer

It is considered a "continuous" layer with the papillary layer, but it is composed of dense and irregular collagenous connective tissue, composed of thick collagen I fibers and elastic fibers.

In this layer there are sweat glands, hair follicles and sebaceous glands, in addition, it has mast cells, fibroblasts, lymphocytes, macrophages and fat cells in its deepest part.

As in the papillary layer, the reticular layer possesses mechanoreceptors: the corpuscles of Pacini (which respond to pressure and vibrations) and the corpuscles of Ruffini (which respond to tensile forces). The latter are especially abundant on the soles of the feet.

- Accessory structures of the skin

The main accessory structures are the sweat glands (apocrine and eccrine), the sebaceous glands, the hair and the nails.

Sweat glands

These can be apocrine or eccrine. Eccrine sweat glands are distributed throughout the body and it is estimated that there are more than 3 million of these, which are importantly involved in body thermoregulation.

These glands can produce up to 10 liters of sweat per day in extreme conditions (people who perform vigorous exercise). These are simple tubular spiral glands, about 4 mm in diameter, found deep in the dermis or in the hypodermis.

They secrete sweat through a duct that opens to the epidermis in the form of a "sweat pore." The secretory unit of these glands is formed by a cubic epithelium, made up of "light" cells, which shed a watery secretion, and "dark" (mucoid cells).

The apocrine sweat glands are only located in the armpits, the areoles of the nipples and in the anal region; These are considered "vestigial" scent glands. Apocrine glands only develop after puberty and have to do with hormonal cycles.

They differ from eccrine glands in that their secretions drain towards the hair follicle and not directly towards the surface of the epidermis. These secretions are slimy and odorless, but when metabolized by bacteria it acquires a characteristic odor.

The ceruminous glands of the external auditory canal and Moll's glands, found in the eyelids, are modified apocrine sweat glands.

Sebaceous glands

The secretions produced by these glands are oily and collectively known as "bait"; These participate in the preservation of the texture and flexibility of the skin. They are found throughout the body, embedded in the dermis and hypodermis, except on the palms of the hands, the soles of the feet and the side of the feet, just below the line where the leg hairs end.

They are particularly abundant on the face, forehead, and scalp. The composition of your secretions is a fatty, wax-like combination of cholesterol, triglycerides, and secretory cellular debris.

Hair and nails

Nails and hair in humans (Source: Nails: NickyayHair: Maria Morri https://www.flickr.com/people/ via Wikimedia Commons)

The hairs are filamentous structures covered by a protein called keratin, which arise from the surface of the epidermis.

They can grow all over the body, except on the labia, on the female and male genitalia (glans penis and clitoris, as well as on the labia minora and majora of the vagina), on the palms of the hands, soles of the feet, and on the phalanges of the fingers.

It fulfills essential functions of protection against the cold (regulation of body temperature) and radiation from the sun (to the scalp); hairs also function as sensory and cushioning structures, but this is especially true for animals.

The hair on the skin of animals also serves as protection (Image by Susanne Jutzeler, suju-photo on www.pixabay.com)

Nails are keratinized epithelial cells arranged in plates. They develop from special cells in the “nail matrix” that proliferate and keratinize; its main function is to protect the "sensitive ends" of the fingertips.

Main organs

The main organs of the integumentary system are:

- The skin, with its dermis and epidermis

- The sweat, eccrine and apocrine glands

- The sebaceous glands

- Hair

- The ones

Diseases

Multiple diseases can affect the integumentary system, in fact, in medicine there is a branch dedicated exclusively to the study of them and this is known as dermatology.

Acne

One of the most common skin disorders is acne, a chronic condition that affects the sebaceous glands and hair follicles, suffered especially by young people at the beginning of puberty.

Warts

Warts are benign epidermal growths caused by infections of the keratinocytes by a papillomavirus; they are common in children, adults and young people, as well as in immunosuppressed patients.

Carcinoma

The most common malignancy of the integumentary system in humans is basal cell carcinoma, which is usually due to exposure to ultraviolet radiation. Although it does not usually present metastasis, this pathology destroys local tissue and its treatment is generally surgical, with a 90% successful recovery.

The second most common cancer in the integumentary system of man is squamous cell carcinoma, which is characterized by being "local" and metastatic invasive.

It deeply invades the skin and attaches itself to the tissues below it. Its most common treatment is also surgical and the factors most related to its appearance are exposure to X-rays, soot, chemical carcinogens and arsenic.

Common infectious diseases

Among the most common infectious skin conditions are cellulite. Leprosy and attack by protozoans such as Leishmania spp.

In addition, diseases of various origins can also present obvious skin manifestations, such as lupus erythematosus.

Integumentary system hygiene

To maintain the correct functioning of the integumentary system and avoid infectious diseases, it is necessary to clean the skin regularly with soap and water using, if possible, soft sponges that allow accelerating the detachment of the superficial layers of dead cells without producing skin abrasions.

The daily hygienic routine of the integumentary system should include baths with plenty of soap and water and thorough drying of the body, paying special attention to the interdigital spaces of the feet and hands.

Appropriate footwear should be used to allow the feet to be ventilated, avoiding excessive sweating and the proliferation of bacteria and fungi.

The moisture of the skin is of utmost importance for its proper maintenance, so the application of moisturizing lotions is essential, especially in the most exposed areas; The use of sunscreen is also recommended to avoid burns.

References

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2. Dudek, RW (1950). High-Yield Histology (2nd ed.). Philadelphia, Pennsylvania: Lippincott Williams & Wilkins.
3. Gartner, L., & Hiatt, J. (2002). Text Atlas of Histology (2nd ed.). Mexico DF: McGraw-Hill Interamericana Editores.
4. Johnson, K. (1991). Histology and Cell Biology (2nd ed.). Baltimore, Maryland: The National medical series for independent study.
5. Kuehnel, W. (2003). Color Atlas of Cytology, Histology, and Microscopic Anatomy (4th ed.). New York: Thieme.
6. Ross, M., & Pawlina, W. (2006). Histology. A Text and Atlas with correlated cell and molecular biology (5th ed.). Lippincott Williams & Wilkins.