The epidermis is the furthermost superficial layer of the skin, in contact with the environment. It consists of layered, flat, and keratin-rich epithelial cells.
Its name derives from the Greek words epi , meaning above, and dermis , meaning skin. Thus, it means above the skin.
It is approximately 0.03 to 0.05 millimeters on the palms of the hands and 2 to 4 millimeters on the soles of the feet.
It acts as a protective covering for the body, enveloping almost all of it. The cells that compose it are formed in the deepest part of the epidermis and are filled with keratin until they reach the exterior. The normal maturation of the cells weakens the cell bonds when they reach the surface and promotes peeling to make way for the new cells that have been created in the depths of the epidermis.
Its thickness varies depending on where it is located. Thus, the palms of the hands and feet have thicker layers to protect them more, and in other areas, such as around the eyes, they are thinner. It is highly sensitive due to its nerve endings and lacks blood vessels.
Melanin is also produced when the skin is exposed to the sun. Its function is to act as a barrier to prevent radiation from passing through to the inner layers of the skin. The greater the amount of melanin, the greater the pigmentation.
Its importance goes beyond the aesthetic, fulfilling essential functions for life. The skin not only surrounds us, including natural openings such as the oral, respiratory and genitourinary mucous membranes, but also connects us to the environment, allowing us to feel and respond to it.
Structurally, it is made up of several layers: epidermis, dermis and hypodermis and a series of elements that constitute the skin appendages (hair and nails).
The skin is also a vital indicator of our overall health. Changes in its colour, texture or appearance can be warning signs of underlying diseases. For this reason, skin care is essential, not only to maintain its protective and aesthetic function, but also as a practice of monitoring our overall health.
Two substances reach the skin surface through the different pores of the skin: sebum, produced by the sebaceous glands; and sweat, secreted by the sweat glands. When they reach the surface of the skin, both secretions mix to form the emulsion known as the hydrolipidic film or mantle, which is essential for maintaining the level of hydration of the skin and which gives the appearance and soft texture of our skin.
The functions of the hydrolipidic film are to moisturise the skin and to act as a barrier to prevent the penetration of germs thanks to its antifungal and bacteriostatic properties; this is due to its acidic pH (4.5-5.9). It also constitutes a barrier against ultraviolet radiation from the sun, thus delaying ageing of actinic origin.
The skin is vital to our overall health and wellbeing. As well as acting as the body’s first line of defence against bacteria and viruses, healthy skin maintains fluid balance and helps regulate body temperature. It is highly sensitive and can recognise the lightest touch as well as pain. It is the largest and most visible organ, covering almost 2m² and accounting for almost 1/6 of our body weight. The condition of the skin can also have a significant impact on our self-esteem. The skin is the largest organ in the human body. In an average adult, it covers an area of approximately 2 square meters and weighs around 5 kg. It is in constant contact with the other organs of the body, and it is through it that our body reveals dysfunctions and ailments that affect us, as well as showing our emotions: we sweat when we are nervous, we blush if we are embarrassed by something, and there are emotions and stimuli that give us “goosebumps.”
It is a living organ with the ability to regenerate, it is waterproof, resistant and flexible, it breathes and remains active 24 hours a day carrying out all kinds of fundamental actions for our organism, the skin is a vital organ for the human body.
Cells
The cells of the epidermis are closely packed together and there is no intercellular substance between them. There are four types of cells in the epidermis:
- Keratinocytes : Present in greater numbers (95%), they are responsible for the production of keratin.
- Melanocytes : Responsible for the production of melanin , the pigment that gives color to the skin.
- Merkel cells : Responsible for the sensation of touch, they are located in the deep region of the epidermis.
- Langerhans cells : They are found in all layers of the epidermis and participate in skin protection, as they have the capacity for phagocytosis and activation of T lymphocytes. We can say that they are defense cells.
Content of each cm 2 of skin
Skin Layers
The skin is made up of the following layers. Each of them has specific functions:
- Epidermis
- Dermis
- Subcutaneous fat layer (hypodermis)
| Epidermis | The epidermis is the thin outer layer of the skin consisting of three types of cells:
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| Dermis | The dermis is the middle layer of the skin. It contains the following:
The dermis is held together by a protein called collagen. Collagen is made by fibroblasts. This layer gives the skin flexibility and strength. It also contains pain and touch receptors. |
| Subcutaneous fat layer | The subcutaneous fat layer is the deepest layer of the skin. It consists of a network of collagen and fat cells. It helps conserve body heat and protects the body from injury by acting as a shock absorber.
This layer also contains cells that can help regenerate the skin after injury. |
In addition to these three main layers, the skin is home to a variety of skin appendages, such as hairs and nails . These elements are not merely aesthetic features; they have specific functions that contribute to the health and protection of our organism. Hairs, for example, help regulate body temperature and act as a sensory barrier, while nails protect the limbs and improve the precision of fine movements.
Dermis and epidermis
Remember that the skin is basically made up of two layers: the epidermis and the dermis. The dermis is located just below the epidermis and is responsible for supporting and nourishing the most superficial layer of the skin.
The dermis is formed by dense connective tissue, consisting of collagen, glycoproteins and fibers of the elastic system. It is also formed by two layers: papillary and reticular.
Read also:
- Human Skin
- Skin layers
- Hypodermis
- Integumentary System
- Epithelial Tissue
Plant Epidermis
The epidermis also covers the body of plants, that is, it is a covering tissue of leaves, roots and stems. It consists of a layer of closely linked, chlorophyllous living cells.
It may also present some types of attachments, such as: stomata, hydathodes, trichomes, absorbent hairs and prickles.
See also: Plant Histology
Layers from a structural point of view
From a structural point of view, the skin is made up of several layers that work together to perform their multiple functions. When these layers are altered or lose continuity, the different basic skin lesions appear .
Stratum corneum
The stratum corneum is the outermost layer of the epidermis and is made up of dead, flattened, nucleated cells. The cells contain a large amount of keratin and are continually shedding.
Lucid layer
The stratum lucidum is more evident in thick skin (palms of the hands and soles of the feet), whereas in areas of the body where the skin is very thin, its presence is not noticeable.
It consists of a layer of flat, eosinophilic and translucent cells. In these cells it is not possible to observe the organelles and the nucleus, which have been digested by the enzymes of the lysosomes.
Granular layer
The stratum granulosum is formed by 3 to 5 layers of flattened polygonal cells, with a central nucleus and cytoplasm accumulated with basophilic granules (keratin-hyaline granules), which will give rise to keratin.
There are also lamellar granules, surrounded by a membrane, which fuse with the cytoplasm of the cells and release their lipid content into the intracellular space, forming a protective barrier that prevents water loss.
Stratum spinosum
The stratum spinosum consists of 5 to 10 layers of cuboidal cells, slightly flattened and with a central nucleus. One distinguishing feature is that the cells have cytoplasmic projections with keratin filaments (tonofilaments), which hold the cells together due to the presence of desmosomes. This arrangement gives this stratum a spiny appearance.
There are also keratinocyte stem cells that began their formation in the germinal layer.
Germinal or basal stratum
The stratum germinativum is the deepest layer of the epidermis and in contact with the dermis.
This layer is responsible for the renewal of the epidermis, presenting intense mitotic activity. The keratinocytes produced are constantly pushed to the upper layers and increase their keratin production. A basal cell takes up to 26 days to reach the stratum corneum, at which point it has reached maturity.
See also: Animal Histology
Functions and characteristics of the skin
What is the functions of the Epidermis and characteristics?
In general terms, we can say that the skin is the covering that covers the surface of the body, that is, the covering that separates the organism from the outside and, in turn, allows it to interact with it.
Formed by different layers, which we will discuss below, all its elements together fulfill the following functions:
- Protection. It represents a protective barrier against the invasion of microorganisms and against the action of mechanical, chemical, thermal and osmotic agents.
- Temperature regulation . Through perspiration, contraction and dilation of blood vessels, and reactions of body hair (such as when we get “goosebumps”), the skin acts as a thermostat for the body’s temperature.
- Hydration. The skin contains natural moisturizing factors (NMF ) that prevent water loss and help keep the skin looking elastic, firm and supple.
- Color and sun protection . The melanin contained in the skin is the pigment responsible for giving color to the epidermis and at the same time protecting us from ultraviolet radiation.
- Vitamin D synthesis . One of the positive effects of the sun on the skin is the synthesis of vitamin D, which is so necessary for bones, teeth, etc., as we saw in the article on the effects of the sun .
- Sensation . It is through the skin that our body can perceive sensations such as touch, pressure, pain, heat, cold… communicating with the central nervous system.
- Absorption . Thanks to the lymphatic and blood vessels we can absorb substances such as topical medications, ointments, lotions, creams, oils, etc.
- Elimination . Various substances are eliminated from the body through sweat and sebaceous secretion.
- Expression of emotions . When we blush or turn pale, for example, we express our emotional state through our skin.
- Emotional well-being and self-esteem . Healthy skin increases people’s self-esteem and improves their relationships with their environment.
- Psychological, social and aesthetic function : Healthy skin facilitates the social life and relationships of the individual with respect to their environment and improves their self-esteem.
pH of the skin
The most important role of the skin is its barrier function or protection against external agents .
The skin’s acid mantle (part of the hydrolipidic barrier) protects us precisely thanks to the acidity of this medium, which is unfavourable for microorganisms.
pH is a measure of the degree of acidity and is measured on a scale of 0 to 14.
From 1 to 7 is the acid zone, with 7 being the neutral pH corresponding to pure water and 7 to 14 corresponding to basic or alkaline pH. The pH of the skin’s acid mantle is between 4.5 and 5.9.
The pH of most of the skin on the body is 5.5 , although it varies slightly from one area to another and also according to sex, being slightly more acidic in men than in women.
Depending on age, pH values from birth to puberty are slightly more alkaline than in the rest of life. There is a marked increase in acidity from puberty onwards and a slight tendency towards alkalinity is seen again with increasing age . There are no differences based on race or skin colour.
The pH is slightly more alkaline in the armpit, groin and interdigital folds; therefore, they are less protected against external factors and are more vulnerable.
In general, vaginal pH is between 4 and 5, although it varies according to the woman’s age and is linked to the hormonal changes she experiences throughout her life and the menstrual cycle. In girls up to puberty and during menopause in women, vaginal pH is around 7.
If the pH value rises to basic levels, the skin’s balance is altered , it loses water and becomes dehydrated due to not being able to synthesize the essential lipids of the epidermis and the barrier function is altered. When the surface pH is more alkaline, itching and dermatitis of a non-specific nature occur . Any change in pH that is not immediately compensated stimulates the skin to produce more acid to restore the balance – the buffer system – The ability to neutralize will depend on the ability of the deeper layers to send acids to the surface.
Factors that affect the pH of the skin
Factors that affect the pH of the skin
The pH of the skin can be altered by:
- Intrinsic factors of the organism
As mentioned, age, body area, genetic factors and sex of the individual, associated with hormonal changes, lead to changes in the pH of our skin.
- External factors
There are external factors that harm our skin or worsen its condition and appearance:
Tips to prevent skin deterioration
Tips to prevent skin deterioration
- Drink 2 liters of water per day.
- Avoid alcohol and cigarettes.
- Maintain a balanced diet, with special emphasis on fruits and vegetables.
- Cleanse your skin daily to prevent clogged pores so that your skin can breathe normally and eliminate impurities. Using creamy soaps for your hygiene also helps keep it nourished.
- Perform physical activity, considering a routine that involves exercising several times a week.
- Take the necessary precautions when exposing yourself to the sun, use sunscreen and not sunblock, with at least SPF 15, applying it half an hour before exposure and reapplying it every 2 hours and after going into the water.
