Skin Layers + Structures, functions and roles of the skin
The skin is the largest organ in the human body, it represents for 16% of its total weight. Composed of several skin layers of tissue, it forms a protective barrier for the body against the external environment, but also performs other vital functions. The medical specialty dealing with the skin and its affections is dermatology.
What is the skin made of?
From a chemical standpoint, the skin comprises on average:
– 70% water.
– 27.5% protein.
– 2% fat.
– 0.5% of mineral salts and trace elements.
It is made up of three layers:
– The epidermis, the surface layer
– The dermis, intermediate layer
– The hypodermis, deep layer
1. The epidermis (1st skin layer)
The epidermis is a semi-permeable covering epithelial tissue. It is made up of three types of cells:
– Keratinocytes, filled with keratin (protein also used in the composition of hair and nails) and lipids
– Melanocytes, which produce the melanin responsible for the pigmentation of the skin
– Langherans cells, which participate in the skin’s immune system
The epidermis itself divides into five layers.
– Horny layer (stratum corneum), composed of corneocytes, results of the final phase of mutation of keratinocytes which gradually rise from the basal layer, and epidermal lipids.
Its lower third constitutes a real protective barrier against exogenous factors (pollution, sun, cold) and endogenous water loss.
– Clear layer (stratum lucidium), which corresponds to a transition phase between the granular layer and the horny layer.
– Granular layer (stratum granulosum), where keratinization of keratinocytes (which evolve into corneocytes) begins.
– Spiny layer or mucous body of squamous, comprising 3 to 10 layers of keratinocytes which gradually flatten towards the surface.
– Basal layer, the deepest part of the epidermis. It ensures the continuous regeneration of the skin by cell division: the cells produced gradually migrate to the upper layers undergoing various mutations. Between these basal cells are intercalated the melanocytes, responsible for melanogenesis.
2. The dermis (2nd skin layers)
The dermis is a connective tissue, which supports the epidermis, protects the vascular network and nerve fibers. The dermis is divided into two layers:
– The papillary dermis (superficial dermis), an intermediate layer rich in nerve endings and in permanent symbiosis with the epidermis, from which it is separated by the dermo-epidermal junction
– The reticular dermis (deep and middle dermis), a dense connective tissue made up of a network of elastic fibers.
It has different types of cells:
– Fibroblasts (cells that synthesize collagen, a protein essential for tissue elasticity)
– Histiocytes and mast cells, which play an important role in the immune reactions of the skin.
3. The hypodermis (3rd skin layers)
The hypodermis is fatty tissue found under the dermis. It is crossed by the vessels and the nerves arriving in the dermis.
It plays several roles:
– Protective, it acts as a shock absorber between the dermis and the bones
– Thermal insulator
– Morphological, it models the silhouette according to the age, sex, nutritional status of the individual
– Energetic, by storing fat.
In the dermis and hypodermis, what are called the skin appendages also originate:
– The eccrine sweat glands (or sweat glands), which produce watery sweat
– The apocrine sweat glands, responsible for body odor
– The sebaceous glands which secrete sebum, this hydrolipidic film that protects the epidermis
– The hair follicles of the hairs and the hair, associated with a sebaceous gland.
The skin is essential for our overall health and well-being. Healthy skin acts as a barrier between the outside world and the inside of our body. This is our first and best defense against:
Cold, heat, dehydration and radiation: the stratum corneum is the one located outermost of the skin. It therefore plays an essential role in protecting the body against its environment and limiting dehydration of the epidermis.
It contains natural hydration factors, derived from the sebaceous lipids of the stratum corneum, including lactic acid and urea. Their water-retention power helps to preserve the elasticity, firmness and suppleness of the skin. If the amount of factors decreases, the skin becomes dehydrated. When the humidity of the stratum corneum (the outermost cell layer of the epidermis, the most superficial tissue of the skin) drops below 8-10%, it becomes rough, dry, and prone to cracking.
When the skin is regularly exposed to UV rays, the production of melanin in the basal layer increases, the skin thickens to protect itself and hyperpigmentation can appear.
The fat cells in the hypodermis also insulate the body from cold and heat.
Pressures, knocks and scratches: once again, the epidermis is our first line of defense. Fat cells in the hypodermis provide shock absorbing protection, protecting muscle tissue and fasciae (the fibrous tissue that surrounds muscles) below.
When the skin is exposed to certain external stimuli, the stratum corneum thickens, for example when calluses form on hands or feet exposed to repetitive rubbing.
Chemicals: The buffering power of the hydrolipid film and the protective acid mantle helps protect the body from harmful alkaline chemicals.
Bacteria and viruses: the horny layer of the epidermis and its protective acid mantle form a barrier against bacteria and fungi. If something enters this first line of defense, the skin’s immune system responds.
Multitasking organ par excellence, the skin plays other essential roles for our health and our well-being:
Temperature regulation: the skin sweats to cool the body and contracts the vascular system of the dermis to retain heat.
- Sensation Control: The nerve endings in the skin make it sensitive to pressure, vibration, touch, pain and temperature.
- Regeneration: the skin is able to repair its wounds.
- Source of energy: Fat cells in the hypodermis serve as important nutrient storage units. When the body needs them, they pass into the surrounding blood vessels and are transported to where they are supposed to act.
The skin also plays an important psychological role: it is the most visible indicator of our state of health. Its appearance influences how others and ourselves perceive ourselves. When the skin is healthy, it can perform its functions better. We feel more comfortable and more confident.
Information: Cleverly Smart is not a substitute for a doctor. Always consult a doctor to treat your health condition.
Photo description: the structure of human skin (skin layers).