SKIN STRUCTURE
Here you have an interactive explanation of the different LAYERS and APPENDICES of the skin.
Start
THE SKIN
More Info
The largest organ in the human body, with almost 2-3 kg weight
APPINDICES:
3 LAYERS:
More Info
More Info
EPIDERMIS
EPIDERMIS
01
Roof
HAIR FOLLICLE
04
DERMIS
02
Framework
SEBACEOUS GLAND
05
HYPODERMIS
03
Food supply cellar
EPIDERMIS
01
Direct contact with the environment
Next
EPIDERMIS
Direct contact with the ouside environment Role: ▹Protection from external aggression ▹ Prevention of water loss The epidermal turnover lasts between 21 and 28 days
Water
Hydrolipidic film
Microbiome
Corneocytes and intercorneocyte cement
More Info
VEGF
Melanocytes
Keratinocytes
NMF
Langerhans cells
Aquaporins
Dermal-Epidermal Junction
DERMIS
02
The external appearance of the skin
Next
DERMIS
Role: Responsible for the density, suppleness and the external appearance of the skin.
More Info
Fibroblasts
HA
Blood vessels
Collagène fibres
Extracellular matrix
Nerve fibres
Elastin fibres
MMP
HYPODERMIS
03
Skin's energy reserve and thermal insulator
Next
HYPODERMIS
It is the deepest layer of the skin. The adipocytes are the fat cells.
Stock absorber
Varies with gender
Varies with eating habits
Thermoregulating barrier
More Info
HAIR FOLLICLE
04
Whole part that contains the hair
Next
HAIR FOLLICLE
Hair shaft
The whole part that contains the hair is called a hair follicle, and it is composed of many parts. The hair is replaced on a 2- to 6-year cycle. The number of cycles is programmed genetically
20 to 25 in one lifetime.
Medullary canal
Bulb
Blood vessels
Arrector muscle
Apocrine sweat gland
More Info
Sebaceous gland
SEBACEOUS GLAND
05
The sebaceous gland produces the sebum
Next
SEBACEOUS GLAND
Sebum, which makes up a portion of the hydrolipidic film, is produced by the sebaceous gland, which is usually connected to each hair follicle. This is why the term pilosebaceous follicle is used.
Sebaceous gland
Sebocytes
Sebum
Blood vessels
More Info
BLOOD VESSELS
They are key player of the dermis. They transfer oxygen and take away waste from the cells. Role: They are responsible for skin nutrition.
DYNAMIC WATER
There are almost 6 to 8 litres of water in the skin.Even though the majority of water in the skin exists in the dermis, yet, it needs to be transferred to every single part of the body. This dynamic water circulates in channels (aquaporins). It is preserved by 3 elements: aquaporins, hydrolipidic film and intercorneocyte cement.
MEDULLARY CANAL
The gland exerts sebum into the canal, where the hair is located. This canal is called the medullary canal.
ARRECTOR PILI MUSCLE
The arrector pili muscle is a tiny band of smooth muscle attached to each hair follicle. Role: It contracts in response to cold or emotional stimuli, causing the hair to stand upright and producing “goosebumps”.
SEBACEOUS GLAND
The hair shaft needs to be lubricated. This is why every hair in our body is attached to a lubricating machine that is producing oil, or sebum. This is why it is called the sebaceous glands.
More Info
VASCULAR ENDOTHELIAL GROWTH FACTOR (VEGF)
This protein is produced by the keratinocytes and targets the endothelial cells on the blood vessel walls to make them grow (angiogenesis).Roles: Dilation and permeability of blood vessels = Skin messenger of redness
APOCRINE SWEAT GLAND
n apocrine sweat gland is a specialised gland found mainly in areas such as the armpits and groin. Role: It produces a thicker sweat that, when broken down by skin bacteria, is linked to body odour and also plays a role in scent communication.
HYPODERMIS
The hypodermis acts as a thermal insulator, as a strategy for storing lipids, indirect sources of energy, in a place that also makes use of these insulating properties.
SEBACEOUS GLAND
The hair shaft needs to be lubricated. This is why every hair in our body is attached to a lubricating machine that is producing oil, or sebum. This is why it is called the sebaceous glands.
MELANOCYTES
Cells which are responsible for the colour of the skin, the eyes and the hair, by producing melanin.Role: Sun protection and skin colour.
CORNEOCYTES
Dead keratinocytes on the surface.
INTERCORNEOCYTE CEMENT
Lipids (ceramides, cholesterols, free fatty acids) and proteins surrounding corneocytes. Role: Fill in the gap between the cells. Such as a wall, cornocytes are the bricks and these fillers are the mortar or the cement (hence this name).
LANGHERHANS CELL
The immune cells of our skin, such as the life guard of the skin (sentinel), fight against invading bacteria and germs. Role: Guarding the skin from infection, key role in immunity.
LANGHERHANS CELL
The immune cells of our skin, such as the life guard of the skin (sentinel), fight against invading bacteria and germs. Role: Guarding the skin from infection, key role in immunity.
MEDULLARY CANAL
The gland exerts sebum into the canal, where the hair is located. This canal is called the medullary canal.
NERVE FIBRES
The nerve fibres transfer feeling (such as pain, discomfort, cold/hot sensations). In healthy skin, they can be up to the tips of the epidermis. However, in sensitive skin, they can be higher than that.
BULB
At the bottom of the medullary canal, there is the dermal papilla, which is the dermis' live cells. This one composed the bulb.
DYNAMIC WATER
There are almost 6 to 8 litres of water in the skin.Even though the majority of water in the skin exists in the dermis, yet, it needs to be transferred to every single part of the body. This dynamic water circulates in channels (aquaporins). It is preserved by 3 elements: aquaporins, hydrolipidic film and intercorneocyte cement.
ARRECTOR PILI MUSCLE
The arrector pili muscle is a tiny band of smooth muscle attached to each hair follicle. Role: It contracts in response to cold or emotional stimuli, causing the hair to stand upright and producing “goosebumps”.
COLLAGEN FIBRES
Collagen fibres are structural proteins that form a supportive framework within the skin.Role: They provide strength, firmness, and elasticity, helping the skin maintain its shape and resilience.
DERMAL-EPIDERMAL JUNCTION (DEJ)
It is the junction between the epidermis and the dermis, sinuous and homogeneous. Roles: Cohesion and communication (diffusion filter: nutrients, metabolites, water, mineral salts).Indeed, there are no blood vessels in the epidermis, on the top, so it needs some mechanisms to exchange between the two layers.
FIBROBLASTS
The main live cell in the dermis is the fibroblast. Role: The fibroblasts produce collagen fibres, elastin fibres and hyaluronic acids.
HYALURONIQUE ACID (HA)
Hyaluronic acid is a linear, non-branched polysaccharide belonging to the glycosaminoglycan (GAG) family.In the skin, HA is a natural component of the dermis and one of the main components of the extracellular matrix.. Role: Skin's hydration (acts as a water reservoir), tone and elasticity.
More Info
DERMAL-EPIDERMAL JUNCTION (DEJ)
It is the junction between the epidermis and the dermis, sinuous and homogeneous. Roles: Cohesion and communication (diffusion filter: nutrients, metabolites, water, mineral salts).Indeed, there are no blood vessels in the epidermis, on the top, so it needs some mechanisms to exchange between the two layers.
HYDROLIPIDIC FILM
Waterproof film on the surface, made from water and lipids (as the name indicates).Water comes from sweat, the atmosphere and the dermis. Lipids come from sebum and the skin lipids of the dead cells. Role: Ensures impermeability of the skin, and hence better protection. Keep water from evaporating.
THE 3 LAYERS
House model
The skin is composed of three layers, arranged from top to bottom: Epidermis, dermis and hypodermis.
If we imagine the skin as a house:
- The epidermis is the roof.
- The dermis is the framework.
- The hypodermis is the food and supplies inside the house (=food supply cellar).
BLOOD CAPILLARIES
The sebaceous gland is fed by blood capillaries that provide nutrients, sugars, hormones and enzymes necessary for its function, in particular 5α reductase, which is a key enzyme in sebum secretion.
KERATINOCYTES
There are living cells in the epidermis, and the majority of cells of this layer (almost 80%). These cells produce keratin, a strong protein important for the nails, hair and teeth. They divide at the bottom of the epidermis and go up until they are eliminated (desquamation): this journey can take up to 28 days.
APOCRINE SWEAT GLAND
An apocrine sweat gland is a specialised gland found mainly in areas such as the armpits and groin. Role: It produces a thicker sweat that, when broken down by skin bacteria, is linked to body odour and also plays a role in scent communication.
KERATINOCYTES
There are living cells in the epidermis, and the majority of cells of this layer (almost 80%). These cells produce keratin, a strong protein important for the nails, hair and teeth. They divide at the bottom of the epidermis and go up until they are eliminated (desquamation): this journey can take up to 28 days.
SEBOCYTES
Inside the sebaceous gland, there are specific cells called sebocytes.Sebocytes have the same basal origin as keratinocytes. Role: They are responsible for secreting sebum on the skin’s surface.
MICROBIOME
The skin is colonised by diverse micro-organisms, including bacteria, fungi and viruses. It exists more than 1000 different species of bacteria on the surface of the skin. Role: They play a beneficial role in maintaining skin balance by protecting it from harmful pathogens, regulating immune responses and strengthening the physical barrier of the epithelium.
SKIN APPENDICES
The skin appendices include the hair follicle, the sebaceous gland, and the sweat or sudoriferous glands.
HYALURONIC ACID (HA)
Hyaluronic acid is a linear, non-branched polysaccharide belonging to the glycosaminoglycan (GAG) family.In the skin, HA is a natural component of the dermis and one of the main components of the extracellular matrix.. Role: Skin's hydration (acts as a water reservoir), tone and elasticity.
More Info
SEBUM
The sebum is a mixture of lipids and an antioxidant.Sebum contains the following lipids:- Squalene (12%)
- Free fatty acids (25%) (such as: Oleic acid, Linoleic acid, Sapienic acid).
- And other lipids (such as: Triglycerides, wax esters, cholesterol esters, ceramides, diglycerides).
The antioxidant naturally found in sebum, keeping it from thickening, is vitamin E.
AQUAPORINS
Aquaporins are proteins that are fixed on the living cells' walls, and they help transfer water between cells.These channels can transfer up to 3 billion molecules of water per second. Role: Water circulation channels, essential for the skin's life and vitality.
NATURAL MOISTURIZING FACTOR (NMF)
It is the natural magnet of the skin, thanks to its hygroscopic properties.NMF could be amino acid, urea and comes originally from the keratinocytes and is composed of the protein filaggrin. Role: Attract water.
EXTRACELLULAR MATRIX
The filler of the dermis is made from three components: collagen, elastin and ground substance (gel which contains the water of the dermis). Role: This matrix gives support, firmness and elasticity to the skin.
HAIR SHAFT
The hair shaft is the body of the hair. It needs to be lubricated, which is why every hair in the body is attached to a lubricating machine (the sebaceous glands).
VASCULAR ENDOTHELIAL GROWTH FACTOR (VEGF)
This protein is produced by the keratinocytes and targets the endothelial cells on the blood vessel walls to make them grow (angiogenesis).Roles: Dilation and permeability of blood vessels = Skin messenger of redness
HAIR FOLLICLE
Any hair in our body has a life cycle, which can last between 2 and 6 years.Each hair follicle can produce up to 25 times the hair it will produce during our lifetime.They could vary in time between different regions of the body.In general, there are 3 phases:
- The longest phase is the live phase, or anagen. This is when the hair grows.
- The catagen phase is when the hair stops growing and then disconnects from the blood vessels.
- Finally, the hair is shed during the final phase or telogen phase, by the appearance of a new live hair, to replace the old dead one.
SEBACEOUS GLAND
Sebaceous glands are therefore found in all areas of the skin except for hairless areas, i.e. the palms of the hands and soles of the feet, as well as the lips.
The distribution and size of the sebaceous glands are not homogeneous. The densest concentrations of sebaceous glands are found on the face and torso. Androgens (primarily testosterone), i.e. male hormones (which can also be found in the female body), are the main factors that increase sebum secretion.
The sebaceous gland is generally located in the dermis, and its size is inversely proportional to the hair’s diameter. This means that the thicker the hair is, the smaller the sebaceous gland is.
SEBACEOUS GLAND
The hair shaft is the body of the hair. This hair shaft needs to be lubricated. This is why every hair in our body is attached to a lubricating machine that is producing oil, or sebum. This is why it is called the sebaceous glands.
More Info
NERVE FIBRES
The nerve fibres transfer feeling (such as pain, discomfort, cold/hot sensations). In healthy skin, they can be up to the tips of the epidermis. However, in sensitive skin, they can be higher than that.
ELASTIN FIBERS
Elastin fibres are protein strands that create a flexible network within the skin. Role: They allow the skin to stretch and return to its original shape, giving it suppleness and resilience.
AQUAPORINS
Aquaporins are proteins that are fixed on the living cells' walls, and they help transfer water between cells.These channels can transfer up to 3 billion molecules of water per second. Role: Water circulation channels, essential for the skin's life and vitality.
COLLAGEN FIBRES
Collagen fibres are structural proteins that form a supportive framework within the skin. Role: They provide strength, firmness, and elasticity, helping the skin maintain its shape and resilience.
NATURAL MOISTURIZING FACTOR (NMF)
It is the natural magnet of the skin, thanks to its hygroscopic properties.NMF could be amino acid, urea and comes originally from the keratinocytes and is composed of the protein filaggrin. Role: Attract water.
MICROBIOME
The skin is colonised by diverse micro-organisms, including bacteria, fungi and viruses. It exists more than 1000 different species of bacteria on the surface of the skin. Role: They play a beneficial role in maintaining skin balance by protecting it from harmful pathogens, regulating immune responses and strengthening the physical barrier of the epithelium.
BULB
At the bottom of the medullary canal, there is the dermal papilla, which is the dermis' live cells. This one composed the bulb.
BLOOD VESSELS
The blood vessels, attached to the hair, bring food and energy to the hair follicle, which is alive.
It produces vitamin D from the sun (important for calcium fixation a bone health) but protects us from the sun.
SUN
The skin covers our body and protects it from the outside environment, against environmental stresses.
ENVIRONMENT
It helps to reflect some body reactions to heat and infection.It regulates the body temperature (thermal regulation).
REGULATION
DERMIS
In old skin, the dermis gradually loses its structures, the DEJ sags and wrinkles appear on the surface. On the contrary, in young skin, the dermis is very dense and robust, giving the skin a plump and firm appearance.
BLOOD VESSELS
The blood vessels, attached to the hair, bring food and energy to the hair follicle, which is alive.
SEBOCYTES
Inside the sebaceous gland, there are specific cells called sebocytes.Sebocytes have the same basal origin as keratinocytes. Role: They are responsible for secreting sebum on the skin’s surface.
MATRIX METALLOPROTEINASES (MMP)
This enzyme works like a cutter to the surrounding tissues around blood vessels (fibres degradation). It facilitates the blood vessels' dilatation. The MMP is produced during sun exposure and when there is an infection.
SEBACEOUS GLAND
This hair shaft needs to be lubricated. This is why every hair in our body is attached to a lubricating machine that is producing oil, or sebum. This is why it is called the sebaceous glands.
BLOOD VESSELS
They are key player of the dermis. They transfer oxygen and take away waste from the cells. Role: They are responsible for skin nutrition.
TRANSEPIDERMAL WATER LOSS (TEWL)
Water travels freely between cells, carrying life. However, they get out of the skin in small quantities if the skin protective barrier is fully functional: This loss is called Trans Epidermal Water Loss.Under normal conditions, TEWL is approximately 5g/m²/h for an adult face. Some mechanisms in the skin reduce this loss to a minimum (such as the hydrolipidic film).
MELANOCYTES
Cells which are responsible for the colour of the skin, the eyes and the hair, by producing melanin.Role: Sun protection and skin colour.
BLOOD CAPILLARIES
The sebaceous gland is fed by blood capillaries that provide nutrients, sugars, hormones and enzymes necessary for its function, in particular 5α reductase, which is a key enzyme in sebum secretion.
FIBROBLASTS
The main live cell in the dermis is the fibroblast. Role: The fibroblasts produce collagen fibres, elastin fibres and hyaluronic acids.
SEBUM
The sebum is a mixture of lipids and an antioxidant.Sebum contains the following lipids:- Squalene (12%)
- Free fatty acids (25%) (such as: Oleic acid, Linoleic acid, Sapienic acid).
- And other lipids (such as: Triglycerides, wax esters, cholesterol esters, ceramides, diglycerides).
The antioxidant naturally found in sebum, keeping it from thickening, is vitamin E.
ELASTIN FIBRES
Elastin fibres are protein strands that create a flexible network within the skin. Role: They allow the skin to stretch and return to its original shape, giving it suppleness and resilience.
CORNEOCYTES
Dead keratinocytes on the surface.
INTERCORNEOCYTE CEMENT
Lipids (ceramides, cholesterols, free fatty acids) and proteins surrounding corneocytes. Role: Fill in the gap between the cells. Such as a wall, cornocytes are the bricks and these fillers are the mortar or the cement (hence this name).
EPIDERMIS
The epidermis' general thickness is almost 0.1mm on average. Thickness can vary across different regions of the body, with the thickest on the palms and the feet.
The thinnest parts are areas like the eye contour. It is a very dense and compact cellular layer.
HYDROLIPIDIC FILM
Waterproof film on the surface, made from water and lipids (as the name indicates). Water comes from sweat, the atmosphere and the dermis. Lipids come from sebum and the skin lipids of the dead cells.Role: Ensures impermeability of the skin, and hence better protection. Keep water from evaporating.
HAIR SHAFT
The hair shaft is the body of the hair. It needs to be lubricated, which is why every hair in the body is attached to a lubricating machine (the sebaceous glands).
EXTRACELLULAR MATRIX
The filler of the dermis is made from three components: collagen, elastin and ground substance (gel which contains the water of the dermis). Role: This matrix gives support, firmness and elasticity to the skin.
MATRIX METALLOPROTEINASES (MMP)
This enzyme works like a cutter to the surrounding tissues around blood vessels (fibres degradation). It facilitates the blood vessels' dilatation. The MMP is produced during sun exposure and when there is an infection.
SKIN OB
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Transcript
SKIN STRUCTURE
Here you have an interactive explanation of the different LAYERS and APPENDICES of the skin.
Start
THE SKIN
More Info
The largest organ in the human body, with almost 2-3 kg weight
APPINDICES:
3 LAYERS:
More Info
More Info
EPIDERMIS
EPIDERMIS
01
Roof
HAIR FOLLICLE
04
DERMIS
02
Framework
SEBACEOUS GLAND
05
HYPODERMIS
03
Food supply cellar
EPIDERMIS
01
Direct contact with the environment
Next
EPIDERMIS
Direct contact with the ouside environment Role: ▹Protection from external aggression ▹ Prevention of water loss The epidermal turnover lasts between 21 and 28 days
Water
Hydrolipidic film
Microbiome
Corneocytes and intercorneocyte cement
More Info
VEGF
Melanocytes
Keratinocytes
NMF
Langerhans cells
Aquaporins
Dermal-Epidermal Junction
DERMIS
02
The external appearance of the skin
Next
DERMIS
Role: Responsible for the density, suppleness and the external appearance of the skin.
More Info
Fibroblasts
HA
Blood vessels
Collagène fibres
Extracellular matrix
Nerve fibres
Elastin fibres
MMP
HYPODERMIS
03
Skin's energy reserve and thermal insulator
Next
HYPODERMIS
It is the deepest layer of the skin. The adipocytes are the fat cells.
Stock absorber
Varies with gender
Varies with eating habits
Thermoregulating barrier
More Info
HAIR FOLLICLE
04
Whole part that contains the hair
Next
HAIR FOLLICLE
Hair shaft
The whole part that contains the hair is called a hair follicle, and it is composed of many parts. The hair is replaced on a 2- to 6-year cycle. The number of cycles is programmed genetically 20 to 25 in one lifetime.
Medullary canal
Bulb
Blood vessels
Arrector muscle
Apocrine sweat gland
More Info
Sebaceous gland
SEBACEOUS GLAND
05
The sebaceous gland produces the sebum
Next
SEBACEOUS GLAND
Sebum, which makes up a portion of the hydrolipidic film, is produced by the sebaceous gland, which is usually connected to each hair follicle. This is why the term pilosebaceous follicle is used.
Sebaceous gland
Sebocytes
Sebum
Blood vessels
More Info
BLOOD VESSELS
They are key player of the dermis. They transfer oxygen and take away waste from the cells. Role: They are responsible for skin nutrition.
DYNAMIC WATER
There are almost 6 to 8 litres of water in the skin.Even though the majority of water in the skin exists in the dermis, yet, it needs to be transferred to every single part of the body. This dynamic water circulates in channels (aquaporins). It is preserved by 3 elements: aquaporins, hydrolipidic film and intercorneocyte cement.
MEDULLARY CANAL
The gland exerts sebum into the canal, where the hair is located. This canal is called the medullary canal.
ARRECTOR PILI MUSCLE
The arrector pili muscle is a tiny band of smooth muscle attached to each hair follicle. Role: It contracts in response to cold or emotional stimuli, causing the hair to stand upright and producing “goosebumps”.
SEBACEOUS GLAND
The hair shaft needs to be lubricated. This is why every hair in our body is attached to a lubricating machine that is producing oil, or sebum. This is why it is called the sebaceous glands.
More Info
VASCULAR ENDOTHELIAL GROWTH FACTOR (VEGF)
This protein is produced by the keratinocytes and targets the endothelial cells on the blood vessel walls to make them grow (angiogenesis).Roles: Dilation and permeability of blood vessels = Skin messenger of redness
APOCRINE SWEAT GLAND
n apocrine sweat gland is a specialised gland found mainly in areas such as the armpits and groin. Role: It produces a thicker sweat that, when broken down by skin bacteria, is linked to body odour and also plays a role in scent communication.
HYPODERMIS
The hypodermis acts as a thermal insulator, as a strategy for storing lipids, indirect sources of energy, in a place that also makes use of these insulating properties.
SEBACEOUS GLAND
The hair shaft needs to be lubricated. This is why every hair in our body is attached to a lubricating machine that is producing oil, or sebum. This is why it is called the sebaceous glands.
MELANOCYTES
Cells which are responsible for the colour of the skin, the eyes and the hair, by producing melanin.Role: Sun protection and skin colour.
CORNEOCYTES
Dead keratinocytes on the surface.
INTERCORNEOCYTE CEMENT
Lipids (ceramides, cholesterols, free fatty acids) and proteins surrounding corneocytes. Role: Fill in the gap between the cells. Such as a wall, cornocytes are the bricks and these fillers are the mortar or the cement (hence this name).
LANGHERHANS CELL
The immune cells of our skin, such as the life guard of the skin (sentinel), fight against invading bacteria and germs. Role: Guarding the skin from infection, key role in immunity.
LANGHERHANS CELL
The immune cells of our skin, such as the life guard of the skin (sentinel), fight against invading bacteria and germs. Role: Guarding the skin from infection, key role in immunity.
MEDULLARY CANAL
The gland exerts sebum into the canal, where the hair is located. This canal is called the medullary canal.
NERVE FIBRES
The nerve fibres transfer feeling (such as pain, discomfort, cold/hot sensations). In healthy skin, they can be up to the tips of the epidermis. However, in sensitive skin, they can be higher than that.
BULB
At the bottom of the medullary canal, there is the dermal papilla, which is the dermis' live cells. This one composed the bulb.
DYNAMIC WATER
There are almost 6 to 8 litres of water in the skin.Even though the majority of water in the skin exists in the dermis, yet, it needs to be transferred to every single part of the body. This dynamic water circulates in channels (aquaporins). It is preserved by 3 elements: aquaporins, hydrolipidic film and intercorneocyte cement.
ARRECTOR PILI MUSCLE
The arrector pili muscle is a tiny band of smooth muscle attached to each hair follicle. Role: It contracts in response to cold or emotional stimuli, causing the hair to stand upright and producing “goosebumps”.
COLLAGEN FIBRES
Collagen fibres are structural proteins that form a supportive framework within the skin.Role: They provide strength, firmness, and elasticity, helping the skin maintain its shape and resilience.
DERMAL-EPIDERMAL JUNCTION (DEJ)
It is the junction between the epidermis and the dermis, sinuous and homogeneous. Roles: Cohesion and communication (diffusion filter: nutrients, metabolites, water, mineral salts).Indeed, there are no blood vessels in the epidermis, on the top, so it needs some mechanisms to exchange between the two layers.
FIBROBLASTS
The main live cell in the dermis is the fibroblast. Role: The fibroblasts produce collagen fibres, elastin fibres and hyaluronic acids.
HYALURONIQUE ACID (HA)
Hyaluronic acid is a linear, non-branched polysaccharide belonging to the glycosaminoglycan (GAG) family.In the skin, HA is a natural component of the dermis and one of the main components of the extracellular matrix.. Role: Skin's hydration (acts as a water reservoir), tone and elasticity.
More Info
DERMAL-EPIDERMAL JUNCTION (DEJ)
It is the junction between the epidermis and the dermis, sinuous and homogeneous. Roles: Cohesion and communication (diffusion filter: nutrients, metabolites, water, mineral salts).Indeed, there are no blood vessels in the epidermis, on the top, so it needs some mechanisms to exchange between the two layers.
HYDROLIPIDIC FILM
Waterproof film on the surface, made from water and lipids (as the name indicates).Water comes from sweat, the atmosphere and the dermis. Lipids come from sebum and the skin lipids of the dead cells. Role: Ensures impermeability of the skin, and hence better protection. Keep water from evaporating.
THE 3 LAYERS
House model
The skin is composed of three layers, arranged from top to bottom: Epidermis, dermis and hypodermis.
If we imagine the skin as a house:
BLOOD CAPILLARIES
The sebaceous gland is fed by blood capillaries that provide nutrients, sugars, hormones and enzymes necessary for its function, in particular 5α reductase, which is a key enzyme in sebum secretion.
KERATINOCYTES
There are living cells in the epidermis, and the majority of cells of this layer (almost 80%). These cells produce keratin, a strong protein important for the nails, hair and teeth. They divide at the bottom of the epidermis and go up until they are eliminated (desquamation): this journey can take up to 28 days.
APOCRINE SWEAT GLAND
An apocrine sweat gland is a specialised gland found mainly in areas such as the armpits and groin. Role: It produces a thicker sweat that, when broken down by skin bacteria, is linked to body odour and also plays a role in scent communication.
KERATINOCYTES
There are living cells in the epidermis, and the majority of cells of this layer (almost 80%). These cells produce keratin, a strong protein important for the nails, hair and teeth. They divide at the bottom of the epidermis and go up until they are eliminated (desquamation): this journey can take up to 28 days.
SEBOCYTES
Inside the sebaceous gland, there are specific cells called sebocytes.Sebocytes have the same basal origin as keratinocytes. Role: They are responsible for secreting sebum on the skin’s surface.
MICROBIOME
The skin is colonised by diverse micro-organisms, including bacteria, fungi and viruses. It exists more than 1000 different species of bacteria on the surface of the skin. Role: They play a beneficial role in maintaining skin balance by protecting it from harmful pathogens, regulating immune responses and strengthening the physical barrier of the epithelium.
SKIN APPENDICES
The skin appendices include the hair follicle, the sebaceous gland, and the sweat or sudoriferous glands.
HYALURONIC ACID (HA)
Hyaluronic acid is a linear, non-branched polysaccharide belonging to the glycosaminoglycan (GAG) family.In the skin, HA is a natural component of the dermis and one of the main components of the extracellular matrix.. Role: Skin's hydration (acts as a water reservoir), tone and elasticity.
More Info
SEBUM
The sebum is a mixture of lipids and an antioxidant.Sebum contains the following lipids:
- Squalene (12%)
- Free fatty acids (25%) (such as: Oleic acid, Linoleic acid, Sapienic acid).
- And other lipids (such as: Triglycerides, wax esters, cholesterol esters, ceramides, diglycerides).
The antioxidant naturally found in sebum, keeping it from thickening, is vitamin E.AQUAPORINS
Aquaporins are proteins that are fixed on the living cells' walls, and they help transfer water between cells.These channels can transfer up to 3 billion molecules of water per second. Role: Water circulation channels, essential for the skin's life and vitality.
NATURAL MOISTURIZING FACTOR (NMF)
It is the natural magnet of the skin, thanks to its hygroscopic properties.NMF could be amino acid, urea and comes originally from the keratinocytes and is composed of the protein filaggrin. Role: Attract water.
EXTRACELLULAR MATRIX
The filler of the dermis is made from three components: collagen, elastin and ground substance (gel which contains the water of the dermis). Role: This matrix gives support, firmness and elasticity to the skin.
HAIR SHAFT
The hair shaft is the body of the hair. It needs to be lubricated, which is why every hair in the body is attached to a lubricating machine (the sebaceous glands).
VASCULAR ENDOTHELIAL GROWTH FACTOR (VEGF)
This protein is produced by the keratinocytes and targets the endothelial cells on the blood vessel walls to make them grow (angiogenesis).Roles: Dilation and permeability of blood vessels = Skin messenger of redness
HAIR FOLLICLE
Any hair in our body has a life cycle, which can last between 2 and 6 years.Each hair follicle can produce up to 25 times the hair it will produce during our lifetime.They could vary in time between different regions of the body.In general, there are 3 phases:
SEBACEOUS GLAND
Sebaceous glands are therefore found in all areas of the skin except for hairless areas, i.e. the palms of the hands and soles of the feet, as well as the lips. The distribution and size of the sebaceous glands are not homogeneous. The densest concentrations of sebaceous glands are found on the face and torso. Androgens (primarily testosterone), i.e. male hormones (which can also be found in the female body), are the main factors that increase sebum secretion. The sebaceous gland is generally located in the dermis, and its size is inversely proportional to the hair’s diameter. This means that the thicker the hair is, the smaller the sebaceous gland is.
SEBACEOUS GLAND
The hair shaft is the body of the hair. This hair shaft needs to be lubricated. This is why every hair in our body is attached to a lubricating machine that is producing oil, or sebum. This is why it is called the sebaceous glands.
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NERVE FIBRES
The nerve fibres transfer feeling (such as pain, discomfort, cold/hot sensations). In healthy skin, they can be up to the tips of the epidermis. However, in sensitive skin, they can be higher than that.
ELASTIN FIBERS
Elastin fibres are protein strands that create a flexible network within the skin. Role: They allow the skin to stretch and return to its original shape, giving it suppleness and resilience.
AQUAPORINS
Aquaporins are proteins that are fixed on the living cells' walls, and they help transfer water between cells.These channels can transfer up to 3 billion molecules of water per second. Role: Water circulation channels, essential for the skin's life and vitality.
COLLAGEN FIBRES
Collagen fibres are structural proteins that form a supportive framework within the skin. Role: They provide strength, firmness, and elasticity, helping the skin maintain its shape and resilience.
NATURAL MOISTURIZING FACTOR (NMF)
It is the natural magnet of the skin, thanks to its hygroscopic properties.NMF could be amino acid, urea and comes originally from the keratinocytes and is composed of the protein filaggrin. Role: Attract water.
MICROBIOME
The skin is colonised by diverse micro-organisms, including bacteria, fungi and viruses. It exists more than 1000 different species of bacteria on the surface of the skin. Role: They play a beneficial role in maintaining skin balance by protecting it from harmful pathogens, regulating immune responses and strengthening the physical barrier of the epithelium.
BULB
At the bottom of the medullary canal, there is the dermal papilla, which is the dermis' live cells. This one composed the bulb.
BLOOD VESSELS
The blood vessels, attached to the hair, bring food and energy to the hair follicle, which is alive.
It produces vitamin D from the sun (important for calcium fixation a bone health) but protects us from the sun.
SUN
The skin covers our body and protects it from the outside environment, against environmental stresses.
ENVIRONMENT
It helps to reflect some body reactions to heat and infection.It regulates the body temperature (thermal regulation).
REGULATION
DERMIS
In old skin, the dermis gradually loses its structures, the DEJ sags and wrinkles appear on the surface. On the contrary, in young skin, the dermis is very dense and robust, giving the skin a plump and firm appearance.
BLOOD VESSELS
The blood vessels, attached to the hair, bring food and energy to the hair follicle, which is alive.
SEBOCYTES
Inside the sebaceous gland, there are specific cells called sebocytes.Sebocytes have the same basal origin as keratinocytes. Role: They are responsible for secreting sebum on the skin’s surface.
MATRIX METALLOPROTEINASES (MMP)
This enzyme works like a cutter to the surrounding tissues around blood vessels (fibres degradation). It facilitates the blood vessels' dilatation. The MMP is produced during sun exposure and when there is an infection.
SEBACEOUS GLAND
This hair shaft needs to be lubricated. This is why every hair in our body is attached to a lubricating machine that is producing oil, or sebum. This is why it is called the sebaceous glands.
BLOOD VESSELS
They are key player of the dermis. They transfer oxygen and take away waste from the cells. Role: They are responsible for skin nutrition.
TRANSEPIDERMAL WATER LOSS (TEWL)
Water travels freely between cells, carrying life. However, they get out of the skin in small quantities if the skin protective barrier is fully functional: This loss is called Trans Epidermal Water Loss.Under normal conditions, TEWL is approximately 5g/m²/h for an adult face. Some mechanisms in the skin reduce this loss to a minimum (such as the hydrolipidic film).
MELANOCYTES
Cells which are responsible for the colour of the skin, the eyes and the hair, by producing melanin.Role: Sun protection and skin colour.
BLOOD CAPILLARIES
The sebaceous gland is fed by blood capillaries that provide nutrients, sugars, hormones and enzymes necessary for its function, in particular 5α reductase, which is a key enzyme in sebum secretion.
FIBROBLASTS
The main live cell in the dermis is the fibroblast. Role: The fibroblasts produce collagen fibres, elastin fibres and hyaluronic acids.
SEBUM
The sebum is a mixture of lipids and an antioxidant.Sebum contains the following lipids:
- Squalene (12%)
- Free fatty acids (25%) (such as: Oleic acid, Linoleic acid, Sapienic acid).
- And other lipids (such as: Triglycerides, wax esters, cholesterol esters, ceramides, diglycerides).
The antioxidant naturally found in sebum, keeping it from thickening, is vitamin E.ELASTIN FIBRES
Elastin fibres are protein strands that create a flexible network within the skin. Role: They allow the skin to stretch and return to its original shape, giving it suppleness and resilience.
CORNEOCYTES
Dead keratinocytes on the surface.
INTERCORNEOCYTE CEMENT
Lipids (ceramides, cholesterols, free fatty acids) and proteins surrounding corneocytes. Role: Fill in the gap between the cells. Such as a wall, cornocytes are the bricks and these fillers are the mortar or the cement (hence this name).
EPIDERMIS
The epidermis' general thickness is almost 0.1mm on average. Thickness can vary across different regions of the body, with the thickest on the palms and the feet. The thinnest parts are areas like the eye contour. It is a very dense and compact cellular layer.
HYDROLIPIDIC FILM
Waterproof film on the surface, made from water and lipids (as the name indicates). Water comes from sweat, the atmosphere and the dermis. Lipids come from sebum and the skin lipids of the dead cells.Role: Ensures impermeability of the skin, and hence better protection. Keep water from evaporating.
HAIR SHAFT
The hair shaft is the body of the hair. It needs to be lubricated, which is why every hair in the body is attached to a lubricating machine (the sebaceous glands).
EXTRACELLULAR MATRIX
The filler of the dermis is made from three components: collagen, elastin and ground substance (gel which contains the water of the dermis). Role: This matrix gives support, firmness and elasticity to the skin.
MATRIX METALLOPROTEINASES (MMP)
This enzyme works like a cutter to the surrounding tissues around blood vessels (fibres degradation). It facilitates the blood vessels' dilatation. The MMP is produced during sun exposure and when there is an infection.