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A
Antibodies
Proteins produced by B lymphocytes to attempt to destroy or neutralise external agents called antigens (bacteria, viruses or other toxic agents).
Apoptosis
Active process of autodestruction of cells, through fragmentation of their genetic material ( programmed cell death)
B
Biopsy
Removal from a living being of a fragment of tissue for testing/sampling.
C
Blood capillary
One of many very fine blood vessels forming complex networks in all tissues. Gaseous and nutritional exchange and elimination of waste takes place via the capillaries.
Langerhans cell
Prime cell of the epidermis involved in the immune response
Somatic stem cells
There are two types of stem cells, embryonic stem cells and somatic stem cells. These cells are not at all or hardly differentiated; they have no precise function. They retain their ability to produce cells identical to themselves and can also give rise to neuronal, muscular, hepatic etc. differentiated cells. Embryonic stem cells are the first to appear when an embryo starts to develop. They are the origin of all the cells of our body. They are therefore considered as non-differentiated (not specialised) and totipotent (capable of differentiating into anything). Somatic stem cells are present in adult living organisms where they are located in each of the organs where they are involved in the latter's renewal.
Ceramides
Special class of lipids naturally present in the skin and the hair and which play a role in the barrier function.
Corneocyte
Anucleated cell, biologically dead, which characterises the state of terminal differentiation of keratinocytes
Basal layer
The deepest layer of the epidermis. Merkel cells, melanocytes and keratinocytes are found there. The keratinocytes divide there before migrating into the upper layers of the epidermis.
Cornified layer
The outermost layer of the epidermis, which ensures the barrier function of the skin (also called the stratum corneum),
Differentiation layer
Layer of the epidermis situated between the renewal layer and the cornified layer. Keratinization occurs in the differentiation layer.
Suprabasal layer
Layer situated above the basal layer and where the keratinocytes begin their differentiation programme. The Langerhans cells are found in this layer.
Histological sections
Preparation for studying the microscopic structure of tissues
Cytokines
Reduced size protein, secreted by the macrophages, responsible for controlling the immune response
D
DED
DED=de-epidermised dermis: inert support material on which the cells of the epidermis are seeded for reconstruction of a functional epidermis.
Dendrites
Branched prolongations of nerve cells or cells of neral origin.
Dermis
Skin compartment, covered by the epidermis and formed from connective tissue
Differentiation
Process of transformation by which cells acquire their functional characteristics.
Cell division
Mechanism by which one cell reproduces itself giving rise to two identical daughter cells. This mechanism, among others, is at the basis of renewal of the epidermis.
E
Enzyme
Protein which accelerates (catalyses) a biochemical reaction such as the chemical transformation of one substance (metabolite) into another (product).
Epidermis
Superficial layer of the skin, covering the dermis formed from keratinised, granular, epithelial tissue.
Dermal equivalent
Support material formed from a dermis containing fibroblasts, or not, and used for seeding keratinocytes. This type of support is used to reconstruct an epidermis on a dermis (or dermal equivalent)
F
Fibroblast
A connective tissue cell which secretes the components of the extracellular matrix (laminin, fibronectin, collagen etc.) and the proteins of the connective tissue.
Growth factors
Substances (proteins) secreted by different types of cells, necessary for cell growth (proliferation, differentiation). Included in this family are: insulin, somatotrophin (or growth hormone), prolactin, certain cytokines etc.
Hair follicle
Invisible part of the hair, embedded 4 mm under the scalp; it is the place where the hair is produced. The hair follicle also contains the sebaceous gland.
G
GAGs
GAGs = glycosaminoglycans: macromolecules (polysaccharides) which form a gel with glycoproteins within which is located the network of dermal fibres. These macromolecules trap water and contribute to maintaining the cohesion and structure of the dermis.
Birbeck granule
Specific organelle of Langerhans cells
Sebaceous gland
Gland attached to the hair follicle responsible for producing sebum
H
Histocompatibility
Compatibility between the tissue antigens of two individuals of the same species, the absence of which provokes graft rejection.
Hypodermis
The deepest compartment of the skin, constituted essentially of fat cells, called adipocytes, and connective tissue.
I
In vitro
(In Latin: "in the glass") Used to describe any biological experiment carried out outside the organism. As opposed to in vivo
In vivo
(In Latin: "in the living") Used to describe any biological experiment carried out within the living organism. As opposed to in vitro
K
Keratinocyte
Cell of the epidermis or hair follicles, responsible for the synthesis of keratin. which is found either in the cornified layer or in the hair shaft.
L
Lipids
Fatty chemical substances found in all living organisms, they play a considerable role in cell structure and their energy function is also important
M
Extracellular matrix
Secreted by the fibroblasts of the dermis, the extracellular matrix is composed of fibres (essentially collagen and elastin), glycoproteins and polysaccharides.
Melanocyte
Cell of the epidermis or hair follicles, responsible for the synthesis of melanin and its transfer to the keratinocytes. Melanin is the natural pigment of skin and hair.
Melanogenesis
Melanin synthesis process
Melanosome
Specific organelles of melanocytes in which melanin is synthesised, stored, transported and finally transferred to the keratinocytes
Basal membrane
All the epithelial tissues (e.g. the epidermis) are supported on a basal membrane (or basal layer) which separates them from the subjacent connective tissue (e.g. the dermis). Its thickness varies from 50nm to 80nm from one epithelium to another depending on its location. It serves as an anchor for the epithelial cells, acts as a filter for their nutrition and is essential for their survival and healing.
Programmed cell death
see apoptosis
O
Organ
Organised part of a body which has one or more determined (physiological) functions.
P
Phenotype
All the apparent characteristics of an individual, which correspond both to the part expressed as the genotype and to phenomena determined by the external environment.
Photo-immunosuppression
Reduction in immune defences induced by sun rays on the skin
Phototoxicity
Phototoxicity is defined as a toxic reaction triggered by pre-exposure of the skin to certain chemical products, followed by exposure to light, or by irradiation of the skin after administration of a chemical product by the systemic route
Phototype
Classification of sensitivity to solar rays based on the colour of the skin and the colour of the hair
Physiology
Science concerning the study of the functions and properties of organs and tissues of a plant or animal
Pigment
Coloured matter present in various plant or animal tissues and organs to which it gives a particular coloration.
Polymerisation
Chemical process that combines several molecules (monomers) to form a macromolecule (polymer).
Protein
Organic macromolecule composed of a blend that may be as many as several thousand amino acids. Proteins are the basic constituents of cells (the word "protein" comes from the Greek "protos" meaning "first")
S
Sebum
Fatty material produced by the sebaceous gland, which naturally lubricates the hair and participates actively in the barrier function of the skin
Stratified
Formed from several layers of cells (stratum = layer, stratified epithelium)
Stratum corneum
see cornified layer
Supporting material
see DED and dermal equivalent
T
TGFb1
TGFbeta1=Transforming growth factor, beta 1: growth factor of the TGFbetafamily. TGFbeta1 is known for inhibiting the growth of epithelial cells, controlling cell differentiation and migration. Its role in tumour angiogenesis and in suppression of the immune response has also been reported
Topical
Acting at the site where a product is applied (onto the skin or on the mucous membranes)
U
Ultraviolet (UV)
Solar radiations characterized by short wavelengths and high enegy content. UV rays cause a great deal of damage to the epidermis and dermis
X
Xeroderma Pigmentosum (XP)
Rare genetic disease in which the enzymes for DNA repair are deficient
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