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A
DNA
Deoxyribonucleic acid located in the nucleus of each cell. DNA is structured in a double helix, and is the support of the genetic information.
Amino-acid
Small molecule of 10 to 15 atoms, the basic component of the proteins of all living things. 20 in number, they join together in chains to form the protein. As an illustration they might be compared with the letters of the alphabet which are the building blocks of our writing system.
Fatty Acid
Organic acid, a major constituent of lipids. A fatty acid has a long hydrocarbon chain and a terminal carboxyl group.
Acne
Acne is a skin disorder involving the sebaceous gland. The canal leading from this gland becomes blocked leading to the formation of spots. Male hormones play a significant role in triggering acne.
Surfactants
Chemical molecules capable of enhancing wetting by water (such as detergents and soaps).
Albinism
A genetic illness characterised by the absence of melanin pigments in the skin and hair.
Androgens
Male hormone which in particular regulate the appeance and the development of the male charcteristics (e.g. testosterone)
Antifungal agent
A substance destroying the fungi and yeast-like organisms responsible for mycosis.
Antigen
Any substance capable of triggering an immune response.
Anucleate
Used to describe a cell without a nucleus.
Apocrine
Describes a sweat gland whose secretions flow into the pilary canal. They are only found in specific zones of the organism (armpit, pubic area, perineum, etc.).
Apoptosis
Or programmed cell death. Biological process during which the cells commit suicid, by fragmentation of their genetic matter.
B
Biopsie
Sample from a living being of a fragment of tissue for microscopic examination.
C
Capillary vessel
Very thin blood vessel organised in a network un every tissues. Gas, nutriment exchange and waste elimination in tissue take place at their level.
Sun capital
All the systems that defend the skin against the harmful effects of the sun. This degree of tolerance is acquired at birth, is not renewable and depends on an individual's phototype.
Langerhans' Cell
Epidermal dendritic cell involved in the immune response.
Merkel Cell
Sensory cell located on the baal layer of the epidermis, involved in the sense of touch.
Ceramides
Particular class of lipids naturally present in the skin and hair.
Intercellular cement
Extra-cellular substance which ensures the cohesion of cells within a tissue.
Connective tissue
Tissue which has the role of supporting the other tissues (or organs of the body) and protecting, nourishing and holding them together.
Corneocyte
An anucleate, biologically dead cell, that characterises the distinctive end state of the keratincocytes.
Corneodesmosomes
Desmosomes that maintain cohesion between the corneocytes in the horny layer.
Corneometer
Device for measuring level of skin moisturisation.
Malpighian layer
Layer of the epidermis 5 to 6 cells deep that become flatter in the superficial part, often called the spinous layer or spinosum stratum.
Meissner Corpuscle
Sensory cell located in the dermis, on the boundary of the epidermis. These receptors are also involved in the sense of touch.
Pacinian Corpuscle
Sensory receptor highly sensitive to pressure and vibrations. They are located deep in the dermis and the hypodermis.
Ruffinian Corpuscle
Sensory receptor that are confined to the dermis and are stimulated by variations caused by tension and stretching.
Horny layer
Differentiation layer
Layer in the epidermis located between the mitotic layer and the horny layer. This is the layer in which keratinisation takes place.
Cysteine
Sulphur containing amino-acid, a constituent of proteins.
Cytokine
Small protein secreted by the macrophages, responsible for regulating the immune response.
D
Dendrite
Branching prolongations of nerve cells, or cells of nervous origin.
Densi-score
Device for measuring skin creasing.
Dermis
Deep layer of the skin, covered by the epidermis and formed from connective tissue.
Desmosome
Connecting zone between two epithelial cells.
Desquamation
Elimination of superficial layers of the epidermis in the form of small flakes.
Cellular differentiation
Process by which an unspecialized cell becomes specialized into one of the many cells that make up the body, such as a heart, liver or muscle or skin cell.
Cell division
Usual method of cell multiplication in which a mother cell divides into two identical daughter cells, each containing a set of chromosomes identical to those of the mother cell.
E
Eccrine
Describes a small sweat gland that leaves its secretions on the skin's surface. Eccrine sweat gland are ubiquitous.
Elasticity
Property of certain bodies of returning to their original shape and volume when the force exerted on them ceases to act.
Enzyme
Protein which accelerates a biochemical reaction such as the chemical transformation of a given substance into another substance.
Epidermis
Superficial layer of the skin, covering the dermis and formed from epithelial tissue.
Epithelium
Tissue formed from one or more layers of cells which covers the body (epidermis), the internal cavities (mucosae) or which makes up the glands.
Eumelanin
Red or brown melanin pigment. The true protective melanin.
F
G
Lymph node
Swelling in a lymph vessel in which the lymph is relieved of waste and infectious agents that it contains by lymphocytes and macrophages.
Genotype
All the genes carried by the chromosomes and which make up an individual's genetic inheritance.
Sebaceous gland
Skin appendage responsible for producing sebum.
Sweat gland
Skin appendage responsible for producing sweat.
Glycoprotein
Protein linked to one or more sugars.
Birbeck granule
H
Hair follicle
Invisible part of the hair buried 4 mm under the scalp and which is the place where the hair is produced.
Henna
Plant from the Middle-East and North Africa. Dried and ground henna leaves produce a powder used to dye hair and nails.
Hypodermis
Deepest layer of the skin essentially made up of fatty cells, the adipocytes, and connective tissue.
Hypothalamus
Part of the central nervous system that controls sleep and sexual activity as well as hunger, thirst, body temperature control mechanisms and certain emotions.
I
In vitro
(Latin words: "in glass") Used to describe any biological experiment carried out outside of the organism. As opposed to in vivo.
In vivo
(Latin words: "in the living") Used to describe any biological experiment carried out within the living organism. As opposed to in vitro.
Infra-red (IR)
Major part of the sun's rays, with a long wavelength, responsible for the heat effect.
MRI
Magnetic resonance imaging. Non-invasive medical imaging method.
K
Keratin
Sulphur rich fibrous protein, insoluble in water and very strong. It forms the essential part of hair fibre, the skin, nails, horns, hooves, feathers and wool. It is also present in the superficial cells of the epidermis.
Keratinised
About an epithelium having keratin as its main protein component.
Keratinocyte
Cell of the epidermis or of hair follicles, responsible for the synthesis of keratin.
L
Lipids
Fatty chemical substances, found in all living organisms, playing a considerable role in cell structure and with an important energetic role as well.
Lipometer
Device for measuring the skin's lipid content.
Lymph
Organic yellow liquid essentially made up of water, lymphocytes and various organic substances (cholesterol) and minerals.
Lymphocyte
Cell found in the lymph nodes, thymus, bone marrow and spleen playing a role in the immune defence system.
M
Melanin
Coloured pigment giving colour to the hair and skin.
Basement membrane
Is described as being the interface between the cells and the extracellular matrix.
Micrometer
Unit of measurement equal to one millionth of a metre or a thousandth of a millimetre (formerly: micron).
Melanocytes
Cells of the epidermis or of hair follicles, responsible for the synthesis of melanin and transmitting it to the keratinocytes.
Confocal Microscopy (C. M)
Method of microscopy using Laser light beams, enabling the same object to be observed at successive depths.
Scanning Electron Microscopy (S.E.M)
Observation method using electron beams enabling surfaces to be examined and relief to be shown. Possible enlargement from 10 to 100,000 times.
Mitosis
Usual method of cell multiplication in which a mother cell divides into two identical daughter cells, each containing a set of chromosomes identical to those of the mother cell.
Programmed cell death
Biological process during which the cells commit suicid, by fragmentation of their genetic matter (apoptosis).
N
Nociception
Neuro-physiological component of pain, that perceives potentially threatening stimuli.
Non-invasive
Procedure of exploring the organism without any risk of its integrity being affected.
O
Organ
Part of an organised body that carries out one or more defined functions.
Organelle
Any structure differentiated from the cell having the role of an organ, for example: mitochondria, Golgi bodies.
Organites
Any structure differentiated from the cell having the role of an organ, for example: mitochondria, Golgi bodies.
Ostium
(Lat. = mouth) The ostia are openings at the skin surface from which hair grows.
P
Squamous
Used to describe a squamous or pavement epithelium has a superficial layer of cells, which are flat. It looks like a pavement.
Peptide
Molecule made up of a small number of amino acids. It is small protein.
pH
Abbreviation of "hydrogen potential".) Index expressing the activity (or concentration) of hydrogen ions in a solution. If the pH is less than 7, the solution is acidic. If it is equal to 7, it is neutral. If it is greater than 7, it is alkaline.
Phenotype
All the apparent characteristics of an individual, which correspond both to the expressed part of the genotype and phenomena defined by the external environment.
Phototype
Classification of sensitivity to solar radiation based on skin, eye and hair colour.
Physiology
Science involving the study of an organ's functions and properties, and the tissue of a plant or animal.
Piercing
Inserting a jewel or decoration into the skin by perforation.
Pigment
Coloured matter in various plant or animal tissue and organs giving it a particular colour.
Plexus
Network of inter-woven nerves and blood vessels.
Protéine
Molecule made up of an association between 4 to several thousand amino acids and forming the essential component of cells (the word "protein" coming from the Greek prôtos which means "first").
R
Replica
Method enabling imprints of the skin's relief to be made.
S
Saturnism
Serious neurological illness due to an intoxication from lead or lead salts.
Scarring
Symbolic ritual marking indicating ethnic membership or initiation.
Sebum
Greasy material produced by the sebaceous glands associated with the hair follicles and which naturally lubricates the hair.
Stratified
Used to describe an epithelium made up of several layers of cells (stratum = layer).
Stratum corneum
View Horny layer.
T
Tattooing
Cultural tradition aiming at introducing pigments into the upper dermis so as to creates coloured designs. Tattoos are indelible.
Thermoregulation
Regulatory mechanism by which the internal temperature of the body of mammals and birds is maintained constant.
Torquemeter
Device for measuring skin torsion.
U
Ultraviolet (UV)
Minority part of solar radiation, short wave but highly energetic. UV rays cause a lot of damage to the epidermis and to the dermis.
V
Lymphatic vessels
Membranous duct punctuated with nodes in which the lymph circulates. They have a very similar structure to that of blood vessels.
Visible radiation
Part of the sun's spectrum visible to the human eye.
X
Xeroderma Pigmentosum (XP)
Rare genetic illness in which the enzymes that repair DNA are deficient. This dillness causes people to be highly sensitive to solar irradiation and are proned to develop cancers.
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