STRUCTURE OF HAIR AND SKIN Human hair has

STRUCTURE OF HAIR AND SKIN Human hair has three distinct layers……. Human skin has three distinct layers too…. .

THE CUTICLE n n n The protective outer layer of the hair, the part that is seen and can be felt. Made up of as many as eleven layers of scales that overlap like tiles on a roof. Hair with many layers or has layers closely packed may result in the hair being resistant because chemicals can’t get into the cortex. Hair that has damage to the cuticle will be porous. The cuticle is colourless but translucent – it lets some light through so the colour of the cortex can be seen.

THE CORTEX n n n The main part where all chemical changes take place and where the natural colour pigments are found. It is made up of long chains of amino acids – polypeptide chains- these are formed into spirals each spiral is called an alpha helix. The alpha helix is called this because it is shaped like a spring/spiral Bundles of spirals entwine together to form fibre bundles which then combine in groups to form the hair. Fibre bundles are held together by salt, hydrogen and disulphide bonds- the salt and hydrogen bonds being broken by heat and/or water but the disulphide bonds need a chemical like perm lotion

THE MEDULLA n This is not always present in the hair and is unimportant for hairdressing purposes.

Hair cross section

THE EPIDERMIS This is the surface layer of the skin it can be seen and felt n This layer of the skin is constantly rubbed away n Most of the epidermis has no blood or nerve supply – it is dead n The epidermis consists of five layers n

THE DERMIS This is the deepest layer of the skin n The dermis has a rich blood and nerve supply n The appendages of the skin can be found here n

MAIN APPENDAGES n n n The follicles from which hairs grow through The dermal papilla from which all cell growth and cell division occurs – found at the base of the hair bulb The sebaceous glands that produce and secrete sebum to waterproof and lubricate the skin and to create an acid barrier against some bacterial infection The sudoriferous (sweat) glands that excrete some waste and help to control body temperature by the evaporation of this sweat The arrector pili muscle that pulls the hair upright to trap air next to the skin to help keep us

FOUR MAIN FUNCTIONS n n n Skin is one of the biggest organs of the body and has four main functions Protection – it protects us from strong sunlight by producing melanin (we look tanned) and from invasion by bacteria (the acidity of sebum) Sensation – it contains nerves that allow us to feel when touched or touching Secretion and excretion – it contains glands for secreting oil and excreting waste Temperature control – the evaporation of sweat helps to cool the skin and the action of the arrector pili muscle helps to trap air around us to insulate from the cold.

Skin Cross Section