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The Skin Introduction the Skin Is Largest Organ in the Human Body The City & Guilds Textbook Level 2 Beauty Therapy: for the Technical Certificate THE SKIN INTRODUCTION The skin is largest organ in the human body. The condition of the skin is subject to constant change and can therefore reflect the general health of an individual. In this section you will learn about: ●● the normal structure of the skin ●● the functions of the skin ●● the key features of the skin ●● skin tones, types and conditions ●● common skin diseases and disorders. Hair shaft Free nerve ending Sebaceaous gland Arrector pili muscle Stratum corneum Pore Meissner's corpuscle Stratum lucidum Nerve fibres Stratum granulosum Epidermis Stratum spinosum Stratum germinativum Papiliary layer Reticular Dermis layer Sudoriferous gland Subcutaneous layer Vein Artery Adipose Root hair Hair follicle Pacinian tissue corpuscle p Cross section of the skin HANDY HINT Structure of the skin The skin has three distinct layers The skin, hair and nails are also ●● epidermis known as the integumentary system. ●● dermis ●● subcutaneous layer/hypodermis. 110 9781510416222_CH02.indd 110 6/21/17 9:22 PM Chapter 2 Anatomy and physiology The surface of the skin is covered in an acid mantle which is a water in oil emulsion formed from a mixture of sweat and sebum. It is also covered with mineral and organic substances such as urea, lactic acid and amino acids. These substances make the skins surface slightly acidic. Epidermis The epidermis has five layers, formed of sheets of cells. The cells are held together by a special adhesive and form tight junctions. There is still some ability for cellular movement between these tight junctions. The five layers are called: 1. stratum corneum (horny layer) 2. stratum lucidum (clear layer) 3. stratum granulosum (granular layer) 4. stratum spinosum (prickle cell layer) 5. stratum germinativum(basal layer). Corneocyte Stratum corneum (dead keratinocyte) Stratum lucidium Lamellar granules Stratum granulosum Langerhans cell Keratinocyte Stratum spinosum Melanin Melanocyte Merkel cell Stratum germinativum p The structure of the epidermis KEY TERMS Skin cells are produced in the stratum germinativum. They migrate Migrate – Move. upwards to the stratum corneum where they are eventually shed. This Emulsion – A liquid where process takes between 24 and 42 days, taking longer as we get older. miniscule droplets of one or The average thickness of the epidermis is only about 0.12mm. It is more liquids are evenly dispersed thickest on the soles of the feet (1.5mm) and thinnest on the eyelids within another. They are often oil (0.05mm). and water droplets, which would usually separate. 111 9781510416222_CH02.indd 111 6/21/17 9:22 PM The City & Guilds Textbook Level 2 Beauty Therapy: for the Technical Certificate Cells within the epidermis There are different types of cells in the epidermis each has a different function. Cell name Function Keratinocytes Keratinocytes (basal cells) make up the majority of cells in the epidermis. They produce keratin, an insoluble protein, and make the cell more resilient. The amount of keratin in the cell increases as the cell migrates towards the skins surface. When they lose their nuclei, keratinocytes become corneocytes. Melanocytes Melanocytes form a type of connective tissue. They produce the pigment melanin which gives colour to the skin and hair. Tyrosine (an amino acid) causes a series of complex chemical reactions in melanocytes to form melanin. Melanin granules are formed in the melanocytes and these pass along the finger like projections called dendrites that inject melanin into the surrounding skin cells. The melanin granules form a protective cap over keratinocytes in the middle layers of the dermis. Melanocytes are evenly distributed to form a layer that absorbs UV, preventing the rays from damaging the deeper layers of the skin. When dendrites become damaged, pigmentation is unevenly distributed within the skin causing patchy pigmentation. Most natural melanin is a mixture two types of melanin: eumelanin – a brown - black pigment pheomelanin – a yellow - red pigment. Lanagerhans Cells Langerhan cells are specialised white blood cells found circulating in the skin. They move around by squeezing through the connective tissue. They are type of macrophage and are involved in the skins reaction to infection and inflammation. KEY TERMS Connective tissue – Connective tissue is the most common tissue in the body. The function of connective tissue is to protect, transport, insulate and support. Amino acids – The building blocks of protein. When you break down protein you are left with amino acids. Pigmentation – Colouration of tissues by pigment. Macrophage – Small white cells of the immune system which move through tissues and remove cell debris and pathogens. Pathogen – The collective term used to describe a type of microbe and includes viruses, bacteria, fungi and parasites. A pathogen has the potential to cause harm. Inflammation – Swelling and tenderness caused by an increase in white blood cells and other substances in an area, in response to a pathogen, irritant or damage. 112 9781510416222_CH02.indd 112 6/21/17 9:22 PM Chapter 2 Anatomy and physiology Layers of the epidermis Stratum germinativum (basal layer) This is the deepest layer of the epidermis and forms a junction between the epidermis layer and the dermis. Skin cells are produced in the stratum germinativum in a process called mitosis which produces new epithelium cells. One cell remains in the stratum germinativum and continues to reproduce while the other migrates through the layers to the stratum corneum where the cycle ends. The stratum germinativum also contains keratinocytes and melanocytes. The melanocytes formed in this layer play an important role in protecting KEY TERMS the skin against harmful UV rays. Eighty per cent of the moisture required Keratinisation – The process by for maintaining a healthy skin surface is found in this layer. which living cells change into hard flat dead cells. It is caused Stratum spinosum (prickle cell layer) by the production of keratin and The stratum spinosum is 8-10 layers deep. Keratin production begins the degeneration of the cells nuclei. in the stratum spinosum and is injected into the cells. The cells have a Nucleus (singular nuclei) – The prickly appearance due to connecting threads called fibrils. This layer part of the cell that contains the includes the langerhans cells which help support our immune system. genetic structure. Corneocytes (also referred to as Stratum granulosum (granular layer) squames meaning scales) – Non- The cells take on a distinctive flattened shape and take on a granular living cells of the outer layers of appearance as a result of keratinisation. The cells begin to differentiate the dermis, fully keratinised with and become corneocytes, they lose their nuclei and organelles and the no nucleus or cytoplasm. Cells of cells functions begin to decrease dramatically. This layer is 3-5 cells thick. the stratum corneum. Stratum lucidum (clear layer) This layer has flat transparent cells, hence the name ‘clear’ layer. There is no melanin present in the cells. The stratum lucidum controls the amount of water that can pass through the skin. This layer is not present in very thin areas of skin. Stratum corneum (horny layer) This is the outer most layer of the epidermis and is in direct contact with the environment. The skin cells are flat and no longer have a nucleus. Their structure is very different from when they were produced in the stratum germinativum. The dead skins cells are continually being shed. About 90 per cent of household dust is dead skin cells. The thickness of the corneum also varies with age, getting thicker as we grow older. This thickening makes the signs of aging more obvious. One major function of the stratum corneum is to prevent the skin dehydrating. This is achieved by the natural moisturising factor (NMF), which is a collection of water soluble substances that absorb water from the air and combine it with their own water content. This allows the stratum corneum to keep hydrated despite exposure to the environment. 113 9781510416222_CH02.indd 113 6/21/17 9:22 PM The City & Guilds Textbook Level 2 Beauty Therapy: for the Technical Certificate KEY TERMS Lipids (ceramides, cholesterol, fatty acids and sebum) also help control water loss and prevent entry of water soluble agents and harmful bacteria Lipids – A group of organic molecules that don’t like water. by providing a waterproofing layer on the skins surface. Lipids also keep They include fats, oils, waxes and the skin supple, preventing it from cracking and breaking which would fat soluble vitamins. allow pathogens to enter into the skin and could cause an infection. Ceramides – Natural lipids, which are an important structure of the Dermis skin. These fats allow the skin to The dermis lies beneath the stratum germinativum. It is a 3-5 mm thick hold onto moisture. layer made up of a tough extensive network of extracellular tissue. The dermis has a high water content. It contains most of the living structures HANDY HINT of the skin, including blood vessels, sweat glands and sebaceous glands. The NMF is water soluble and easily The main functions of the dermis are to: removed from the skins cells, ●● provide strength and flexibility which is why repeated exposure to ●● provide a system of capillaries to nourish the cells of the lower layers water makes the skin drier and why of the epidermis and remove waste products regular application of hand cream is ●● help control temperature and blood pressure. important after washing hands. Layers of the dermis The dermis has two layers: ●● papillary layer ●● reticular layer. Epidermis Melanocytes Papillary layer Sebaceous gland Arrector pili muscle Blood vessel Sweat gland Nerve Reticular layer Fat cells Subcutaneous tissue Apocrine gland Hair follicle p Layers of the dermis The papillary layer This is composed of loose connective tissue. The surface of the papillary layer is covered with tiny irregular shaped projections called dermal papillae.
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