Structure+and+Cells+of+skin


 * Structure of Skin **

The skin is composed of 3 layers.


 * 1) Epidermis – outer most region “upon the dermis”, has 4 cell types and consists of 4-5 layers
 * 2) Dermis – region below epidermis, mainly connective tissue
 * 3) Hypodermis – below dermis, mainly adipose and areolar connective tissue. Anchors skin to underlying structures and acts as padding/insulation (not going to go into great detail). [[image:ucanaandp/Anatomy_The_Skin_-_NCI_Visuals_Online.jpg width="564" height="500"]]

The cells of the epidermis are: Keratinocytes Melanocytes Langerhans cells Merkel cells
 * //Cells of the Epidermis//**
 * produce keratin ® which is a fibrous protein
 * They originate in deepest part of epidermis, and they are pushed up by new cells beneath.
 * They are dead by the time they reach the outer surface
 * Their function is for protection
 * These produce the melanin pigment
 * They are found in deepest part of epidermis
 * The melanin pigments shield from us sun damage (to a degree).
 * The numbers of this cell type increase with a suntan
 * Their function is for protection
 * These are macrophages produced in the bone marrow
 * They are found in the middle part of the epidermis as they form a network around the keratinocytes
 * Involved in immune system activation so again they are protective.
 * Together with sensory nerve ending form the touch receptors
 * They are located in the deepest part of the epidermis


 * Layers of the Epidermis **

There are 5 epidermial layers: Stratum basale Stratum Spinosum Stratum Granulosum Stratum Lucidum (not on this picture) Stratum Corneum
 * Deepest layer
 * Single row of new keratinocytes
 * 10-25% melanocytes
 * Occasional merkel cells
 * Several cells thick
 * Keratinocytes, melanin granules and langerhans cells
 * 3-5 cell layers
 * Keratinocyte appearnce changes
 * Flattened, organelles disappear
 * Produce kertohyline – keratin precursor
 * Lamellated granules – water-proofing lipid
 * few rows od dead keratinocytes
 * Found in thick skin only – palms, finger tips, soles of feet
 * ¾ epidermal thickness
 * 20-30 cell layer
 * Outer keratinised, waterproof protective layer
 * Cells are dead
 * Protection from abrasion and penetration
 * Rendering the body relatively insensitive to biological, chemical, and physical assaults

// Papillary layer // // Reticular layer of dermis // Tensions lines Flexure lines
 * The Dermis **
 * The dermis is the connective tissue layer below the epidermis.
 * It contains the usual cells of CT: fibroblasts, macrophages, mast cells and WBC’s and fibres – collagin, elastin and reticular fibres
 * Also there are nerve fibres, blood and lymphatic vessels.
 * Hair follicles, oil and sweat glands are also located in this region
 * It has 2 layers
 * Upper thin layer
 * Collagen, elastin fibres/blood vessels
 * Forms papillae that contain pain and touch receptors.
 * In palmar skin, forms ridges which push out epidermal ridges
 * Provides grip and forms fingerprints
 * Deep to papillary layer – 80% of dermis
 * Irregular connective tissue
 * Mainly collagen fibres
 * Fibres are arranged longtitudinally in head and limbs and circularly in neck and trunk. This is important for surgeons – cut made in same direction as fibres heals better
 * Formed by dermal fold near joints
 * At these points dermis secured to deep structures
 * Folds allow sliding of dermis during joint movement

3 pigments contribute to skin colour - Melanin (yellow – black) Carotene (orange) Present in epidermis, dermis & subcutaneous layer Haemoglobin (red) Present in skin blood vessels – provides pinkish hue of fair skin.
 * Skin Colour **
 * Only pigment that is made in the skin.
 * Made in mealnocytes and the passed on to keratinocytes

Human skin comes in different colours and this is not a random allocation – populations with darker skin tend to be found nearer the equator where greater protection from sun is required and those who don’t require as much “protection” have lighter skin. All individuals have relatively the same number of melanocytes – the colour difference come from the kind and amount of melanin made.

Introduction

Appendages of the Skin
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