sect 2 - ref skin histology

8/9/2019 Sect 2 - Ref Skin Histology

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section twot w oSkin Histology

Structure of the skin page 12The epidermisStructureFunctions

The process of melanogenesis page 15The dermisStructureFunctions

NATURAL SCIENCE FOR YOUR SKIN


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The structure of the skin

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the epidermis

HYDRO-LIPIDICMANTLE

EPIDERMIS

Dermal/epidermalJunction

DERMIS

Collagen

Elastin

Fibroblast

STRATUMCORNEUM

MIDDLE LAYER

Basal Layer

EXTRA-CELLULARMATRIX

Microcirculation

structureThere are six basic layers to the epidermis

1. Stratum Disjunctum (outermost layer) - the top 4-5 layers of the stratumcorneum have have been renamed the Stratum Disjunctum, as these are thelayers we naturally desquamate .

2. Stratum Corneum - this is a dead horny layer of cells, roughly 14 cell layersthick, continually shedding and is the last step in which the young keratinocyteis formed into a hard water-resistant corneocyte. The thickness of the stratumcorneum depends on U.V. exposure or other skin conditions.

3. Stratum Lucidum - a clear transparent layer is thicker on the soles of our feetand the palm of our hands or wherever a callous has become apparent.

4. Stratum Granulosum - this is the layer where keratinisation takes place, thenucleus disintegrates and the cell starts to become more void as it starts to fillwith keratin. Keratinocyte becomes a corneocyte .

5. Stratum Spinosum - named after the tiny fibrils that join the cells together inthis layer. This is the first step of cellular differentiation , the process of changingfrom an immature cell to a fully functional end cell, no longer able to divide orgrow, Langerhans cells are found in this layer, forming part of the immunesystem and helping to break down bacteria.

6. Stratum Basale Stratum or Germinativum (innermost layer) - this is the layerwhere keratinocyte cells constantly divide through mitosis. These cells havenuclei and other organelles.


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the epidermisfunctionsPhysical protection

CELL TURNOVERDesquamation process involves continuous shedding of epithelial cells as aprotective and 'self cleansing' mechanism.

Cell turnover or keratinisation is the process of change that keratinocytes haveto undergo before they reach the Stratum Corneum to function as a barrier cell.During this process the cytoplasm of the cell is completely replaced with keratinprotein and the moisture of the cell and fragments of the nucleus are encapsulatedin lamellar bodies, which later release their contents as part of the NaturalMoisturising Factor (NMF).

The renewal time of epidermal cells is about 19 days and each cell spends anaverage of 10 days in its migration, making the total cell turnover approximately 29days.

CHEMICAL PROTECTIONThe Acid Mantle is made up of a combination of sebum and sweat that togetherproduce an acidic substance on the surface of the skin to ward off fungi andbacteria.

Melanin is produced by the melanocytes in the Stratum Germinativum in a processcalled Melanogenesis. Melanin produced in the melanocyte is transferred to thekeratinocytes in packets called melanosomes via the dendritic projections of themelanocyte. Melanin protects against U.V. radiation.


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the process of melanogenisis

Fa ir Skin Tanne d Skin

Basal layer

Melanocyte

Melanosomes

Dendrite

Keratinocyte


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the dermisstructureThe dermis consists of a mass of connective tissue formed by fibroblasts in whichcollagen and elastin are embedded. The Dermis also contains blood vessels,lymphatic vessels, nerves, tactile corpuscles, sebaceous and sudoriferous glandsand hair follicles, the latter three usually referred to as appendages . The Dermishas two major divisions:

Papillary layer - This is the thinner layer of the two and contains small, loose elastinand collagen fibres. It is aiso rich in blood and nerve supply, providing the basallayer with nutrients and sensation.

Reticular layer - Consist of denser collagen bundles and coarser elastin fibres. Thisis the area that carries most of the physical stress of the skin and also gives the skinits pliability.

DERMIS STRUCTURE

Collagen Elastin Apendages

derm is

hypoderm isFibroblast

epidermis epidermis

Extracellular matrix composed ofcollagen, elastin fibrils,glycocaminoglycans, polysaccarides,proteoglycans


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the dermisfunctionsCOLLAGENCollagen is formed in fibroblasts and is made up of molecules consisting of threepolypeptide chains wrapped around each other as a triple helix which providesrigidity to the molecule, preventing it from stretching, maintaining the tone andstructure of the skin.

The reasons for collagen to break down are :

Collagen degenerates with age .

Collagen degenerates with sun damage as it is easily cross-linked byfree radicals (elastosis).

UVA inhibits collagen formation.

Old collagen is broken down by collagenase at a very precise rate, butunfortunately this rate speeds up with age and exposure to free radicals andeventually more collagen is broken down than the body can produce.

ELASTINElastin is produced by fibroblasts and can be seen as a network of elastic tissuethat keeps the skin toned and tight. Elastin gives the skin its resilience and elegantfeel and provides 'spring' and 'snap' to a young face.

The reasons for elastin to break down are: Elastin is also affected by free radical activity and is broken down by the

enzyme elastase at a very precise rate, which again speeds up with age,resulting in sagging of the skin.


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dermisGROUND SUBSTANCEThis is the extra-cellular packing material, also known as "the matrix', that collagen

and elastin is suspended in. This matrix consists mainly of water andglycoaminoglycans.

Glycoaminoglycans serves to:

maintain water balance in the dermis

add support for other dermal components :

act as a matrix for cell migration, metabolism and growth.

APPENDAGESThe appendages include the hair follicles, sebaceous glands and the sweatglands . The one aspect they all have in common is that they reside in the dermisand open either directly or indirectly into the Stratum Corneum.

Pilosebaceous unit (hair follicle and attached sebaceous gland)

Hair Follicle - is a tube of epidermal cells that extend into the dermis.

Sebaceous Glands - open into the hair follicle. The Sebum consists of water,oil, fatty acids and protein and makes up a very important part of the acidmantle and lubricates the skin and hair shaft. Sebaceous secretions arecontrolled by the endocrine system and become active during puberty, but lessactive as a person ages.

Sweat Glands or Sudoriferous Glands

Eccrine Glands - open directly onto the surface of the skin.

Apocrine Glands - open into the hair follicle, but are larger than the sebaceousglands and are located deeper within the dermis. Apocrine glands secrete asticky, cloudy and odourless fluid which can be broken down by bacteriacausing the characteristic human odour.

Acid Mantle

Combinations of sweat from apocrine glands and oil from sebaceous glands.

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sect 2 - ref skin histology

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