Skin - Structure and function 1

Integument meaning

The outer layer, e.g. the skin..

Some examples of microrganisms (for referance) E

What are the 3 originial layers of the skin and what are their functions.,.

Epidermis — Protection from dehydration

Dermis - Tensile Strength

Subcutis/ hypodermis - energy storage (fat)

What are the original 2 layers of the embryo skin and what does this further differentiate into…

Ectoderm over a mesoderm..

Ectoderm divides into a basal cell layer AND an outer layer (periderm)

Betweeen the basal cell layer (stratum germinitvum) and the Periderm = the statum intermedium

Once the embryo is developed what happens to the periderm…

IT will be lost

What are Melanocytes of

Neural crest origin

What are langerhan cells of

Bone marrow origin.

How is the Dermis developed (embryologicallly)

• Originially a loose collection of cells from the mesenchyme

• Will increase in thickness and number of fibres..

• Originally COllagen —→ Elastin fibres beceome increasinglng organised

• ground substances are also secreted + development of nerves and blood vessels..

• Lipocytes = develop in the second half of gestation ( fat cells under the skin = subcutaneous dermis layer…

What happens to the skin in mid- late pregnancy

• skin splits into 4 layers of the epidermis

• Periderm is lost

• cells of the epithelium = Keratinocytes (presenece of keratin)

What type of epithelium is skin

STATIFIED SQAUMUS EPITHELIUM

(4 distinct layers ABOVE the basement membrane)

What is the embryology of a hair follicule

• Proliferate from the epidermis

• hair bud + has a FEW mesenchymal cells

• Epidemal cells grow around a papilla….

Keratinocytes (bricks what 3 things do they need )

• Individual skin cells in epidermis…

• Strength

• joined together

• attachment to the underlying dermis…

What gives the keratinocyte is STrength…

KERATIN!!!

fillament forming proteins for mechanical support… differenly expressed in different layers in the skin. Links cells nuclear membrane to the plasma membrane at desmosomes…

What is hyperkeratosis

• excessive keratin production

• can hurt the dog

What is a desmosomes

• strong links between ketarocytes..

• provide intra cytoplasmic signalling +tightly fitting,..

• Desmosomes = made of STRONG proteins which hold the skin toether BUT can also unzip.. Some diseases will target desmosome protiens causing the cells to unzip…

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What is pemphigus foliaceus

• Immune mediated disease against desomome proteins..

• causes prominate pustules (wbc + epithelia)

What is a Hemidesomosomes..

Attatches the epidermis to the dermis.

Stong link between the keratin and the intersitial collagen

many of these molecules and can lead to congenital + autoimmune diseases…

Epidermis in Mammals

If see RBC then this means that the sample has gone beneath the epidemis…

What are the 4 skin layers (in to out)

Stratum Basalis

STratum Spinalis

Stratum GRanulosum

Stratum Cornean (dead skin)

Post mortem skin layers

How does skin thickness vary…

Rete Ridges = protections into the epidermis… help to anchor the skin

How do keratinocytes develop…

develop from the basement membrane and work upwards..

Those skin cells will then move upwards..

Cytoskeleton is attatched too :

• Tight junctions

• desmosomes

• hemidesmosomes.. ( cells - dermal proteins)

What do Keratinocytes prodoce…

• Extracellular lipids - from sebaci=eous glands

• SKIN = immunologically acti ve

Stratum basale function

This is the base layer of cells and it is a single layers of cuboidal cells, proliferative and anchoring..

• single layer cuboidal cells

• skin stem cells (pluripotent)

• proliferative and anchoring

• has keratinocyte - keratinocyte : desmosomes..

What influences the growth FROM the stratum basale…

• Growth factors + hormones (e..g epidermal growth factor, insulin growth factor, cortisol, thyroid hormones)

• Inflammaroty mediatios (Il1, il6…)

• Drugs and Vitamins… Vit D + Vit A..

Stratum Spinosum

1- 20 cells thick (largest layer)

Polyhedral cells - many desmosomes/ intracellular bridges

upper layer will produce involucrin (histology)

Statum spinulosum zoomed in..

Many desmosomes in the spinosum layer…

How does the stratum granulosum appear…

• has granules (contains keratohyaline granules) Bind the cells together AND allows secretention of extracellular lipids and enzymes…

• very thin layer

• Desomosomes = corneodesmosin…

• Flattened cells + nuclei start to shrink..

Stratum granulosum

What is the stratum lucidum…

• Present in hairless/ thickened skin

• not often animals

• high intracelllular keratohyalin + intracellular lipids, appears like a see - through layer…

Stratum corneum

_ sqaunmes

no nucleas

cornicfied envwlope + lipids + hydrophobix ends outwards - to help waterprooding.

This is a corneodesmosome..

How is the cornicfied envelopme produced…

• This is the outermost layer of the stratum corneum

• Starts of as a lipid bilyare and many proteins end up embedded in the layer

• very strong + tough outer layer…

What is the purpose of fillaggrin..

• Facilitates the collapse of corneocytes into building blocks for an impermeable surface barrier..

• Break down of fliaggrin forms natural moisturising + uv protection..

What does filaggrin break down produce…

• urocanic acid

• Pyrrolidone carboxylic acid + excellent uv protection..

What is the horny layer modified with

Corneodesmosomes.. membranes are replaced to form organised layers of lipi and collapsed cells..

What are common defects of the Corneal epithelium…

TGM 1 mutation in terriers, sever hyperkeratosis… Thin cornified envelopes..

Significant decreasein TGM1 mRNA

What is Desqaumation

• continual loss of cells

• mediated by protinases

• shouldnt be visibell.

• IS there is an enzyme defeiciency then theire will be rafts of skin coming off NOT lots of skin cells falling off.