The Skin Flashcards
State the layers of skin that makes up the epidermis.
4 or 5 layers of cells making epidermis - basal, spinosum, granulosum, and corneum composed almost all over the body.
In areas of thick skin, there’s an additional layer which is the lucidum.
Describe the classification and features of the epithelium that makes up the epidermis.
The epithelium that forms the epidermis is classified as pluristratified squamous epithelium.
A surface specialisation consisting of a more or less thick layer of keratinized cells.
Describe the cells of the basal layer.
Composed of one single layer of basophilic cells - cuboidal to local columnar.
All cells anchored to the basal membrane underneath through hemidesmosomes and focal adhesions.
Expression of keratin 5 &14. By using specific antibodies for keratins, this layer can be identified.
Cell junctions (between cells) are joined by specific desmosomes.
Describe the stem cells in the basal layer.
The basal layer contains stem cells of epidermis, which is defined as unipotent as able to only differentiate into keratinocytes.
The skin undergoes rapid turnover. To avoid dramatic thickness reduction, new cells need to be produced and differentiated.
State and describe a pathological condition associated with the basal layer.
Epidermolysis, where the interaction of the basal layer with basal membrane is affected. This causes detachment of epidermis from dermis, causing blisters and then wounds.
This can be secondary to production of old antibodies against proteins of hemidesmosomes, or genetic defects affecting protein anchoring the basal layer to epidermis.
Describe cells of the spinious layer (stratum spinosum).
Cells have a spinious appearance.
The spinous layer above the basal layer is 4-8 sheets.
These cells do not proliferate anymore and have a larger size with cell-cell attachment using desmosomes.
Keratin filaments (keratin 1 and 10) tend to aggrege in thicker bundles.
In the cytoplasm 2 types of membrane bounded granules can be seen: melanosomes and keratinosomes.
Describe cells of the granular layer (stratum granulosum).
Cell have a flattened appearance.
Cytoplasm filled with non-membrane bound granules.
Granular layer composed of 3-5 layers.
Granules are associated to tonofilaments, which contains filaggrin & thistorich proteins able to aggregate filaments into fibrils.
Loricrin is involved in the formation of the cornified envelope.
Lipid content of keratinosomes released which guaranteens impermeabilization of the skin.
What junctions chracterize the cells of the granular layer?
Adherent and occluding junctions characterise granular layers.
Why are occludin junctions important?
Occluding junction important to limiting loss of water through skin.
Occludin is one of proteins that form occluding junctions.
In mice knockouts for proteins of occluding junctions there is a rapid loss of water and newborns die from dehydration.
Describe cells of the cornified layer.
Dead cells that has lost nucleus.
corneocytes: have organelles filled with keratin filaments and immersed in a matrix of fillagrin and loricrin +involucrin submembrane.
Insoluble lipids located outside the PM.
Enzyme transglutaminase responsible for cross-linking of these constitution proteins.
Desmosomes modified called corneodesmosomes.
Loss of cornified lamellae is regulated enzymatically by enzymes which digest corneodesmosomal components.
Describe the condition Harlequin-type ichthyosis.
Ability to secrete lipids containing lamellar bodies (keratinosomes) is compromised.
Skin is inelastic and forms thick armour which compresses abdomen and chest.
Difficulty breathing and death in first dew days of life.
Caused by mutation in membrane transporters involved in transport of lipids across the PM.
What are Langheran’s cells? What do they do?
They are cells of the monocyte macrophage lineage.
Antigen presenting cells.
Regulating immune surveillance of skin.
What are Merkel’s cells? What do they do?
They are sensory mechanical receptors.
They have a synptic contact with sensory afferent nerve endings.
Characterised by the presence of a few melanosomes and 18 nm neurosecretory granules.
Have expanded terminal bulbs - part of afferent nerve fibers which together with cells make the merkel corpuscles.
Where are Merkel’s cells located?
In the basal layer in between keratinocytes.
How is melanin produced?
Melanin is produced from amino acid tyrosine by the activity of enzyme tyrosinase which converts tyrosine into DOPA. Other procedures then follow.
There’s the production of melanin which gives colour to skin and hair, and pheomelanin which gives a yellow-red colour.
