Skin Flashcards
Epidermis type and origin
It is an epithelial layer of ectodermal origin
Dermis type and origin
It is connective tissue of mesodermal origin
Skin appendages
Sweat glands
Sebaceous glands
Hair
Nails
Types of skin
Thick skin
This skin
Epidermis cell types
It is formed of Stratified squamous keratinized epithelium
Has keratinocytes and non-keratinocytes
Keratinocytes are:
Arranged in 5 layers Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum
Stratum basale
Germinal layer
Single layer of columnar cells
Cytoplasm is basophilic due to high ribosomal content
Many mitotic figures
EM:
Contains IF (tonofilaments)
There are desmosomes between cells and hemidesmosomes at the basment membrane
Stratum spinosum
Prickle cell layer
Several layers of polygonal cells with central nuclei
Some mitotic figures
Has many spinous interdigitating processes and intercellular bridges ending with desmosome
Many tonofilaments in the cytoplasm
Stratum granulosum
Granular layer
3-5 layers of polygonal cells with central nuclei
The cytoplasm contains basophilic non-membranous granules called keratohyaline granules
EM:
There are membrane coated lamellar granules that reease lipid-containing substance in the intercellular space. This forms a barrier against invasion with foreign materials resembling intercellular cement
Stratum lucidum
Clear layer
It is translucent thin layer of eosinophilic flattened cells containing eledin
EM:
Cells have no organelles, no nuclei and the cytoplasm is mainly formed of closely packed tonofilaments embedded in an electron dense matrix
desmosomes are still present
Stratum corneum
Horny layer
Superficial cells are shed
Consists of many layers of flattened non-nucleated keratinized cells
Cytoplasm is filled with filamentous scleroprotein called keratin
Malpighian layer
Stratum basale + stratum spinosum
Renewal occurs every 15-30 days
Non-keratinocytes examples
- Melanocytes
- Langerhan’s cells
- Merkel’s cells
Melanocytes origin
Derived from the neural crest
Ectodermal
Melanocytes
Sites
Between cells of stratum basale and in hair follicles
Melanocytes
LM
They have rounded cell bodies with central nuclei
They long cytoplasmic processes extend between cells of Malpighian layer
Melanocytes
EM
Cytoplasm contains numerous smal mitochondria, well-developed Golgi and rER
Not attatched to keratinocytes by bind to the basal lamina by hemidesmosomes
Epidermal-melanin unit
One melanocyte maintains an association with a given number of keratinocytes
Epidermal-melanin unit
One melanocyte maintains an association with a given number of keratinocytes
Function of melanin
Fuse with lysosomes and occupy a supranuclear position protecting the dividing nucleus from UV rays
Albinisim
Genitic defect in tyrosinase enzyme so no melanin is produced
Melanocytes are DOPA +ve or -ve
DOPA +ve
Keratinocytes are DOPA +ve or -ve
DOPA -ve
Melanophages/Melanophore cells are DOPA +ve or -ve
DOPA -ve
Langerhan’s cells
Origin
Derived from the mesenchyme from the bone marrow
Langerhan’s cells
Site
Inbetween cells of stratum spinosum
Langerhan’s cells
Structure
Branched star-shapped cells with intended nuclei and clear cytoplasm
Have characteristic rod-shapped granules called Birbeck’s granules
Langerhan’s cells
Function
Antigen-presenting cells for lymphocytes
Merkel’s cell
Sites
They are present in thick skin
Merkel’s cell
Structure
Large dark cells
Resemble keratinocytes but cytoplasm contains small dense granules
Associated with nerve endings
Merkel’s cell
Function
May act as mechanoreceptors or may heave DNES-cell like activity
List layers of dermis.
Papillary layer
Reticular layer
Mention components of reticular layers of dermis in thick skin
It consists of dense connective tissue that contains the following:
- Abundant collagen fibers type I and elastic fibers.
- Sweat glands.
- Sympathetic nerve fibers, free nerve endings and encapsulated sensory organs (e.g. Pacinian corpusles).
Papillary layer
Outer layer beneath the epidermis
It consists of loose CT rich in cells, free nerve endings and blood capilaries for nutrition of the epidermis
The dermis contains
Sweat glands, hair folicles and sebaceous glands
Dermo-epidermal junction
Interdigitations between the dermal papillae and epidermal ridges
Sites of thick skin
Covers palms of hand and soles of feet
Thin layer sites
Covers everywhere except palms and soles
LOOK AT THE TABLE OF THICK SKIN AND THIN SKIN
Soft keratin
Tonofilament –> keratohyaline –> eleidin –> soft keratin
Hard keratin
Tonofilaments –> hard keratin
Pigment of red hair
Pheomelanin
