Skin Flashcards
What are the layers of the skin?
Epidermis
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
Dermis - made of thick fibrous and elastic tissues
Hypodermis (subcutis)- fatty connective tissue
What are key functions of the skin?
Barrier to infection
Waterproofing
Thermoregulation
Protection against trauma
Protection against UV light
Vitamin D synthesis
Key organ for sensation
What is the stratum basale (basal layer/germinative layer)? What cells does it consist of? How does the epidermis grow?
The single layer of cells that rest against the basement membrane
Basal epithelial cells (stem cell population of epidermis) and melanocytes (produce melanin)
The epidermis grows from the basal layer, upwards to the surface, where dead cells are shed into the environment and are replaced by new cells growing up from below.
Where are melanocytes found? What is their function and where do they arise from? What hormones stimulate the production of melanin?
They are usually only found in the basal layer of the skin (at a density of 1000-2000 per mm2
They synthesise melanin and transfer it to surrounding keratinocytes in special organelles called melanosomes
MSH and ACTH (adrenocorticotropic hormone) stimulate the production of melanin
They arise from neural crest cells of the embryo and migrate to the epidermis during development
What does the colour of skin depend on?
THE NUMBER OF MELANOCYTES is about equal between races (so the colour of skin doesn’t depend on the number but rather the AMOUNT and type of melanin synthesised and stored in keratinocytes - the darker the basal layer, the darker the skin
Where are langerhans cells and merkel cells found? What are their functions?
Langerhans cells can also be found in the stratum spinosum. They are antigen recognition cells and increase in number in inflammatory situations.
Merkel cells can also be found. They are specialised sensory cells (these 2 cells can’t be readily seen without special stains)- fine touch (basal layer)
Describe the stratum spinosum of the epidermis. What cells are found in them? Why is it called the prickle cell layer?
It is usually the largest layer of the epidermis. (majority of the cells of the epidermis are keratinocytes)
It comprises plump polygonal keratinocytes which are closely bound together by desmosomes (on light microscopy can be viewed as intercellular adhesions)
In tissue processing, the keratinocytes try to retract from one another (and desmosomes will be visible as prickles/spikes between the cells)
Describe the Stratum granulosum layer of the epidermis
Comprises a cell layer of flattened squames
Here, the epidermal keratinocytes mature and as their cytoplasm becomes filled with keratohyaline granules, they die → therefore the the outermost layer of the epidermis stratum corneum is acellular comprising plates of keratin
Describe the stratum corneum layer of the epidermis
An acellular layer
Comprises of plates of keratin (present in the form of dead keratinised squames)
At certain parts of the body especially the palms and soles, the stratum corneum is especially thick – sites of abrasion and thus the thick layer helps to resist abrasive forces.
Which layer of the epidermis does keratin form?
The stratum granulosum
What are epidermal adnexae?
They are down growths of the epidermis into the underlying layers of the skin: dermis and subcutis. (all adnexae are down growths)
They include hair follicles and their associated sebaceous glands, and specialised types of glands that produce different types of sweat: the eccrine sweat glands and apocrine sweat glands.
What are sebaceous glands? Where are they found? What type of secretion do they carry out?
They are present in association with hairs in the skin
They produce a sebaceous secretion that lubricates and waterproofs hair. → this is done by discharging the contents of entire cells onto the surface of the hair follicle. Aka holocrine secretion (a specific mode of secretion involving secretion of entire cytoplasmic materials) Entire cells are lost (found in dermis)
What are apocrine glands? What are they associated with and where are they found?
They are associated with hair follicles. They are found in the armpits, groins, on the genitals and around the anus
They are also found in the external auditory canal where they form ceruminous glands that produce ear wax
They are simple coiled tubular glands they produce secretions through apocrine secretions → the secretion comprises elements of the cytoplasm of these cells which bud off from the luminal surface
They can be recognised as their epithelial cells have an eosinophilic cytoplasm with surface budding
What are eccrine glands? What epithelium are they lined by?
They are the commonest sweat glands, found everywhere (in the skin).
They produce thin watery secretions recognised as sweat
They are recognisable as coiled tubes, 2 cell layers thick in the dermis. The 2 cell layers: inner layer of tightly coiled secretory cells surrounded by an outer layer of myoepithelial cells (which contract to force the secretions to the surface of the skin)
They secrete via a merocrine process (merocrine gland secretions rely on exocytosis across the luminal membrane of the secretary cells) → known as eccrine secretion in eccrine glands.
Lined by simple cuboidal epithelium
What are rete pegs?
The pegs help to anchor the epidermis onto the underlying dermis.
