MSS Structure and Function of Skin Flashcards
What does the integument, or integumentary system refer to?
Integument:
3 layers of the skin
– Epidermis
– Dermis
– Hypodermis
Hairs, Glands, Nails, Sense organs
What are the main functions of the skin?
1) Barrier (protection), against: Dehydration, Infection, Injury, Solar radiation
2) Thermoregulation
3) Sensation
4) Repair
5) Vitamin D production, which is then metabolised to the active form elsewhere in the body
Label this to show the layers of the skin
how is epidermis across different parts of the body?
e.g. thin epidermis found on the abdomen - where there is not a lot of friction expected
Thick epidermis is expected where you expect a lot of friction - the heel, elbows
The epidermis has 4 main layers. Describe the first layer
note-Main cell type in all layers is called keratinocytes
Basal layer (Stratum basale):
- innermost, single layer of cells in epidermis
- It contains stem cells (constantly proliferating) + is attached to the dermis
- Daughter cells constantly move ‘up’ + differentiate through the epidermis, until they are shed from the outer surface (every 20-50 days)
The epidermis has 4 main layers. Describe the 2nd layer
Stratum spinosum - spiny layer
- Thickest of the layers of living cells (i.e. with nuclei)
- Differentiating and moving distally; not dividing
- Cells have many desmosomes (junctions), visible at high magnifications as ‘spines’ between the cells - strong bonds holding the epidermis together, this makes this layer tough and resilient
The epidermis has 4 main layers. Describe the 3rd layer
stratum granulosum - granular layer
- Thinner layer; 1-4 rows of cells w prominent ‘keratohyalin’ granules- precursor keratin
- contain lamellar bodies containing lipids - needed for outer layer of epidermis - seen by electron microscopy
- Cells are differentiating to form the outermost layer
The epidermis has 4 main layers. Describe the 4th layer
stratum corneum - cornified layer
The outer protective layer of the epidermis.
- Has squamous (flat) cells which have lost their nuclei and are cornified - full of ‘horny’ keratin protein, thus tough and resistant to injury.
- Fully differentiated keratinocytes
- Non-polar lipids are between the cells - (formed from the lamellar bodies in the granular layer), to waterproof the skin
Other epidermal cell types inc:
- melanocytes (pigment)
- Langerhans cells (defence)
- Merkel cells (sensation)
Describe melanocytes
- Melanocytes in the epidermis produce melanin pigment granules called melanosomes
- Melanosomes are transferred to basal keratinocytes through long dendrites
- This process is protective against UV light
How is melanin pigment arranged?
Keratinocytes arrange melanin in a cap on top of the nucleus- this is the sunny side, so melanin will protect against impinging sunlight!!
Melanin is mostly arranged in basal layer
What are Langerhans cells?
Function: Immune system. APCs
They are dendritic cells, forming a network – seen
here with a special stain.
H&E appearance: Small, pale cells in non-basal
layers of epidermis (L). Hard to see with H&E
only.
Describe vitamin D production in the epidermis
where is vit D converted to active form?
Vit D3 made in the epidermis, mostly in basal cells, also stratum spinosum
This process needs UV light (fine balance)
Vit D3 is converted to active form in liver and kidney (1,25 dihydroxyvitamin D3)
The second layer of the skin is the dermis, describe this type of connective tissue
- Dense = full of collagen fibres;
- Irregular = fibres run in all directions (not parallel)
- Functions: Collagen (made by fibroblasts) provides tensile strength + so impact/abrasion protection
- contains elastin protein to provide elasticity.
- rich in blood vessels to carry blood and nerve supply for epidermis.
The dermal-epidermal border is often wavy, why is this?
Dermal-epidermal border is often wavy to resist shear forces (rubbing sideways).
- esp on hands = fingerprints, also feet
- dermis can have finger like papillae - dermal papilla
- rete ridges are what form the fingerprint; ridges of epidermis going down to the dermis
Label this
What does this show?
Describe the hypodermis, the thickest layer of skin. How does it appear on H&E?
AKA fascia or subcutis
Made of fat cells, containing glands, hair follicles, nerves and blood vessels
Is site for subcutaneous injection
Function: provides insulation, cushioning and energy storage
Each thin circle is cytoplasm of one fat cell (adipocyte) - The circle surrounds one big fat droplet, unstained with H&E, because actual fat is extracted in histology processing
Label
Describe hair
Hair - rudimentary in humans over much of body (unlike most mammals), but keeps the head warm
Hair follicles are also a site of acne
Acne is when a follicle becomes blocked and can get infected
Describe nails
- protects ends of fingers
- you can get infection in the fold called the hyponychium
- nail matrix is where nail is going to be made
- nail plate is made of HARD keratin
Describe sense organs in the skin, using this diagram to help
Describe Meissner’s and Pacinian corpuscle
