Integument 3; The Epidermis Flashcards
What is the alternative name for keratinisation in the epidermis?
Cornification
What type of epithelium is found in the epidermis?
Stratified squamous keratinised epithelium
Ho do cells move inside the epidermis in order to provide protection?
Move in an escalator motion to supply the constant turnover of cells
How is the skin protected during trauma?
Accelerated turnover of cells and thickening of the skin
How else is the epidermis strengthened in order to provide protection?
Cross-linkage of keratin filaments (this uses profillagrin in keratohyalin granules)
What are the 2 different pathways through which a drug can permeate the skin?
Intracellular
Transcellular
What is the function of hemi-desmosomes?
Anchor basal cells to the basement membrane
What is the function of desmosomes?
Desmosomes attach keratinocytes to each other
What is the function of corneo-desmosomes?
Corneo-desmosomes attach corneocytes to one another
What happens when corneo-desmosomes enzymatically degrade?
This causes desquamation
How are desmosomes affected by auto-immune disease?
The proteins that make up desmosomes and hemi-desmosomes become targets for auto-immune disease so are damaged
How does the epidermis function as a barrier?
- Keeps water, electrolytes and macromolecules in
- Keeps infectious agents and chemicals out
How does the epidermis contribute to homeostasis?
- Maintains water and electrolyte balance
- Helps to maintain temperature (thermoregulation)
How does hair on the epidermis aid with protection?
Provides physical protection and UV protection
How do sebaceous gland aid with protection?
Vitamin E present in sebaceous gland secretions (important antioxidant)
What other epidermal structures aid with protection?
Hooves, claws and nails
Explain the structure of the stratum corneum using the bricks and mortar theory
- Corneocytes are the bricks and the cell membrane is converted to a resilient cell envelope consisting of cross-linked protein and covalently bound lipids.
- Lipids are the mortar, lamellar lipids in the intercellular space (ceramides, cholesterol, long chain fatty acids)
How do the lipids in the stratum corneum provide waterproofing?
- Intercellular lipids are hydrophobic so prevent transepidermal water loss
- The keratinocytes and sebum-derived lipids also help to make the epidermis waterproof.
What are the two ways in which there can be alterations in epidermal growth in response to skin damage?
- Abnormal cornification
- Epidermal hyperplasia
What are the causes and effects of abnormal cornification?
- Caused by trauma, metabolic disorders or disease
- Off sets the balance between proliferative basal cells and loss of corneocytes
- This can result in hyperkeratosis (thickened stratum corneum)
What happens during epidermal hyperplasia?
Increased number of cells in the epidermis, usually in the stratum spinosum
What alterations can be seen in epidermal fluid balance when skin is damaged?
Odema (occumulation of fluid between cells)
Intracellular fluid accumulation
What is acantholysis?
A loss of desmosomes -> these become an autoimmune target where toxins/enzymes are released by microbes
How does inflammation of the epidermis occur?
- Begins in the dermis with increased blood flow, odema and migration of WBCs into tissues
- The accumulation of WBCs can progress to crusts
What are the two alterations that can be seen in epidermal pigmentation with skin damage?
Hyperpigmentation = increased melanin production or number of melanocytes
Hypopigmentation = a lack of melanin, melanocytes or melanin transfer from cell to cell.
What structures are equivalent to footpads in ruminants, pigs and horses?
- The bulb in ruminants and pigs
- The frog in horses
What two additional structures do horses have? (Equivalent to carpal/metacarpal pads)
- Chestnut (carpal/ tarsal pads)
- Ergot (metacarpal/ metatarsal pads)
How is the skin of the footpad adapted to act as a shock absorber?
A thick subcutis with adipose tissue, collagen and elastic fibres and thickly cornified epidermis, plus stratum lucidium.
What helps to anchor the foot pads to the skeleton?
Ligaments
What sweat glands are found in the footpad and what do they help with?
Eccrine sweat glands help to provide grip with the watery sweat
What 3 structures are found in all nails, claws and hooves?
All have a wall, a sole and a foot pad
What are the collective functions of nails, claws and hooves?
- To protect distal digit
- To be used as tools for scratching and digging
- As weapons
- For blood circulation (esp. in horses)
What is the ‘horn’ on these structures?
Highly keratinised epidermis
What is the coronet?
The junction between the skin epidermis and the hoof
What causes the transverse ridges on hooves?
Periods of disturbed growth
How is the epidermis of the nail/ claw/ hoof anchored to the underlying dermis?
By interdigitations (laminae)
What is unique about the dermis/ the quick?
The quick is closely adhered to the periosteum of the distal phalynx and as such, here is no subcutis here
What structures enable cats to keep claws retracted?
Dorsal elastic ligaments
What structure helps to suspend the pedal bone in the hoof?
What is the other benefit of this structure
Laminae
Transfers forces from none to hoof walls
What happens during laminitis?
1) Inflammation of laminae causes detachment of the pedal bone
2) Pulling action of the deep digital flexor tendon can result in rotation and sinking of the distal phalynx
3) Pedal bone can penetrate the sole
How do horses’ hooves aid venous return?
Compression of the frog/ footpad forces the digital cushion outwards and squashes the hoof cartilages.
Venous plexus’ in the cartilage are squashed, squeezing blood in the digital veins
What are the 3 layers of the hoof wall?
1) Stratum externum = thin outer layer continuous with the stratum corneum
2) Stratum medium = contains pigments and tubules which aid structural support
3) Tratum internum = epidermal laminae extend and interdigitate with laminae of dermis
How are horns and antlers formed?
Structures initially formed from a bone core and covered by integument
Which layer of the integument are horns and antlers derived from?
The epidermis
