Integument 3 Flashcards
hoofs, footpads and antlers
What type of epithelium would be found in the footpads?
- keratinised stratified squamous epithelium because they are thick
What is the epidermis?
- a self-renewing stratified squamous keratinising epithelium
How can the epidermis do constant turnover of skin cells?
- the moving escalator
How can the moving escalator provide protection?
- accelerated turnover can be protective e.g., noxious stimuli on skin surface
- thickening also protects if trauma (e.g., if an animal scratches a lot thickening can prevent breaking skin)
How can cross-linkage of keratin filaments occur in cornification?
- by enzyme like profilagrin in keratohylaine granules and envelop proteins
What are envelop proteins important for in cornification?
- waterproofing
In cornification and keratinisation there is also a lipid seal between corneocytes what is this called and what does it lead to?
- bricks and mortar
- this means that if things want to cross the skin then they will have to cross intracellularly, transcellularly or transfolicaularly
What do Hemi-desmosomes do?
- anchor basal cells to basement membrane
What do desmosomes do?
- attach keratinocytes to each other in a deeper layer of the dermis
What do corneo-desmosomes do?
- attach corneocytes to each other (enzymatically degrade -> desquamation)
What can be targets in autoimmune disease?
- the proteins comprising desmosomes and hemi-desmosome
A major function of the epidermis to act as a what?
- a barrier
What does the epidermal barrier do?
- keep water, electrolytes and macromolecules in
- keep infectious agents and chemicals out
How does the epidermal barrier contribute to homeostasis?
- water and electrolyte balance
- temperature and thermoregulation
The epidermal barrier also provides protection via the epidermal layers themselves plus specialised epidermal structures - what are these?
- Hair (physical protection, UV, sensory, swatting)
- Antioxidant (vitamin E in) sebaceous gland secretion
- Hooves, claws and nails as weapon and barriers
The stratum corneum is the bricks and mortar - what are corneocytes (the bricks)?
- flattened cells
- aggregation of keratin filament (by filaggrin)
- cell membrane is converted to a resilient cell envelop consisting of cross-linked protein covalently bound lipids
The lipids in the stratum corneum make the bricks what happens here in terms of water proofing?
- lipids released from stratum granulosum into intracellular space
- included ceramides, cholesterol, long chain fatty acids
- hydrophobic, so prevent transepidermal water loss
- the keratinocyte and sebum-derived lipids also make the epidermis waterproof
There are huge number of factors influencing the skin but limited ways for the skin to respond - what are these responses?
- alterations in epidermal growth or differentiation
- alterations in epidermal fluid balance and cellular adhesion
- inflammation of epidermis
- alterations in epidermal pigmentation
What two things can result from alteration in epidermal growth or differentiation?
- abnormal cornification
- epidermal hyperplasia
What is abnormal cornification?
- insult affects balance between proliferative basal cells and loss of corneocytes
What can cause abnormal cornification?
- inflammation, surface trauma, metabolic or nutritional disorders, the environment
What can abnormal cornification result in?
- can result in hyperkeratosis (thickened stratum corneum)
Alteration is epidermal growth or differentiation can also lead to epidermal hyperplasia what is this?
- alteration of epidermal growth and proliferation (increased number of cells, usually in stratum spinosum)
What is epidermal hyperplasia often a very common response to?
- A variety of stimuli, often chronic like allergies
Alterations in epidermal fluid balance and cellular adhesion can lead to what?
- oedema and intracellular fluid accumulation
- acantholysis (loss of desmosomes)
What is oedema and intracellular fluid accumulation due to?
- due to epidermal inflammation or infection
What causes acantholysis (loss of desmosomes)?
- autoimmune target
- toxins/enzymes released by microbes
Describe inflammation of the epidermis?
- begins in dermis with increased blood flow, oedema, migration of white blood cells (usually neutrophils) into tissues
What can accumulation of WBCs progress to in inflammation?
- pustules then crusts
What can alteration in epidermal pigmentation cause?
- hyperpigmentation (increased melanin production or number of melanocytes)
- hyperpigmentation or pigmentary incontinence (lack of melanin, melanocytes or melanin transfer to cells)
When does hyperpigmentation occur?
- occurs commonly secondary to chronic inflammation, due to melanocyte-stimulating factors released from cells
What are footpads?
- cushions on which animals walks
What does the number of digit pads correspond to?
- the number of digits
What are digital footpads homologous with?
- the bulb in ruminants and pigs
- the frog in horses
What other pads do horses have?
- vestigial metacarpal/metatarsal pads (ergots)
- carpal/tarsal pads (chestnuts)
What is a footpads structure?
- thick subcutis with adipose tissue, collagen and elastic fibres
- hairless
- thick cornified epidermis for protection
- additional epidermal layers sometimes visible (stratum lucidium)
What is the function of a footpad?
- functions as a shock absorber
What anchors the pads to the skeleton?
- ligaments
(flexor digitorum profundus)
(manica flexoria)
(flexor digitorium superficialis)
(interflexorius)
What do footpads for grip?
- eccrine sweat glands for increased grip
Nails, claws and hooves are what type of structure?
- homologous
What animals are nails, claws, and hooves found in?
- Nails = primates
- claws = carnivores and birds
- hooves = ungulates
What are similar components to nails, claws and hooves?
- wall
- sole
- footpad
What do nails, claws, and hooves function to do?
- protect the distal digit
- tools for scratching, digging etc.
- weapons
- blood circulation (horses)
What are nails, claws and hooves made from?
- highly keratinised epidermis (called horn)
Where do nails, claws and hooves grown from?
- grow from the epidermis at their base and gradually slide distally
What is the junction between the skin and epidermis and hoof called?
- the coronet
What do periods of disturbed growth result in, in nails, hooves and claws?
- result in transverse ridges (parallel with the base/ground)
Nail/claw/hoof is an epidermal structure how it is anchored to the underlying dermis?
- by interdigitations (laminae)
What layer do nails, claws and hooves lack?
- they lack a subcutis
The dermis (claw) is closely adhered to what?
- closely adhered to periosteum of the distal phalanx
What enables cats to keep their claws retracted?
- the elastic dorsal ligaments of cats keep claws retracted = sharper claws
What are specialisations of the horses digits?
- they have one long skinny digit III which is good for running
What is the bad things about the horse having one long skinny digit III?
- large forces on distal phalanx bone
- poor venous return of blood
How is the distal phalanx suspended?
- laminae suspend the distal phalanx (pedal bone) within the hoof
How do laminae aid the hoof?
- help transfer force from the bone round the whole hoof
What can inflammation of the laminae (laminitis) cause?
- detachment of the laminae which causes a pulling action of deep digital flexor tendon which can result in rotation and sinking of the distal phalanx
- in severe cases this can cause the pedal bone to penetrate through the sole
Most animals have muscles in their feet which squeeze blood back to the heart horses don’t have this - explain venous return in horses:
- compression of the frog pushes the digital cushion outwards and squashes the hoof cartilages
venous plexuses in the cartilages are squashed, squeezing blood out into the digital veins - digital veins have valves so no backflow
- with each step, compression of the cartilages aids venous return
Hoof structure: The epidermis of the hoof wall is split into 3 layers what are these?
- stratum externum
- stratum medium
- stratum internum
Describe the stratum externum of a horse hoof?
- thin outer layer
- continuous with stratum corneum of the perioplic epidermis
Describe the stratum medium of the horse hoof:
- tubular and intertubular hard horn
- tubules = hard rods orientated parallel with hoof wall (support)
- this layer may contain pigment
Describe the stratum internum?
- epidermal laminae extend and interdigitate with laminae of dermis (corium)
- non-pigmented
How are horns and antlers initially formed?
- structures initially formed from a bone core covered by integument
What species have antlers?
what species have horns?
- antlers seen in cervids (deer)
- true horns seen in bovids (included cattle, sheep, antelope)
