Integument 2 Flashcards
What are the 2 types of lamellae found in the hoof?
- Dermal
- Epidermal
What is the major blood supply to the hoof?
Palmar digital arteries
- Branch and anastomose within the hoof
- Form circumflex artery of sole, lamellar arteries, branches to digital cushion, frog, lamellae of heels and bars and palmar coronet
What is the horn of the hoof?
The epidermis
What is the corium of the hoof?
The dermis
Describe the structure of the horn of the hood
- Has the following structures:
- Inter-tubular horm formed by regions between papillar
- Hollow horn tubules formed by coronary papillae
- Epidermal lamellae
Describe the corium of the hoof
- Highly vascular
- Dense connective tissue
- Papillae produce hollow horn tubules
- Grows like normal dermis
- Start of dermal lamellae
Describe the lamellae of the hoof
- Innermost layer of hoof wall
- Stratum internum
- Primary and secondary epidermal lamellae present
Describe the secondary lamellae
- Epidermal and dermal
- Little lamellae of main primary lamellae (like bristles)
- Interdigitate with each other, strenghtening dermal-epidemal bond
- Only present in equidae
- Increases area of basement membrane
Briefly outline hoof growth
- Occurs from basal cells of coronet
- Formation of tubules dur to papillae (hollow)
- Intertubular horn
- Forms stratum medium
- Growth zones confined to top or proximal region of wall
- Basal cells of tubular hoof wall and periople proliferate nonstop throughout life of horse
- Proximal lamellae poliferate at rate similar to hoof wall proper, but do not form horn, just sliding
- Basal cells slide along the basement membrane
- Secondary lamellae slide over the BM
- Rate is near 0 in lamellar regions below this
Describe the attachment between basal cells and the basement membrane of the hoof
- Hemidesmosomes
- Protein bridge between inside and outside of cell
- Laminin-5
- Staggered ratchet-like attachment of hemidesmosomes to BM
- Allows grab-slide-grab movenent as horn grows
What breaks down in laminitis?
- Laminin-5 of hemidesmososmes connecting the basal cells to the basement membrane
- Leads to basement membrane degrading
Describe matrix metalloproteinases
- Zinc dependent enzynes
- Degrade hemidesmosomes
- Substrates: Collagen (IV, VII), laminin-1/5
- TIMPs
Describe the dermal lamellae
- From lamina dermis
- Attached to pedal bone
- Grow outwards
- Interdigitate with corresponding epidermal lamellae
Describe the formation of the horn tubules in the hoof
- Form from papillae in the corium
- Grow down to form hollow tubules
Describe the effect of laminitis
- Inflammation of laminae
- Failure of regulation at junction ebtween corium and basal cell layer
- Failure of adhesion of cells to underlying basement membrane
- Detachment and mechanical deformation of dermal epidermal junction
What is the underlying function of pruritus?
Removal inciting agent
Define pruritus
- An unpleasant sensation that elicits the desire or reflex to scratch/rub/lick/chew
Describe pruriceptive pruritus
- Due to stimulation of peripheral receptors in skin (healthy nervous system)
- Usually due to skin disease
Describe neuropathic pruritus
- Generated in DNS in response to
- Circulating pruritogens (e.g. cholestasis(
- Pharmacological mediators (e.g. intraspinal morphine)
- Anatomical lesions of PNS or CNS e.g. syringomyelia in CKCS
Describe the nociceptors
- Itch and pain
- Unmyelinated slow conducting C-fibres
- Some dedicated purely to its (and temp change)
- Some also A-delta fibres
Outline the interaction between itch and pain
- Painful stimuli can inhibit itch
- Inhibition of pain with gamma-receptor agonists leads to pruritus
- Blocking spinal kappa-opiod receptors induces pruritus
Where are sensory nerves found in the skin?
- Hair follicles and specialised encapsulated structures (e.g. meissner’s, Pacini’s Ruffini’s corpuscles)
- Also as fine network of free nerve endings intra- or sub-epidermally
- Mostly the free nerve endings
Describe the role of keratinocytes in pruritus
- Express range of neuropeptide mediators and receptors involved in pruritus
- Opiods, nerve growth factor, substance P, vanilloid receptor, proteinase activated receptor type 2 (PAR2), voltage gated ATP channels
- Epidermis with C-neuron acting as itch receptor
Describe the role of mast cells in pruritus
- produce pro-inflammatory mediators e.g. histamine
- Thought to be pruritogenic
- Some also have positive feedback to increase production of pro-inflammatory mediators
- Some have direct pruritogenic effect e.g. IL-31
Describe the role of IL-31 in pruritus
- Directly pruritogenic
- Binds to receptors on skin neurones
- Activates Janus kinase (JAK) enzymes
- Stimulates pruritic nerve impulse to the brain
- Association with allergic skin disease
- Important focus of therapy to block JAK1 pathways
What do the A-beta neurons respond to?
- Light touch
- Moving stimuli
What do the A-delta neurons respond to?
- Pain (nociceptors)
- Thermal
- Mechanical
- Chemical, including pruritogens
What do the C neurons respond to?
- Pain (nociceptors)
- Thermal
- Mechanical
- Chemical, including pruritogens
Describe the neural pathway for pruritus
- Sensory afferent from skin (nociceptor C-neurones)
- Dorsal nerve root to spinal cord
- Dorsal horn (synapse with transmission neurones)
- Cross and ascend in lateral spinothalamic tract
- Thalamus to internal capsule
- Sensory cortex
What is pruritis modified by?
- Emotional factors
- Competing cutaneous sensations
What cranial nerves carry sensory fibres from the head?
- V (trigeminal)
- VII (facial)
- IX (glossopharyngeal)
- X (vagus(
Describe the neuronal regulatory mechanisms of pruritus
- Scratch stimulates fast-conduction A-beta neurones
- Activates inhbitory neuronal circuits
- Widespread surround inhibition of area of pruritus
Explain how distraction can reduce pruritus
- Increased activity from descending pathways from reticular formation
- Activation of inhibitory circuits in dorsal horns of spinal cord
- Closes gated mechanism
- Diminishes afferent itch messages
Describe peripheral sensitisation in pruritus
- Scratching increases local infalmmation
- Leads to production of pruritogens by inflammatory cells
- Increases C-fibre responsiveness
- Less stimulation require to elicit itching
Describe central sensitisation in chronic pruritus
- Inflammation of skin
- Altered perception of gentle mechanical/other stimuli
- Perceived as pruritus (allokinesis)
Outline the summation effect in pruritus and hreshold of itch
- Pruritus from multiple sources e.g. allergen, environmental factors, ectoparasites, infection, stress factors
- Combine and go over the pruritic threshold leadig to clinical pruritus
- Increased stimulation to itch
- Removal of factors will lead to reduced pruritus
What environmental factors contribute to pruritus?
- Heat enhances (lowers threshold of pruritus receptors)
- Heat/humidity provides better climate for microflora
Describe common manifestations of pruritus in the dog
- Scratching
- Licking
- Rubbing
- Nibbling
- Temperature changes
Describe common manifestation of pruritus in the cat
- Often secretive
- Overgrooming, hair plucking = vomit hairballs, tufts of hair around house, hair in faeces
- Bilaterally symmetrical alopecia (inguinum, caudal sides, along back)
Describe common manifestations of pruritus in the horse
- Rub
- Stamp
- Bite
- Scratch
- Buck/kick
- Temperature changes
List some therapeutic interventions used to control pruritus
- Distraction
- Removal of pro-inflammatory mediators e.g. IL-31
- Reduction of inflammation e.g corticosteroids
- Blockage of peripheral inflammatory mediators (antihistamines)
- Moisturiser
- Topical cooling preparations (calamine, menthol)
- Anti-epileptics and gabapentin for neurogenic pruritus
What are the main functions of horns?
- Protection/fighting
- Display
Compare antlers and horns
- Antlers found on cervids, made of bone, branched, shed each year
- Horns: bovids, made of bony core with keratin sheath, not branched, permanet part of animal
Describe the structure of antlers
- Formed of bone
- Develop in summer from rosary on frontal bone of skull
- Develop covered in furry skin (velvet)
- Connective tissue develops under skin (will later ossify, mostly calcium phosphate)
- Blood supply to velvet reduced once developed
- Velvet shed prior to mating season
What is the function of velvet in antler development?
Supplies nutrients and oxygen to groing antlers
What does velvet develop from?
Normal skin, triggered to differentiate into velvet in order to coat antler
