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Endo > Integument 2 > Flashcards

Integument 2 Flashcards

1
Q

What are the 2 types of lamellae found in the hoof?

A
  • Dermal

- Epidermal

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2
Q

What is the major blood supply to the hoof?

A

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
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3
Q

What is the horn of the hoof?

A

The epidermis

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4
Q

What is the corium of the hoof?

A

The dermis

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5
Q

Describe the structure of the horn of the hood

A
  • Has the following structures:
  • Inter-tubular horm formed by regions between papillar
  • Hollow horn tubules formed by coronary papillae
  • Epidermal lamellae
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6
Q

Describe the corium of the hoof

A
  • Highly vascular
  • Dense connective tissue
  • Papillae produce hollow horn tubules
  • Grows like normal dermis
  • Start of dermal lamellae
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7
Q

Describe the lamellae of the hoof

A
  • Innermost layer of hoof wall
  • Stratum internum
  • Primary and secondary epidermal lamellae present
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8
Q

Describe the secondary lamellae

A
  • 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
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9
Q

Briefly outline hoof growth

A
  • 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
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10
Q

Describe the attachment between basal cells and the basement membrane of the hoof

A
  • 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
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11
Q

What breaks down in laminitis?

A
  • Laminin-5 of hemidesmososmes connecting the basal cells to the basement membrane
  • Leads to basement membrane degrading
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12
Q

Describe matrix metalloproteinases

A
  • Zinc dependent enzynes
  • Degrade hemidesmosomes
  • Substrates: Collagen (IV, VII), laminin-1/5
  • TIMPs
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13
Q

Describe the dermal lamellae

A
  • From lamina dermis
  • Attached to pedal bone
  • Grow outwards
  • Interdigitate with corresponding epidermal lamellae
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14
Q

Describe the formation of the horn tubules in the hoof

A
  • Form from papillae in the corium

- Grow down to form hollow tubules

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15
Q

Describe the effect of laminitis

A
  • 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
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16
Q

What is the underlying function of pruritus?

A

Removal inciting agent

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17
Q

Define pruritus

A
  • An unpleasant sensation that elicits the desire or reflex to scratch/rub/lick/chew
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18
Q

Describe pruriceptive pruritus

A
  • Due to stimulation of peripheral receptors in skin (healthy nervous system)
  • Usually due to skin disease
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19
Q

Describe neuropathic pruritus

A
  • 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
20
Q

Describe the nociceptors

A
  • Itch and pain
  • Unmyelinated slow conducting C-fibres
  • Some dedicated purely to its (and temp change)
  • Some also A-delta fibres
21
Q

Outline the interaction between itch and pain

A
  • Painful stimuli can inhibit itch
  • Inhibition of pain with gamma-receptor agonists leads to pruritus
  • Blocking spinal kappa-opiod receptors induces pruritus
22
Q

Where are sensory nerves found in the skin?

A
  • 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
23
Q

Describe the role of keratinocytes in pruritus

A
  • 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
24
Q

Describe the role of mast cells in pruritus

A
  • 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
25
Q

Describe the role of IL-31 in pruritus

A
  • 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
26
Q

What do the A-beta neurons respond to?

A
  • Light touch

- Moving stimuli

27
Q

What do the A-delta neurons respond to?

A
  • Pain (nociceptors)
  • Thermal
  • Mechanical
  • Chemical, including pruritogens
28
Q

What do the C neurons respond to?

A
  • Pain (nociceptors)
  • Thermal
  • Mechanical
  • Chemical, including pruritogens
29
Q

Describe the neural pathway for pruritus

A
  • 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
30
Q

What is pruritis modified by?

A
  • Emotional factors

- Competing cutaneous sensations

31
Q

What cranial nerves carry sensory fibres from the head?

A
  • V (trigeminal)
  • VII (facial)
  • IX (glossopharyngeal)
  • X (vagus(
32
Q

Describe the neuronal regulatory mechanisms of pruritus

A
  • Scratch stimulates fast-conduction A-beta neurones
  • Activates inhbitory neuronal circuits
  • Widespread surround inhibition of area of pruritus
33
Q

Explain how distraction can reduce pruritus

A
  • 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
34
Q

Describe peripheral sensitisation in pruritus

A
  • Scratching increases local infalmmation
  • Leads to production of pruritogens by inflammatory cells
  • Increases C-fibre responsiveness
  • Less stimulation require to elicit itching
35
Q

Describe central sensitisation in chronic pruritus

A
  • Inflammation of skin
  • Altered perception of gentle mechanical/other stimuli
  • Perceived as pruritus (allokinesis)
36
Q

Outline the summation effect in pruritus and hreshold of itch

A
  • 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
37
Q

What environmental factors contribute to pruritus?

A
  • Heat enhances (lowers threshold of pruritus receptors)

- Heat/humidity provides better climate for microflora

38
Q

Describe common manifestations of pruritus in the dog

A
  • Scratching
  • Licking
  • Rubbing
  • Nibbling
  • Temperature changes
39
Q

Describe common manifestation of pruritus in the cat

A
  • Often secretive
  • Overgrooming, hair plucking = vomit hairballs, tufts of hair around house, hair in faeces
  • Bilaterally symmetrical alopecia (inguinum, caudal sides, along back)
40
Q

Describe common manifestations of pruritus in the horse

A
  • Rub
  • Stamp
  • Bite
  • Scratch
  • Buck/kick
  • Temperature changes
41
Q

List some therapeutic interventions used to control pruritus

A
  • 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
42
Q

What are the main functions of horns?

A
  • Protection/fighting

- Display

43
Q

Compare antlers and horns

A
  • 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
44
Q

Describe the structure of antlers

A
  • 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
45
Q

What is the function of velvet in antler development?

A

Supplies nutrients and oxygen to groing antlers

46
Q

What does velvet develop from?

A

Normal skin, triggered to differentiate into velvet in order to coat antler

Endo (30 decks)

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