PATHOLOGY - Equine Endocrine Disease and Laminitis Flashcards
What is laminitis?
Laminitis is inflammation and/or fluid accumulation between the dermal and epidermal lamellae
Describe the blood supply to the laminae
The laminae are supplied by the laminar arteries which branch from the circumflex arteries and are drained by the laminar veins which drain into the circumflex veins
Why are the digital veins so sensitive to vasoactive mediators?
The digital veins are highly muscular are are thus very sensitive to vasoactive mediators
What are the three classifications of laminitis?
Hyperinsulinaemia-associated laminitis (HAL)
Sepsis associated laminitis
Supporting limb laminitis
What are the four possible triggers of laminitis?
Activation/infiltration of white blood cells
Increased pro-inflammatory mediators
Decreased anti-inflammatory mediators
Increased COX-2
What are the two main theories of laminitis?
Vascular theory
Enzymatic theory
What does the vascular theory propose as the triggering factors of laminitis?
Endothelial cell dysfunction
Release of vasoactive mediators
List three possible causes of endothelial cell dysfunction resulting in laminitis?
Insulin resistance
Hyperglycaemia
Hyperinsulinaemia
How does endothelial cell dysfunction and/or vasoactive mediator release trigger laminitis according to the vascular theory?
Endothelial cell dysfunction and vasoactive mediators cause a disruption in blood flow to the laminae resulting in vasoconstriction which results in an increase in fluid movement from the vessels into the interstitial space causing an increase in interstitial hydrostatic pressure and oedema between the laminae. This results in the formation of arteriovenous shunts between the circumflex vessels, causing blood to bypass the laminae resulting in ischaemia, inflammation and necrosis causing seperation of the dermal and epidermal laminae
What does the enzymatic theory propose as the triggering factors of laminitis?
Increased matrix metalloproteinase (MMP) activity
What is the normal function of matrix metalloproteinases (MMPs) in the hoof?
Normally, matrix metalloproteinases are involved in normal growth of the hoof through enabling the epidermal laminae to glide past the dermal laminae to allow for hoof growth
How does increased matrix metalloproteinase (MMP) activity trigger laminitis according to the enzymatic theory?
Increase matrix metalloproteinase (MMP) activity can result in the break down of the extracellular matrix (ECM) and basement membranes which form the junction between the dermal and epidermal laminae, resulting in laminae seperation
Describe how insulin resistance can contribute to laminitis
Insulin resistance reduces glucose uptake by the laminae which causes seperation of the dermal and epidermal laminae
Describe how hyperglycaemia can contribite to laminitis
Hyperglycaemia causes increased insulin secretion and as insulin is a pro-inflammatory mediator this causes endothelial cell dysfunction and vasoconstriction
What can occur following seperation of the dermal and epidermal lamellae?
Pedal bone rotation and possible pedal bone sinking