Disorders of the equine liver READING Flashcards
How is the liver involved in protein metabolism? 3
- synthesises 90% plasma proteins
- transamination to produce new amino acid and a new keto acid
- ammonia elimination
What makes urea?
2 ammonia molecules + carbon dioxide
How is the liver involved in carbohydrate metabolism? 4
- -synthesis/storage/release of glucose
- glycogen storage
- G6P oxidation
- G6P used to synthesise FAs and cholesterol
- release glucose into systemic circulation
Role of liver in lipd metabolism?
- esterify FAs into Tgs which are packaged with protein, carbohydrates and cholestero to from VLDL and HDL
- use of FFAs for energy
Role of liver in bile secretion?
- bile released from hepatocytes. major component is bile acids, into duodenum, >95% reabsorbed (enterohepatic circulation)
- bilirubin is a breakdown product
- liver conjugates bilirubin
What is the mononuclear phagocyte system?
-hepatic macrophages = Kuppffer cells. These produce many inflammatory mediators and have an important role in filtering portal blood
Clinical signs of hepatic dysfunction
vary greatly, non-specific, depend on extent and duration of hepatic disease, usually >80% hepatic function must be lost.
COMMON = depression, anorexia, colic, HE, weight loss, icterus
LESS COMMON = photosensitisation, diarrhoea, bilateral laryngeal paralysis, haemorrhagic diathesis, ascites, dependent oedema
What might the colic be due to?
acute hepatocellular swelling or biliary obstruction (cholelithisais)
Clinical signs of HE
vary from mild depression, to manic behaviour, head pressing, stupor
Pathogenesis of HE? 3
Likely to be multi-factorial:
- reduced clearance of ammonia
- imbalance between AAA and BCAA may result in increased concentration of false NT produced in brain
- other theories exist too
When does weight loss occur?
most likely with chronic liver disease. due to decreased intake + loss of normal hepatic metabolic activities
3 broad causes of icterus
hyperbilirubinaemia caused by:
- increased haemolysis
- impaired hepatic uptake or conjugation
- impaired excretion of bilirubin
How do you diagnose increased bilirubin production/haemolysis? 2
usually increased unconjugated +/- conjugated if liver capacity exceeded
Diagnosis - impaired hepatic uptake or conjugation
increased unconjugated, possible cause is acute hepatocellular disease, also anorexia
Most common type of icterus in horses = ?
impaired hepatic uptake or conjugation
Cause of increased excretion of bilirubin
cholangitis, colangiohepatitis etc. if conjugated bilirubin concentration is greater than 30% total, indicates H
What is phylloerythrin?
photodynamic agent formed by bacteria in gut, absorbed conjugated and excreted by liver
How does phylloerythrin cause photosensitisation?
UV light exposure causes activation of electrons within the molecule to an excited state, leading to free radical formation –> cell membrane damage and necrosis. Lesions in non-pigmented skin (UV light absorbed more efficiently).
Why might diarrhoea be seen? 3
alterations in intestinal microflora, portal hypertension, deficiency of bile acids
What is haemorrhagic diathesis? When might it be seen?
predisposition to bleeding. Subclinical coagulopathy common, rare to see clinical signs
3 specific indicators of liver dyfunction
increased bile acids, increased sorbitol dehydrogenase (SDH) and increased gamma-glutamyl transferase.
Why do hepatic ultrasonography?
determines size, changes in hepatic parenchyma, dilated bile ducts, choleliths, can only image 20% liver
Why liver biopsy? 3 Where?
diagnosis, prognosis, treatment, 12-14th ICS, submit for histopathologic evaluation +/- culture, poor prognosis if bridging fibrosis
What is essential to do before taking a liver biopsy?
Evaluate coagulation parameters
General treatment principles - icterus 8
- primarily supportive
- maintain animal until liver regenerates sufficiently
- sedation if HE present (xylazine, detomidine)
- correct fluid deficits and acid-base imbalances
- IV glucose
- treat HE
- dietary management
- anti-inflammatories
Treatment of HE 5
- liquid paraffin, magnesium sulfate (reduce toxin absorption)
- mannitol (cerebral oedema)
- oral neomycin (decrease bacterial production of ammonia)
- oral lactulose (limit ammonia absorption)
- oral BCAA (no evidence)
Dietary management
high carbohydrate, limit protein (but not too much, more important to ensure quality protein to ensure malnutrition doesn’t occur)
What is DMSO
dimethyl sulfoxide - may help dissolve intrabiliary sludge or small stones
Suggest some anti-inflammatories 3
- flunixin meglumine
- DMSO
- pentoxifylline - shown to reduce hepatic fibrosis in humans
Another name for pyrrolizidine-alkaloid toxicity
ragwort poisoning
Why might horses ingest ragwort?
Accidental (usually unpalatable), contaminated pasture or hay. problems if chronic ingestion (e.g 4-12 weeks)