Ch.33Dzesofthehepatobiliarysystem Flashcards
Pathologic changes in the liver
biliary hyperplasia
death of hepatocytes
fibrosis
What percentage of reserve capacity does the liver have?
close to 80% can be removed before regeneration and recovery are no longer possible
In which part of the biliary tree does most cell division take place?
Rappaport’s zone 1 (the portal area)
–>Then cells pushed to central lobular area
What are reasons the liver will not regenerate?
-antimitotic agents such as pyrrolizidine alkaloid metabolites or antineoplastic drugs that prevent cell division
-restricted by connective tissue
-fibrosis
Icterus is due to
failure of uptake, conjugation or excretion of bilirubin
Why is diarrhea in cattle seen with chronic liver disease?
-related to portal hypertension & increased hydrostatic pressure
Why does ascites occur with liver failure?
-portal hypertension caused by venous blockage producing INC hydrostatic pressure
-protein leakage into peritoneal cavity
-lymph leakage caused by cirrhosis or veno-occlusion
C/S of pruritus with liver disease occurs because
retention of bile salts
**not usually seen in cases of liver dz in horses
What does hepatic photosensitization, dermatitis lesions look like:
-white areas–> skin becomes erythematous, then thickend with keratin crusts and then becomes necrotic
Hepatic photosensitization is caused by what agent?
photodynamic agent phylloerythrin
–formed in the GI tract of lg animals by bact degradation of chlorophyll
- after absorption into portal circulation, phylloerythrin should be conjugated by liver and excreted into bile
-phylloerythrin accumulates in skin & reacts to sunlight & emits energy that causes lesions
A change in fecal color is not usually seen in adults with liver dz, however can see changes in young animals with simple digestive tracts. What fecal color changes can you see in young animals?
Stercobilin metabolism of bilirubin seen with cholestasis–> feces are lighter in color
Why can hemorrhage occur with liver disease?
When clotting factors are not synthesized in adequate amounts, such as factor I, II, V, VII, IX, X
- terminal hemolytic crisis caused by RBC fragility
**advanced liver disease
Why is tenesmus (+/- rectal prolapse) seen in some cattle with liver disease?
- assoc with diarrhea
-hepatic encephalopathy
-aggrevated by edema of the bowel secondary to portal hypertension
Define hepatic encephalopathy
syndrome caused by hepatic dysfunction or portosystemic shunting of intestinal blood
- potentially reversible metabolic or neurotransmitter disorder
-characteristic lesions in the CNS (altered astrocytes)
Clinical signs of hepatic encephalopathy
-behavioral changes
-depression & incoordination
-walk aimlessly
-head pressing
-apparent blindness
-foot stomping
What product in the brain is correlated with severity of hepatic encephalopathy?
glutamine
Blood ammonia is associated with hepatic encephalopathy, which is believed to be through which mechanism?
Ammonia not being metabolized by liver to urea
–> astrocytes contain the enzyme glutamine synthase, which adds a molecule of glutamate to ammonia to form glutamine
Besides ammonia what other substances have been implicated in the clinical signs of hepatic encephalopathy?
-manganese deposits in brain
-imbalance of inhibitory & excitotary neurotransmission (GABA)
-false neurotransmitters
-INC tryptophan, phenylalanine, tyrosine
-aromatic amino acids
Besides liver, GGT is present in what other organs?
kidney
pancreas
**high levels in young animals from colostrum
Which enzyme is the most sensitive indicator of disease in the horse?
GGT
**will remain elevated for weeks
Besides liver, ALP is present in what other organs?
bone
intestine
macrophages
placenta
Which liver enzymes are increased in cholestasis?
ALP
GGT
Which liver enzymes are increased d/t hepatocellular damage?
AST
LDH, SDH, GDH
SDH in horses should be interpreted with other liver enzymes because it can increase d/t
decreased tissue perfusion–> hypoxia or dehydration
Where is ammonia produced from?
GI tract from digestion of proteins and amino acids, absorbed by GIT into blood and carried to liver in portal circulation
What is ammonia converted to?
urea in the hepatic urea cycle
Why in ruminants is serum urea nitrogen low and ammonia is often high?
because rumen bacteria synthesize protein from urea, ruminants have been off feed
What is the albumin half-life in the following species:
cattle
horse
sheep
Horse: 19.4 days
cattle: 16.5 days
sheep: 14 days
Is hypoalbuminemia/hypoproteinemia a common feature of liver disease in horses?
not common/rare in horses
Amino acid ratios are altered in liver disease to what ratio?
short branched chain amino acids are decreased
aromatic amino acids increased
Increased total bilirubin is caused by:
liver failure
bile blockage
excess production d/t hemolysis
fasting animals (esp horses)
direct bilirubin to total bilirubin ratio in horse & cattle
horse: direct: total= 0.3
cattle: direct: total = 0.5
what is the primary bile pigment?
bilirubin– produced from heme
breakdown of erythrocytes (rbcs), then
heme converted to bilverdin
–> bilirubin
**in macrophage system
Unconjugated bilirubin is bound to?
albumin
Within the hepatocyte bilirubin is conjugated to
diglucuronide or glucose (horse)
Will the kidneys filter conjugated vs unconjugated bilirubin?
conjugated bilirubin
**when concentrations are high enough
IN the GIT bilirubin is convered to what compound?
urobilinogen by anaerobic bacteria
What is the pathway for urobilinogen?
– absorbed by GIT & re-excreted by liver
–excreted in urine
What is the benefits of measuring urobilinogen in urine?
If complete biliary blockage– no urobilinogen in urine
If hemolysis– increased urobilinogen in urine
**must be measured within 1-2 hours or amount detected will be erroneously low
Increased serum bile acid concentrations in horses can be caused by:
hepatocyte damage
blockage of bile flow
shunting of portal blood to systemic circulation (bypassing liver)
What does the liver synthesize bile acids from?
cholesterol
What are the primary bile acids connugated with amino acids before excretion into the bile?
cholic
chenodeoxycholic acids
Which form of bile acids are present within the intestine?
conjugated
**they are soluble & form micelles with fat b/c detergent properties
Where are bile acids resorbed?
w/in the ileum
– enterohepatic ciruclation 95% of bile acids
What is the difference between cattle and horses when measuring serum bile acid concentrations?
cattle have hourly fluctuation in bile acid concentrations
Liver biopsy is most beneficial in which group of diseases?
diffuse or zonal lesions: toxic, infectious, & metbaolic liver dzes
**focal lesions are easily missed on biopsy
What is the difference in location for liver biopsy among sp:
cattle
horse
sm ruminant
cattle: 11th ICS
horse: 12-14th (ideally 14th)
sm rum: 9th or 10th
What are indicators of a poor prognosis for liver disease?
albumin: less than 2.6 g/dL in horses
INC globulin
prothrombin time (PT) > than 30% normal
INC GGT, ALP (esp if SDH/LDH normal to dec)
Severe histopath abnromalities )PA tox
What are terminal clinical signs of liver disease?
development of hemolytic crisis in the horse
marked hepatic encephalopathy in patient with fibrotic liver
What is the most common cause of acute hepatitis and hepatic failure in N. America?
Theilers disease
What are the 2 forms of Theilers disease?
- complication of equine origin biologic product (serum/plasma)
- recent equine origin biology product administration
Which population of horses is at most risk for development of Theilers disease?
Disease of adult horses
- post foaling mares & post castration geldings at increased risk d/t freq us of prophylactic tetanus antitoxin in those horses
Which viruses have been implicated as the etx agent of Theilers disease?
Theilers dz associated virus
Equine parvovirus hepatitis
Equine hepacivirus
Clinical signs of Theilers disease arise typically after what time frame of administration of blood products?
1 to 3 months
Theilers disease can be diagnosed via histopath/necropsy, what are the lesions
liver is small, “dish rag appearance”
Histo: widespread necrosis of hepatocytes– most severe in the centrilobular and midzonal areas; eosinophilic granular mass around normal architecture in which ghost out lines of necrotic hepatocytes are present
Differentials for Theilers disease (acute hepatitis)
heavy metal and organic hepatotoxins (PA)
Diets containing what protein source are beneficial in preventing worsening signs of hepatoencephalopathy?
Diets high in branched chain amino acids
-sorghum, milo or beet pulp
Which medications can be administered to reduce ammonia production and absorption from the GI tract?
oral neomycin, lactulos and mineral oil
Which sedatives should be avoided in horses with hepatoencephalopathy?
benzodiazepines (midazolam/diazepam)
Why are IV fluids (+/-dextrose) recommended in treatment of liver disease?
to reduce hepatic work load and maintain plasma volume
Black disease is also named
infectious necrotic hepatitis
**highly fatal disease occurs worldwide
What is black disease caused by?
Clostridium novyi type B
When does black disease occur?
require an anaerobic environment for growth, so black dz occurs only when there has been enough damage to liver to provide anaerobic environment for bug to grow
What parasite is associated with black disease?
liver flukes: fasciola hepatica, but also Fascioloides magna or Dicrocelium dendriticum (france)
The C. novyi strainst hat cause black disease produce which two exotoxins?
alpha toxin and beta toxin
How does C. novyi alpha toxin enter cells
by receptor mediated endocytosis & inhibits ras and rho guanosin triphosphates by glycosylation
How does C. novyi beta toxin enter cells
necrotizing and hemolytic phospholypase C (lecithinase)
C. novyi type B is widely distributed in soils and its spores are continuously ingested and shed in feces of grazing animals. How does black disease occur?
C. novyi spores enter macrophage system– particularly Kupffer cells of liver
–anaerobic conditions develop– resident spores geminate & enter a vegetative state–> exotoxins produced by the bacteria then damage neurons, vascular endothelium and other tissues–> death
What is the most common clinical presentation associated with black disease?
peracute death
** c/s prior to death are nonspecfic
How does black disease get its name?
Venous congestion darkens the skin– which gives the disease its common name
**affected animals do not show red urine or bleeding from the nose or rectum
What are the primary necropsy lesions of Black disease?
single or multiple areas of hepatic necrosis that appear yellow to white in color and are surrounded by a broad zone of hyperemia
What sample is ideal for fluorescent antibody identification of C. novyi type B?
impression smears from the liver lesions
Prevention of black disease
fluke control–> pasture or range management, control of water sources, strategic tx of animals with appropriate anthelmintics, limiting access to streams/ponds/marshes
clostridial bacterins (vaccines)
Bacillary hemoglobinuria or “Redwater” disease is caused by whic organism?
Clostridium haemolyticum
What is the major toxin of C. haemolyticum?
beta toxin– phospholipase C that causes hetpaocyte necrosis, hemolysis and dmage to capillary endothelium
What is the primary action of C. haemolyticum beta toxin
induce localized hepatic necrosis & intravascular hemolysis
Like C. novyi, C. haemolyticum is also found in teh soil. When does disease occur?
when insult to the liver providdes an anaeorbic condition required fo rabcterial growth and toxin production
Bacillary hemoglobinuria is a regionalized disease, to which locations?
limited to alkaline soils (but can be endemic in regions with acid soils)
outbreaks tend to follow flooding
distribution tends to be erradic
Bacillary hemoglobinuria can be present with peracute death, but reports of what clinical signs are observed?
rectal bleeding or bloody feces
severe hemoglobinuria– dk red, port-wine colored urine reported
blood is thin and coagulates slowly
What is the pathognomonic lesions of bacillary hemoglobinuria?
ischemic hepatic infarct– zone of hyperemia at its interface with viable liver titsue
**unlike a classic infarct– bacillary hemoglobinuria results form progressive nelargement of focus of coagulative necrosis caused by bacterial toxins
Laboratory confirmation of Bacillary hemoglobinuria is performed through:
identification of both the causative bacteria and the toxin
When vaccinating for prevention of bacillary hemoglobinuria or prevention of black disease, what is the timing?
timing of vaccination must be determiend by local climate and liver fluke season
–short liver fluke season– vaccinate once
–long liver fluke season– vaccinate twice
liver enzymes in neonatal foals tend to be significantly more elevated in comparison to adults. What of serum bile acids?
serum bile acids greater in foals than adults for first 5 weeks of life
What is Tyzzer’s disease? and which age range does it affect?
acute hepatitis
foals: 7-42 days of age
What is the causative organism of Tyzzer’s disease?
Clostridium piliforme : gram negative, flagellated, spore-forming intracellular obligate anaerobc
Multiple strains can infect horses, which two distinct strains?
E and R1
What are predisposing factors to the development of Tyzzers disease?
-bacterial spores shed in feces of carrier horses
-high-protein & nitrogenous diets fed to nursing mares
-time of year, age, resident statu sof mare, heavy rain fall in spring
-foals born between march and may more likely to develop disease
-foals from younger mares
-immunocompromised foals
Diagnosis of Tyzzers disease
PM: acute, widespread multifocal areas of necorsis and hepatitis, with intrahepatocellular filamentous bacteria present ath tpierphery of the lesion
Prognosis of Tyzzers disease?
Poor- high fatal, foals die within 2 to 48 hours of showing clinical signs
Other possible bacterial causes of hepatitis/abscess formation in foals (besides tyzzers)
leptospirosis
actinobacillus equuli
streptococcus zooepidemicus
listeria moncytogenes
bartonella henselae
others
In blood transfusions in foals, what volume of blood products are foals likely to develop liver failure?
4L or more
**19.5 times more likely to develop liver failure than foals receiving a lower volume
Deferoxamine
iron chelator
enhances urinary iron elimination & decreases hepatic iron accumluation after blood trasnfusion in healthy foals
Kernicterus is mroe likely to develop in foals with total bilirbin of what level?
tbili of 27 mg/dL or greater
Iron toxicity in foals usually manifests when?
Foals given iron prior to receiving colostrum, colostral acquired glutahtion or other susbtances may be protective against hepatotoxicity
When do C/S of iron toxicity occur after supplementation in foals?
2 to 5 days post admin