Liver Flashcards
What is the normal colour of the liver?
Typically a reddish-brown, but may be brown in animals, such as cattle, sheep and pigs, that have been bled out
Why might a liver be yellow-brownish in colour?
Accumulation of fats in the liver can cause it to have a yellowish-brown appearance
Why might a liver be greenish/yellow?
Post-mortem changes can cause areas of pallor or darkening or greenish-yellow discolouration, especially adjacent to the gall bladder
What is the weight of the liver dependent on?
The weight of the liver as a proportion of body wieght can vary depending on factors includin the species (higher in carnoviores comapred to herbivores), nutritional status (hepatic storage of glycogen and fat) and age (liver weight decreases with age).
What is the percentage of body weight of the liver?
Dog = 3-4%
Horse = 1-1.5%
What blood vessels deliver blood to the liver?
Portal vein – provides 70-80% of the blood inflow
Hepatic artery
From which organs does the blood in the portal vein come from?
Collects blood from the spleen, pancreas, stomach and intestines
From what blood vessel does the hepatic artery originate from?
From the ceoliac artery, which arises from the aorta
What blood vessels drain blood from the liver?
Hepatic vein to the caudal vena cava
After blood enters the liver from the portal vein and hepatic artery, what structures for sit flow through before arriving in the hepatic veins?
Portal vein and hepatic artery > hepatic sinusoids > across hepatic lobule > central vein > interlobualr veins > hepatic veins
Within the functional unit, the hepatic acinus, what are the 3 zones?
Zone 1 – periportal region. The area that recievs the blood frm the portal vein and hepatic artery first
Zone 2 – midzonal region. Receives blood next
Zone 3 – centtilobular region. Recives the blood last before it drains into the central vein
What are the metabolic differences between the 3 zones of the hepatic acinus?
Zone 1 – periportal will receive blood with the highest oxygen and nutrient content
Zone 3 – centrilobualr will receive blood with lower oxygen and nutrient content. Hepatocytes in zone 3 also have higher levels of metabolic enzymes. These factors make this zone the most sensitive to injury by toxic compounds
Name 3 circulatory disorders affecting the liver.
- Congenital portosystemic shunts
- Post-hepatic conditions affecting outflow of blood from the liver
- Intra-hepatic or pre-hepatic conditions associated with abnormal portal vein inflow
How can portosystemic shunts be classified?
Whether the anomlous blood vessel is within the liver or not
How does an intra-hepatic portosystemic shunt form?
Large blood vessel connects the portal vein directly to the hepatic vein, which is a lower resistance path than through the lobule and smaller sinusoides, so a significant portion of blood flow is through this shunt and bypasses the functional part of the liver
How does an extrahepatic portosystemic shunt form?
Large blood vessel connect the portal vein/tributaries of the portal vein, bypassing the liver and through extra-hepatic anomalous vein to connect to the systemic circulation (caudal vena cava or hepatic vein).
Distinguish which breeds are affected by which type of portosystemic shunt.
Extrahepatic – small (wEe) dog breeds
Intra-hepatic – large (bIg) dog breeds
Distinguish intra and extrahepatic CPSS.
Intrahepatic CPSS – left or right portal vein branch to hepatic vein or directly with caudal vena cava
Extra-hepatic CPSS – left or right gastric vein or splenic vein to the caudal vena cava or azygous vein
What are the functional consequences of congenital portosystemic shunts?
- Reduced hepatic perfusion
- Small liver due to underperfusion – microhepatica
- Poor growth due to less liver and so less functional capacity
- Hepatic encephalopathy, as the liver is unable to detoxify waste products and these build up and affect the central nervous system
Will congenital portosystemic shunts result in increased blood pressure in the portal venous system – portal hypertension?
No – offer a lower resistance route
How does heart disease affect outflow from the liver?
Especially right sided CHF, which will increase pressure in the caudal vena cava which can be referred back through the hepatic vein to the liver and impair outflow of blood from the liver
How does hepatic vein/vena cava obstruction affect outflow from the liver?
Luminal obstruction (thrombus), vessle wall thickening (neoplasia, inflammation), external compression (by a mass, such as an abscess or tumour)
What are the consequences of impairment of post-hepatic outflow?
- Hepatic passive venous congestion – dilation of the sinusoids and central vein and becoming packed full of the blood, can extend to portal vein
- Hepatomegaly – blood pools and congest in the liver may make it appear larger so there is some degree of hepatomegaly
- Chronic passive congestion may develop an enhanced lobular or reticular pattern on the sectioned surface of the liver (nutmeg liver). Reddening due to congestion and the yellowish colour caused by accumulation of fat, create enhanced lobular pattern
Could post-hepatic conditions causing passive congestion of the liver cause an increased blood pressure in the portal venous system (portal hypertension)?
Yes
Name 3 intra-hepatic and pre-hepatic conditions associated with abnormal portal vein inflow.
- Advanced chronic liver disease with fibrosis
- Portal vein obstruction – thrombosis, inflammation, abscess, neoplasia
- Portal vein hypoplasia – portal vein is smaller than normal
Could intra-hepatic conditions, such as diffuse liver fibrosis or pre-hepatic conditions, such as portal vein hypoplasia, be a cause of portal hypertension?
Yes
What are the potential causes of portal hypertension?
- Post-hepatic conditions affecting outflow of blood from the liver
- Intra-hepatic or pre-hepatic conditions associated with abnormal portal vein inflow
What are the potential consequences of portal hypertension?
- Ascites
- Acquired portosystemic shunts – intra-hepatic and re-hepatic causes of portal hypertension (not by passive hepatic congestion, such as heart failure). Allow portal blood to flow directly to the systemic venous system bypassing the liver
What are the possible responses to hepatic injury?
- Hepatocellular vacuolation
- Necrosis
- Hepatocellular regeneration
- Inflammation
- End stage liver (cirrhosis)
- Hyperplastic and neoplastic changes
What are the possible hepatocellular vacuolar changes?
- Vacuoles may contain lipid (fatty change), water (hydropic change) and glycogen
- Potential gross changes – enlargement, altered colour change (pallor or yellow-brown), or altered consistency (greasy if lipid accumulation, increased fragility)
Why do cats’ livers appear more brown than dogs’ livers?
Cats can store more fat in their livers so can end up naturally appearing more brown than dogs
What are the 2 mechanisms of lipid accumulation in the liver?
There is excess delivery of free fatty acids to hepatocytes, causing negative energy balance and metabolic/endocrine disease
Reduced hepatocellular capacity to metabolise fats often due to hepatocellular injury – hypoxia, toxins, dietary deficiencies lipotropes for lipid metabolism
What are the causes of water accumulation/hydropic change in the liver?
Various toxins
Metabolic insults
Hypoxia
What are the causes of glycogen accumulation?
Associated with hyperadrenocorticism or corticosteroid administration – ‘steroid induced hepatopathy’
What is a property of the liver on PME if there is significant fat present?
It can cause the liver to be bouyant in water
What does a focal/random pattern of necrosis suggest of the cause?
Scattered, randomonly distributed foci of necrosis. Typical of some infectious agents, such as bacteria, viruses, protozoa, migrating parasites. May be of little functional significance to the liver
What is the appearance of focal/random necrosis?
Area of necrosis in hepatocytes and there is variable amounts of erythrocytes in necrosis. So typical gross appearance is one or more white/grey or reddish foci (if lots of blood associated with them).
What does a zonal pattern of necrosis suggest of the cause?
Zone 3/certrilobular/periacinar most commonly affected as it is more prone to hypoxia as it receives blood last and also the hepatocytes in zone 3 contain a lot of metabolic enzymes and so may activate toxins
What are some typical causes of zonal necrosis?
- Hypoxia/ischaemia
- Exposure to some toxins
- Some severe viral infections, such as canine adenovirus 1
Describe the appearance of zonal necrosis.
Multiple areas of necrosis, paler pink, surrounding central veins. In some areas, these join, known as bridging necrosis. This results in a gross pattern of mottled appearance, with colour intensity perhaps dictated by amount of haemorrhage. Microscopy needed to identify necrotic areas. Pattern sometimes called enhanced lobular pattern/enhanced reticular pattern.
What are the causes of massive necrosis?
- Severe toxic injury
- Vitamin E/selenium deficiency in pigs/hepatosis dietetica
Describe the appearance of massive necrosis.
Red appearance due to red blood cell snow filling the spaces left by the necrotic hepatocytes. There is a fine rim of surviving hepatocytes along the edge of the lobules but most have died and been replaced with blood
You submit a liver biopsy in formalin for histopathology. The pathology report report indicates a vacuolar hepatopathy. What type of material could be present in the vacuoles?
Lipid, water or glycogen – intracellular accumulation of lipid, water or glycogen can all create cytoplasmic vacuolation. Sometimes some features of the vacuolated hepatocytes may allow the pathologist to suggest the most likely material.
A 6 month old frenhc bulldog has severe jaundice and rasied liver enzymes. Severe centrilobular necrosis is rpeorted on a liver biopsy submitted for histopathology. Of the aetiologies, which should you include as the potential cause of the hepatic necrosis?
Recent hepatotoxin ingestion and severe hypoxia
What are the vague clinical signs of liver disease?
Inappetence
Lethargy
Weight loss
Vomiting
Diarrhoea
Polyuria/polydipsia
What are the specific clinical signs of liver disease?
- Jaundice/icterus) - hyperbilirubinaemia – normal is 10-1 umol/L, 10-35umol/L high but not appear yellow, so significantly high to appear yellow
- Ascites
- Hepatic encephalopathy
- Coagulopathy
Summarise the cycle of bilirubin.
Bilirubin from senescent RBC, macrophages break down these in liver, spleen and bone marrow. Bilirubin bound to albumin and uptaken into liver cells. Stored in gall bladder and excreted when gall bladder contracts and is released when eating
Distinguish pre-hepatic, hepatic and post-hepatic jaundice.
- Pre-hepatic for a process prior to the liver, such as increased breakdown of RBC, so patients would be anaemic
- Hepatic would be inherent liver disease, as we can’t convert these
- Post hepatic is something wrong with the pancreas or gall bladder
Why do effusions in liver disease occur?
From either increased hydrostatic pressure or low albumin
What is hepatic encephalopathy?
Toxins that accumulate in bloodstream such as ammonia due to liver disease affects rain function. With extreme hepatic dysfunction or portosystemic shunting