Anatomy and function of the liver Flashcards
Which species groups have more liver lobes: herbivores or carnivores?
Carnivores
This is perhaps linked to locomotion: in the carnivore, the lumbar region is highly mobile, so many liver lobes allow “sliding” motion to occur.
True/false: cats can have high variability in their number of liver lobes.
True: lobes may split or merge.
True/false: when liver lobes are damaged, they regenerate and become identical to their previous form.
False: liver lobes regenerate irregularly, but down at the microscopic level, they are still functional.
Describe the blood supply to the liver
- All veins, arteries and. nerves enter the caudal surface of the liver at the hylus
- The liver has a double blood supply:
- Hepatic artery is rich in oxygen, provides approx. 30% of blood
- Hepatic portal vein is rich in nutrients from the gut, relatively poor in oxygen. Provides approx. 70% of blood.
- Hepatic veins pick up outflow from the liver
Describe blood outflow from the liver
- Hepatic veins pick up outflow from the liver and join the caudal vena cava as it runs through (need to dig in the liver to observe this)
- The caudal vena cava runs through a notch in the liver
What is a portal vessel?
Portal = capillary system at both ends
Horses have no gallbladder. What is the significance of this if a horse is starved?
- Starved horse becomes jaundiced
- This is because there is no stimulus for bile to be released
- Components of bile then end up and build in circulation, staining the membranes of the eye and mouth
- This doesn’t happen in other species because bile can just be stored in the gallbladder if they are starved
1
Caudal vena cava
2
Hepatorenal ligament
3
Right triangular ligament
4
Caudate process
5
Portal vein
6
Right hepatic duct
7
Bile duct
8
Right hepatic lobe
9
Quadrate hepatic lobe
10
Falciform ligament and round ligament
11
Left lateral hepatic lobe
12
Left medial hepatic lobe
13
Portal vein with branches
14
Hepatic artery and portal lymph nodes
15
Left lateral hepatic lobe
16
Left triangular ligament
What is the hepatic parenchyma?
- Functional part of the liver
- Principal cell type: hepatocytes
- Histological area of the liver responsible for most hepatic functions
What is the hepatic stroma?
The structural tissue of the liver
Most species have sparse collagen fibres in their liver, except for…
Pigs (they have more collagen, which can be observed as pale outlines of hexagons)
Describe the morphology and functions of hepatocytes
- Polyhedral with round nucleus and prominent nucleolus
- Metabolise and stores materials (nutrients and toxins) absorbed from the small intestine
- Secrete bile
Describe the morphology and function of Kupffer cells
- Morphology: like macrophages
- Defend against vascular-carried pathogens and remove debris (e.g. dead RBCs)
- Found in the sinusoids
Describe the morphology and function of Ito cells
- Contain big intracytoplasmatic vacuoles
- Involved in tissue fibrosis and retinal metabolism (stored Vitamin A)
1
Branch of the hepatic portal vein
2
Branch of the hepatic artery
3
Lymphatic vessel
4
Branch of the bile duct
What structure is shown here, consisting of three vessels?
Portal triad
Hepatic sinusoid
fenestrated blood vessel running along the plate of hepatocytes where portal blood and hepatic arterial blood mix.
In the hexagon of a portal triad, where central vein is in the middle and hepatic artery and portal vein are positioned at the edge, sinusoids run in from the edge to the centre.
What does a portal triad (a.k.a. a portal tract) contain?
- At least one branch of the hepatic portal vein
- At least one branch of the hepatic artery
- At least one bile duct
These are surrounded by connective tissue.
Portal canal
Space containing the portal triad
1
Plates (or cords) of hepatocytes
2
Central vein (a.k.a. terminal hepatic venule)
3
Bile duct
4
Hepatic portal vein
5
Hepatic artery
6
Hepatic sinusoids
In which direction in the liver lobule does bile flow?
Bile flow is centrifugal, flowing outwards from the centre
In which direction in the liver lobule does blood flow?
From the edges towards the centre, feeding into the central vein
1
Hepatic acinus
- Term given to area created by circling the two adjacent central veins.
- Emphasises the vascular supply to the hepatic parenchyma and the direction of blood flow.
- Zone 1 - closest to the portal tract, receives most oxygenated blood.
- Zone 3 - least oxygenated blood. Closest to central vein.
2
Hepatic lobule
- Smallest grossly visible structural unit in the liver.
- Perfect one = hexagonal prism.
3
Portal lobule
- Triangular area centred on the portal tract.
- This imaginary area stresses exocrine glandular function.
- Local biliary obstruction affects cells in these areas.
Cells in which zone will be most affected by direct-acting toxins (perilobular necrosis)?
Zone 1
They receive the most oxygenated blood and are closest to the branches of the hepatic portal vein, as well as the biliary system.
Cells in which zone will be most affected by hypoxic injury?
Zone 3
Zone 3 hepatocytes already receive the least oxygenated blood
Cells in which zone are most susceptible to centrilobular necrosis?
Zone 3
Zone 3 has higher biotransformation/detoxification activity e.g. via the cytochrome P450 enzyme system
Therefore, this zone is most susceptible to toxins activated by cytochromes.
1
Classical lobule
2
Portal lobule
3
Hepatic acinus
What is the function of the gallbladder?
Storage, concentration and release of bile
What is the function of bile?
Fat digestion and hepatic excretion
Which direction does bile flow?
In the opposite direction of blood flow in the liver.
From the liver to the duodenum.
True/false: blood and bile flow in opposite directions in the liver.
True.
What is enterohepatic recirculation and why could it be a problem?
Enterohepatic recirculation: when a substance in the gut is absorbed by the hepatic portal vein, then excreted into bile, then present in the gut, and absorbed by the hepatic portal vein again.
This used to a problem with strong opiates for anaesthesia; the animal would wake, fall asleep again and so on. An IM dose of the reversal then had to be given to slowly counteract the continual reappearance of the anaesthetic.
1
Gallbladder
2
Bile duct
3
Cystic duct
4
Hepatic ducts
Describe the wall of the gallbladder
Smooth muscle wall
Under autonomic supply
Describe where bile is produced and how it moves from here
- Hepatocytes produce bile into tubes called bile canaliculi
- Bile can then enter the gallbladder via the cystic duct
- To enter the duodenum, bile flows down the common bile duct, joins the pancreatic duct and is excreted into the duodenum
