Histopathology Flashcards
What are the hepatocytes supported by?
Not much! A thin capsule (Glisson’s capsule) surrounds the liver and blood vessels and ducts.
A delicate scaffold of reticular fibres (collagen type III)
How are the hepatocytes arranged?
Into polygons called (classic) lobules, which contain single layer stacks of hepatocytes in ‘plates’ (see pic)
How is the blood flow in a lobule arranged?
Blood comes in from portal triads at some of the at the corners, with sinusoids..central vein in the middle, which then drains into the hepatic vein.
What structures make up a portal triad?
A bile duct and 2 vessels, hepatic a and portal v
Sinusoid arrangement?
Mixture of deoxygenated portal blood (80%) and oxygenated hepatic a blood (20%). They run in from portal triads to the centre, and some run along the edge of the lobule, contacting hepatocytes above and below +/- on sides.
Describe the exchange surface
The hepatocyte is bathed in plasma, because the sinusoids are leaky. So essentially the extracellular Space of Disse is continuous (in terms of plasma) with the sinusoid lumen.
Hepatocytes have microvilli to increase the exchange surface area.
How is the HEPATIC lobule arranged what is the pathological significance?
Triangular blood flow, outside in direction, with triads supplying the section of the lobule it is the vertices of (1 triad has flow into 3 adjacent lobules, and 6 triangles).
Each double triangle is diamond, with 3 zones.
Zone 1 is the most peripheral, the base of the triangle. 2 is middle, 3 is the tip.
Zone 1 is high in oxygen, toxins and nutrients.
Zone 3 is the opposite. Has implications for damage in terms of toxins and hypoxia.
What is bile made up of and where do the components come from?
Produced by liver cells, consists of bile salts (surfactants) that emulsify fat and facilitate lipid and fat soluble vitamin digestion.
They are synthesised from cholesterol, and are resorbed in the terminal ileum? and recycled. Also contains bile pigments which make it green due to bilirubin- the break down products of Hb when RBC are broken down in the spleen and liver.
Describe the bile flow
The ducts collect from the centre and flow out.
Begin BETWEEN hepatocytes (bile cannaliculi) and collect in the triads.
The ducts from lobules come together to form the R and L hepatic ducts, then join to become the common hepatic duct. Joins the cystic duct to become the common bile duct, which joins the pancreatic duct to drain into the duodenum.
How does the gall bladder fill?
When the sphincter of Oddi is closed, bile travels back up to be stored in the gall bladder.
What is the structure and function of the gall bladder?
(pic) Smooth muscle sac with simple columnar epithelium and tough serosa.
It concentrates bile by the removal of fluid, and contracts to release bile.
What can go wrong with bile?
Gall stones are spontaneous precipitates of cholesterol and or bile salts. If large they may just sit there. If small enough to pass into the common bile duct can cause problems.
How is gall bladder activity controlled?
Fat in the duodenum stimulates cholecystokinin release. This stimulates GB contraction and relaxation of sphincter of Oddi, thus bile squirts into the duodenum.
What does pancreatic juice contain? Function?
Bulk of the digestive enzymes come from here (some on the epithelial brush border of SI) - proteases, lipases, amylases, nucleases and bicarbonate ions. Thus it has a digestive function BUT also acts to neutralise stomach acid.
What are the two functions of the pancreas?
(pic) Endocrine- islets of Langerhans and exocrine (ducts and lobules)
How is the exocrine pancreas arranged?
Acini (see pic- football shaped balls of cells with a duct in the middle), opening onto a duct, which converge on larger pancreatic ducts.
How are enzymes stored in the pancreas?
In zymogen granules (see pic, pale staining on H and E) at the apical surface of lobule cells.
How are zymogen granules activated? What can go wrong?
By enzymes and bile salts. If bile reaches the pancreas it auto-digests.
eg. When you get a gall stone blocking sphincter of Oddi, thus bile travels up pancreatic duct and activates zymogens.
Can be fatal e.g. if aorta digested
What is the general structure of the liver and what is its embryological origin?
It is a hollow organ (the largest single one), made up of hepatocytes. It is an outgrowth of the gut tube and is epithelial tissue of ENDODERMAL origin
What are the 12 functions of the liver?
- Major store of glycogen (with skeletal muscle) and glycogenolysis (breakdown of glycogen to glucose)
- Gluconeogenesis - breakdown of lacGc acid, amino acid and glycerol to glucose
- Synthesis cholesterol and other fats from glycerol and fa]y acids
- Makes lipoproteins that makes lipid soluble
- Makes ketone bodies, which are energy sources for other Gssues
- Liver makes all plasma proteins except anGbodies - provides colloid osmoGc
pressure of blood - Makes all non-essenGal amino acids
- Detoxifies metabolic wastes (ammonia, generated in Gssues converted to urea)
- Stores iron for making haemoglobin
- Destroys hormones
- Destroys toxins (alcohol and drugs)
- Makes bile and stores it in gall bladder
Hepatocyte characteristics?
Make up 75% of liver by weight.
Cuboidal, six sides. 1-2 nuclei, many are tetraploid or polyploid (extra sets of DNA).
Have prominent RER, golgi complexes and secretory vessels. Also smooth ER and mitochondria
Regeneration of hepatocytes (which make up 75% of the liver weight)
Occurs via division of mature hepatocytes, life span ~150 days.
Good regenerative capacity e.g. transplants, post Hep A.
Less regenerative potential: hepatitis B, C and alcohol abuse (cirrhosis and atrophy).
What is the blood supply to the liver?
Venous blood from gut (hepatic portal system) and arterial supply.
