Pancreas, Liver & Gallbladder
Pancreas, Liver & Gallbladder
- Produces bile for fat digestion.
- Bile stored in gall bladder.
Biliary tree (exocrine system)
- Although it's branches are usually neighbors of portal veins and hepatic arteries, it is quite separate from them.
- Bile contains various substances necessary for fats absorption.
- Metabolic hormones
- Blood clotting factors
Two sources of blood for liver:
- Hepatic artery (from aorta)
- Portal vein (from intestines)
They communicate with each other.
- Aorta - Hepatic artery - Liver receives freshly oxygenated blood.
Branches of hepatic arteries join the sinusoids at various stages, so the two vascular networks communicate.
- Intestines - portal vein - Liver receives blood containing nutrients absorbed from intestines.
Then branches of the portal vein gives rise to venous sinusoids that pass between plates of liver cells. These form tributaries of the hepatic vein that take blood from liver to IVC and then heart.
Stain for the liver
- Hepatocytes are epithelial cells.
- Stains used to observe liver: H&E, Methylene blue
- Stain used to demonstrate glycogen in the liver: Carmine dye
Cells of the liver
Endothelial cells: lining of blood vessels, sinusoids and lymphatics
Kupffer cells: They are macrophages that scattered along the endothelium. Not particularly easily seen in the histological images, except when they ingest dark material, such as Indian ink.
- Found at the corners between lobules.
- Contain branches of hepatic arteries, portal veins, and bile ducts.
- Some autonomic nerves also present, but cannot be seen.
- Branches arise from portal triads pass between straight lines of hepatocytes, through the hepatic sinusoids towards the centre of the lobule, where they open into the central vein.
Intrahepatic biliary tree:
- Bile canaliculi are tiny ducts that pass between hepatocytes and drain into bile ducts in the portal triad.
- The epithelium of the bile duct is either cuboidal or columnar.
- Bile canaliculi are too small to observe under light microscopic preparation. But the bile duct system is easily seen due to it's epithelium having tightly packed nuclei that are stained dark.
- Space of Disse(space between hepatocytes & the sinusoids)
blocked --> hepatocytes and blood cant change materials
--> toxins accumulate & body unable to metabolize nutrients
- If the hepatocytes swell more and block the sinusoids, it leads to build up of pressure in the portal vein and it's tributaries and result in portal hypertension.
- If either the bile canaliculi or the bile duct is blocked, bile wont be released into the intestine.
- Rather, the constituents of the bile pass into blood stream and colour the skin yellow.
- Thus, the fat wont be absorbed.
- Faeces become fatty and float.
- Faeces appear pale, while urine become darker than normal
Gallbladder (stores bile)
- Simple columnar epithelium with microvili on the surface.
- No muscularis mucosae, only externa muscularis.
- It's epithelium is highly folded and have dark stained tightly packed nuclei.
Cystic duct & Spiral valve of Heister
- Cystic duct:
a) Bile comes in and out of the gallbladder through the cystic duct.
b) This duct contains a spiral valve of Heister, which is a spiral outgrowth of mucosa.
Overall, right/ left hepatic duct + cystic duct --> drain into common bile duct --> common bile duct + pancreatic duct together drain into duodenum at the duodenal papillae.
- Contains serous secretory acinar units, which drain into highly branched duct system.
- Appears dark with H&E since it consists of serous cells. (like parotid gland)
- Produces hormones: glucagon, insulin, somatostatin & pancreatic peptides.
- Insulin, meaning island. The endocrine tissue is arranged as islands in the sea of exocrine tissue.
- Being endocrine system, they are not at all connected with the duct system.
- Typical endocrine feature:
a) islets vary in size.
b) Each islet contains pale cells arranged in cord with capillaries between.
1) Islets are very vascular and the RBC are visible in the image.
2) Several cell types within islets of Langerhan:
- Alpha (20%): mostly around the edges of the islet.
- Beta (70%): mostly in the middle of the islet.
- Delta (5-10%): produce somatostatin.
- PP or F cell (2%): produce pancreatic peptides.