Lecture 33 Flashcards
Hepatopancreatic Ampulla (of Vater) - Gall bladder and Pancreas
Bile made in liver, but gall bladder stores and concentrates bile
Pancreas makes digestive enzymes that are active in the small intestine. Pancreas also makes bicarbonate-rich fluid that allows buffering of the environment in the small intestine; lots of acidity in stomach, so material that
enters duodenum is acidic and the enzymes require a more neutral environment for activity
Pancreas releases digestive enzymes and bicarbonate-rich fluid into duodenum through pancreatic duct. Before the pancreatic duct opens up into duodenum, pancreatic duct merges with common bile duct that has conc bile. Then, all contents enter duodenum at the hepatopancreatic ampulla or the ampulla of Vater
How bile leaves liver
Bile is made in hepatocytes. Release bile salts and bile
acids at apical domain into bile canaliculi. Bile canaliuli, at periphery of the classic liver lobule, will merge into bile ductules, and these pool all the bile into bile ducts are at the periphery of the classic lobule.
This leads the bile out of the liver
Bile from liver to duodenum
Bile leaves liver via left and right hepatic ducts. The hepatic ducts then fuse to form the common hepatic duct
Before the common hepatic duct reaches the duodenum, the bile is diverted into the cystic duct, which is a place that has sphincters (smooth muscle cells that regulate the flow of bile). The cystic duct connects to gall bladder; The bile here sits and gets
concentrated. water is getting removed, so the bile acids and salts get concentrated.
Then when you have food in duodenum, bile is released back through the cystic duct then into the common bile duct, which then goes to duodenum
Gall bladder - appearance/composition
Bile enters lumen of gall bladder.
Mucosa of gall bladder is arranged in branched folds to increase SA for absorption, they are not finger-like projections.
Simple columnar ep without goblet cells. Under ep is lamina propria. The ep cells look have a lil bit of surface protrusions, forming little domes, but not a brushborder; these cells are absorptive, and the water, material and electrolytes they transport will end up in
capillaries present in loose ct/ lamina propria (vascular environment)
Also has thick smooth muscle bundles that run longitudinally and transversely.
Gall bladder - function (inactive and active)
If gallbladder not active, ep does not do much.
If gallbladder is activated, it activates sodium pumps and chloride, and the sodium chloride goes in the spaces in b/w the cells and in the extracellular environment. Can see active ep in the EM b/c of the spaces opening in b/w
the ep cells
If you have increase in osmolarity outside of the cell, the water will passively flow through the cell to equilibrate the high conc of salt. Therefore, there is isosmotic material transported into the blood stream from gall bladder cells
The way water is transported in various diff locations in body is by transporting sodium and electrolytes, and then water passively follows. This removes water from lumen of
gallbladder and the water is absorbed or carried away in the capillaries.
Gallbladder cells have lots of sodium pumps in the lateral cell membrane. To pump all the sodium, cell needs lots of energy. In EM, can
see dark-stained worm-like things in cytoplasm, which is mitochondrium. Mitochondria are present in ep in abundance to make energy for sodium pumps that deliver sodium into extracellular environment and water is removed from lumen of
gallbladder.
Overall, gall bladder epithelium pumps Na+ and H2O to blood stream
Pancreas
Pancreas is a compound gland with 1 main pancreatic duct and several accessory ducts that open into the main duct. In cross section, the ducts are sparse in the pancreas due to the fish bone arrangement of the duct system.
- In other compound glands, like salivary gland, the cross sec has glands that have tree arrangement of duct system
Exocrine pancreas
Serous secretory acini with nuclei at periphery. Has lots of blue staining basophilic at base of cells and eosinophilic centre with lumen in centre.
In b/w serous secretory acini is CT and may find intercalated duct (smaller or relatively same size as serous secretory acinus with nuclei arranged like a bracelet with simple cuboidal ep).
- In pancreas, do not find many striated duct, but can find serous acini and intercalated ducts
Intercalated duct inserts itself into the acinus. There is also centroacinar cells in the centre and also lining the intercalated duct
- In contrast, in parotid, centre of acinus is where the duct opens up and do not see a nucleus
Secretory acinar cells at periphery also make enzymes that will be packaged in zymogen granules before being released
Endocrine pancreas
Islets of Langerhans, arranged with capillaries, lighter in colour in H and E compared to serous secretory acini
Duct cells of pancreas
Bicarbonate-rich fluid
Acinar cells
Digestive enzymes
Enzymes that are needed to breakdown food groups are produced in the RER, and then go through golgi, then packaged into zymogen granules; Seen in apical cytoplasm
In h and e, zymogen granules appear pink in color. In EM, zymogen granules appear as dark vesicle circles in apical cytoplasm, right
adjacent to the lumen.
Enzymes:
- trypsinogen (trypsin is main enzyme) breaks down reduced proteins to amino acid
- amylase breaks down starch and glycogen to maltose
- lipase breaks down fats to fatty acids and glycerol
All these diff enzymes are inactive in the zymogen granules, or else we will eat ourselves. Some conditions like pancreatic cancers or inflammation in pancreas can cause enzymes to be pre maturely activated, which is dangerous, leading to death
Enzyme activation in small intestine
Enzyme activation occurs at surface of enterocytes in small intestine. Brush border of microvilli have actin microfilaments in centre and membrane contains transmembrane proteins that form fuzzy material on surface called glycocalyx. Glycocalyx is made up of membrane-bound enterokinases (not really kinases, but are enzymes)
Pancreas sends inactive enzymes (trypsinogen, chymotrypsinogen, procarboxypeptidase) into intestinal lumen. Inactive enzymes meet the membrane bound enterokinases, which then transform trypsinogen to trypsin
Then, trypsin causes cascade of enzyme activation downstream (makes active chymotrypsin, then makes active carboxypeptidase), leading to break down of food at cell surface of enterocytes
Enteroendocrine cells
Epithelium of small intestine
Makes a lot of hormones: secretin and cholecystokinin
Hormones are released into fenestrated capillaries in CT surrounding the intestinal
glands.
How the small intestine communicates with gall bladder and pancreas
As you eat food, there is acidic chyme (food) from stomach, it enters duodenum. Enteroendocrine cells in the ep of small
intestine makes secretin hormone that will reach the duct cells of the exocrine pancreas, which will make bicarbonate ions. Bicarbonate ions are then secreted into pancreatic duct. The bicarbonate ions will equilibrate the acidity and raise pH so enzyme activity will be optimal.
Enteroendocrine cells also make cholecystokinin, which stimulates acini of the pancreas to release zymogen granules and deliver the digestive enzymes into duodenum.
Cholecystokinin also stimulates smooth muscle cells of gall bladder; they contract
in the gallbladder and deliver bile. Bile helps emulsify lipids for digestion
H and E: Parotid gland
Serous Acini
• dark granular cytoplasm
• round basal nuclei
• nuclei at periphery
Striated Ducts
• Lighter smooth cytoplasm
• round central nuclei
• lumen present
H and E: Sublingual gland
Mucous Acini
• very light cytoplasm
• flat basal nuclei
