Liver, Biliary Tree and Pancreas Flashcards
Into where does the stomach empty chyme?
The duodenum
What are the key properties of chyme?
- Acidic
- Hypertonic
- Partly digested
How is the acidic nature of chyme corrected?
By HCO3- secreted from the pancreas, liver, and duodenal mucosa
When is HCO3- produced?
During the production of gastric acid
How is the hypertonicity of chyme corrected?
Osmotic movement of water into the duodenum across its wall
How is digestion of chyme completed?
- By enzymes from the pancreas and duodenal mucosa
- With bile acids from the liver
What components is bile made up of?
- Bile acid dependant
- Bile acid independant
What is the bile acid dependant component of bile secreted by?
Cells lining the canaliculi
What does the bile acid dependant component of bile consist of?
- Bile acids (salts)
- Cholesterol
- Bile pigments
Name the two primary bile salts
- Cholic acid
- Chenodeoxycholic acid
What happens to bile salts in bile?
They are conjugated to amino acids and travel as micelles in the bile
Where do bile salts play a major role?
In the digestion and absorption of fat
What is the name of the majority bile pigment?
Bilirubin
What secretes the bile acid independent component of bile?
Cells lining the intra-hepatic bile ducts
What does the bile acid independant component of bile consist of?
Alkaline juice (HCO3-) like that form pancreatic duct cells
Label this diagram
- A - Liver lobules
- B - Interlobular portal triads
- C - Central veins
- D - Hepatocytes
- E - Sinusoids
What supports the livers function?
Its microscopic structure
What is the basic functional unit of the liver?
A lobule surrounding a central vein
What does the central vein of a liver lobule do?
Drains blood from the liver to the systemic veins
Where does blood entering the liver lobule come from?
The hepatic portal vein and hepatic arteries
Where does blood entering the lobule from the hepatic portal vein and the hepatic arteries enter the vessels?
At the periphery of the lobule
How does blood entering the lobule via the hepatic portal vein and hepatic artery reach the central vein?
It flows through sinusoids
What lines sinusoids?
Hepatocytes
Where is bile formed?
Canaliculi
What happens to bile once it has been produced in canaliculi?
It flows towards the periphery into bile ducts
Label this diagram
- A - Deep lymphatic duct receiving lymph from perisinusoidal space
- B - Blood flowing in sinusoids from interlobular (hepatic) artery and (portal) vein
- C - Perisinusoidal spaces (of Disse)
- D - Peribiliary arterial plexus
- E - Hepatocytes
- F - Central vein
- G - Bile flowing from hepatocytes into bile canaliculi, to interlobular biliary ducts, and then to bile ducts in the extrahepatic portal triad
- H - Bile canaliculi
- I - Interlobular portal triad
- Ii - Hepatic portal vein
- Iii - Hepatic artery
- Iiii - Biliary duct
What are the main functions of hepatocytes?
- Produce bile
- Detoxify blood
What is the main function of the central vein?
Transports clean blood to hepatic vein
What does the duodenum do in response to gastric emptying?
Secretes cholecystokinin (CCK)
What effect does CCK have?
It stimulates the contraction of the gall bladder
What is the effect of the contraction of the gall bladder?
It ejects concentrated bile acids together with enzymes from the pancreas
What organs release alkali for digestion?
- Pancreas
- Liver
What is alkali released from the pancreas and liver in response to?
Secretin
What are bile acids released through?
The Ampulla of Vater
What is the role of bile acids?
Aid with the digestion and absorption of fats
Where do bile acids go once they have been released?
They continue to the terminal ileum
What happens to bile acids in the terminal ileum?
They are actively absorbed by the epithelium
What happens once bile acids have been absorbed by the ileum epithelium?
Venous return from the gut enters the hepatic portal blood
What happens when bile acids have reached the hepatic portal blood?
Hepatocytes actively take up bile acids, and re-secrete them into the Canaliculi
What is the ultimate fate of most bile acids?
- Most are recovered
- Some are unconjucated by the gut bacteria and lost
How is the loss of unconjugated bile acids dealt with?
Hepatocytes subsequently replace them
What happens to bile acids in between meals?
They return to the liver
When are bile acids secreted by canaliculi cell walls?
A long time before they are next needed
What happens to bile acids that are secreted before they are needed?
They are stored in the gall bladder
How is the volume of bile acids that needs to be stored reduced?
Bile acids are concentrated by the transport of salt and water across the gall bladder epithelium
What is the clinical importance of the concentration process of bile acids?
It increases the risk of precipitation, leading to gall stones
What are the consequences of gallstones?
Often asymptomatic, but can cause very painful biliary colic
What causes biliary colic?
The movement of gallstones into the neck of the gall bladder of biliary tree
What often follows biliary colic?
- Inflammation
- Infection of the gall bladder
What is inflammation of the gall bladder called?
Cholecystitis
When may pain from gallstones be worse?
After eating
Why may pain from gallstones be made worse after eating?
The secretion of CCK will cause the gall bladder to contract
What does the exocrine pancreas secrete?
- Alkaline juice (HCO3-)
- Enzymes
What enzymes does the exocrine pancreas secrete?
- Proteases
- Trypsin(ogen)
- Chymotrypsin
- Elastase
- Carboxypeptidase
- Amylases
- Lipases
What kind of organ is the exocrine pancreas?
A gland
What are the main components of the exocrine pancreas?
- Acini
- Ducts
What do the pancreatic acini do?
Secrete enzymes
In what form do the pancreatic acini secrete enzymes?
Mostly as inactive precursors
What happens to the enzymes being secreted from the pancreatic acini?
Packaged into condensing vacuoles, forming zymogen granules
What happens to zymogen granules?
They are secreted by exocytosis
Where are zymogen granules activated?
In the intestine
How are zymogen granules activated?
By enzymatic cleavage
What do the pancreatic ducts do?
Secrete alkaline juice
Why is HCO3- present in the blood at elevated concentrations?
Due to gastric acid secretion
How does the cellular mechanism of secretion of HCO3- in the pancreatic duct differ from in other cells?
It doesn’t
ha ha trick question i got u
What is the mechanism of secretion of HCO3-?
- Na-K-ATPase sets up a Na+ concentration gradient
- Hydrogen ions are exported from the duct cell into ECF using the Na+ concentration gradient
- H+ ions combine with HCO3- to from H2O and CO2, which are taken up into the cell
- H2O and CO2 reform H+ and HCO3- inside the cell
- HCO3- is exported into the duct lumen
- H+ ion is recycled, ‘going round in a circle’ to carry more HCO3- from the ECF to the lumen
What is duct secretion of HCO3- stimulated by?
Secretin
What releases secretin?
Jejunal cells
What is secretin released from jejunal cells in response to?
Low pH
What facilitates secretin’s action?
Cholecystokinin (CCK)
What are the two sources of pancreatic secretion?
- Acinar
- Duct
What is pancreatic acinar secretion stimulated by?
Cholecystokinin (CCK)
Where is CCK released from?
Duodenal APUD cells
What is CCK secretion and thus pancreatic acinar secretion stimulated by?
- Hypertonicity
- Fats
What stimulates pancreatic duct secretion?
Secretin
What is secretin release and thus pancreatic duct secretions stimulated in by?
Low pH
What is CCK secreted by the duodenum in reponse to?
Gastric emptying
What does CCK stimulate?
Contraction of the gall bladder muscle
What is the result of the contraction of the gall bladder muscle?
Biliary secretion
Are fats soluble in water?
No, relatively insoluble
What is the result of fats being relatively insoluble in water?
They tend to aggregate into large globules
What is the result of the aggregation of fats into large globules in water?
It prevents the effective action of digestive enzymes
What exacerbates the formation of large globules of fat in the stomach?
Acid
What do bile acids enable in the duodenum?
With regards to fats
Enable fats to be incorporated into small micelles
How big are the micelles formed with the aid of bile acids in the duodenum?
4-6nm
Describe the structure of the micelles that fats are incorporated into in the duodenum?
- Fats in the middle
- Polar components of the bile acids on the outside
What is the purpose of the bile acid-fat micelles?
- Generate a high surface area for the action of lipases
- Carry products into the ‘unstirred layer’
What do lipases do to the bile acid-fat micelle?
Cleave the fatty acids from glycerol
Where is the ‘unstirred layer’ found?
Immediately next to the mucosa
What happens at the ‘unstirred layer’?
Fatty acids can be released to slowly diffuse into the epithelial cells
What happens to fatty acids once inside the epithelial cells?
They are reconstituted into triacylglycerols, and re-expelled as chylomicrons
What are chylomicrons?
Structured small particles made up of lipids covered in phospholipids
What do chylomicrons do?
Facilitate the transport of fat in the lymphatic system from the gut to systemic veins
What is steatorrheoa?
Fatty faeces
What causes steatorrheoa?
Bile acids or pancreatic enzymes not being secreted in adequate amounts, resulting in fat in the faeces
What are the symptoms of steatorrheoa?
Faeces that-
- Pale
- Float
- Smell foul
What are bile pigments?
Excretory products
What is the most common bile pigment?
Bilirubin
When is bilirubin produced?
As a product of haemoglobin breakdown
What happens to bilirubin after production?
It is conjugated in the liver and secreted in the bile to be excreted in faeces
What happens if bilirubin cannot be excreted?
It accumulates in the blood, giving the condition known as jaundice
What is inevitable when ingesting food and water?
We also risk ingesting toxins
What toxins are we at risk of ingesting when eating and drinking?
- Chemical
- Bacteria
- Viruses
- Protozoa
- Nematodes
- Cestodes
- Trematodes
What are nematodes?
Roundworms
What are cestodes?
Tapeworms
What are trematodes?
Flukes
How can the defence mechanisms that the GI tract has to deal with toxins be subdivided?
- Innate
- Adaptive
What are the types of innate immunity?
- Physical
- Cellular
What physical innate defences are present in the GI tract to deal with toxins?
- Sight
- Smell
- Saliva
- Stomach acid
- Small intestine secretions
- Colonic mucus
- Anaerobic environment
- Peristalsis
- Segmentation
How does the sight and smell of food act as a defence?
If food looks or smells bad, you don’t eat it
How does memory act as a defence?
If food tastes bad, you don’t eat it next time
What pH is saliva?
7.0
What does saliva contain?
- Lysozyme
- Lactoperoxidase
- Complement
- IgA
- Polymorphs
How does saliva act as a defence?
It washes toxins down into the stomach
How does stomach acid act as a defence?
Low pH kills the majority of bacteria and viruses
What are the small intestine secretions?
- Bile
- Proteolytic enzymes
How do the small intestine secretions act as a defence?
- Means there is a lack of nutrients
- Cause the shredding of epithelial cells
What is the purpose of the colonic mucus?
Protects the colonic epithelium from it’s contents
What areas in the GI tract have an anaerobic environment?
- Small bowel
- Colon
What is the normal intestinal transit time?
12-18hrs
What happens if peristalsis is slowed?
Gut infections are prolonged
Give an example of an infection that can be prolonged by slowed peristalsis?
Shigellosis