Session 6 - Liver, Biliary Tree and Pancreas

Question 1

State the 3 key properties of chyme leaving the stomach

Answer 1

1) Acidic
2) Hypertonic
3) Partially Digested

Question 2

What are the bile acid dependent components of bile? Where are they secreted from?

Answer 2

o Secreted into canaliculi by hepatocytes

o Contains bile acids and pigments: Acids include – cholic acid, chenodeoxycholic acid conjugated to AAs

Question 3

What are the bile independent components of bile? What secretes it?

Answer 3

o Secreted by duct cells

o Contains alkaline juice like pancreatic duct cells

Question 4

What is the structural unit of the liver?

Answer 4

Lobules

Question 5

Describe the structure of a structural unit of the liver.

Answer 5

Hexagonally shaped.

Central vein in the middle.

Each corner has a portal triad which contains:

1) Arteriole - branch of hepatic artery, entering liver
2) Venule - branch of hepatic portal vein, entering liver
3) Duct - leaving liver

Question 6

State the dual blood supply of the liver.

Answer 6

• Arterial blood from the coeliac trunk – the hepatic artery proper
• Hepatic portal vein, from which nutrients and toxins taken from the small intestine are drawn to the liver.

Question 7

What are the secretions of the exocrine pancreas?

Answer 7

• Alkaline juice – water, few ions, lots of bicarbonate
• Enzymes:

o Proteases – Trypsinogen, chymotrypsinogen, proelastase, pro-carboxypeptidase

o Amylases

o Lipases

Question 8

What is the exocrine gland of the pancreas made up of? What does each part secrete? Explain how pancreatic enzymes are synthesised and secreted.

Answer 8

Exocrine gland is made up of acini and ducts. Acini secrete enzymes and ducts secrete alkaline juice.

Acinar secretion:

1. Enzymes synthesised on ribosomes as inactive precursors and packaged into condensing Vacuoles by golgi complex
2. Forms zymogen granules ready to be secreted
3. When signal received, zymogen granules secreted by exocytosis and activated in intestine by enzymatic cleavage

Question 9

State a biomarker for pancreatic disease

Answer 9

pancreatic amylase

Question 10

What hormone stimulates pancreatic acinar secretions?

Answer 10

CCK

Question 11

acinar secretion stimulating hormone - Where is it released from and what is it stimulated by? What other functions does it have? How does this hormone allow the pancreas to begin making enzymes when food is placed into the mouth?

Answer 11

• CCK released from duodenal APUD cells
• Stimulated by hypertonicity and fats in duodenum.
• Receptors for CCK and gastrin are very similar and therefore can be stimulated by each other. CCK inhibits secretion of acid into the stomach
• Vagus nerve also stimulates CCK by the release of Ach – Acini are innervated by branches of vagus nerve, allows pancreas to begin to make enzymes when you first put food in your mouth.

Question 12

Explain the process by which alkaline juice is made

Answer 12

Alkaline juice produced by duct cells:

1) HCO3 present in blood at elevated concentration due to gastric secretion of acid
2) Sodium conc gradient generated by Na-K-ATPase, with high sodium in ECF and low in cell
3) Na-H+ antiporter used to get Na into cell and H+ out of cell.
4) H+ combines with HCO3 in ECF to form h2o and co2.
5) CO2 taken into cell and combines with H2O to form H+ and HCO3
6) HCO3 enters lumen.

Question 13

What hormone stimulates duct secretion? Where is it released from and in response to what? What relationship does this hormone have to the acinar secreting hormone?

Answer 13

Duct secretion is stimulated by secretin which is released by jejunal cells in response to low pH.

CCK allows secretin to bind more effectively to receptors.

Question 14

Explain how bile acids digest fats

Answer 14

Bile acids:

1) Emulsify fat into much smaller globules = Increase SA for lipases to act
2) Lipases digest the globules and release FFAs. Released fatty acids form micelles with bile acids which contain cholesterol, vitamins and phospholipids
3) Micelles carry FAs and other things to unstirred layer next to epithelial cells
4) Fatty acids etc are released slowly, entering the cells by diffusion.
5) Fatty acids are then resynthesized to lipids in epithelial cells and exported to lymphatics as chylomicrons.

Question 15

Where is bile acid stored and how is it stored?

Answer 15

Stored in gall bladder and concentrated by reduction of volume (transport of salt and water across gall bladder epithelium)

Question 16

How is bile released from its storage area?

Answer 16

• CCK secreted by duodenum stimulates contraction of gall bladder muscle
• Ejects concentrated bile acids

Question 17

What happens to bile acids after usage?

Answer 17

Once used, Bile acids then continue to terminal ileum where they are actively absorbed by epithelia and return to the liver via hepatic portal blood. Hepatocytes actively take up the bile acids and re-secrete them into the canaliculi.

Some bile acids lost – unconjugated by bacterial action in gut. Hepatocytes synthesise new ones to replace.

Question 18

What is the condition called where fat appears in faeces? Why would it occur?

Answer 18

Steatorrhea - not enough bile acids or pancreatic enzymes secreted

Question 19

What is the fibrous layer that covers the liver called?

Answer 19

Glisson’s capsule

Question 20

Label

Answer 20

Question 21

What are the 3 sections that make up the gallbladder? Which section is a gallstone most likely to be lodged?

Answer 21

o Fundus – Rounded end portion of gallbladder. Projects into inferior surface of liver

o Body – Mid section. In contact with transverse colon and proximal duodenum.

o Neck – Connects to the cystic duct. Common location for gallstones to become lodged

Question 22

Label

Answer 22

Question 23

Label

Answer 23

Question 24

What is the relationship between the IVC and the liver?

Answer 24

Liver attached to IVC right through the middle

Question 25

Label

Answer 25

Hepatopancreatic ampulla of Varter

Question 26

Label the tributaries of the hepatic portal vein

Answer 26

Question 27

Name the arteries which supplies the pancreas.

Answer 27

• Supplied by splenic artery
• Head is also supplied by the superior and inferior pancreaticduodenal arteries which are branches of the gastroduodenal and superior mesenteric arteries

Question 28

Name the venous drainage of the pancreas

Answer 28

Venous drainage of the head is by superior mesenteric vein and by the splenic veins

Question 29

Name the arterial and venous drainage of the spleen

Answer 29

Splenic artery and vein

Question 30

How does H. pylori modify gastric physiology and result in peptic ulcers?

Answer 30

• Bacteria colonising the pyloric antrum results in inflammation which induces G cells to secrete Gastrin
• Gastrin stimulates parietal cells to produce more acid into stomach lumen, increasing acid load damaging the duodenum and forming ulcers.