6. The Liver, Biliary Tree, and Pancreas

Question 1

What is the chyme like that enters the duodenum?

Answer 1

Acidic, hypertonic, and partly digested.

Question 2

How is the acidic nature of chyme corrected for in the duodenum?

Answer 2

HCO3- secreted from pancreas, liver, and duodenal mucosa - prduced during the production of gastric acid.

Question 3

How is the hypertonic nature of chyme corrected for in the duodenum?

Answer 3

By the osmotic movement of water into the duodenum across its wall.

Question 4

How is the partly digested nature of chyme corrected for in the duodenum?

Answer 4

Digestion completed by enzymes from the pancreas and duodenal mucosa, with bile acids from the liver.

Question 5

What are the two components of bile?

Answer 5

Bile acid dependent and bile acid independent.

Question 6

What secretes the bile acid dependent component of bile?

Answer 6

Cells lining the canaliculi.

Question 7

How do bile salts travel?

Answer 7

Conjugated to amino acids, and travel as micelles.

Question 8

What is the role of bile acids/salts?

Answer 8

Major role in digestion and absorption of fat.

Question 9

What are the parts of the bile acid dependent component of bile?

Answer 9

Bile acids/salts, cholesterol, and bile pigments.

Question 10

What is the major bile pigment?

Answer 10

Bilirubin.

Question 11

What secretes the bile acid independent component of bile?

Answer 11

Cells lining the intra-hepatic bile ducts.

Question 12

What does the bile acid independent component of bile consist of?

Answer 12

Alkaline juive, HCO3-, like that from pancreatic duct cells.

Question 13

What is the basic functional unit of the liver?

Answer 13

A lobule surrounding a central vein, which drains blood from the liver to the systemic veins. Blood from the hepatic portal vein and hepatic arteries enter at the periphery of the lobule through sinusoids lined by hepatocytes to the central vein.

Question 14

What does the duodenum secrete in response to gastric emptying?

Answer 14

Cholecystokinin.

Question 15

What does cholecytokinin do?

Answer 15

It stimulates the contraction of the gall bladder, ejecting concentrated bile acids together with enzymes from the pancreas.

Question 16

What are bile acids released through?

Answer 16

The ampulla of vater.

Question 17

What is the path of bile acids?

Answer 17

Released through the ampula of vater, continue to the terminal ileum, actively absorbed by the epithelium.

Question 18

How are bile acids recycled?

Answer 18

Venous return from gut enters hepatic portal blood, hepatocytes actively take up bile acids and re-secrete them into canaliculi.

Question 19

Why are some bile acids not recovered?

Answer 19

they are unconjugated by gut bacteria and lost.

Question 20

How are lost bile acids replaced?

Answer 20

By hepatocytes replacing them.

Question 21

Where are bile acids stored?

Answer 21

In the gallbladder.

Question 22

How is the volume of bile acid stored in the gallbladder reduced?

Answer 22

The bile acids are concentrated by the transport of salt and water across the gall bladder epithelium.

Question 23

What is the risk of concentrating bile acids in the gallbladder?

Answer 23

Precipitation, leading to gall stones.

Question 24

When do asymptomatic gallstones become symptomatic?

Answer 24

When they move into the neck of the gall bladder of biliary tree.

Question 25

What are the symptoms of gallstones in the neck of the gall bladder or biliary tree?

Answer 25

Biliary colic or obstruction followed by inflammation and sometimes infection.

Question 26

What is cholecystitis?

Answer 26

Inflammation of the gallbladder from gall stones in the neck of the gallbladder or in the biliary tree.

Question 27

Why is biliary colic pain worse after eating?

Answer 27

The secretion of cholecystokinin will cause the gall bladder to contract.

Question 28

What are the exocrine secretion of the pancreas?

Answer 28

Alkaline juice (HCO3-), and enzymes - proteases (trypsin, chymotrypsin, elastase, carboxypeptidase), amylases, and lipases.

Question 29

What are the partsof the exocrine pancreas?

Answer 29

Acini and ducts.

Question 30

What is the acini of the exocrine pancreas?

Answer 30

Secrete inactive precursors of enzymes, package into condensing vacuoles -> zymogen granules that are secreted by exocytosis.

Question 31

What do the ducts of the exocrine pancreas do?

Answer 31

Secrete alkaline juice (HCO3-).

Question 32

How is alkaline juice secreted?

Answer 32

Na-K-ATPase sets up the Na+ concentration gradient, H+ exported into ECF using gradient. H+ combines with HCO3- -> H2O and CO2 - taken up into cell. Reform H+ and HCO3- inside the cell. HCO3- exported into the duct lumen and H+ is recycled.

Question 33

What stimulates alkaline juice secretion by the pancreatic ducts?

Answer 33

Secretin.

Question 34

What causes secretin release?

Answer 34

Low pH causes jejunal cells to release it.

Question 35

How are the acinar secretions of the pancreas controlled?

Answer 35

Stimulated by cholecystokinin (released from duodenal APUD cells in response to hypertonicity and fats).

Question 36

How are duct secretions of the pancreas controlled?

Answer 36

Stimulated from secretin (released from jejunal cells in response to low pH).

Question 37

Why is effective action of digestive enzymes against fats hard?

Answer 37

Fats are insoluble in water, so tend to aggregate into larger globules, so enzymes aren't as effective.

Question 38

How do bile acids help fat digestion in the duodenum?

Answer 38

The bile acids enable fats to be incorporated into small micelles, with fats in the middle and polar components of bile acids on the outside. The micelles have a high surface area for lipase action and carry the products into the unstirred layer next to the mucosa to diffuse into epithelial cells.

Question 39

What happens to micelles of fat in the epithelial cells?

Answer 39

Reconstituted into triacylglycerols and re-expelled as chylomicrons - small particles made of lipid covered in phospholipids which facilitate transport of fat in lymphatic system from gut to systemic veins.

Question 40

What causes steatorrhoea?

Answer 40

If bile acids or pancreatic enzymes are not secreted in adequate amounts.

Question 41

What is steatorrhoea?

Answer 41

Fat in the faeces. This makes them pale, float, and smell foul.

Question 42

What causes jaundice?

Answer 42

The bile pigment bilirubin is made from haemoglobin breakdown. It is normally conjugated in the liver and secreted in the bile to be excreted. If it can't be excreted, it accumulates in the blood - jaundice.

Question 43

What is jaundice?

Answer 43

An accumulation of bilirubin in the blood.