5. Pancreas And Liver

Question 1

What are the properties of chyme?

Answer 1

Hypertonic - increases as digestion takes place
Acidic
Only partially digested

Question 2

What helps to make chyme less hypertonic and digest it further?

Answer 2

Water from ECF

Secretions from pancreas (enzymes, bicarbonate ions), from liver (bicarbonate ions, bile)

Question 3

Why is chyme hypertonic?

Answer 3

Food produces lots of solutes that are dissolved in gastric juice
Stomach wall is largely impermeable to water so water cannot dilute solute in chyme

Question 4

What does the acinus secrete in the pancreas?

Answer 4

Enzymes - amylase/lipase (active), proteases (inactive) - trypsin, chymotrypsin, elastase, carboxypeptidase

Question 5

What do the centroacinar cells secrete?

Answer 5

Aqueous component of pancreas secretions

Question 6

What happens in the pancreatic ducts?

Answer 6

Modifies aqueous secretions

Question 7

What are the pancreatic secretions innervated by?

Answer 7

Parasympathetic - vagus, hormones

Sympathetic inhibits

Question 8

What is the acinus of the pancreas stimulated by?

Answer 8

Vagus and chylocystokinin (CCK)

Question 9

How are the enzymes produced in the acinus?

Answer 9

Formed on RER
Moved to Golgi
Condensing vacuoles
Concentrated in zymogen granules 
Released with appropriate stimulus

Question 10

What are zymogen granules?

Answer 10

Membrane bound

Contain zygomen - inactive precursor of an enzyme

Question 11

What signifies pancreatic damage?

Answer 11

Pancreatic enzymes (amylase, lipase) appear in blood

Question 12

What happens if pancreatic secretions are at higher flow rate?

Answer 12

Increased secretion of HCO3

Question 13

What is the liver for?

Answer 13

Energy metabolism
Detoxification
Plasma protein production
Secretion of bile

Question 14

Why do hepatocytes contain lots of RER/SER and Golgi?

Answer 14

Very active at producing proteins/lipids for export

Question 15

Why do heaptocytes contain lots of glycogen?

Answer 15

Needed when glucose needs to be accessed quickly

Question 16

What is in a portal triad?

Answer 16

Bile duct
Branch of hepatic artery
Branch of portal vein

Question 17

What is the hepatic acinus?

Answer 17

Functional unit of liver

3 zones - 1 is closest to portal triad, 3 is closest to central vein

Question 18

Which zone of the acinus is most likely to be damaged by ischeamia?

Answer 18

3

Question 19

Which zone of the acinus is most likely to be damaged by toxins?

Answer 19

1

Question 20

Where does the venous blood from the gut drain through?

Answer 20

The liver, in portal vein

Question 21

What flows into the liver?

Answer 21

Venous portal blood
Arterial blood
All flowing towards central vein, which then drains into hepatic veins (vena cava)

Question 22

What flows out of the liver?

Answer 22

Bile, along canaliculi

Bile ducts to duodenum

Question 23

What are the 2 components of bile?

Answer 23

Bile acid dependent

Bile acid independent

Question 24

What is bile acid dependent component secreted by?

Answer 24

Secreted by hepatocytes into canaliculi

Question 25

What is bile acid independent component secreted by?

Answer 25

Secreted by duct cells

Question 26

What is release of bile acid independent component stimulated by?

Answer 26

Secretion

Question 27

What does bile acid dependent component contain?

Answer 27

Bile acids and pigments

Question 28

What is bile acid independent component made of?

Answer 28

Similar alkaline solution to pancreatic duct cells

Question 29

How can bile salts help remove cholesterol?

Answer 29

Fibre can bind cholesterol to other bile salts and allow it to be excreted in faeces

Question 30

What are the 2 primary bile acids?

Answer 30

Cholic acid

Chenodeoxycholic acid

Question 31

What are bile salts?

Answer 31

Bile acids that are conjugated with the amino acids (glycine, taurine)

Question 32

Why do we have bile salts, not just bile acids?

Answer 32

Bile acids are not always soluble at duodenal pHs - bile salts generally are
Bile salts have an amphipathic structure (hydrophilic end and hydrophobic end) - act at oil/water interface, crucial for emulsification of dietary lipids

Question 33

Why do bile acids need to emulsify fat into smaller units?

Answer 33

Lipids tend to form large globules by the time they reach the duodenum
This gives a low SA for enzymes to act
Bile acids can help disperse droplets and increase SA for lipases to act
Bile acids then form micelles with products of lipid breakdown

Question 34

What are micelles?

Answer 34

Vehicle to carry hydrophobic molecules through an aqueous medium

Question 35

What are the products of lipid digestion?

Answer 35

Cholesterol
Monoglyceride
Free fatty acids

Question 36

What happens when micelles come in contact with brush border of enterocyte cells?

Answer 36

• Lipids diffuse down conc gradient into intestinal epithelial cell
• Inside the cell, lipids are re-esterified back to triglycerides, phospholipids and cholesterol
• Then packaged with apoproteins to form chylomicrons

Question 37

How are chylomicrons transported out of enterocytes?

Answer 37

Exocytosis from basolateral membrane
Then enter lymph capillaries (lacteals) as too big to enter blood capillaries
Travel through lymphatic system, then re-enter vascular circulation at the thoracic duct into left subclavian/internal jugular vein

Question 38

Where are bile salts reabsorbed and where do they go?

Answer 38

In terminal ileum, return to liver in portal blood, liver extracts bile salts and reuses them

Question 39

What does the gallbladder do?

Answer 39

Stores bile

Concentrates bile - removes water and ions

Question 40

What stimulates gallbladder contraction?

Answer 40

CCK - relaxes sphincter of oddi

Question 41

What happens if bile acids or pancreatic lipases are not secreted in adequate amounts?

Answer 41

Fat appears in faeces (steatorrhoea)