FRS 3. Digestion

Question 1

Describe the salivary glands role in digestion

Answer 1

secretion of digestive enzymes (amylase and lipase) along with mucus and fluid for lubrication of swallowing and disolving of nutrients

Question 2

Describe the stomachs role in digestion

Answer 2

secretion of HCL and pepsinogen

Question 3

Describe the pancreas role in digestion

Answer 3

Secretion os NaHCO3 and a range of enzymes and zymogens for intraluminal digestion of protein, carbohydrate and fats

Question 4

Describe the livers role in digestion

Answer 4

secretion of bile acids, handling of nutrients after absorption

Question 5

Describe the gall bladders role in digestion

Answer 5

storage and concentration of bile acids and excretion of molecules by liver

Question 6

Describe the small intestines role in digestion

Answer 6

main site of action for pancreatic enzymes, mucosal enzymes on brush border for completion of carbohydrate, and protein digestion, absorption of nutrients and electrolytes by passive facillitated or active transport

Question 7

Describe the large intestine role in digestion

Answer 7

absorption of electrolytes, colonic bacterial fermentation of undigested food components, absorption of short chain fatty acids and other bacteria products, absorption of water and production of faeces

Question 8

Why is pancreatic juice alkali?

Answer 8

Buffers acidic secretion of the stomach

Protects mucosa

Provides the right pH for pancreatic enzymes

Question 9

What are the consequences of damage to the pancreas?

Answer 9

major consequence for nutrition as well as general health

Question 10

What role does the pancreas play in carbohydrate digestion?

Answer 10

Secretes α-amylase, which digests the α1-4 bonds in starch and glycogen

Question 11

What role does the pancreas play in fat digestion?

Answer 11

Lipase and colipase are secreted and work with bile acids to digest lipids.

Question 12

What role does the pancreas play in protein digestion?

Answer 12

There are a range of pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase, elastase) which are needed to digest the wide range of peptide bonds in dietary proteins.

Question 13

How are pancreatic proteases secreted?

Answer 13

as zymogens (inactive precursor proteins) to prevent digestion of human
tissues, and are activated in the gut lumen.

Question 14

List the zymogens

Answer 14

• tripsinogen
• chymotrypsinogen
• proelastase
• procarboxypeptidase A
• procarboxypeptidase B

Question 15

How is trypsin activated from its zymogen form?

Answer 15

Trypsinogen is activated by another enzyme, enterokinase, which is sited on the brush border of the gut
mucosa and the trypsin released activates the other zymogens.

Question 16

What is the product of amylase digestion?

Answer 16

disaccharides and oligosaccharides, which are further digested by enzymes on the brush border of the mucosa.

Question 17

What is dietary fibre and its role?

Answer 17

non-digestible
carbohydrates (dietary fibre) enter the large intestine where they are fermented by the colonic bacteria.
○ Form short-chain fatty acids (acetic, propionic and butyric acid) and gas
○ SCFA produced from 60g of carbohydrates in the colon may provided up to 10% of our daily energy needs

Question 18

Oligosaccharides:

Answer 18

Most oligosaccharides are composed of three to 10 monosaccharide units. Oligosaccharides
are not digestible by human gut enzymes.

Question 19

Polysaccharides:

Answer 19

polysaccharides are carbohydrates chains composed of more than 10 of monosaccharide
units.

Question 20

What are reducing sugars?

Answer 20

Reducing sugars are those which contain aldehyde groups.
○ E.g. glucose, galactose, glyceraldehyde (monosaccharides) and lactose, maltose (disaccharides) and
maltotriose.

Question 21

What is the difference between salivary and pancreatic amylase?

Answer 21

Salivary and pancreatic amylases are isoenzymes.
○ Very similar, but are coded for by different genes, which are expressed in the salivary glands and
pancreas respectively.

Salivary amylase begins the process of starch digestion and pancreatic amylase completes it.

Question 22

What bonds are found in starch?

Answer 22

Consists of:
○ amylose with α1-4 bonds
○ Amylopectin with α1-4 bonds and α1-6 glucose-glucose bonds between glucose units

Question 23

What are the main enzymes involved in protein digestion?

Answer 23

Stomach:
● Pepsin

Small intestine (pancreatic enzymes):
● Trypsin, chymotrypsin and carboxypeptidase
● Continues at brush border with aminopeptidase

Question 24

What bonds do proteases break down?

Answer 24

Trypsin - acts on lysine and arginine residues

Chymotrypsin - acts on large hydrophobic residues, such as tryptophan, tyrosine and phenylalanine

Elastase - broad specificity on attacking bonds next to small amino acids (glycine, alanine, serine)

Carboxypeptidase - removes amino acids from carboxyl end of peptide chain.

Question 25

What are the main pancreatic secretions required for fat digestion

Answer 25

Pancreatic lipase - acts on water insoluble triglycerides

Co-lipase - inhibits adsorption onto the water:lipid interphase, which would denature lipase

Question 26

What is acute pancreatitis?

Answer 26

acute inflammatory condition in which pancreatic enzymes autodigest the gland.
○ Acini become damaged, which activates zymogens

The disease can be relatively mild and self-limiting, or very serious, leading to ongoing morbidity or even death.

Question 27

What are the main causative factors for pancreatitis in the UK?

Answer 27

• gallstones

- alcohol

Question 28

What are the symptoms of acute pancreatitis?

Answer 28

○ nausea/vomiting
○ sudden onset of abdominal pain
○ Fever
○ Hypotension
○ shock
○ Multi-organ failure.

Question 29

Describe the biochemical changes seen in acute pancreatitis?

Answer 29

○ Increased serum amylase and lipase
○ Decreased serum calcium and albumin
○ Increased serum TAG

Question 30

What are other causes of pancreatitis?

Answer 30

○ Infections e.g. mumps, tumour
○ Drugs e.g. azothioprine, furosemide, oestrogens, opiates, steroids
○ Iatrogenic (e.g. post surgical)
○ Pancreatic duct obstruction
○ Genetic
○ Hyperlipidaemia, Hypercalcaemia

Question 31

What is the pathophysiology of pancreatitis?

Answer 31

● Normally there are several mechanisms which protect the pancreas from the enzymes it produces; enzymes
are initially translated as proenzymes and packaged into granules containing enzyme inhibitors.
● It is not clear what mechanisms actually start off the processes which result in acute pancreatitis.
● However the activation of trypsin is a result; this in turn activates other enzymes.
● Inflammatory mediators cause a local inflammatory response and in severe cases a systemic inflammation

Question 32

What is chronic pancreatitis

Answer 32

ongoing inflammation of the pancreas, leading to the destruction of endocrine and
exocrine function.

Question 33

What causes chronic pancreatitis?

Answer 33

often secondary to repeated acute attacks or alcohol abuse. Also:
■ Hereditary
■ Trauma
■ Hypercalcaemia
■ Idiopathic
■ Tropical

Question 34

What are the symptoms of chronic pancretitis?

Answer 34

90% of acinar tissue has to be lost before symptoms of malabsorption are seen

○ recurrent abdominal pain
○ diabetes mellitus (loss of pancreatic islets)
○ weight loss (due to malabsorption)
○ steatorrhoea (incomplete breakdown of fats in the diet).

Question 35

Why is amylase a useful test for pancreatic function?

Answer 35

Small enough to pass through glomerulus to urine.

Blood amylase is low and constant
○ Greatly increases in acute pancreatitis or salivary gland inflammation.

Question 36

What are the serum amylase results seen in acute pancreatitis?

Answer 36

○ Rises within 5-8 hrs of onset of symptoms, normalises by day 4.
○ 4-6 times ULN – (normal <100 U/L).
○ Low specificity.

Question 37

What are some causes of hyperamylasaemia.

Answer 37

○ Pancreatic disease
○ Other intra-abdominal disease
○ Ruptured ectopic pregnancy
○ Salivary gland lesion
○ Renal insufficiency
○ DKA
○ Tumours
○ Drugs
○ Macroamylase: complexes between IgG or IgA and amylase – cannot be filtered through the kidney,
increase 2-8 fold.

Question 38

What are the urine amylase results seen in acute pancreatitis?

Answer 38

● Urine amylase (normal 30-600 U/L)
● Improve diagnostic performance by measuring amylase and creatinine in paired serum and urine samples
(normal 1-5%) (6-13% in acute pancreatitis)).
● Can help exclude macroamylasaemia:
○ ↑serum amylase, ↓urine amylase.
● Amylase isoenzymes: differentiate between S and P.

Question 39

When should pancreatic function tests be ordered?

Answer 39

● Diagnosis of CP is suspected

● Imaging tests normal or inconclusive

Question 40

What are the serum lipase results seen in acute pancreatitis?

Answer 40

○ Rises within 4-8 hrs of onset of symptoms
○ peaks at 24 hrs
○ normalises within 8-14 days.
○ 5-10 times ULN – (normal 30-210 U/L).
● Higher clinical sensitivity and specificity than amylase.

Question 41

What are the tests of pancreatic damage?

Answer 41

● Serum amylase
● Urine amylase
● Serum lipase

Question 42

What are the tests of pancreatic function

Answer 42

● Direct and Indirect function tests
● Faecal chymotrypsin
● Faecal elastase

Question 43

What are the direct tests of pancreatic function?

Answer 43

(invasive tests)
○ Gold standard: secretin-pancreozymin test
■ Measures pancreatic enzymes i.e. trypsin in duodenum aspirate over 2 hrs
■ The secretin stimulation test measures the ability of the pancreas to respond to secretin.
■ A collection tube is placed in the 3rd part of duodenum under fluoroscopic guidance.
■ Duodenal fluid is continuously collected and bicarbonate concentration is measured
■ Test is difficult and expensive.

○ Lundh test:
■ Measures [bicarb], amylase or trypsin activity following a meal
■ Historical

Question 44

What are the indirect tests of pancreatic function?

Answer 44

○ Tests based upon the principal that a pancreatic enzyme cleaves an absorbable substance from a
nonabsorbable molecule
■ P-aminobenzoic acid from N-benzoyl- l-tyrosyl- paminobenzoic acid in the NBT-PABA test
■ Fluorescein from fluorescein dilaurate in the Pancreolauryl test
○ Test doses of non absorbable precursors were given orally and pABA or fluorescein measured in urine
○ Tests limited by the complexity of absorption and metabolism
○ Neither test is now available in the UK

Question 45

Describe Faecal chymotrypsin

Answer 45

Faecal test for proteolytic enzymes.
○ Produced in an inactive form in the pancreas and then activated in the small intestine to digest food proteins.
○ Low values indicate pancreatic insufficiency.

Question 46

Describe Faecal elastase

Answer 46

Useful marker of pancreatic insufficiency.
○ Endopeptidase and sterol binding protein.
○ Faecal Elastase is a proteolytic enzyme secreted by the acinar cells of the pancreas. Unlike other
pancreatic enzymes such as Chymotyrpsin, Elastase-1 is not degraded during intestinal transit, and so
the stool concentration reflects exocrine pancreatic function
○ Pancreatic elastase is detected using ELISA with two monoclonal antibodies highly specific for human
pancreatic elastase 1.