Lab 4: Digestion Flashcards
Where does the majority of protein digestion take place?
Duodenum
When starch is in contact with iodine what colour does it go?
Black
What percent of the weight of the pancreas supports exocrine function?
80%
α- amylase digests what?
α1-4 bonds in starch and glycogen
Name the 4 pancreatic protein digesting enzymes?
Trypsin
Chymotrysin
Carboxypeptidase
Elastase
The pancreatic protein digesting enzymes are secreted as?
Zymogens
Why are the pancreatic protein digestion enzymes secreted as zymogens?
To prevent digestion of human tissues
These enzymes would digest the proteins in the cells in which they are synthesised
Describe the activation of trypsinogen?
Activated by enterokinase, an enzyme located on the brush border of the gut mucosa
Describe the activation of the zymogens from the pancreas?
- Activated on the brush border of the gut
- Trypsinogen needs to be activated first by enterokinase, an enzyme located on the gut mucosa.
- Trypinsogen is activated to trypsin.
- Trypsin acts to activate the other zymogens (chymotrypsin, carboxypeptidase, elastase)
Why is it the only protein digesting enzymes that are secreted in their zymogen form and not pancreatic lipase and amylase?
Because amylase and lipase are not dangerous to human tissue
Therefore can be secreted in their active form
Why is it important for bicarbonate to be secreted by the duct cells in the pancreas?
Important to neutralise the gastric acid and have the pH in the small intestine slightly alkaline as the pancreatic enzymes are active at this pH.
What is the products of amylase digestion?
Disaccharides and oligosaccharides
The enzymes on the brush border of the mucosa digests which carbohydrates?
- Disaccharides and oligosaccharides (the products of amylase digestion)
- Lactose
- Sucrose
What are “reducing sugars”?
Those that contain aldehyde groups e.g. glucose, galactose, lactose etc
All monosacchrides are reducing sugars
Give an example of isoenzymes?
Isoenzyme is when two or more enzymes has an identical function but different structure
Salivary amylase and pancreatic amylase
Why are salivary and pancreatic amylase known as isoenzymes?
They are very similar.
Has the same action but are coded by different genes, which are expressed in the salivary glands and pancreas respectively
What does the Benedict’s test indicate?
The presence of reducing sugars
i.e. all monosaccharides and maltose
What does the Barfoed’s test indicate?
Specific for monosaccharides
Useful to indicate the presence of glucose
What is the difference between oligosaccharides and polysaccharides?
Oligosaccharides: Composed of only a few number of monosaccharide units (up to 10 sugar units)
Polysaccharides: Composed of more than 10 monosaccharide units.
What are the 2 components of starch?
Amylose and amylopectin
What is the glycosidic bonds for amylose and amylopectin
Amylose is composed of α 1 - 4 glycosidic bonds.
Amylopectin is composed of α 1 - 4 and α 1 - 6 glycosidic bonds.
Describe the break down of starch?
- Starch has two components: amylose and amylopectin.
- Amylase breaks down α 1 - 4 glycosidic bonds.
- Amylose gets broken down into maltose
- Amylopectin gets broken down into dextrins (branched chains because of the presence of α 1 - 6 glycosidic bonds)
- Both maltose and dextrins are broken down into glucose (by the brush border enzyme, maltase)
Why does the break down of amylopectin and amylose different?
- Both are broken down by amylase
- Amylopectin break down produces dextrin because the α 1 - 6 glycosidic bonds are present, which cannot be broken down by amylase therefore form these branched structures known as dextrin.
- Amylase contains only α 1 - 4 glycosidic bonds, therefore are broken down into maltose
Which bonds does amylase digest?
α 1 - 4 glycosidic bonds.
Describe why cellulose is not digested by amylase?
Made up of β 1 - 4 glycosidic bonds
NOTE: amylase breaks down α 1 - 4 glycosidic bonds only
Why is cooked potato starch digested by amylase but raw potato starch is not?
- Raw potato starch is composed of large starch granules that has a small surface area and is highly bound helical structure.
- When cooked, the potato starch undergoes a physical change called gelation. The starch granules burst and the helical structure is disrupted leaving tangled chains of amylopectin.
- Amylopectin can be digested by amylase
What happens to carbohydrates not digested by amylase?
- Some e.g. lactose and surcose, are digested by oligosaccharidase i.e. surcase and lactase. Therefore, not requiring amylase activity.
- Others are broken down by enzymes released by bacteria in the large intestine.
What happens to the indigestible carbohydrates?
- They get broken down by enzymes released by bacteria in the large intestine.
- The products of the bacterial digestion are short-chain fatty acids.
- The short-chain fatty acids are either used by the bacteria, or absorbed by the cells in the LI with a small amount being transferred to the liver.
What are the main enzymes involved in protein digestion?
- Pepsin (stomach secretion)
- Trypsin (pancreatic secretion)
- Chymotrypsin (pancreatic secretion)
- Carboxypeptidase (pancreatic secretion)
- Elastase (pancreatic secretion)
What other compounds (other than the lipases) are needed for fat digestion? Their function
Bile salts and lecithin, a phospholipid
Used to emulsify the fat
Define acute pancreatitis?
Acute inflammatory condition in which pancreatic enzymes autodigest the gland
What are the main causative factors of pancreatitis in the UK?
Gallstones and alcohol
describe the pathogenesis of acute pancreatitis?
- The mechanism that starts the process is not clear.
- This unknown mechanism results in the activation of trypsin, which in turn activates the other zymogens.
- This causes injury to the acinar cells.
- In response to the injury, inflammatory mediators are released.
Defin chronic pancreatitis?
Ongoing inflammation of the pancreas
Leading to the destruction of endocrine and exocrine function.
What is the most common cause of chronic pancreatitis in the UK?
Alcohol abuse
What are the symptoms that patients usually present with when chronic pancreatitis?
Recurrent abdominal pain
Diabetes mellitus (due to loss of pancreatic islets)
Weight loss (due to malabsorption)
Steatorrhea (due to incomplete breakdown of fats in the diet)
What is Steatorrhea?
The excretion of abnormal quantities of fat with the faeces owing to reduced absorption of fat by the intestine.
What are some environment factors that can effect enzyme activity?
Temperature (above 40ºC might denature)
pH
Why is Raftilose not digested by amylase?
No glucose glucose bonds
Give some examples of causative factors for acute pancreatitis?
- Gallstones
- Alcohol
- Infections e.g. mumps
- Tumours
- Drugs e.g. furosemide
- Pancreatic duct obstruction
Aetiologies of Chronic Pancreatitis?
- Alcohol
- Hereditary
- Trauma
- Trophical
What are the tests to assess pancreatic damage?
- Serum amylase
- Urine amylase
- Serum lipase
What are the tests to assess pancreatic function?
- Direct and indirect function tests
- Faecal chymotrypsin
- Faecal elastase
If serum amylase levels are high but there is no other significant finding in the rest of the pancreatic tests what can be the cause?
Lots of different possible causes that can hyperamylasemia (high levels of amylase)
- Ruptured ectopic pregnancy
- DKA
- Tumours
- Drugs
What is macroamylasaemia and what would the showings be on the pancreatic damage test?
This is when the amylase makes complexes with IgA or IgG preventing it to be filtered from the kidneys.
↑serum amylase, ↓urine amylase.
↑serum amylase, ↓urine amylase would indicate which condition?
Macroamylasaemia
Describe the direct and indirect pancreatic function tests
Direct
- Invasive.
- Measure pancreatic enzymes.
- Two types: secretin-pancreozymin test (gold standard) and Lundh test:
Indirect
- Give the patient a non-absorbable molecule and test to see if the pancreatic enzymes cleaves it into an absorbable molecule.
Neither test is used in the UK
If the level of faecal elastase is low which kind of pancreatitis is this?
If the level of faecal elastase is high which kind of pancreatitis is this?
↓ low = Chronic pancreatitis
↑ high= Acute pancreatitis
What would be the followings levels in acute pancreatitis:
serum amylase
urine amylase
serum lipase
Faecal elastase
serum amylase: Rises within 5-8 hrs of onset of symptoms, normalises by day 4
urine amylase: Same as serum amylase.
serum lipase: Rises within 4-8 hrs of onset of symptoms, peaks at 24 hrs and normalises within 8-14 days
Faecal elastase: Rise
Protein digestion is continued at the brush border by which enzyme?
Amino peptidase
