Gastrointestinal Tract - Digestion of Biomolecules Flashcards
Where does the digestion of carbohydrates start?
In the mouth
What enzyme is found in the mouth that begins the digestion of carbohydrates?
Salivary amylase
What happens to salivary amylase in the stomach?
Its action is diminished
Why does salivary amylase not work in the stomach?
The pH of the stomach is too low
Other than the mouth where does amylase work?
The small intestine
What form is amylase in the small intestine?
Pancreatic amylase
Why does amylase work in the small intestine but not the stomach?
Because the pH of the small intestine rises
Where does pancreatic amylase enter the small intestine?
The duodenum
What breaks down maltose?
Maltase
Where is maltase found?
The brush border
In general what happens to disaccharides in the GIT?
Disaccharides are broken down into simple sugars
Where in the GIT are disaccharides broken down into simple sugars?
The small intestine
What must simple sugars pass through in order to enter the bloodstream?
The apical membrane
How do glucose and sodium enter enterocytes?
They must bind to protein in order to enter the enterocyte
Explain the process of sodium and glucose entering an enterocyte.
Sodium must be pumped out of one cell and into another to set up the concentration gradient across the basal lateral membrane
How does glucose move from an enterocyte to the bloodstream?
By diffusion
What happens when glucose enters the bloodstream?
It passes through to the liver
What happens to glucose in the liver?
It is either stored in the liver or used by the body
Whether or not glucose is stored in the liver depends on what?
It depends on the levels of insulin in the body
Explain how insulin controls how much glucose is stored by the liver.
(2)
Increased insulin causes glucose to be stored as glycogen in the liver
Low insulin causes glycogen to be used
What is the name of the protein that carried glucose across membranes?
Transport proteins
What is another name for simple sugars?
Monosaccharides
Where exactly in the bloodstream do monosaccharides enter?
They enter the portal circulation
What are proteins also called?
Polypeptides
What happens to proteins in the gastric phase?
In the gastric phase hydrochloric acid and pepsin breaks down polypeptides into peptide fragments
What enzyme is used to break down polypeptides?
Pepsin
What are proteins broken into in the gastric phases?
Peptide fragments
How long does it take for proteins to be broken down into peptide fragments?
This process takes hours
What is the brush border?
Microvilli of the small intestine
What part of the intestine receives the chyme?
The duodenum
What is present in pancreatic juices that helps break down peptide fragments?
Sodium carbonate (alkaline)
Enzymes - pancreatic amylase and zymogens
What enzymes are present in pancreatic juices?
2
Pancreatic amylase
Zymogens
What are zymogens?
Inactive enzymes responsible for breaking down proteins
Why are zymogens used to break down proteins?
Zymogens are inactive in the pancreas but become active in the duodenum so as to not damage the pancreas
What is cystic fibrosis?
Blockage of pancreatic juice which leads to inflammation due to incomplete breakdown of proteins
What does the chyme in the small intestine containing broken down peptide fragments trigger?
It triggers the enterogastro reflex
What is the enterogastric reflex?
2
This is releases enterogasterones
This relaxes the hepatopancreatic sphincter which causes it to open
What happens when the hepatopancreatic sphincter opens?
This allows pancreatic juice to enter the small intestine
What enters the small intestine when the hepatopancreatic sphincter opens?
(3)
Trypsinogen
Chymotrypsinogen
Procarboxy-peptidase
What is trypsinogen converted into in the SI?
Trypsin
What converts trypsinogen into trypsin?
enteropeptidase
Where is enteropeptidase found?
Mucosa
What does trypsin do?
2
Converts chymotrypsinogen into chymotrypsin
Converts procarboxypeptidase into carboxypeptidase
What is chymotrypsinogen converted into?
Chymotrypsin
What is procarboxypeptidase converted into?
It is converted into carboxypeptidase
How do proteins enter the blood stream?
Co-transport with sodium
How do proteins enter cells using co-transport with sodium?
2
A concentration gradient on the basal membrane side needs to be set up for sodium
Need to decrease sodium concentration levels in enterocyte to create gradient
What do proteins use to enter the blood stream?
Protein carriers
Where in the blood stream do proteins enter?
The portal circulation
Where does the digestion of lipids begin?
The mouth
What is found in the mouth that digests lipids?
Lingual lipase in saliva
What percentage of lipids are digested in the mouth?
10% of a lipid is digested
What happens to lingual lipase in the stomach?
It becomes ineffective
Why do lipids become ineffective in the stomach?
Low pH
What form are lipids in the stomach?
Fat globules
Are lipids polar or non-polar?
They are non-polar
Lipids are non-polar what does this mean?
They are hydrophobic
What happens to lipids in the small intestine?
They form clumps
How are lipids broken down in the SI?
Lipases (enzymes) from the pancreas enter the SI and have an affect on lipids
What needs to be done to lipids before lipases can work efficiently?
The lipids need to be emulsified
How are lipids emulsified?
Using bile salts
What happens to bile salts when there not needed?
2
They are stored in the gall bladder
They are dehydrated first then stored
What are bile salts said to be?
amphipathic
Bile salts are amphipathic, what does this mean?
They have a hydrophilic/polar side and a hydrophobic/non-polar side
How do bile salts emulsify lipids?
2
Bile salts bind to outside of fat droplet
Chyme binds to inside of fat droplet
Explain the effects of pancreatic juice on lipids.
3
Pancreatic juice contains pancreatic lipase
Lipase acts on the fat droplet
Lipase breaks down into free fatty acids, monoglyceride, monolipids
What does pancreatic lipase break lipids into to?
3
Free fatty acids
Monoglycerides
Monolipids
What is formed after the pancreatic lipase has worked on the lipids?
Micelles
How do micelles enter enterocytes?
They diffuse through the apical membrane
Describe the process of lipids entering circulation.
4
They are packaged into chylomicrons by the smooth endoplasmic reticulum and the golgi apparatus
Enter lacteals containing lymph fluid
Lymph brought to the thoracic duct
Lymph drains into general circulation
Why do chylomicrons enter the lacteals?
2
Chylomicrons are too big to enter capillaries
Therefore, they bypass them by entering the lacteals in the lamina propria
Where in the tissue are lacteals present?
The lamina propria
What do lacteals contain?
Lymph fluid
Where are lipids brought in the lymph fluid?
The thoracic duct
