Digestion Flashcards
(15 cards)
Digestion and absorption of carbohydrates.
How does the digestion of carbohydrates work?
- Amylase breaks the glycosidic bonds in starch to produce maltose.
- Maltase which is a membrane bound disscharide breaks the glycosidic bond in maltose and breaks it down into glucose.
- Sucrase breaks down sucrose into glucose and fructose. Lactase breaks down lactose into glucose and galactose.
Where is amylase produced?
In the salivary glands and pancreas.
Where are membrane-bound disaccharidases found?
They are embedded in the cell membrane of the ileum epithelial cells.
How are glucose molecules absorbed across the ileum of the small intestine?
- If the concentration of glucose in the ileum is higher compared to the epithelial cells it can move into the cells via facilitated diffusion.
- If it is lower it moves via co-transport.
Digestion and absorption of proteins.
How does the digestion of proteins work?
- Endopeptidases break the peptide bonds in the middle of the polypeptide chain to create smaller chains and a higher number of ends for the exopeptidases.
- Exopeptidases break peptide bonds at the end of chains to release individual amino acids.
- Membrane-bound dipeptides break peptide bonds in dipeptides and release individual amino acids.
How are amino acids absorbed across the ileum of the small intestine?
- If the concentration of amino acids in the ileum is higher compared to the epithelial cells it can move into the cells via facilitated diffusion.
- If it is lower it moves via co-transport.
Digestion and absorption of lipids.
Where are bile salts produced and released?
They are produced in the liver and secreted into the small intestine.
Where is lipase produced and released
It is produced in the pancreas and secreted into the small intestine.
How does the digestion of lipids work?
- The bile salts emulsify large lipid droplets into smaller lipid droplets in order to increase their surface area for digestion.
- Lipase then breaks the ester bonds between the fatty acids and glycerol molecules to release fatty acids and monoglycerides.
- The monoglycerides and fatty acids combine with the bile salts to form micelles.
How does the absorption of lipids work?
- The micelles carry fatty acids and monoglycerides to the epithelial cells.
- The micelles make them water-soluble and allow for the maintenance of a concentration gradient across the epithelial cell membrane.
- The micelles release the fatty acids and monoglycerides and they move through the membrane via simple diffusion as they are lipid-soluble.
- Once inside the epithelial cells the monoglycerides and fatty acids are used to remake triglycerides.
- The Golgi apparatus then packages the lipids with proteins to form vesicles called chylomicrons.
- The chylomicrons then leave the epithelial cells and go into the lymphatic system, via exocytosis.
- The lipids drain into the Circulatory system near the heart.
What is the role of the liver in digestion?
It produces bile which emulsifies lipids and increases their surface area to make digestion more efficient. The bile salts also neutralise the stomach acid and make sure the pH in the small intestine remains alkali. This is important because the enzymes in the small intestine work best in alkali conditions.
How are the epithelial cells of the small intestine adapted for absorption of food?
- The epithelial cells make up the villi of the small intestine. They increase the surface area of the small intestine which increases the rate of absorption.
- The epithelial cells have microvilli that further increase the surface area.
