Topic 3 - Digestion & Absorption Flashcards
What is the small intestine responsible for?
Nutrient absorption
How is the small intestine adapted to its function?
Epithelium lining contains villi that contains a network of capillaries.
What does pancreatic amylase do?
Enzyme that breaks down carbohydrates in the pancreas.
What does trypsin and chymotripsin do?
Break down proteins and peptides
What does lipase do?
Enzyme that digests lipids into glycerol and fatty acids.
What is the main reaction used in digestion?
Hydrolysis
What does amylase do?
Catalyse the breakdown of starch
What do membrane bound disaccharidases do?
Help the breakdown of disaccharides into monosaccharides
What does lipase do?
Capitalise the breakdown of lipids into monoglycerides and fatty acids
What are bile salts?
Produced by the liver and emulsify lipids causing them to form small droplets
What are micelles?
Tiny structures formed when monoglycerides and fatty acid stick with the bile salts
How is fructose absorbed?
Facilitated diffusion through a transporter protein
How are monoglycerides and fatty acids absorbed?
Through diffusion
How are amino acids absorbed?
Facilitated diffusion
What is the role of amylase?
Hydrolyses starch into maltose.
Where can amylase be found?
In the saliva, pancreas and small intestine. Enters the small intestine via the ‘common duct’
Where does the digestion of carbohydrates take place?
1) Begins in the mouth (saliva).
2) Some takes place in the stomach, however amylase in rapidly inactivated due to low pH of HCl.
3) In the epthelial cells of the small intestine.
What is the role of maltase?
Hydrolyses maltose to glucose - breaking glycosidic bonds
What is the role of lactase?
Hydrolyses lactose into glucose and galactose - breaking glycosidic bonds
What is the role of sucrase?
Hydrolyses sucrose to glucose and fructose - breaking glycosidic bonds
What is step 1 in the digestion of lipids?
Emulsification
What happens in the emulsification of lipids in the stomach?
Solid lipids are turned into fatty acid liquid containing fat droplets.
What happens in the emulsification of lipids in the small intestine?
Bile, containing bile salts are secreted. Bile salts bind to fatty acids and breaks the fatty droplets into smaller ones via emulsification. This increases the surface area of the fatty droplets for action of digestive enzymes (lipase).
What is step 2 in the digestion of lipids?
Digestion of the lipids
Where does the digestion of lipids take place?
Takes place in the lumen of the small intestine
What happens in lipid digestion in the small intestine?
Lipase breaks down lipids into glycerol and fatty acids. (breaks ester bonds)
Where is lipase produced?
Produced in the pancreas and secreted into the small intestine by the pancreas.
Where does protein digestion begin?
Begins in the lumen of the stomach by protease enzymes.
What is the role of endopeptidases?
Hydrolyse peptide bonds within the polypeptide chain, creating smaller polypeptides.
What is the role of exopeptidases?
Hydrolyse the penultimate peptide bonds at the ends of the polypeptide chain to produce dipeptides.
What is the role of dipeptidases?
Hydrolyse dipeptides into amino acids which are then released into the cytoplasm.
Through what process are amino acids and monosaccharides absorbed?
Through a co-transport mechanism with Na+ ions, then facilitated diffusion into the blood.
How does glucose enter the cells?
By diffusion, co-transported using co-transporter proteins or co-transport with Na+ ions. (Sodium enters down an electrochemical gradient)
How are lipids absorbed?
1) The monoglycerides and fatty acids associate with phospholipids and bile salts to form micelles.
2) Micelles diffuse across the cell membrane.
3) Once inside the epithelial cell, they are resynthesised to triglycerides inside the ER and golgi. This produces a golgi vesicle (chylomicron).
4) Chylomicron then binds to membrane and is released by exocytosis.
5) Chylomicron enters a lacteal and this transports the chylomicron away from the intestine, and into the blood.
How are amino acids/glucose absorbed via co-transport?
1) Sodium ions are actively transported out of the epithelial cell into the blood.
2) This reduces the sodium ion concentration in the epithelial cell.
3) Sodium ions can then diffuse from the lumen down their concentration gradient into the epithelial cell.
4) The protein the sodium ions diffuse through is a co-transporter protein, so either glucose or amino acids also attach and are transported against their concentration gradient.
5) Glucose then moves by facilitated diffusion from the epithelial cell to the blood.
