Section 3- Digestion Flashcards
What part of the digestive system stores and digests food?
Stomach
What it special about the ileum to increase product absorption?
Inner walls folded into villi- gives larger surface area.
Villi has microvilli again increasing surface area.
Where is food further digested by enzymes?
Illeum
What does the large intestine do?
Absorb water
What is digestion?
The breaking down of large insoluble molecules into small soluble ones that can be assimilated into cells.
What are some of the adaptions of the small intestine?
Lots of villi for larger surface area
Long and tightly packed for larger surface area
Small diffusion distance
Rich blood supply
What does chemical digestion do?
Hydrolyses large, insoluble molecules into smaller, soluble ones.
What are the 3 main digestive enzymes?
- Carbohydrases
- Peptidases
- Lipases
What enzymes are involved in carbohydrate digestion?
Amylase
Maltase
Sucrase/ lactase
Where is amylase produced and what does it do?
Produced in saliva and by the pancreas
Hydrolyses glyosidic bonds of starch to form maltose
Where is maltase found and what does it do?
Found on the lining of the ileum
Hydrolyses maltose to a-glucose
Where is sucrase/ lactase found?
Found on the lining of the ileum
What does lipase do?
Hydrolyses the ester bond of triglyceride to form a monoglyceride and fatty acid.
What is lipid digestion sped up by?
Bile
Neutralises acid from the stomach which ensure correct conditions for enzymes released into small intestine.
What needs to happen before the lipids can be digested?
Must be emulsified by bile salts produced by the liver.
This breaks down large fat molecules into smaller, soluble molecules (micelles), increasing surface area.
What enzymes are involved in protein digestion are what are their roles?
Endopeptidases- hydrolyse peptide bonds within polypeptide chain.
Exopeptidases- hydrolyse the peptide bonds between terminal amino acids.
Dipeptidases- break dipeptides into amino acids.
What are 2 structures that produce amylase?
Salivary glands
Pancreas
Why does the stomach not have villi or microvilli?
Food in the stomach has not been hydrolysed into soluble molecules.
Cannot be absorbed so are unnecessary.
What are 3 enzymes produced by the epithelium of the ileum?
Maltase
Sucrase
Lactase
How is the ileum adapted for absorbing the products of digestion?
- Wall of ileum is folded (villi)
- Thin walls lined with epithelial cells
- Large network of blood capillaries
How are the villi specialised for the absorption of the products of digestion?
Increase surface area for diffusion
Very thin walls –> reduces diffusion distance
Well supplied with blood vessels –> maintain diffusion distance- can carry away absorbed molecules
Epithelial cells lining the villi have microvilli
How are triglycerides absorbed?
Non-polar monoglycerides and fatty acids diffuse across epithelial cell membrane.
Triglycerides are re-synthesised in SER and Golgi
Combined with proteins and cholesterol forming CHYLOMICRONS
Chylomicrons move into lacteals by exocytosis
Chylomicrons carried through lymphatic system enter bloodstream at vena cava
What are 3 organelles that you would expect to be well-developed in epithelial cell of ileum?
Endoplasmic reticulum- re-synthesis triglyceride from monoglyceride and fatty acid
Golgi apparatus- form chylomicrons from triglycerides, cholesterol and lipoproteins
Mitochondria- provide ATP required for co-transport of glucose and amino acid molecules
In addition to microvilli, what is another feature of the epithelial cells that would increase the rate of absorption of amino acids?
Increase in number of protein channels and carrier proteins
Why would endocellulases and exocellulases act at different places on a cellulose molecule?
Active sites are different shapes
So different enzyme-substrate complexes are formed.
How do chylomicrons leave the epithelial cell?
Exocytosis
Too large
What type of enzyme would you find bound to the membrane of cells lining the small intestine?
Dipeptidases
How could a mutation of a gene cause someone to be unable to digest lactose?
Changes primary structure
No complementary active site to glucose
Describe the role of micelles in the absorption of fata into the cells lining the ileum?
Micelles composed of monoglyceride, fatty acids, bile salts
Make fatty acids more soluble in water
Bring fatty acid to cell lining
Maintain higher concentration of fatty acid to cell
Fatty acid absorbed by diffusion
