3-3 Digestion and absorption Flashcards
1
Q
What is digestion?
A
- The hydrolysis of large biological molecules into smaller molecules which can be absorbed across cell membranes.
2
Q
How are carbohydrates digested?
A
- Carbohydrates are digested by many different enzymes.
- Amylases in the mouth digest larger polymers
- Maltase’s in the ileum break down monosaccharides
- Sucrases break down sucrose
- Lactose breaks lactose
3
Q
How are lipids digested?
A
- Lipids are digested by lipases which hydrolyse the ester bond between the monoglycerides and fatty acid.
- Before being broken down in the ileum, lipids are emulsified int micelles by bile salts released by the liver.
4
Q
What is the purpose of emulsification in lipid digestion?
A
- Emulsification increases the surface area and speeds up the chemical reaction.
5
Q
How are proteins digested?
A
- Proteins are digested by enzymes called peptidases of which they are divided into 3 main groups.
6
Q
What are the 3 main peptidase groups?
A
- Endopeptidases, hydrolyse peptide bonds between specific amino acids in the middle of a polypeptide.
- Exopeptidases, hydrolyse bonds at ends of polypeptides.
- Dipeptidases, break dipeptides into individual amino acids.
7
Q
What happens to the products of digestion?
A
- Absorbed by cells lining the ileum of mammals.
8
Q
What happens to amino acids after digestion?
A
- Amino acids are absorbed by facilitated diffusion through specific carrier molecules in the surface membrane of epithelial cells.
- With each amino acid, on Na+ is also taken up, therefore amino acid absorption occurs via a process known as co-transport.
- A diffusion gradient for Na+ is maintained by their active transport through the base of epithelial cells where amino acids pass by facilitated diffusion.
9
Q
What happens to monoglycerides and fatty acids after digestion?
A
- Monoglycerides and fatty acids are polar so they can easily diffuse across the cell membrane into the epithelial cells lining the epithelium.
- Once inside they are transported to the endoplasmic reticulum where they are reformed into triglycerides again.
- After this they move out of the cells by vesicles into the lymph system.
