Digestion and absorption Flashcards
What is digestion?
Large insoluble molecules are hydrolysed into smaller soluble molecules that can be absorbed across cell membranes
What two enzymes are involved in the hydrolysis of carbohydrates to monosaccharides?
- Amylase
- Membrane-bound disaccharidase
Where is amylase produced?
- Pancreas
- Salivary glands
Where does digestion of carbohydrates begin?
Mouth
How does amylase work?
It hydrolyses polysaccharides into the disaccharide maltose, by hydrolysing the glycosidic bonds
Where are membrane-bound disaccharidases found?
- Duodenum
- Ileum
Give two examples of membrane-bound disaccharidases?
- Sucrase
- Lactase
What do sucrase and lactase do?
Hydrolyse sucrose and lactose into monosaccharides (fructose and glucose, galactose and glucose)
What three enzymes hydrolyse proteins?
- Endopeptidases
- Exopeptidases
- Membrane-bound dipeptidases
What do endopeptidases do?
Hydrolyse peptide bonds between amino acids in the middle of a polymer chain
What do exopeptidases do?
Hydrolyse peptide bonds between amino acids at the end of a polymer chain
What do membrane-bound dipeptidases do?
Hydrolyse peptide bonds between two amino acids
Where does protein digestion occur?
- Begins in the stomach
- Continues in duodenum
- Fully digested in ileum
What digests lipids?
- Lipase
- Bile salts
Where is lipase produced?
Pancreas and then is secreted into duodenum and ileum
What does lipase do?
Hydrolyses the three ester bonds in triglycerides to form monoglycerides and fatty acids
What do bile salts do?
Emulsify lipids to small droplets. Increases surface area for lipase to act on
Where are bile salts produced?
Liver
What are micelles?
Water soluble vesicles, formed from fatty acids, glycerol, monoglycerides and bile salts
What do micelles do?
Deliver fatty acids, glycerol and monoglycerides to the epithelial cells of the ileum for absorption
How is the ileum adapted for absorption?
- Covered in villi, which have thin walls surrounded by a network of capillaries
- Epithelial cells have even smaller microvilli
- These increase the surface area, provides a shorter diffusion pathway, and maintains a concentration gradient
What does the digestion of proteins produce?
Amino acids
How are monosaccharides and amino acids absorbed?
Co -transport
