3.3: Digestion and absorption Flashcards
Define digestion
Larger insoluble molecules are hydrolysed into smaller soluble molecules that can be absorbed across cell membrane
Where is amylase produced?
Pancreas and salivary glands
What reaction does amylase catalyse?
Starch (polysaccharide) into maltose (disaccharide) by hydrolysing glycoside bonds
Where is maltase found?
Membrane of epithelium cell
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 dipeptidases do?
Hydrolyse dipeptides into amino acids
Where does protein digestion occur?
Starts in the stomach, continues into the duodenum and fully digested in the ileum
Lipid digestion (9)
1) Lipid droplets are mixed with bile salts to from smaller droplets - emulsified
2) Smaller droplets increase surface area for faster hydrolysis by lipase
3) Triglycerides hydrolysed into glycerol, fatty acids and monoglycerides
4) Bile salts, glycerol and fatty acids from micelles
5) Micelles make fatty acids soluble in water and bring bring them to the surface of epithelial cells
6) Fatty acids enter epithelial cells by simple diffusion
7) At the SER fatty acids and glycerol are recombined to form triglycerides
8) At the Golgi, triglycerides are modified, proteins are added to from lipoproteins (chylomicrons) and packaged into vesicles
9) Chylomicrons are transported into lymph vessels by exocytosis and then enter the blood
Describe glucose and amino acid absorption (6)
1) Na+ ions are actively transported out of epithelial cell into the blood
2) This creates a concentration gradient of Na+
3) Na+ and glucose enter by facilitated diffusion using cotransporter proteins
4) Na+ diffuse into cell down its concentration gradient
5) Glucose moves into cell against its concentration gradient
6) Glucose moves the blood by facilitated diffusion
