12.9 - Digestion & Absorption Flashcards
What happens during digestion? (in terms of molecules)
Large biological molecules are hydrolysed to smaller molecules SO they can be absorbed across cell membranes.
What produces digestive juices and what is their function?
Digestive juices are produced by the GLAND CELLS and they release hydrolytic enzymes to facilitate digestion.
What are polypeptides and proteins hydrolysed into and by what enzymes?
What are carbohydrates hydrolysed into and by what enzymes?
What are fats hydrolysed into and by what enzymes?
Hydrolysed into amino acids by proteases. (broad term)
Into simple sugars (monosaccharides) by carbohydrases.
Into glycerol, fatty acids and monoglycerides by lipases.
What enzymes do these glands produce?
- Salivary Glands
- Stomach
- Pancreas
- Ileum
- Salivary Glands = salivary amylase
- Stomach = endopeptidases (e.g pepsin) & exopeptidases
- Pancreas = pancreatic amylase, lipases & exopeptidases
- Ileum = membrane bound dipeptidases & disaccharidases
What do enzymes do in digestion and what for?
They hydrolyse large insoluble food molecules (polymers) into small soluble molecules (monomers) SO they can be absorbed through the lining of the intestine.
Describe the role of the enzymes of the digestive system in the complete breakdown of starch. (4)
1) Salivary + Pancreatic amylase hydrolyses starch -> maltose.
2) By hydrolysing glycosidic bonds.
3) Maltose is hydrolysed into glucose.
4) By maltase.
Which enzyme gets denatured in the stomach during starch digestion, and which enzyme carries on the process?
Salivary amylase is denatured in the stomach due to its acidic PH.
So pancreatic amylase continues to hydrolyse the starch into maltose in the small intestine.
Where is maltose hydrolysed into glucose to be absorbed?
In the membrane of the epithelial cells.
Why can’t carbohydrates be absorbed across the epithelial cell membrane, and which can?
They are too large, only monosaccharides (monomers) can be transported across the E.C.M as they are small enough and are complementary to the binding sites of specific carrier / channel proteins that move specifically complementary monomers across the E.C.M.
Monosaccharides are absorbed by facilitated diffusion and co transport by specific carrier proteins.
Describe how glucose is absorbed from the ileum (via epithelial cells in the E.C.M) into the blood. (5)
1) Na+ ions are actively transported (using ATP) out of the epithelial cell into the blood (by Na/K pump)
2) This creates a concentration gradient of Na+ ions - between the lumen of the ileum and the epithelial cell)
3) Na+ and glucose enter by facilitated diffusion using complementary co-transporter proteins. ( They have 2 binding sites complementary to each, only when both molecules bind will the molecules be moved across the membrane.)
4) Na+ diffuse into the cell DOWN its concentration gradient.
5) Glucose moves into the cell AGAINST its concentration gradient.
6) Glucose moves into the blood by facilitated diffusion (via carrier protein).
Why must sodium ion concentration be low inside the epithelial cells?
So that glucose/AA co-transport can take place. If the sodium ions are not actively transported into the blood from the cell, then the concentration of sodium ions will rise in the cells.
Then facilitated diffusion will stop, as glucose/AAs cannot enter the cell without sodium, so this would stop AA/glucose absorption.
Describe how amino acids are absorbed from the ileum into the blood. (5)
1) Na+ ions are actively transported out of the epithelial cell into the blood. (by Na/K pump)
2) This creates a conc. gradient of Na+ ions (between the ileum and the epithelial cell).
3) Na+ ions and amino acids enter by facilitated diffusion - co-transport through same carrier protein.
4) Na+ move into the cell DOWN its conc. gradient.
5) Amino acids move into the cell AGAINST its conc. gradient.
6) Amino acids move into the blood by facilitated diffusion.
Where can lipids only be digested?
Within the lumen of the ileum (SI).
What happens to lipids in the stomach?
They are churned into fat droplets.
Where is bile produced, stored and released? What does it contain and what does it do?
Produced - liver
Stored - gall bladder
Released - into the small intestine with the food
Contains - bile salts
Bile salts - emulsify (not break) fat droplets, forming micelles - increasing the SA of the lipids for the action of lipase enzymes so digestion = faster.
