3.3 Digestion + Absorption Flashcards
Define digestion
The hydrolyisis of polymers to monomers for absorption across cell membranes
What do all membrane-bound disaccaridases do to disaccharides
Hydrolyse glycosidic bonds within the disaccharide to form the two monosaccharides
What does maltase hydrolyse into what
Maltose into two glucose molecules
What does lactase hydrolyse into what
Lactose into glucose and galactose
What does sucrase hydrolyse into what
Sucrose into glucose and fructose
Function of amylase
Hydrolysises glycosidic bonds within starch to form maltose
Outline the three stages to absorption of glucose
- Sodium ions activly transported out of ileum epithelial cell into blood
- Glucose co-transported with sodium ions from gut to ileum epithelial cell
- Glucose moves by faccilitated diffusion from ileum epithelial cell to blood
Explain the first stage of abosoption of glucose
- Sodium ions actively transported out of ileum capillary cell into blood by sodium-potassium pump
- ATP hydrolysis changes the carrier proteins shape, to allow movement of sodium ions
Explain the second stage of glucose absorption
- Maintains a diffusion gradient for sodium ions to enter the ileum epithelial cell from the gut through carrier proteins by faccilitated diffusion
- Glucose is co-transported with sodium ions
- Glucose moved into ileum epithelial cell through a co-transport protein by facillitated diffusion
Explain the third stage of glucose absorption
Glucose moves by faccilitated diffusion from ileum epithelial cell to blood capillary through a carrier protein
Explain the function of lipase
Hydrolyses ester bonds within triglycerides to form monoglycerides and fatty acids
What are the functions of bile salts
- Emulsify lipids into smaller droplets
- Form micelles
Why do bile salts emulsify lipids into smaller droplets
- Increase their surface area
- Faster hydrolysis by lipase
Describe and explain how bile salts form micelles, and their function
- Formed of bile salts, monoglycerides and fatty acids
- Micelles allow fatty acids to become more soluble
- Transports monoglycerides and fatty acids to ileum cell wall, to be absorbed into the ileum epithelial cell
- Fatty acids diffuse through the cell membrane
Explain the first process of lipid absorption
- Micelles contain bile salts and monoglycerides
- Movement of ileum brings micelles into contact with ileum epithelial cell where it breaks down
- Monoglycerides and fatty acids are absorbed by epithelial cell via simple diffusion
Outline the stages of lipid absorption
- Micelles
- Modification
- Chylomicrons
Explain the second stage of lipid absorption
- Monoglycerides and fatty acids transported to smooth endoplasmic reticulum, where they are reformed to triglycerides
- Triglycerides transported to SER where associated with cholestrol and proteins to form lipoproteins
- They form chylomicrons
Explain the third stage of lipid absorption
- Chylomicrons transported by vesicles to cell-surface membrane
- **Vesicles fuse with cell-surface membrane **and are released by exocytosis
- Chylomicrons enter lacteal
Function of endopeptididases
- Hydrolyse internal peptide bonds in the middle of polypeptide chains
- Create more terminal ends and smaller polypeptide chains
- Increase the surface area for exopeptididases to act
Function of exopeptididases
Hydrolyse peptide bonds at terminal ends of polypeptide chains
Describe the apperance of dipeptidases and where they are produced
- Membrane-bound
- Duodenum wall
Outline the three stages to amino-acid absorption
- Sodium ions activly transported out of ileum epithelial cell into blood
- Amino-acids move co-transported
- Amino-acids move into blood
Explain the first stage of amino-acid absorption
- Sodium ions activly transported out of ileum epithelal cells into blood by sodium-potasium pump
- ATP hydrolysis changes the carrier proteins shape, to allow movement of sodium ions
Explain the second stage of amino acid absorption
- Maintains a diffusion gradient for sodium ions to move into the ileum epithelial cell from the gut by facillitated diffusion
- Amino-acids are co-transported with sodium ions
- Amino-acids move into ileum epithelial cell from the gut through a co-transport protein via facilitated diffusion
Explain the final stage in amino-acid absorption
Amino-acids move by faccilitated diffusion from the ileum epithelial cell to the blood capillary by a protein carrier
