digestion + absorption Flashcards
(17 cards)
describe the importance of micelles in absorbing lipids into the epithelial cells of the ileum
- micelles made of monoglycerids, fatty acids and bile salts
- bile salts make fatty acids more soluble in water
- micelles carry fatty acids to the epithelial cells of the ileum
- fatty acids released from micelles and absorbed into epithelial cell by simple diffusion
when lipids are digested, they first form smaller droplets and then micelles are formed. explain the advantages of these stages (3)
- lipid droplets increase the surface area for lipase
- this speeds up hydrolysis
- micelles bring fatty acids, monoglycerides to epithelial cell
how are golgi apparatus involved in the absorption of lipids?
- they modify triglycerides
- they combine proteins with triglycerides to form chylomicrons
- these are packaged into vesicles
How is starch digested?
Starch is digested by amylase, breaking 1-4 glycosidic bonds into maltose, produced by salivary glands and the pancreas, then maltase converts maltose to glucose in the ileum.
How are proteins digested?
Proteins are digested by exopeptidases that act on terminal or penultimate peptide bonds to make dipeptides or amino acids, and endopeptidases that hydrolyse central peptide bonds to create shorter polypeptide chains. Both types are made in the stomach and duodenum, with stomach proteases requiring HCl for activation. Dipeptidases, made in the duodenum, further break down peptides into amino acids.
What is the full process of lipid digestion?
Lipid digestion begins with emulsification by bile, increasing the surface area. Lipase then breaks down triglycerides into fatty acids and glycerol. Monoglycerides and fatty acids have their ester bonds hydrolysed.
Where is bile made and stored?
Bile is made in the liver and stored in the gall bladder.
How are amino acids or glucose absorbed after digestion?
Absorption occurs at the epithelial cells/brush border cells in the ileum. Sodium is actively transported out of the cells into the bloodstream, creating a low concentration of sodium inside the epithelial cell, allowing sodium to diffuse back in through a co-transporter along with glucose or amino acids. Glucose or amino acids, now in high concentration in the cell, diffuse out into the bloodstream via facilitated diffusion.
What is a micelle made of?
A micelle is made of monoglycerides, fatty acids, and bile salts.
What are the advantages of micelles?
Micelles maintain a concentration gradient of fatty acids in the ileum and are water-soluble, allowing for more effective transport through the ileum.
Describe the absorption of fatty acids and glycerol from micelles.
Micelles reach the brush border/epithelial cells, break down into monoglycerides and fatty acids, which then diffuse through the cell membrane of epithelial cells. Inside the epithelial cells, they recombine to form triglycerides and then chylomicrons by adding proteins, phospholipids, and cholesterol. Chylomicrons leave the cell by exocytosis into the lacteal.
How is faeces made?
Faeces are made by the absorption of water from food that remains unabsorbed in the large intestine/colon.
Where is amylase made?
Amylase is made in the salivary glands, pancreas, and duodenum.
Where are proteases made?
Proteases are made in the stomach, pancreas, and duodenum.
Where are lipases made?
Lipases are made in the duodenum and pancreas.
Why do minerals and vitamins not need to be digested?
Minerals and vitamins do not need to be digested because they are already small enough to diffuse and are soluble, allowing for absorption.
What is the advantage of activating stomach proteases with HCl?
Activating stomach proteases with HCl prevents the digestion of muscle tissue.
