3.3.3 Digestion And Absorption Flashcards
What is digestion?
When large insoluble molecules are hydrolysed into smaller soluble molecules that can be absorbed across cell membranes.
What are the structures in the digestive system?
Salivary glands, oesophagus, stomach, pancreas, small intestine, large intestine, and rectum
What is physical digestion?
The physical breakdown of food…
-broken down into smaller pieces by teeth
-churned by stomach muscles to break it up
It increases surface area for chemical digestion
What is chemical digestion?
The hydrolysis of large insoluble biological molecules to smaller soluble ones so that they can be absorbed by epithelial cells in the ileum of the small intestine.
It is the action of enzymes.
What are the enzymes involved in digestion of carbohydrates?
Amylase and membrane-bound disaccharidase (Maltase, sucrase, lactase)
What is amylase?
Enzyme produced in the pancreas and salivary glands, and secreted into the mouth and small intestine to hydrolyse polysaccharides into disaccharides.
Starch into maltose
What is membrane-bound disaccharidase?
Enzyme produced and attached to the epithelial lining of the ileum.
Hydrolyses disaccharides into monosaccharides (glucose, fructose, galactose)
Includes maltase, sucrase, lactase
What enzymes are involved in digestion of proteins?
Endopeptidase, exopeptidase and membrane-bound dipeptidase
What is endopeptidase?
Hydrolyses peptide bonds between amino acids in the middle of a polypeptide chain
What is exopeptidase?
Hydrolyses peptide bonds between amino acids on the ends of a polypeptide chain.
What is membrane-bound dipeptidase?
Hydrolyses peptide bonds between dipeptides to produce amino acids
Where are peptidases produced?
Endo and exo- pancreas
Dipeptidase- epithelial lining of ileum
Where are proteins digested?
Starts in stomach and continues in ileum.
What two features play a role in the digestion of lipids?
Lipase and bile salts
What is lipase?
An enzyme produced in the pancreas
Hydrolyses the ester bonds in triglycerides to form monoglycerides and fatty acids
Digestion takes place in the small intestine.
Where are lipids digested?
Small intestine
What are bile salts?
Produced in the liver and stored in the gall bladder
Emulsifies lipids to form micelles (tiny droplets)
This increases the surface area for lipase to hydrolyse lipids.
Describe the physical digestion of lipids
Lipids are coated in bile salts to create an emulsion
This causes lipids to split up into micelles
Many small droplets of lipoids provides a large surface area to enable the faster hydrolysis action by lipase.
Describe the chemical digestion of lipids
Lipase hydrolyses lipids (micelles) into monoglycerides (glycerol) and fatty acids
What is a micelle?
A water-soluble vesicle formed from fatty acids, glycerol, monoglycerides and bile salts.
They deliver the fatty acids, glycerol and monoglycerides to the epithelial cells of the ileum for absorption.
What is exocytosis?
Transport of materials out of a cell through the cell-surface membrane
How are fatty acids absorbed into the bloodstream once inside micelles?
They enter the epithelial cell by simple diffusion (as they are non-polar)
The shorter fatty acid chains diffuse directly into the bloodstream
The longer fatty acid chains recombine with monoglycerides and glycerol to form triglycerides in the RER
The triglycerides are packaged into chylomicrons at the Golgi
These are transported to a lacteal (a lymph vessel in the villi) via exocytosis, where they enter the bloodstream
