Digestion and absorption Flashcards
What is the definition of digestion?
relatively large, insoluble biological molecules are hydrolysed into smaller soluble molecules that can be absorbed across the cell membranes into the bloodstream.
Enzymes in digestion
they are essential, catalyse the hydrolysis.
carbohydrates, what are they hydrolysed to
simple sugars
Digestion of carbohydrates by amylases and membrane bound disaccharideases.
In the mouth and small intestine
Amylase - carbohydrase which hydrolyses starch into maltose.
Maltose is hydrolysed into glucose by maltase.
Amylase is made in salivary glands, pancreas and small intestine.
Maltase is a disaccharidase which is found in cell surface membranes of the epithelial cells lining the small intestine
Lining of the small intestine is folded and microvilli are present.
in the lumen of the gut:
starch + amylase = Maltose
Maltose + Maltase:
in epithelial cells of small intestine - Glucose
Digestion of protiens by proteases.
in the lumen of the stomach
endopeptidase hydrolyses peptide bonds within proteins
creates smaller protien chunks.
This is in a low, HCl pH
Fluid secreated by the pancreas travels to the small intestine and helps to neutralize the acidic mixture and increase the pH
This pancreatic juice has endo and exo peptidases.
Endopeptidases hydrolyse peptide bonds within chains to form dipeptides.
Exopeptidases hydrolyse peptide bonds at the ends of the polypeptide chains to produce dipeptides.
dipeptidase within cell surface membranes in the epithelial cells of the small intestine hydrolyses to amino acids released in the cytoplasm of the cell
Lumen of gut: Protein - endopeptidase - polypeptides -
Inside cell surface membranes of epithelial cell: - Exopeptidase - Dipeptides - Dipeptidase - Amino acids.
Digestion of lipids by lipases
Emulsifacation:
IS NOT DIGESTSION
Fatty liquid arrives in the small intestine
bile (made in the liver, stored in the gall bladder and secreted into the small intestine.
The bile salts bind to the fatty liquid and break it down by emulsification.
this increases the surface area of the fatty droplets for action of digestive enzymes.
Digestion:
in the lumen of the small intestine
Lipase made in pancreas and secreted into the small intestine
Lipids - Bile salts - emulsified lipids - lipase - Fatty acids + glycerol
Co-transport mechanisms for the absorption of amino acids
Amino acid co-transport proteins (carrier molecules) found within the surface membrane of epithelial cells.
Only transport amino acid with sodium ions present.
for every sodium ion that is transported into the cell, an amino acid is transported in.
Facilitated diffusion.
(down a concentration gradient.)
amino acids diffuse across the epithelial cell and then pass into the capillares via facilitated diffusion.
Sodium ion concedtration gradient is maintained by active transport out of the cell to the blood via sodium - potassium pump.
Absorption of monosaccharides.
the glucose carrier proteins in the cell surface membrane of the small intestine work in a similar way to the amino acid carrier protiens.
Sodium ions and glucose molecules are co-transported into the epithelial cells.
Facilitated diffusion
Glucose molecules diffuse across the epithelial cell and enter the capillary at the other end of the cell by facilitated diffusion.
Concentration gradient of sodium is maintained by actively transporting sodium ions into the blood.
What is the role of micelles in the absorption of lipids?
Fatty acids, monoglycerides and glycerol are products from lipid digestion
Absorbing these products requires micelles.
Monoglycerides and fatty acids are not very solluble so micelles aid the transport into epithelial cells.
micelles break down and add to a pool of fatty acids and monoglycerides that are dissolved in the small intestine solution around the epithelial cells.
They enter the epithelial cells by diffusion.
(non-polar)
Short fatty acid chains within epithelial cells can move directly into the blood by diffusion
Longer fatty acid chains recombine with monoglycerides and glycerol to form triglycerides in the endoplasmic reticulum.
Packaged into lipoprotiens called chylomicrons
transported into a leacteal.
absorption
the transport of small, soluble molecules across cell membranes.
into the bloodstream
gland in digestion
an organ that releases/produces/secretes enzymes/mucus/other chemicals.
that are addded to food/secreted into the flow of food to aid physical/chemical digestion/flow of food.
what enzyme does the small intestine make
maltase
