Transcript of food . All the digestive enzymes are proteins

DIGESTION OF VARIOUS FOODS:
Carbohydrates are large polysaccharides or disaccharides
which are combination of monosaccharide bounded to one
another by condensation this mean that hydrogen ion has
been removed from one of monosaccharide , while hydroxyle
removed from the next , which combined with water to form
water , when carbohydrate are digested back into
monosaccharides specific enzyme return hydrogen&hydroxyl
ion to the polysaccharides &separate the monosaccharides
from each other this process called hydrolysis.
Fat consist of triglycerides which are combination of 3 fatty
acids molecules combined with single glycerol molecule , in
condensation 3 molecules of water removed , digestion of
triglycerides consist of the reverse process , the fat digesting
enzyme returning molecules of water to the
triglyceridesoleculese &there by splitting the fatty acid
molecules away from the glycerole so that digestive process
is one of hydrolysis .
Finally proteins are formed from amino acids and bounded
together by peptide linkage , in this linkage , a
hydroxyle ion is removed from one amino acid
&hydrogen ion removed from the next . Thus the
amino acid in protein chain are bounded together by
condensation ,&digestion occure by the reverse effect
called hydrolysis , the proteolytic enzyme returning the
water to the protein molecules to split them in to amino
acids , therefore,the chemical digestion of the 3 types
of food is in the same basic process of hydrolysis ,the
only difference lie in the enzyme required to promote
the reaction for each type of food . All the digestive
enzymes are proteins
Digestion of CHO:
1- digestion of CHO in month &stomach :
When food is chewed , it is mixed with saliva , which contains alpha –
amylase , secreted mainly by the parotid glands . This enzyme hydrolyses
starch in to the disaccharide maltose &other small polymers of glucose
that contain 304 glucose molecules , but the food remaine in the mouth
only a short time &probably not more than 5%of all starch that eaten will
become hydrolized by the time the food is swallowed .
Digestion continues in stomach for as long as one hour befor the food
become mixed with stomach secretion , then the activity of salivary
amylase is blocked by the acid pf gastric secretion because it is inactive
once as the PHof the medium falls below 4, nevertheless, on the average
30- 30%of the starch will be hydrolysed mainly to maltose.
2- digestion of CHO in the S.I.
A- BY PANCREATIC AMYLASE :pancreatic secretion contain large
quantity of alpha amylase that is identical in it is function with salivary
amylase , within 15 – 30 minutes after chyme empties in to the duodenum
&mixed with pancreatic juice , virtually all the starch are digested .in
general . The starch are converted in to maltose &other small glucose
polymers .
B- BY INTESTINAL EPITHELIAL ENZYMES hydrolyses of disacch.
&small glucose polymers in to monosach.:
The enterocytes lining the villi of S.I contain 4 enzymes lactase , sucrase ,
maltase, &alpha dextrinase which are able for splitting the disaccharides
lactose , succarose, maltose as well as small glucose polymers in to their
constituant monosaccharides , these enzymes are located in the
membrabe of microvilli brush border of the enterocytes . They are digested
as ehey become in contact with these membrane
Lactose splitted in to galactose &glucose
Succarose
fractose &glucose
Maltose & small polymers → glucose moleculess
Digestion of proteins :
1- in stomach :
Pepsine the important peptic enzyme of the stomach , it is
most active at PH 2-3 &inactive at PH above 5 for this
enzyme to cause any digestive action on protein the stomach
juice must be acidic , Hcl secreted by the parietal cell at PH
about 8 but it mixed with the stomach contents &with
secretion of other glandular cells of stomach , the PH ranges
from 2-3 .one of the important pepsine digestion is its ability to
digest collagen which is the major constituent of the
intracellular connective tissue of meat , therefore ,digestive
enzyme of GIT pentrate meat &digest the cellular protein
,pepsine usually providing 10-20%of the total protein
digestion .
2- digestion of proteins by pancreatic secretion :
Most protein digestion occure in the upper S.I.under the
influence of proteolytic enzyme of pancreatic secretion ,
when the proteins leave stomach , they are mainly
proteoses, peptones &large poly peptides . Trypsine
&chymotrypsine split protein molecules in to small poly
peptides , carboxypolypeptides cleave the indivisual
amino acids from the carboxyl end of the polypeptides .
Elastase digestt elastin fiber that hold meat together ,
only small percentage of protein are digested to amino
acoids by pancreatic juice , most remaine as di or tri
peptides &some even larger
Digestion of peptides by peptidase in the enterocytes:
The last digestion of ptroteins is achieved by the enterocytes
that line the villi of S.I.mainly in the duodenum &jujenum,
these cells have a brush border that consist microvilli
projecting from the surface of each cell, in the cell membrane
of each microvilli are multiple peptidase that protrude through
the membrane to the exterior , where they come in contact
with intestinal fluid 2 types of peptidase enzymes are
especially important , aminpoly peptidase &several
dipeptidase , they splitting the remainder larger polypeptides
into tri &di peptides are transported through the microvilli
membrane to the interior of the enterocyte
Finally inside enterocyts are other peptidases that are specific
for the remaining linkage between amino acids within minutes
all the last di &tripeptides are digested to single amino acids
Digestion of fat :
A small amount of of triglycerides digested in the stomach by lingual
lipase that is secreted by limgual glands in the mouth &swallwed
with saliva , the amount of digestion is less than 10%, essentially all
fat digestion occure in the S.I.
Emulsification of fat by bile acid &lecithen :
Emulsification of faty mean breaking of fat globules in to small sizes
so that the water soluble enzyme can act on the surface of the
globule , emulsification achieved partially by agitation in the stomach
with products of stomach digestion , but mainly by the influence of
bile . Both of bile salt & lecithin are important for emulsification
Bile salt & lecithin molecules are highly soluble in fat , therefore,the
fat soluble portion of bile salt molecule dissolve in the surface layer
of the fat globule &other portion soluble in the surrounding fluid ,
this effect greatly decrease the surface tension of fat & make the fat
globule readily fragmentable by agitation in the S.I .
DIGESTION OF TRIGLYCERIDE BY PANCREATIC LIPASE :
The most important enzyme for digestion of triglycerides (neutral fat)
is pancreatic lipase enough to digest all triglycerides the enterocyte
of small intestine contain small quantity of enteric lipase but it is
usually unimportant . Most of triglycerides of diet are split into free
fatty acids & 2 monoglyceride
ROLE OF BILE SALT IN ACCELERATING FAT DIGESTION :
During triglyceride digestion , monoglycerides& free fatty acids are
formed they become dissolved in the central fatty portion of the
micells which cause reducing the concentration of these end
products of digestion in the vicinity of the fat globule &digestion
process can proceed.
The bile salt micells also act as transport medium to carry
monoglycerids &free fatty acids to the brush border of intestinal
epithelial cells &they are absorbed , on delivery of these end
products bile salts are again released back in to chyme &used again
&again.