Structure of the stomach.
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Made up of two parts.
Fundus- part to which the esophagus is
attached. Constitutes the main body of
the stomach
Pylorus- part leading into the intestine.
Constricted area leading into the
intestine.
Main functions of the stomach is as a
storage organ for undigested food. (1 to
5 hours)
pH of normal stomach contents is about
1.6 to 1.8.
3 types of cells found in gastric glands:
Parietal cells
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secrete hydrochloric acid
Chief cells
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produce pepsin and possibly other
enzymes
Mucous cells
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Secrete mucin.
Gastric secretion
Beaumont's work on gastric digestion:
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Dr. William Beaumont 1822
found that the lining of the empty
stomach was covered with a layer of
mucus which was neutral or alkaline 'in
reaction.
When food entered the stomach or
when the stomach lining was
stimulated by mechanical irritation the
membrane became bright red and a
colorless juice welled up from the
openings of small glands.
found that fatty foods required a longer
time to digest than lean.
Gastric Glands
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are numerous small glands scattered
throughout the walls of the stomach
Gastric juice
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Digestive fluid secreted by gastric
glands.
Usually 2 to 3 liters is secreted every 24
hours.
light-colored, thin fluid decidedly acidic
in reaction.
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Resting stomach usually contains about
50 ml. of a liquid.
Psychic stimulation; the thought, sight,
and taste of food will increase the flow
of gastric juice.
Presence of food in the stomach
amount of secretion depends on the
kind of food.
Presence of protein digestion products
in the intestine
Gastrin
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Produced by mucous membrane
An internal messenger, or hormone,
stimulating the gastric glands.
Is thought by some to be histamine.
Enterogastrone
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a hormone that liberated from the
intestinal mucosa
Enzymes found in the gastric Juice:
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Pepsin- acts on proteins, the most
important.
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Rennin- in some species acts on casein
causing milk to curdle
Lipase- hydrolyzes fat.
Hypo-acidity
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Acidity in stomach is less than normal.
common in cancer of the stomach and
pernicious anemia
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Pepsinogen
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Hyperacidity
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Acidity in the stomach is greater.
Common in ulcers of the stomach
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Phenolphthalein gives the total acidity
because this indicator changes color on
the alkaline side of neutrality, at a pH of
about 9.0;
Topfer's reagent indicates free HCI
because it changes color at a pH of
about 3.0 to 4.0.
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Mett's method
Hollander's theory
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HCI is produced in the parietal cells by
the hydrolysis of chlorides such as NaCl.
The NaOH formed is immediately
neutralized by reacting with buffers
such as NaH2PO4 and NaHCO3
HCI in the gastric juice converts
pepsinogen to the active enzyme
pepsin.
Active
pepsin
converts
more
pepsinogen into pepsin. (autocatalytic
reaction)
Measurement of Peptic activity
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the zymogen, or inactive precursor, of
pepsin
2 methods the body converts Pepsinogen into
pepsin:
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How are total acidity and free HCl determined
in a gastric analysis?
hydrolyzes proteins into proteoses and
peptones
attacks peptide linkages in which
tyrosine and phenylalanine are
involved.
Optimum pH .5 and 2.0.
Will clot milk at a pH of 5
fine glass tubes containing coagulated
egg albumen are placed in a beaker,
together with a sample of the gastric
contents incubated at 37°C in 24hrs
Sorensen titration
Van Slyke amino nitrogen determination
Rennin
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Pepsin
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most important enzyme in the gastric
juice
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Proteolytic enzyme found in the gastric
juice of some animals.
Casein is precipitated in human
stomach by pepsin and not rennin.
Is used to clot milk for making cheese
and preparing junket.
Acts best at a pH of 6.0 to 6.5
Chemistry in the precipitation of casein by
rennin:
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Rennin acts on a protein of milk
changing it into paracasein.
Paracasein combines with calcium to
form calcium paracaseinate
precipitation of calcium paracaseinate
the milk is said to curdle.
Gastric absorption
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Very little absorption of food materials
takes place in the stomach.
Some monosaccharides, salts, and
drugs may be absorbed.
Chyme
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liquefied stomach contents
Gastric Lipase
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A fat-hydrolyzing enzyme produced by
gastric secretion.
most active at pH 5
How long does food normally stay in the
stomach?
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Action of gastric lipase:
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The amount of fat hydrolyzed in the
stomach is small, and only fats which
are in an emulsified form are attacked.
Fats do not emulsify well in an acidic
medium; hence emulsification does not
take place to any great extent in the
stomach.
Carbohydrates requires about 2 hours.
fatty foods and meat requires 4 or 5
hours
How does the stomach empty itself?
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By peristalsis, it moves the chyme
toward the pyloric opening into the
intestine.
Can stomach digest itself?
Other Digestion in the Stomach:
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Increased
acidity
makes
starch
digestion takes place.
Digestion of this sugar formation of
glucose and fructose.
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Importance of the germicidal action of the
gastric juice:
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It prevents intestinal infections.
If the acidity of the stomach contents is
low, fermentations will occur.
Protoplasm of the living cells is alkaline
in reaction. Since pepsin requires an
acid medium, conditions are not correct
in the living cells for its action.
Living cells contain an antienzyme
which inhibits the action of pepsin.
Therefore no, stomach cannot digest
itself.