FACTORS INFLUENCING GASTRIC ACTIVITY
Motor and secretory activities of the stomach are modified, usually simultaneously and in the same direction, by a number of factors, both local (gastric) factors and external or systemic factors. Chief among them are the following:
LOCAL FACTORS
LOCAL (GASTRIC)
FACTORS INFLUENCING GASTRIC ACTIVITY
1.
Character of the Food. A meal that is sufficiently high in fat to yield
an intragastric fat content in excess of about 10% empties much more slowly and
stimulates considerably less acid secretion than does a meal predominantly
of protein. The inhibitory effect of fat on gastric secretion is not a
local one but a result of the hormone, which is released systemically when fat
enters the duodenum. This enterogastric inhibitory action of fat and
cholecystokinin is much more effectively achieved by the ingestion of 15 to 30
mL of a vegetable oil before meals.
A
meal exclusively or mainly of starch tends to empty more rapidly, though
stimulating less secretion, than does a protein meal. Thus, other factors being
equal, a person may expect to be hungry sooner after a breakfast of fruit
juice, cereal, toast, and tea than after one of bacon, eggs, and milk. The
amount of gastric secretion and gastric acidity is highest with the ingestion
of proteins. This relationship of quantity and rate of secretion and its acid
or pepsin concentration is subject to great individual variations as well as
variations in a single individual under different conditions.
2.
Consistency of the Food. Liquids, whether ingested separately or with
solid food, empty from the stomach more rapidly than do semisolids or solids.
This does not apply to liquids such as milk, from which solid material is
precipitated on contact with gastric juice; milk also releases CCK from its fat
content. In the case of foods requiring mastication, the consistency of the
material reaching the stomach should normally be semisolid, thereby
facilitating gastric secretion, digestion, and evacuation. Important exceptions
to the general rule that liquids are weak stimulants of gastric secretion are
(1) the broth of meat or fish, by virtue of their high secretagog content, and
(2) coffee, which derives its secretory potency from its content both of
caffeine and of the secretagogs formed in the roasting process.
SYSTEMIC FACTORS
SYSTEMIC
(EXTERNAL) FACTORS INFLUENCING GASTRIC ACTIVITY
1. Hunger. A
meal eaten at a time of intense hunger tends to be evacuated more rapidly than
normally, apparently as the consequence of the heightened gastric tonus.
Because hunger results from the depletion of body nutrient stores, it is
understandable on teleologic grounds that in the hunger state, the body should
have some mechanism for hastening the delivery of ingested nutrients into the
intestine. Levels of the hormone ghrelin are higher when the stomach is empty and
one becomes hungry, possibly signaling the time to consume a meal. Ghrelin also
has prokinetic effects that accelerate gastric emptying.
2. Exercise.
Mild to moderate exercise such as walking, particularly just after eating,
increases gastric emptying of the meal compared with resting conditions. With
strenuous exercise, gastric contractions are temporarily inhibited and gastric
emptying decreases. Secretory activity does not appear to be materially
influenced by exercise.
3. Position.
Gastric emptying is facilitated in certain individuals when lying on the right
side when the position of the body is such that the pylorus and duodenum are in
a dependent position. In the supine position, gastric emptying is delayed
because the gastric content pools in the dependent fundic portion. No evidence
is avail- able that secretion is affected by position. For patients with
gastrointestinal reflux symptoms, sleeping in the right recumbent position may
reduce nocturnal symptoms, because delayed gastric emptying can cause reflux
symptoms.
4. Emotion. The
retarding effect of emotional states on gastric motility and secretion has been
documented by clinical and experimental observations. In healthy humans, anger,
fear, labyrinthine stimulation, painful stimuli, preoperative anxiety, and
intense exercise slow gastric emptying. The influence of emotions on gastric
activity may be augmentative or inhibitory, depending on whether the emotional
experience is of an aggressive (hostility, resentment) or depressive (sorrow,
fear) type, respectively.
5. Pain. Severe
or sustained pain in any part of the body (as from a kidney or gallbladder
stone, migraine, or sciatic neuritis) inhibits gastric motility and evacuation
by nervous reflex pathways.
