stim u lated, sig nals are trans mit ted first into the spi nal cord and
then back to de scend ing co lon, sig moid, rec tum and anus
through para sym pa thetic nerve fibres in the pel vic nerves.
These sig nals greatly in ten sify the peristaltic waves and re lax
the in ter nal anal sphincter, thus con vert ing the weak ef fort of
in trin sic myenteric def e ca tion re flex into a pow er ful pro cess of
def e ca tion. Such that some times it is ef fec tive in emp ty ing the
large bowel all the way from splenic flexure of co lon to anus.
Defecation signals also initiate other effects such as taking
deep breath, closure of glottis and contraction of abdominal
wall muscles to force the contents of the colon downward.
However, the defecation reflexes can purposely be activated by
taking a deep breath to move the diaphragm downward and
then contracting the abdominal muscles to increase the
pressure in abdomen, thus forcing fecal contents into rectum to
cause new reflexes.
Reflexes initiated in this way are not as effective as those that
arise naturally. So, the people who often inhibit their natural
reflexes are likely to become severely constipated.ïFlatulence and burping is a sign of normal healthy
individual with friendly gut flora. Do you know?
Everyone has gas and burping and passing gas are absolutely
normal. However, many a people think that they burp or pass
gas too often or possess much gas i.e flatulence.
Actually gas is air in the digestive tract, caused by swallowing
and breakdown of certain foods in the large intenstine, which
leaves the body when we burp through mouth or through anus
by passing gas. Usually, when we eat or drink too fast, smoke
or drink carbonated or fizzy drinks, we tend to swallow more air.
Some of this swallowed air is absorbed in small intestine, of
which it passes to large intestine and is finally passed through
anus as gas.
Another fact that contributes to gas formation is that all the food
we eat is not digested by stomach and small intestine. Those
undigested carbohydrates and fibre of foods passed to large
intestine are broken down by bacteria inhabiting the colon and
produce CO 2 ,H 2 , CH 4 or H 2 S gas which is eventually passed
through anus. Most carbohydrate containing foods may
produce gas i.e. beans, broccoli, cauliflower, cabbage,
mushrooms, apples, peaches, whole wheat, fruit drinks,
packaged foods, bread, milk and milk products etc. It is not
necessary that foods producing or causing gas in one person
will release or cause the same in other person. A healthy
individual may have 18-21 flatulences per day indicating a
healthy gut flora. They flourish by feeding upon unused food in
large intestine and also produce some short chain fatty acids
that promote the growth of other beneficial bacteria.
ïHow do we know and differentiate between
Hunger and fullness. Do you know?
Stomach hunger involves a complex interaction between the
digestive system, endocrine system and brain. When our body
needs refueling, one start feeling tired and weak and also find it
difficult to concentrate and work. The stomach begins to ache
and rumble, which indicates true stomach hunger. On the
contrary, if we do not feed food when the body requires it, the
physical symptoms intensify i.e. cause a continuing tetanic
contraction lasting for 2-3 min. Hunger and fullness is regulated
by hypothalamus in brain. Once you have fed your body
enough food to satisfy its needs, signals registering fullness or
satiety are sent to hypothalamus.
It takes approximately 20 min for fullness signals to transmit
from the stomach back to the brain. But if one eats too fast and
doesn’t pay attention, it is easy to overside this system and end
up eating more than what is required by our body.
Hunger contractions are most intense in young, healthy people
having high degrees of gastrointestinal tonus. It also increases
by lower than normal levels of blood sugar.ïVomiting is a protective reflex in response to
obstruction in any part of gastrointestinal tract.
Do you know?
Vomiting is the process by which the upper gastrointestinal
tract rids itself of its contents when almost any part of upper
tract becomes excessively irritated, over distended or even
overexcitable. Excess distention or irritation of the duodenum
provides an especially strong stimulus for vomiting. It is a
protective reflex that removes toxic materials from GI tract before
they can be absorbed. However, excessive or prolonged
vomiting with its loss of gastric acid cause metabolic alkalosis.
The vomiting reflex is co-ordinated through a vomiting center in
the medulla. The reflex begins with a stimulation of sensory
receptors and is often accompanied by nausea. These sensory
signals originate mainly from pharynx, oesophagaus, stomach
and upper portions of small intestine. These nerve impulses are
transmitted by both vagal and sympathetic afferent nerve fibres
to the vomiting centre in brain stem. From here, motor impulses
that cause actual vomiting are transmitted from vomiting centre
by way of fifth, seventh, ninth, tenth and twelfth cranial nerves to
upper GI tract, through vagal and sympathetic nerves to lower
GI tract and through spinal nerves to diaphragm and
abdominal muscles.
Minutes before vomiting occurs, antiperistalsis begins to occur
i.e. peristalsis up the digestive tract rather than downward. This
may begin as far down in the intestinal tract as the ileum, with
the antiperistaltic wave travelling backwards up the intestine at
a rate of 2-3 cm/s. These waves can actually push a large share
of lower small intestine contents to duodenum and stomach
within 3-5 min. As a result, the duodenum becomes overly
distended, which becomes the exciting factor that initiates the
actual vomiting act.
Once the vomiting onsets, strong intrinsic contractions occur in
both duodenum and stomach along with partial relaxation of
oesophageal-stomach sphincter and the vomiting begins to
move from stomach to oesophagus. After adequate
stimulation of vomiting centre, a specific vomiting act involving
abdominal muscles takes over and expels the contents to the
exterior. Apart from the irritative stimuli of GI tract, vomiting can
also be triggered by nervous signals arising in areas of brain
i.e. in fourth ventricle called chemoreceptor trigger zone. Any
electric stimulation of this area or administration of certain
drugs directly stimulate this zone and initiate vomiting.