This document describes the process of ingestion, digestion and absorption of food by the gastrointestinal system. It discusses the roles of the mouth, esophagus, stomach, small intestine and colon. The mouth chews and swallows food which is propelled through the esophagus to the stomach. The stomach stores, mixes and slowly empties food chunks (chyme) to the small intestine where nutrients are absorbed. The colon absorbs water from waste and stores feces until defecation. Regulatory mechanisms such as hormones and nerves coordinate movement and emptying between organs.

2. INGESTION OF FOOD:
• Hunger: is an intrinsic desire that the
person needs to ingest enough food.
• Appetite: Is the type of food that a
person preferentially seeks.

3. MASTICATION (CHEWING):
• The teeth is responsible for chewing.
• The anterior teeth (incisors) provide a strong
cutting action, and the posterior teeth
(molars) provide a grinding action.
• Chewing reflex is done by rebound
contraction.
• Most of the muscles of chewing are
innervated by the motor branch of the fifth
cranial nerve.

5. SWALLOWING
(DEGLUTITION):
• Is a complicated mechanism, principally
because the pharynx subseries respiration and
swallowing.
• Swallowing can be divided into:
(1) A Voluntary Stage.
(2) A Pharyngeal Stage.
(3) An Esophageal Stage.

7. • The esophagus functions primarily to conduct food rapidly
from the pharynx to the stomach.
• The esophagus normally exhibits two types of peristaltic
movements:
1- Primary peristalsis
2- Secondary peristalsis
1- Primary peristalsis:
• Is simply continuation of the peristaltic wave that begins
in the pharynx and spreads into the esophagus during the
pharyngeal stage of swallowing.
• 8 to 10 seconds, 5 to 8 seconds (gravity pulling).
• If the primary peristaltic wave fails to move all the food
then secondary peristaltic waves initiates.

8. 2- Secondary peristalsis:
• Result from distention of the esophagus itself by the
retained food.
• Initiated partly by:
A. intrinsic neural circuits in the myenteric nervous
system.
B. Glossopharyngeal and vagal efferent nerve fibers.
• Function of the Lower Esophageal Sphincter
(Gastroesophageal Sphincter) = prevent significant
reflux of stomach contents into the esophagus.
• Additional Prevention of Esophageal Reflux by
Valvelike Closure of the Distal End of the
Esophagus.

10. • stomach

11. MOTOR FUNCTIONS OF THE
STOMACH:
(1) storage of large quantities of food until the food
can be processed in the stomach, duodenum, and
lower intestinal tract.
(2) mixing of this food with gastric secretions until it
forms a semifluid mixture called chyme.
(3) slow emptying of the chyme from the stomach
into the small intestine at a rate suitable for
proper digestion and absorption by the small
intestine.

13. STORAGE FUNCTION OF THE STOMACH:

15. MIXING AND PROPULSION OF FOOD
IN THE STOMACH:
• Gastric glands of the stomach secretes the digestive juices.
• The long presence of food causes mixing waves which is a
weak peristaltic constrictor waves.
• every 15 to 20 seconds.
• Powerful peristaltic action potential–driven constrictor
rings that force the antral contents under higher and
higher pressure toward the pylorus.
• “Retropulsion”: is the combination of pyloric squeezing
and constrictive peristalsis in the stomach.
• Hunger Contractions: when the stomach has been empty
for several hours or more. And the whole stomach
contracts.
• Hunger pangs: mild pain in the pit of stomach.

17. STOMACH EMPTYING:
• “Pyloric pump”: Is promoted by intense peristaltic
contractions in the stomach antrum.
Control of Stomach Emptying:
1- Stomach factors:
• Degree of filling.
• Effect of gastrin.
2- Duodenal factors (inhibitory feedback):
• Enterogastric inhibitory nervous feedback
reflexes.
• Hormonal feedback by Cholecystokinin (CCK).

18. • Hormone gastrin from the G cells of the antral mucosa.
• Cause secretion of highly acidic gastric juice by the stomach glands.
• Gastrin likely promotes stomach emptying.
• Increased food volume in the stomach promotes increased
emptying from the stomach.
• Stretching of the stomach wall does elicit local myenteric reflexes in
the wall
• Multiple nervous reflexes are initiated from the duodenal wall
(enteric nervous system, inhibitory sympathetic nerve fibers in
stomach, inhibation vagus nerves in stomach).
• Hormones cholecystokinin from mucosa of the jejunum.
• Inhibitor to block increased stomach motility caused by gastrin.
• Secretin and glucose-dependent insulinotropic peptide, also called
gastric inhibitory peptide (GIP).

19. MOVEMENTS OF
THE SMALL
INTESTINE

20. MIXING CONTRACTIONS
(SEGMENTATION CONTRACTIONS):
• The contraction of the intestine they divide
the intestine into spaced segments that have
the appearance of a chain of sausages.
• Chyme is propelled through the small intestine
by peristaltic waves.
• Peristaltic activity of the small intestine is
greatly increased after a meal.
• chyme into the duodenum, causing stretch of
the duodenal wall.

22. • Factors that enhance the intestinal motility are:
1. gastrin,
2. CCK,
3. insulin,
4. motilin, and
5. serotonin.
• Factors that inhibit the intestinal motility are:
1. secretin
2. glucagon

23. • Function of the peristaltic intestinal wave is:
1. Spread of chyme to the intestinal mucosa.
2. Progression of chyme toward the ileocecal valve.
• When reaching the chyme in the ileocecal valve they
blocked for several hours until the person eat
another meal then the gastroileal reflex begins
which intensifies the peristalsis in the ileum and
forces the remaining chyme through the ileocecal
valve into the cecum of the large intestine.

24. • Peristalsis in the small intestine is normally weak.
• Peristaltic rush is a “powerful and rapid peristalsis”
caused by intense irritation to the intestinal mucosa as a
result of infectious diarrhae.
• The ileocecal valve prevents backflow from the colon to
the small intestine.
• Ileocecal sphincter is a thickened circular muscle.
• Feedback control of the ileocecal sphincter:
• When the cecum is distended, contraction of the ileocecal
sphincter becomes intensified and ileal peristalsis is
inhibited – delay emptying. Ex:
1. Inflamed appendix.
2. Partial paralysis of the ileum.

25. MOVEMENTS
OF THE COLON

26. • The principal functions of the colon are:
(1) absorption of water and electrolytes from
the chyme to form solid feces.
(2) storage of fecal matter until it can be
expelled.
The proximal half of the colon – absorption.
The distal half of the colon – storage.
Movement of colon is by two process:
Mixing Movements—“Haustrations.”
Propulsive Movements—“Mass Movements.”

27. Mixing Movements—“Haustrations”:
• Same manner that segmentation movements occur in the
small intestine.
• This process done by means of contraction of circular
muscles of large intestine, but in some cases leads to
intestinal occlution.
• The circular and lungitudinal muscels “which is formed by
3 strips called tenea coli” contractes leading to bulge feces
outward into baglike sacs called haustrations.
• Each haustration reaches peak intensity in about 30
seconds and then disappears during the next 60 seconds.
• in the cecum and ascending colon they slowly propulse the
colonic content.
• 80 to 200 milliliters of feces are expelled each day.

29. Propulsive Movements—“Mass
Movements”:
• From the cecum to the sigmoid, mass movements can take over
the propulsive role.
• one to three times each day.
• A mass movement is a modified type of peristalsis
characterized:
1. a constrictive ring occurs in response to a distended or irritated
point in the colon, usually in the transverse colon.
2. propelling the fecal material in this segment en masse further
down the colon.
• A series of mass movements usually persists for 10 to 30
minutes.
• They then cease but return perhaps a half day later.
• When they have forced a mass of feces into the rectum, the
desire for defecation is felt.

31. Initiation of Mass Movements by
Gastrocolic and Duodenocolic Reflexes:
• These reflexes result from distention of the
stomach and duodenum.
• Irritation in the colon can also initiate intense
mass movements.
• A person with (ulcerative colitis) frequently
has mass movements that persist almost all
the time.

32. DEFECATION or EGECTION:
• The rectum is empty of feces because a weak
functional sphincter exists.
• A sharp angulation contributes additional resistance
to filling of the rectum.
• When a mass movement forces feces into the rectum,
the desire for defecation occurs immediately,
including reflex contraction of the rectum and
relaxation of the anal sphincters.
• Continual dribble of fecal matter through the anus is
prevented by tonic constriction of:
(1) an internal anal sphincter
(2) an external anal sphincter

33. • The external sphincter is
controlled by nerve fibers
in the pudendal nerve,
which is part of the
somatic nervous system
and therefore is under
voluntary, conscious, or at
least subconscious
control.
• subconsciously, the
external sphincter is
usually kept continuously
constricted unless
conscious signals inhibit
the constriction.

34. Defecation Reflexes:
• Is done by Intrinsic reflex mediated by the local enteric
nervous system in the rectal wall.
1. First feces enter the rectum.
2. Distention of the rectal wall initiates afferent signals
that spread through the myenteric plexus to initiate
peristaltic waves in the descending colon, sigmoid, and
rectum, forcing feces toward the anus.
3. The internal anal sphincter is relaxed by inhibitory
signals from the myenteric plexus.
4. If the external anal sphincter is also consciously,
voluntarily relaxed at the same time, defecation occurs.
• Parasympathetic fortified defecation reflex.

38. • Defecation signals entering the spinal cord initiate
other effects, such as taking a deep breath, closure
of the glottis, and contraction of the abdominal
wall muscles.
The peritoneointestinal reflex results from irritation of
the peritoneum; it strongly inhibits the excitatory enteric
nerves and thereby can cause intestinal paralysis, especially
in patients with peritonitis.
The renointestinal and vesicointestinal reflexes inhibit intestinal
activity as a result of kidney or bladder irritation.