Gastrointestinal I - #16
Dr. Gwirtz
2/19/03, 11AM
Scribe – Matthew Stine
Page of 7
Checked By Dr. Gwirtz!!
GI Motility: Part 3 – Colon, Diarrhea, Vomiting, Gas and Good Times
Note: This lecture began on Slide #60 in the GI Motility Slides.
I.
Colon
A. Anatomical Subdivisions of the Colon
1. Terminal Ileum empties into the Cecum through the
ileocecal valve.
2. Ascending Colon, Transverse Colon, Descending Colon,
Sigmoid Colon, rectum.
B. Function of the Ileocecal Valve
1. Prevents back-flow of fecal material from colon into small
intestine.
2. Normally remains mildly constricted. Distension of colon
causes contraction of ileocecal valve to delay emptying.
3. Slows emptying of ileal contents into cecum. Prolongs stay
of chyme in ileum, and therefore, facilitates absorption.
3. Relaxed by gastroileal reflex (myenteric/PNS reflex),
gastrin (increases small intestine motility).
4. Does not control the entry of material from the intestine to
the colon.
C. Functions of the Colon.
1. 750 - 1000 ml chyme enters colon daily
2. Absorption of water and electrolytes from the chyme. This
Occurs primarily in proximal half of colon.
3. Storage of fecal matter until it can by expelled. Occurs in
distal half. Approximately 100-150 ml of material defecated daily.
D. Movements of the Colon
1. Mixing Movements - Haustrations
a. Bulging out like bag-like sacs
b. Fecal matter moves slowly analward
c. Myogenic; myenteric plexus mediated
d. Sluggish (4-6 per min). Each contraction lasts 60
seconds. It takes 15 hours to move across transverse colon.
e. Longitudinal smooth muscle is not continuous. You see
bulging upon contraction.
f. Dig into fecal material to allow maximal absorption of
water and electrolytes.
g. Regulated by myenteric plexus in proximal colon
h. Regulated by PS nerves in distal colon
2. Propulsive “Mass” Movements
a. Peristaltic contractions.
Gastrointestinal I - #16
Dr. Gwirtz
2/19/03, 11AM
Scribe – Matthew Stine
Page of 7
b. Usually occur 1-3 times daily, especially 15 min after
eating breakfast.
c. Initiated by: gastrocolic, duodenocolic reflexes (as soon
as stomach fills, reflex stimulation of colon); intense PS
stimulation (caused by anger, hostility, fright); overdistension of
colon; irritation : enterotoxins (produced by bacteria), parasites,
food antigens (food allergies), bile, laxatives
d. Transmitted through parasympathetic (pelvic) nerves and
myenteric plexus.
e. Modified type of peristalsis.
f. Persists 10-20 min: if defecation does not occur, new set
of mass movements might not recur for another half day or day
g. Chemoreceptors & mechanoreceptors in cecum &
ascending colon feedback to regulate ileocecal tone
1. controls delivery of chyme into colon.
E. Emotions and Colonic Motility
1. Anger and resentment, hostility, “fight or flight” response
increase motility - diarrhea.
2. Depression, sadness, long term fear decreases motility –
constipation.
F. Defecation (Pooing) Reflexes – 2 reflexes in one. Receptors in the
rectum sense stretch
1. Mass movement
a. forces poo into rectum; rectal distension initiates desire
to defecate - reflex reaction is transient.
b. Reflex contraction of the rectum and relaxation of the
internal (involuntary) and external (voluntary) anal sphincters
2. Intrinsic myenteric defecation reflex
a. weak (myenteric) smooth muscle contraction
3. Parasympathetic defecation reflex
a. strong
4. Relaxation of external anal sphincter leads to pooage. If
contraction maintained, defecation reflex dies out after few minutes. It is a
conscious decision. If you choose not to poo, you will not.
5. Defecation reflexes initiate other effects
a. deep breath, valsalva maneuver
b. increases abdominal pressure to force colonic contents
down and help inhibit (relax) external anal sphincter
6. If inhibited, sensation subsides. Reflexes weaken with persistent
inhibition. If inhibit too often, constipation results. Frequency of pooing,
time of day when it is performed is matter of habit.
a. most individuals 5-7 times weekly, after breakfast
Gastrointestinal I - #16
Dr. Gwirtz
2/19/03, 11AM
Scribe – Matthew Stine
Page of 7
b. Some people only poo 2-3 times a week normally, so
when assessing whether a patient is constipated or not, you must
take an accurate history and take note of normal pooing habits.
II. Constipation
A. Definition: Slow movement of feces through the large intestine;
frequent malfunction of the colon.
1. Often associated with large quantities of hard, dry poo in the
descending colon, which accumulates because of the long time available
for the absorption of fluid. There is a lot of water absorption.
2. Can result in diverticulosis, hemorroids or other complications.
a. Diverticulosis is an inpocketing of the wall of the colon
caused by abnormally high intra-abdominal pressures.
These pockets can fill with feces and cause irritation,
infection or even cancer.
B. Symptoms:
1. Depression (decreases motility), restlessness, dull headache,
anorexia, nausea, bad breath, coated tongue, abdominal discomfort with
heaviness and swelling.
C. Causes:
1. Usually due to irregular bowel habits (inhibiting normal
defecation reflexes).
2. Overuse of laxatives. Long continuous use of laxatives weakens
the defecation reflex.
3. Anal lesions, pain. Pain leads to a decrease in motility in the
colon.
4. Diabetes mellitus (autonomic neuropathy). Destruction of
parasympathetic NS influence. Diabetes also destroys ganglion cells of
myenteric plexus.
5. Hypothyroidism – decreases motility
6. Pregnancy – progesterone decreases motility in the colon.
7. Fear, pain  sympathetic stim   BF   mucus production
&  motility. Norepinephrine from the SNS causes vasoconstriction,
reducing blood flow.
D. Hirschsprung's Disease (Megacolon)
1. Most frequent cause is absence of myenteric plexus in sigmoid
colon. There are damaged or absent ganglion cells.
2. As a result, neither defecation reflexes nor peristaltic motility
can occur through this area, and therefore, the end result is
constipation.
3. Constipation is so severe that bowel movements occur only once
every week or so, causing accumulation of large quantities of poo in
the bowel. One patient on record went over 1 year without his normal
time to think and reflect on the day’s activities.
Gastrointestinal I - #16
Dr. Gwirtz
2/19/03, 11AM
Scribe – Matthew Stine
Page of 7
a. This guy had the absolute pleasure of having the rocks of
poo in his colon chiseled out by a very lucky surgeon.
Good times indeed.
4. Management is difficult; and thankfully, this disorder is not
common.
a. Now this disease is caught in infancy and treated early
before any “hard” problems ensue.
E. Treatment of Constipation
1. Dietary (fiber 20-30 gm daily). Fiber increases motility because
we lack the necessary enzymes to digest it. Because of that, the fiber pulls
water into the colon, loosening the poo and making it easier to pass.
2. Behavioral counseling
3. Laxatives, stool softeners – on a short-term basis only.
4. Digital disimpaction. This does not involve computers, rather it
involves fingers; fingers of physicians questioning their choice of
specialty.
III. Diarrhea = Good Times
A. Rapid movement of fecal matter through the large intestine. Can be
serious and debilitating due to loss of fluid and electrolytes.
1. A patient can lose up to 12 L of fluid with especially wretched
diarrhea.
2. Bacterial (e.g. cholera) infection in the gut can also produce
greater secretions, increasing fluid output.
B. Causes of Diarrhea
1. Major cause: infection in GI tract (enteritis)
a. Enterotoxins, parasites, food antigens, intense PS
stimulation, overdistension of colon – increase colon motility.
2. Generalized increased motility
3. Increased rate of small intestinal secretion
a. Example: cholera toxin stimulates excessive secretion of
electrolytes and fluid from the crypts of Lieberkuhn in distal ileum
and colon.
i. There is a lot of water in the colon, which is
unable to handle very much water.
ii. There is also less time for water absorption.
4. Osmotic (malabsorptive)
a. fats, cholesterol, lactose, sorbital, laxatives, etc. (any
nutrient not absorbed in the small intestine. These nutrients will
pull water into the colon.
5. Secretory (deranged electrolyte transport).
a. cholera toxin, VIP tumor (causing massive release of fluid
into the small intestine), bile salt malabsorption (bowel irritant),
neoplasm, bacteria, etc.
6. Abnormal GI motility
Gastrointestinal I - #16
Dr. Gwirtz
2/19/03, 11AM
Scribe – Matthew Stine
Page of 7
a. peristaltic rush, psychogenic (anger, hostility).
7. Exudative (blood, mucus, pus)
a. viral, bacterial – can increase mucus secretions.
IV. Vomiting
A. Means by which upper GI tract rids itself of its contents when
excessively irritated, overdistended or overexcited.
B. Stimuli: distention, inflammation or irritation of duodenum; abnormal
sensory signals outside GI tract (heart (angina), kidneys, eyes, nose, psychic (bad
smells), pancreas, uterus, testicular pain, semicircular canals)
C. Mechanism:
1. Afferent signals sent via vagus and sympathetic nerves to
vomiting center in medulla for processing.
2. Efferent signals mediating vomiting sent to upper GI tract,
diaphragm, abdominal muscles.
3. Vomiting center coordinates input to produce a preprogrammed
emetic response.
a. CTZ (chemoreceptor trigger zone), vestibular system,
cerebral cortex, thalamus, hypothalamus, peripheral sites
4. Vomiting can also be caused by nervous signals arising in areas
of the brain outside of the vomiting center, such as the chemoreceptor
trigger zone (CTZ), which is next to the vomiting center.
a. CTZ (receptors) stimulated by: drugs (apomorphine,
morphine, digitalis, ipecac), rapid changes in direction of
motion (seasickness, car, swing), GI irritation (radiation,
chemotherapeutic agents, toxins).
D. Chemoreceptor Trigger Zone
1. Lies on the floor of 4th ventricle - outside the blood brain barrier
a. Senses blood borne chemicals that induce emesis
2. Sends afferents to vomiting center when stimulated by emetics
or motion sickness
a. via H1 ( Histamine) & cholinergic receptors in vestibular
system. Antihistamines can be a treatment for nausea.
3. Vomiting center then initiates emesis (vomiting)
E. Vomiting Act – Nausea – Initial event.
1. Conscious recognition of subconscious excitation in an area of
the medulla closely associated with or part of the vomiting center
2. Prodrome of vomiting. Can be caused by irritative impulses
coming from the GI tract, impulses originating in lower brain associated
with motion sickness, or from cerebral cortex to initiate vomiting
F. Vomiting Act - Retching
1. Antiperistalsis (reverse peristalsis, towards oral end) occurs in
early stages; may begin as far down as the ileum. The start point for this
depends on the location of the irritation.
2. Stimulus - overdistension, especially in duodenum
Gastrointestinal I - #16
Dr. Gwirtz
2/19/03, 11AM
Scribe – Matthew Stine
Page of 7
3. A single antiperistaltic wave travels backward up the intestine 23 cm/sec; pushes contents up to duodenum and stomach in 3-5 min. - this
wave begins "retching" process
4. “Retching" process = contraction of diaphragm agains a closed
glottis, also known as a dry heave.
a. causes strong negative intra-thoracic pressure, which
opens the esophagus.
b. LES then opens by relaxation
G. Vomiting Act
1. During vomiting, strong contractions in duodenum and stomach,
and relaxation of LES, move contents into esophagus.
2. Vomiting then involves abdominal muscle contraction to
increase intragastric pressure and to expel vomitus out of the mouth.
3. Deep inspiration
4. Open upper esophageal sphincter
5. Close the glottis
6. Close the posterior nares (hope so!, even though this might be
endlessly funny to see happen to someone else)
7. Diaphragm and abdominal muscles contract
8. Lower esophageal sphincter relaxes
9. Expulsion of gastric contents upward through the esophagus
H. Consequences of prolonged vomiting
1. There are physical, metabolic and psychological consequences
for consistent, prolonged vomiting. Just be aware of the physical, and
psychological signs listed in the notes. There will not be any questions on the
metabolic pathways covered in the flow chart in the slides. That will be covered
in renal. Know though, that there are electrolyte imbalances (hypokalemia,
hyponatremia, and hypovolemia).
2. Causes severe problems in fluid and electrolyte balance
a. loss of H+, K+ causing metabolic alkalosis and
hypokalemia. There is also loss of Na+, causing hyponatremia.
3. Anti-emetics include:
a. antihistamines (act on H1 receptors in vomiting center
and cortex and in vestibular system)
b. anticholinergics – act cerebrally on vomiting center and
CTZ.
c. phenthiazines
V. Sources of Gases, Flatulence, Bad Smells (Flatus)
A. Swallowed air – usually burped on out of stomach through mouth,
more so if you are male.
B. Gases released due to bacterial action on food (stachyose, sorbital,
lactulose), especially in the colon. Bacteria act on undigested nutrients, which
releases gases.
Gastrointestinal I - #16
Dr. Gwirtz
2/19/03, 11AM
Scribe – Matthew Stine
Page of 7
C. Diffusion of gases from blood into GI tract: oxygen, nitrogen, carbon
dioxide. Gases can also move from the GI into the blood.
D. Emotions – such as depression (inhibit GI motility and allow gas to
accumulate).
E. Bowel obstruction – torsion (twisting), tumors, hernias allow gas to
accumulate.
F. Post-operative decrease in GI motility allows gas to accumulate
G. Inflammatory disease (ulcer, colitis)
VI. Composition of Gases in the GI Tract
A. Stomach: 50 cc.
1. contains nitrogen, oxygen, carbon dioxide from swallowed air,
foods (carbonated beverages) and most of it is belched out.
B. Small intestine:
1. Not much gas because it passes through very rapidly to the
colon.
2. Contains contains nitrogen, carbon dioxide, hydrogen, methane no oxygen
3. As gas passes through small intestine, it produces borborygmi
(abdominal sounds) a rate of 8-12 per min.
a. You can auscultate to hear these sounds, and this is often
done to assess normal intestinal motility.
C. Large intestine – mostly from bacteria working on undigested food.
1. Contains: nitrogen, carbon dioxide, methane, hydrogen,
hydrogen sulphide - no oxygen
2. Explosive!
a. Helps guys get the ladies.
3. Expelled periodically
a. 14 times or so daily.
D. Food Sources
1. Beans, cabbage, broccoli, brussel sprouts, cucumbers, radishes,
raisins, onions, cauliflower, corn, vinegar
2. Milk products in lactase deficiency
3. Fermentation of foods by bacteria
E. Amount of Gases Expelled by GI Tract – Flatus
1. Amount: 7-10 liters of gas enter large intestine daily
2. Expel 600 ml daily with a normal diet (14 X daily)
3. Remainder of gas is absorbed through intestinal mucosa
4. Normally, we do not recognize that we are even doing it. This is
known as silent, but deadly.
5. Many other people in your surrounding vicinity recognize that
you are doing it, so STOP!!