Download large intestine

LARGE ITESTINE
Dr. Mujeeb Ahmed Shaikh
Dr. Mohammed Sharique Ahmed
Qaudri
LARGE INTESTINE
• Large Intestine consist of
– Cecum,
– Appendix,
– Colon
• ascending colon,
• transverse colon and
• descending colon,
– end part of descending colon forms S shape sigmoid colon
– and straight part rectum.
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Primarily a drying and storage organ
• Each day it receives about 500ml of chyme.
• The content received consist of
– Indigestible food residues (cellulose)
– Unabsorbed biliary components
– Remaining fluid
• Extracts more H2O and salt from the contents and
the remains to be eliminated is known as feces
• Primary function of large intestine is to store
feces.
LARGE INTESTINE
• We will discuss
1. Motility
2. Secretion
3. Digestion
4. Absorption
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MOTILITY IN LARGE INTESTINE
• Haustral Contraction or Segmentation
• Mass movement [strong peristaltic waves]
Haustral Contraction [Segmentation
Contraction]
• Initiated by the autonomous rhythmicity of
colonic smooth muscle cells.
• They help to mix the contents of colon and
expose contents to mucosa to facilitate
absorption.
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Haustral Contraction [Segmentation
Contraction]
• They occur less frequently may be after every
30mins [they are like segmentation contraction in
small intestine but in small intestine they occur
10-12/min].
• Haustral contraction are largely controlled by
locally mediated reflexes involving the intrinsic
plexus.
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Mass movement [strong peristaltic
waves]
• They move the material from one portion of
intestine to another.
• They occur 3-4 times per day, generally after
meals and increase in motility moves the feces
forward in few seconds.
• When material reaches the rectum, rectal
distention initiates the defecation reflex.
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Mass movement [strong peristaltic
waves]
• Gastro-colic Reflex – when food enters the
stomach, mass movements are triggered in
the colon.
• It is mediated from stomach to the colon by
gastrin and extrinsic autonomic nerves.
• It pushes the colonic contents into rectum
triggering the defecation reflex.
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SECRETION
• Large intestine secretes alkaline NaHCO3,
mucus solution.
• Its function is to protect large intestine from
mechanical and chemical injury.
• Mucus provides lubrication to facilitate the
passage of feces.
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DIGESTION
• There are no digestive enzymes secreted,
therefore, no digestion takes place in large
intestine.
• However, the colonic bacteria do digest some
of the cellulose for their use.
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The large intestine absorbs salt and water,
converting the luminal contents into feces.
• The colon normally absorbs salt and H2O.
• Sodium is actively absorbed, Cl follows
passively down the electrical gradient, and
H2O follows osmotically.
• The colon absorbs token amounts of other
electrolytes as well as vitamin K synthesized
by colonic bacteria.
FECES
• About 500ml of material entering the colon
per day from the small intestine, colon
absorbs about 350ml, leaving 150g of feces to
be eliminated per day.
• Feces contains 100g of water and 50g of solid
[undigested cellulose, bilirubin
[stercobilinogen], bacteria, unabsorbed food
residue.
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The colon contains myriad beneficial
bacteria
• 500 to 1000 different species of bacteria
typically live in the colon.
• Functions
– Enhance intestinal immunity
– promote colonic motility
– help maintain colonic mucosal integrity and
– make nutritional contributions.
• Promote absorption of calcium, magnesium, and zinc.
DEFECATION REFLEX
• Feces are eliminated by defecation reflex.
 How this reflex works?
• When mass movements of colon move the feces
into the rectum. Distention of rectum initiates the
reflex.
• Stretch receptors in the wall of rectum send
impulses to the spinal cord ( S2,S3,S4),
parasympathetic nerves causes contraction of
smooth muscle of rectum and sigmoid colon and
relaxation of internal sphincter.
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DEFECATION REFLEX
• If external anal sphincter [which is skeletal muscle
is also relaxed defecation occurs].
• External anal sphincter is under voluntary control,
therefore, can prevent defecation despite
defecation reflex.
• When defecation occurs, it is assisted by
voluntary straining movements that involve
contraction of abdominal muscles and forceful
expiration against closed glottis which increases
intra-abdominal pressure.
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CONSTIPATION
• When more water is absorbed from the feces,
they become hard and dry.
• Normally frequency of passing stool vary. It
maybe once a day, or after every meal or once
every 2 or 3 days or once a week.
CAUSES OF CONSTIPATION
1. Ignoring the urge to defecate
2. Decreased colonic motility due to low bulk diet,
aging, emotion, anxiety.
3. Colonic spasm, tumor in colon.
4. Injury to nerve pathway.
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INTESTINAL GAS OR FLATUS
• It is derived from two sources
1. Swallowed air [up to 500ml of air may be
swallowed during a meal].
2. Gas produced by bacterial fermentation in
the colon. Most gas in the colon is due to
result of bacterial activity, but the quantity
and the nature of gas produced depend on
the type of food eaten and colonic bacteria.
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INTESTINAL GAS OR FLATUS
• Food such as beans, contain carbohydrate that
human can not digest but can be attacked by gas
producing bacteria.
• Gases produced are Hydrogen, Hydrogen
Sulphide, Nitrogen, Carbon dioxide and Methane.
• Amount of gas per day passed is about 200ml.
• The smell is largely due to sulphides.
• Gas passing through the luminal contents give
rise to gurgling sounds known as BORBORGYMI.
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References
• Human physiology by Lauralee Sherwood,
seventh edition
• Text book physiology by Guyton &Hall,11th
edition
• Text book of physiology by Linda .s
contanzo,third edition