lec 9 Flashcards
The small intestine functions
the digestion and absorption of nutrients
The small intestine
- mixes nutrients with digestive enzymes,
- exposes the digested nutrients to the absorptive mucosa,
- propels any non-absorbed material to the large intestine
Segmentation contractions
A section of small intestine contracts, sending the intestinal contents (chyme) in both orad and caudad directions.
Segmentation contractions
section of small intestine contract then relaxes and the contents move back into the segment
segmentation contractions produces
back-and-forth movement
This back-and-forth movement produced by segmentation contractions causes
mixes nutrients with digestive enzymes, without any net forward movement of the chyme.
exposes the digested nutrients to the absorptive mucosa
The maximum frequency of the segmentation contractions in the small intestine is determined by the frequency o
electrical slow waves in the intestinal wall
maximum frequency of the segmentation contractions =
12 per minute in the duodenum and proximal jejunum)
maximum frequency occurs
only under extreme conditions of stimulation
the maximum frequency of terminal ileum
8-9 contractions per minute
atropine effect on The segmentation contractions
The segmentation contractions become exceedingly weak when the excitatory activity of the enteric nervous system is blocked by the drug atropine
Peristaltic contractions function
1.cause progression of chyme toward the ileocecal valve, Cause propel the chyme through the small intestine toward the large intestine
to spread out the chyme along the intestinal mucosa
peristalsis occurs
after digestion and absorption have taken place.
peristaltic waves are
highly coordinated Contraction behind the bolus and, simultaneously, relaxation in front of the bolus cause the chyme to be propelled caudally
The peristaltic reflex is
coordinated by the enteric nervous system
The peristaltic waves can occur velocity
of 0.5 to 2.0 cm/sec (averages only 1 cm/min)
The peristaltic waves faster in
the proximal intestine
The peristaltic waves slower in
the terminal intestine
The peristaltic waves are normally weak and usually die out after traveling only
3 to 5 centimeters, rarely travel farther than 10 centimeters
The peristaltic waves forward movement of the chyme is very slow so it takes
3 to 5 hours for passage of chyme from the pylorus to the ileocecal valve
Activity of the small intestine is greatly increased
- after a meal
- gastro-enteric reflex
- several hormonal factors
Activity of the small intestine is greatly increased after a meal is caused by
the beginning entry of chyme into the
duodenum, causing stretch of the duodenal wall.
gastro-enteric reflex is initiated by
distention of the stomach and conducted principally through the myenteric plexus from the stomach down along the wall of the small intestine
enhance intestinal motility by
gastrin, CCK, insulin, motilin, and serotonin
inhibit small intestinal motility by
secretin and glucagon
peristalsis, is predominates in
the esophagus, and the large intestine
segmentation contractions is predominates in
the large intestine and small intestine
Peristaltic rush
powerful and rapid peristalsis due to infectious diarrhea
peristalsis in the small intestine
normally weak,
Peristaltic rush is initiated
- by nervous reflexes that involve the autonomic nervous system and brain stem
- myenteric plexus reflexes
Weak anti-peristalsis is sometime seen
in the colon
Gut law
waves pass regularly in an oral-caudal
direction
The powerful peristaltic contractions (rash)
1.travel long distances in the small intestine within minutes
2.sweepingتكنس the contents of the intestine into the colon and
thereby relieving the small intestine of 1.irritative chyme and 2.excessive distention
Movements caused by the muscularis mucosae and muscle fibers of the Villi
1.cause short folds to appear in the intestinal mucosa> ↑ the surface area→ ↑ absorption
2.individual fibers from this muscle extend into the intestinal villi and cause them to
contract intermittently
ggg
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