GI IX Flashcards
What 4 parts make up the large intestine?
Large Intestine is compose of Cecum Colon (ascending, transverse and descending) Rectum Anus
What is the role of the large intestine?
(Describe a unique factor of the large intestine).
Digestion and absorption of meal that was not done in the small intestine (small contribution)
Absorption of water
Store the waste products of meal for elimination
Contains a unique biological ecosystem - of commensal bacteria.
Describe the colon outer layer.
How many layers does the colon consist of? How does this compare to other segments of the intestine?
Similar to other segments of the intestine, the colon consists of 4 layers except that outer longitudinal layer of muscularis consists of three distinct bundles of muscle fibers called tenia colic (ribbons of the colon). These bands cause the colon wall to form a series of sacs called “Haustra”.
Describe difference between tenia colic and haustra.
Slide 3
outer longitudinal layer of muscularis consists of three distinct bundles of muscle fibers called tenia colic (ribbons of the colon). These bands cause the colon wall to form a series of sacs called “Haustra”.
Describe the emptying of the ileum.
Ileocecal sphincter (what does it separate?)
What opens the sphincter? What happens next?
How does electricity affect ileocecal valve?
Ileocecal sphincter is normally closed and separates the ileum from the cecum.
Short range peristalsis in ileum opens this sphincter allowing squirting of chyme into cecum.
The electrical activity of the small intestine does NOT propagate through the ileocecal valve.
After the contents enter the cecum and proximal colon- ileocecal sphincter contracts – prevents reflux into the ileum.
Describe the regulation of the colonic function.
Describe local reflexes.
Describe long reflex arcs.
Regulated primarily though not exclusively by neural pathways.
Local reflexes:
activated by the passage of a bolus of fecal material – stimulates short bursts of Cl- and fluid secretion – involves 5-hydroxytryptamine (5-HT) and Ach.
Long reflex arcs:
Gastrocolic reflex: Distension of the stomach – increases colonic motility and mass movement of fecal material – involves 5-HT, Ach. stimulated by stretch receptors. enteric NS secretions (Cl and fluid secretions) usually mediated by 5-HT and Ach. these cells secreting 5-HT are in the colon. (enterochromaffin cells) don’t see a lot of endocrine type of cells in colon (in small intestine have S, D cells etc..have way more in small intestine.)
Orthocolic reflex: activated on rising from bed – promotes morning urge of defecation in some people.
Where are enteroendocrine cells located? What do they secrete? When/What stimulates this secretion?
Describe the effect on gastric emptying, intestinal motility, Cl- and fluid secretion.
Enteroendocrine cells (terminal ileum, colon) – secrete Peptide YY(“Ileal brake”) – in response to lipid in the lumen.
It decreases gastric emptying and overall intestinal motility.
It also reduces Cl- and thus fluid secretion by intestinal cells.
What reduces propulsion of the chyme? Why is this necessary?
(Enteroendocrine cells (terminal ileum, colon) – secrete Peptide YY(“Ileal brake”) – in response to lipid in the lumen.
- It decreases gastric emptying and overall intestinal motility.
- It also reduces Cl- and thus fluid secretion by intestinal cells.)
By reducing fluidity of intestinal contents and inhibiting intestinal motility –peptide YY reduces propulsion of chyme.
This allows more time for digestion and absorption in the small intestine
Describe the two distinct forms of colonic motility.
Two distinct forms of colonic motility:
- Short duration; and
- Long duration
Where do short duration contractions originate? How does it affect the colon?
What type of contractions? Describe effect.
Short duration contractions (8 sec) originate in circular muscles at intervals – divides the colon into segments or haustra.
These are segmental contractions – mix and circulate contents.
Optimizing the absorption of water and salts.
What are taeniae coli?
What do they produce?
The colon has three non-overlapping bands of longitudinal muscles – taeniae coli.
They produce long duration contractions (20 – 60 sec).
How does propulsion of bolus in large intestine compare to small intestine?
How often do high-amplitude propagating contractions occur in healthy individuals? What is the purpose?
Propulsion of bolus is less vigorous than small intestine.
Contents are moved back and forward between haustra – maximizes their contact time with epithelium.
High-amplitude propagating contractions – occur in healthy individuals 10 times/day from cecum to rectum- clears the colon.
Describe parasympathetic innervation of colon.
Effect? What specific types of nerves (2) and where do they originate?
Parasympathetic Innervation enhances motility (expulsive contractions and haustrations).
Vagus (via intramural plexi) - controls haustrations in the cecum, ascending and transverse colons;
Pelvic nerves from sacral spine to intramural plexi – controls descending and sigmoid colons, rectum, and anal canal.
Describe sympathetic innervation of colon.
Describe the plexuses. From where do each extend?
Superior Mesenteric Plexus (to intramural plexi in Cecum, ascending and transverse colons);
Inferior Mesenteric Plexus and Superior Hypogastric Plexus (to intramural plexi of descending and sigmoid colons);
Inferior Hypogastric Plexus (to intramural plexi of descending and sigmoid colons;
What is the major role of the colonic epithelium?
What is an exception?
Major role of colonic epithelium is to absorb/secrete electrolytes and water rather than nutrients.
However, they absorb short-chain fatty acids -SCFA (e.g. butyrate) – salvaged from non-absorbed carbohydrates by colonic bacteria.
now SCFA (not seen in small intestine bc we don’t prod. those by ourselves. SCFA are prod. by colonic bacteria…they are “our friends” the bacterial can metabolize undigested food or carbohydrates/fibers. can prod. the short chain fatty acids.
butyrate..colonic epithelial cells, need butyrate for survival. need these butyrate for energy supply. need bacterial to supply us this butyrate. when take long term antibiotics can affect/destroy colonic mucosa and no supply of butyrate and colonic epithelium is affected. this is how we sort of have symbiotic relationship w the bacteria.
