Lecture 10 : the Colonic Phase Flashcards
What is the main function of the large intestine?
- absorb a small amount of water
(last area that can absorb water) - store the waste product of meal
Major role of colonic epithelium is to absorb/secrete electrolytes and water rather than nutrients.
What separates the ileum from the cecum and prevents reflux from the cecum into the ileum?
Ileocecal valve guarding the small intestine to prevent contents from being send back
What is the main regulator of colonic function?
NEURAL
What activates the local Reflexes?
Via which nervous system?
What do these reflexes stimulate?
- Passage of bolus of fecal material (stretch)
- Enteric NS
- short bursts of Cl- and 5-HT and Ach
What are the 2 LONG Reflex Arcs?
What activates them?
- Gastrocolic Reflex
- activated by DISTENSION of stomach
- stimulated by vagus (Ach and 5-HT)
- why we poop after eating*
2. Orthocolic Reflex: - rising from bed
- promotes morning poop
What cells secrete Peptide YY?
What is the signal to secrete peptide YY?
What is its function?
- Entereendocrine cells
- LIPID (should have been absorbed way before the colon)
- Decreases gastric emptying and GASTRIC MOTILITY (slow things down)
- also reduces fluid secretion
- reduces propulsion of chyme to give more time for DIGESTION & absorption
What are the 3 layers of non-overlapping longitudinal muscles in the Colon Called?
What are the colonic segments called?
Taeniae coli
Haustra
- mix and circulate contents via SEGMENTAL contractions
(no propulsive movement unless there is a stimulus to move the fecal material)
Propulsion of bolus is MORE vigorous in the colon as opposed to the small intestine.
True or False
FALSE
- propulsion is less vigorous in the colon
- Contents are moved back and forward between haustra – maximizes their contact time with epithelium.
How do the following affect Colon motility
- Parasympathetic Innervation
- What does Vagus control?
- What do Pelvic nerves control? - Sympathetic
- Parasympathetic Innervation
= enhance motility
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.
- Sympathetic
= reduce motility
What histological feature is present in the small intestine that is NOT present in the colon?
What glands are present in both?
NO villi in the colon!
- no large scale absorption in the colon since most absorption has occurred in the small intestine
Glands of Lieberkuhn (also in the small intestine)
-tubular glands enriched with GOBLET CELLS
What is the only unique nutrient absorbed by the Colon?
How are they absorbed on the luminal side of the colon?
What drives this absorption?
- Short- Chain Fatty Acids (SCFA) - butyrate
- Na-Dependent!
- via Sodium Monocarboxylate Transporters (SMCT)
- symporters - gradient established by Na-K ATPase
What produces Short Chain fatty acids?
Colonic Bacteria
(not digestion!)
-in individuals who take antibiotics long term the BUTYRATE/ short chain fatty acids are destroyed
What are 3 structures/transporters unique to the COLON?
- Short-chain fatty acids
- Sodium Monocarboxylate Transporters (SMCTs)
- ENaC
- epithelial sodium channel
ONLY IN THE COLON!!!
SGLT1 and SMCT’s both depend on sodium to transport their individual nutrients
How is Na absorbed in the DISTAL colon?
last mechanism to prevent the loss of water
ENaC
- channel is opened by NT’s or hormones
- transported into blood via Na-K ATPase
What does ENac prevent?
How is this changed in patients with Bowel inflammation?
Loss of Water in the stool
- reduced ENaC in patients with bowel inflammation
= diarrheal symptoms
What are the negatives of broad-spectrum antibiotics?
Disrupts colonic microflora
(symbiosis between bacteria and cells of colon)
- may cause overgrowth of pathogenic bacteria in GI
= intestinal and systemic infections!
How can severe intestinal infections caused by bacteria be cured?
What causes this serious infection?
What bacteria does this predispose people to?
- Fecal Transplant
(also for infants with kwashiorkor)
- Antibiotics
- C. Difficile
Fecal transplant:
It involves diluting stool with a liquid, like salt water - pumping it into the intestinal tract via an enema, a colonoscope or a tube run through the nose into the stomach or small intestine.
Where does the colon terminate?
What type of muscle does the colon lack?
What are two important sphincters?
Which is voluntary?
- Rectosigmoid junction
- Circular
- Internal Anal (thick circular muscle)
External Anal
- striated muscle wrapped around canal
- innervated by pudendal nerves, thus VOLUNTARY
Where is most striated muscle found?
Pharynx, upper 1/3 of esophagus, and rectum
What produces mass movement of feces?
What relaxes the internal anal sphincter?
What is tonically contracted because it is under voluntary control?
High amplitude propagating contractions
- rectum fills with fecal material
- Filling of rectum
- releases VIP and NO - External Anal Sphincter
What is the cause of colon cancer, the 2nd most prevalent cancer in males?
What is the initial sign of cancer?
- Rapid turnover of the colonic epithelium and exposure to bacterially synthesized or environmental toxins
- Polyps are the initial sign of cancer
- Colon cancer mortality can be reduced substantially by early detection and removal of polyps.
What is the major issue of Hischprung’s disease in regards to the colon?
What alleviates the symptoms?
- segment of the colon is permanently contracted
–causing obstruction (usually diagnosed in infants).
- ENTERIC NVS does NOT develop properly
- Surgical excision of affected segment alleviates the symptoms
