GI 09 Flashcards
Large intestine anatomy
cecum, colon (ascending, transverse, descending), rectum, anus
Purpose of large intestine
digestion and absorption of meal that was not accomplished in small intestine, absorption of wter, storage of waste products for elimination, and commensal bacteria
What sphincter separates small intestine from large intestine
ileocecal sphincter
when does ileocecal sphincter open
Short range peristalsis in ileum opens sphincter allowing squirting of chyme into cecum
does electrical activity from ileum propagate into large intestine
nope
regulation of colonic function is primarily controlled by what?
neural pathways
local reflexes of colonic control
Activated by passage of a bolus of fecal material - stimulates short bursts of cl and fluid secretion , involves serotonin and Ach
Long reflex arcs involved in colonic function
Gastrocolic reflx - distention of stomach increases colonic motility and mass movement of fecal material (involves serotonin and Ach)
Orthocolic reflex - activated on rising from bed and promotes morning urge of defecation in some people
What is secreted in response to lipid in lumen of colon
peptide YY (PYY) is secreted from entoerodocrine cells in terminal ileum and colon
what is peptide yy (PYY)
“ileal break”
decreases gastric emptying and overall intestinal motility, reduces chloride and thus fluid secretion by intestinal cells, and by reducing fluidity and inhibiting motility it reduces propulsion of chyme, allowing for greater digestion and absorption time in small intestine
Two forms of colonic motility
short duration
long duration
short duration colonic motility
Contractions ~8s that originate in circular muscles at intervals - divides colon into segments ./ haustra –> these are segmental contractions that mix and circulate contents and optimize absorption of water and salts
long duration contractions of colon
20-60s, produced by longitudinal muscles (taeniae coli) - propel bolus (less vigorous than small intestine)
contents are moved back and forward between haustr which maximizes time of contact with epithelium)
HIGH AMPLITUDE PROPAGATING CONTRACTIONS OCCUR IN HEALTHY INDIVIDUALS 10X/DAY FROM CECUM TO RECTUM TO CLEAR THE COLON
this was in red so she wants us to know it
What controls descending and sigmoid colons, rectum, and anal canal (neurally speaking)
pelvic nerves from sacral spine
SNS activity on colon does what
decreases motility
Major role of colonic epithelium is to absorb nutrients, or water and electrolytes?
water and electrolytes
What major nutrient DOES the colon absorb
Short chain fatty acids salvaged from non-absorbed carbohydrates by colonic bacteria
How are SCFA’s absorbed in the colon
absorbed in luminal side in sodium dependent manner using symporters (sodium monocarboxylate transporters) driven by NKA gradient
How is sodium absorbed in distal colon
ENaC
What opens ENaC
Neurotransmitters or hormones - driven by NKA gradient
What other way can water and chloride flow in colon
tight junctions - maintinas electrical neutrality and prevents water loss in stool
What happens if you have reduced ENaC expression
you get bowel inflammation and diarrhea
What are the nutrients bacteria can take up and use to make their own shit that we then absorb or excrete
Urea, bilirubin, primary bile acids, cnjugated bile acids, fiber
Internal and external sphincters - what muscles are they made of
Inner - thick circular muscle
external - striated muscle wrapping around the canal, innervated by puendal nerves
Filling of rectum causes what to internal anal sphincter
Generation of VIP, NO and relaxation of internal sphincter
Hirschsprung’s disease
Segment of colon is permanently contracted, causing an obstruction - this can lead to surgical excision of the bad area - usually found in infants
