Large Intestine

Question 1

Voluntary control of defecation is possible because…

Answer 1

the parasympathetic system at that level is controlled by the pelvic branches instead of the vagus

Question 2

the ileocecal sphincter relaxes due to…

Answer 2

mechanoreceptors that sense the stretch in the ileum; they also close the sphincter behind it

Question 3

four types of motility in the large intestine

Answer 3

mixing/segmentation; mass movement; reservoir; defecation

Question 4

transit time through the large intestine

Answer 4

varies considerably

Question 5

rectosphincteric reflex

Answer 5

pressure on the inside of the internal anal sphincter causes relaxation of the sphincter muscles and reflexive relaxation of the external anal sphincter

Question 6

commensal bacteria in the colon perform what function?

Answer 6

breakdown of some indigestible products of the small intestine which can then be digested

Question 7

hirschsprung’s disease; rate; pathophysiology

Answer 7

1:5000 births; the colon is devoid of enteric neurons which causes a backup of chyme behind that region; this results in megacolon which is normally treated surgically in infancy

Question 8

ileogastric reflex

Answer 8

distension in the ileum causes lack on contraction in the stomach

Question 9

gastroileal reflex

Answer 9

distension in the stomach causes movement in the ileum

Question 10

colonocolonic reflex

Answer 10

distension in the distal colon prevents motility in the proximal colon

Question 11

gastrocolic reflex

Answer 11

distension in the stomach produces motility in the colon and promotes defecation

Question 12

emesis is controlled by.. and receives inputs from

Answer 12

the emesis center in the medulla; chemoreceptors in the GI tract and mechano receptors in the throat

Question 13

chemoreceptor trigger zone is in the ….

Answer 13

fourth ventricle and triggers emesis

Question 14

retching is characterized by

Answer 14

opening of the LES to allow contents into the esophagus but having the UES stay closed

Question 15

water secretion in the intestine is coordinated by…

Answer 15

crypt cells via the CFTR channels

Question 16

water secretion is regulated by

Answer 16

secretagogues:
neural: ACh, VIP and serotonin
para/endocrine: gastrin, CCK, NO

Question 17

water migration mechanism

Answer 17

Na/K/2Cl transporter brings in Cl
Cl leaves via CFTR
Na and H2O follow paracellularly

Question 18

water secretion increases with…

Answer 18

muscle contraction; blocked by Immodium which blocks enteric neurons

Question 19

sodium absorption locations along the GI tract

Answer 19

Na/H duodenum
Na/solute - small intestine
Parallel (Na/H + HCO3/Cl) - ileum and colon (little bit in rectum)
ENaC - colon

Question 20

Chloride (secretion absorption GI tract)

Answer 20

Passively everywhere by potential difference
anion exchanger ileum and below
Parallel with sodium ileum and colon (little bit in rectum)

Question 21

Potassium (secretion/absorption in GI tract)

Answer 21

passive paracellular pathways in the small intestine
active secretion in the colon K leak channel
active absorption in the rectum K/H pump
passive secretion in the colon

Question 22

water moves in the GI tract via

Answer 22

paracellular pathways (instead of aquaporins)

Question 23

in tight tight junctions, the solution produced is…

Answer 23

hypertonic

Question 24

things that cannot be absorbed in the lumen have what effect on bowel movements?

Answer 24

increased osmotic pressure leads to more frequent bowel movement - osmotic diarrhea; common with lactose intolerance

Question 25

how much bacteria live in the GI tract?

Answer 25

10^14 >1000 species

Question 26

where do most bacteria live?

Answer 26

colon, decreasing to stomach, big increase in mouth

Question 27

GALT/MALT

Answer 27

Peyer’s Patches in the ileum contain a large amount of lymphoid tissue
intra-epithelial lymphocytes
lamina propria lymphocytes
M cells - ingest bacteria and hand them off to dendritic cells that pass them to macrophages and T cells for consumption and IgA production
Dendritic cells can also pass things off to intra-epithelial lymphocytes
Paneth cells- defensin