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GI Week 4 > Water and Electrolyte Movements and Intestinal Motility > Flashcards

Water and Electrolyte Movements and Intestinal Motility Flashcards

1
Q

Define anismus

A

anal sphincter dyssynergia (or muscle incoordination)

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2
Q

What is a purgative?

A

a substance that promotes bowel loosening and movement; cathartic; laxative

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3
Q

Define tenesmus

A

feeling that you need to pass stool even when bowels are empty

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4
Q

What are the two main pumps acting in the transport process for the GI tract?

A
  1. the Na/K ATPase of course

2. the H/K ATPase

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5
Q

What are the two main channels involved in transmembrane ion transport in the GI tract?

A

CFTR and a K channel

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6
Q

What’s the difference between and exchanger and a cotransporter?

A

exchangers swap substances in opposite directions (antiporter)

cotransporters move substrances in the same direction (symporter)

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7
Q

What are some examples of exchanger in the GI tract?

A

the NHE Na/H exchanger

Cl/HCO3-

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8
Q

What are some examples of the cotransporters?

A

2Na/Glucose cotransporter
Bile salts with Na
Amino acids with Na
PepT1 with H/peptides

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9
Q

About how much fluid enters the gut in a day?

A

9 liters

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10
Q

How much of that fluid is reabsorbed?

A

8.9 liters - in the small and large intestines

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11
Q

What proportion of water presented will the large intestine reabsorb?

A

90%

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12
Q

WHat are the two routes for water movement across the gut epithelium?

A

transcellular or paracellular

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13
Q

In general, what molecules will regulate tight junction permeability in the gut?

A

cytokines
bacterial toxins
hormones that modify claudins

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14
Q

In general terms, what drives water movement in the gut?

A

osmotic gradients driven by electrogenic or electroneutral ion transport processes

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15
Q

Both fluid absorption and excretion can occur simultaneously in the small intestine. Which cells do which?

A

cells at the tis of villi absorb the fluid

cells down in the crypts secrete fluid driven by chloride ion secretion

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16
Q

Is the Na/Cl absorption that mediates fluid uptake electrogenic or electroneural

A

electroneutral

Na+ = Cl-

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17
Q

What are the two main antiporters that are required for NaCl absorption?

A

It’s the coupled activity of the Sodium/H exchanger (NHE) and the Cl/bicarb exchanger in the epical membrane

(along with the NaK ATPase and the KCCl transporter on the basolateral side)

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18
Q

Is the uptake of Na and glucose via the SGLT1 electroneutral or electrogenic?

A

electrogenic

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19
Q

If it’s electrogenic, how is it ultimately balanced?

A

Cl (and water) will flow passively via the tight junctions to balance the charge

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20
Q

Why do oral rehydration salts contain NaCl and glucose?

A

help to promote water uptake

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21
Q

What drives fluid EXCRETION in the crypts of lieberkuhn?

A

chloride secretion

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22
Q

How does the chloride that will be secreted enter the enterocyte?

A

it’s actively taken up by the Na/K/2Cl symporter (NKCC1) at the basolateral membrane

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23
Q

How does the Cl in the enterocyte exit on the luminal side?

A

CFTR

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24
Q

AFter the Cl- leaves, what balances the charge?

A

potassium (K+) will exit on the basilar side via the Ca++ activated K channel

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25
Q

Where in the small intestine is calcium actively absorbed? How?

A

in the duodenum

thorugh a Ca++ channel on the brush border membrane

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26
Q

Again, what binds calcium intracellularly?

A

calbindin

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27
Q

How does the calcium exit the enterocyte?

A

via the basolateral CA ATPase pumps (exchanged with Na) or it’s exocytosed

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28
Q

What vitamin enhances expression of the apical Ca++ channel and calbindin?

A

vitamin D

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29
Q

What percentage of ingested iron is absorbed? Where?

A

only 3-6%

Primarily in the duodenum

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30
Q

What does excess absorption of iron lead to?

A

hemochromatosis

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31
Q

What about gastric physiology helps with iron absorption?

A

the acidity aids its reduction to the FE2+ form which is necessary for uptake

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32
Q

Teleologically, why does blood flow to the gut increase during a meal?

A

because active transport of solutes (esp Na) requires osygen and glucose so blood flow increases to increases delivery

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33
Q

What two neurotransmitters will stimulate Cl secretion in a long reflex?

A

ACh and VIP

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34
Q

What will be released by stroking the mucosa in a short reflex?

A

5-hydroxytrypatmine from local enterochromaffin cells

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35
Q

Any agent that elevates cAMP will cause the CFR to do what?

A

open, resulting in copious secretion in both the small and large intestine

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36
Q

What are some exacmples of substances that would do that?

A

prostaglandins, VIP, cholera toxin

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37
Q

What is guanylin? Secreted by what?

A

it’s a gastrointestinal polypeptide that is secreted by goblet and ECL cells

38
Q

What does guanylin bind to? In general, what does this trigger?

A

guanylyl cyclase type C (GC-C) receptors on the epithelial cells

promotes secretion

39
Q

More specifically, what does guanylin binding to the GC-C receptor trigger?

A

it raises concentration of intracellular cGMP, which increases Cl secretion through the CFTR into the lumen

40
Q

What drug will similar activate the guanylate cyclase type C receptor (GC-C) to treat constipation?

A

linaclotide

41
Q

How does this relate to diarrhea caused by E coli?

A

E coli has a heat-stable toxin that will also bind to the GC-C receptor and cause increased secretion

42
Q

Desiccation of stool in the large intestine is facilitated largely by uptake of what ion?

A

Na+

43
Q

What channel allows Na to enter the cell in the large intestine? Electroneutral or electrogenic?

A

an electrogenic ENaC (it’s the same on that’s found on the renal collecting duct epithelial cell)

44
Q

How do we get increased expression of ENacs in the distal colon in response to a low-salt diet?

A

aldosterone will increase the expression of the ENaCs, thus increasing the colon’s ability to reclaim sodium from the stool and water along with it

45
Q

How does electroneutral NaCl absorption also occur in the colon?

A

the Na/H exchanger

46
Q

What are some examples of secretagogues in the intestines?

A 
parasympathetic activity with Ach
VIP/NO
Histamine
Prostaglandins
gastrin
secretin
motilin
serotonin
long-chain fatty acids
bile salts
bacterial toxins
47
Q

What are some examples of absorbagogues in the itnestines?

A 
sympathetic activity
somatostatin
aldosterone
short chain fatty acids
bile salts
opioids
48
Q

True or false: most diarrhea is osmotic.

A

false…sort of

most diarrhea consists of a mix of secretion, osmotic and/or motility problems

49
Q

About how long does it take for chyme to travel the 5 meter length of the small intestine?

A

2-4 hours under normal circumstances

50
Q

About how long does chyme travel the 1 meter length of the large intestine?

A

2.5 days under normal circumstances

51
Q

Mass peristalsis promote rapid forward propulsion. How often do they occur?

A

1-3 times/day

52
Q

Besides mass peristalsis, what are three examples of motile processes?

A
  1. segmental contractions
  2. alterations in the surface configuration of the mucosa
  3. tonic contraction of the sphincters
53
Q

What two things does segmentation do to help digestion and absorption?

A

mixing to help enzymes get at the food and also slows transit so the food is exposed to absorptive surfaces longer

54
Q

THe patterns of segmentation depend on the frequency of basal electrical ruythm and amplitude - initiated by focal increase in what ion?

A

Ca2+

55
Q

How far do the segmental contractions usually propagate?

A

only a few centimeters

56
Q

About how many BER cycles are there per minute in the jejunum? Ileum?

A

12 per minute in the proximal jejunum

declines to 8 BER cycles/min in the distal ileum

57
Q

The more action potentials, the higher the _____ of the BER wave and the higher the smooth muscle mechanical response.

A

amplitude

remember that you can’t alter the frequency of the BER - it’s set

58
Q

What are some substances that will increase small intestinal motility?

A 
ACh from the vagus and enteric plexus
motilin
serotonin
substance P
prostaglandin
gastrin
CCK
insulin
59
Q

What are some substances that will decrease intestinal motility?

A

epinephrine
secretin
glucagon
anything that actives opioid receptors

60
Q

in general terms, what is the primary regulator of motility?

A

the enteric nervous system

61
Q

When will a migrating motor complex occur?

A

4 hours after a meal (it will stop if you eat something)

62
Q

WHy does erythromycin almost always cause diarrhea as a side effect?

A

it will bind motilin receptors, acting as a prokinetic

63
Q

True or false: the sphincter of Oddi does not open during MMCs, so you don’t get bile release

A

false - it does open and this may be important for preventing cholestasis

64
Q

True or false: MMCs occur in both the small and large intestine.

A

false - only in the small

65
Q

True or false: the ileocecal sphincter is tonically contracted.

A

True - to limit reflux of colonic contents into the ileum

66
Q

DIstension of the ___ will cause a reduction in ileocecal sphincter tone while distention of the ))))) will increase tone.

A

distention of ileum = decreased tone

distention of cecum = increased tone

67
Q

What are the two reflexes involved in small intestinal motility?

A
  1. peristaltis reflex
  2. intestinointestinal reflex
  3. ileal-gastric reflex
  4. gastro-ileal reflex
68
Q

What is the peristaltic reflex

A

we’ve already talked about it

distension of the gut wall signals the enteric nervosus system to coordinate proximal contraction and distal relaxation

69
Q

What is the intestinointestinal reflex?

A

overdistension or traumatization of the itnestine results in relaxation of the entire gut (adynamic ileus)

note that this is the usual condition after abdominal surgery

70
Q

Describe the ileal-gastric reflex.

A

distention of the ileum decreases gastric motility

it’s a long reflex involving the vagus nerve

71
Q

What is the gastro-ileal reflex?

A

increased gastric activity increases ileal contractions and relaxes the cecum and ileocecal sphincter

long reflex to “make room” - same concept as the gastro-colic reflex

72
Q

What is the frequency of the BER in the large intestine?

A

only 2/min - motility is very slow (that’s why it takes 2.5 days to only go 1 meter)

73
Q

What characteristic of the teniae coli makes proulsion less effective in the large intestine?

A

contraction is not well organized

74
Q

What do we call the peristaltic-like contractions that result in loss of visicle haustra and forward ropulsion along the entire length of the intestine?

A

mass movements

75
Q

How does emotional state alter reflex control of the large intestine?

A

changes in autonomic activity like increased sympathetic activity will decrease colonic motility by action of epinephrine

increased parasympathetic activity increases colonic motility by action of acetylcholine

76
Q

Describe the colonocolonic reflex?

A

distension in one part of the colon relaxes other parts of the colon (enteric nervous system and modulation by sympathetics)

77
Q

What are the two important mediators of the gastro-colic reflex?

A

5-HT and ACh

78
Q

what group of nerves provide extrinsic input to the colon and inhibition of the internal anal sphincter?

A

pelvic nerves

79
Q

What nerves stimulate the external anal sphincter?

A

somatic pudendal nerves

80
Q

What anatomical aspect of the rectum will partially occlude and retard fecal flow?

A

transverse folds

81
Q

Distention of the rectum will initiate what reflex?

A

the rectosphincteric reflex

82
Q

What happens in the rectosphincteric reflex?

A
  1. urge to defacate
  2. relaxation of the internal anal sphincter
  3. reflex contraction of external anal sphincter to prevent inadvertent expulsion
83
Q

Then what happens after the distension occurs if you don’t poop?

A

accomodation of the distension occurs and the internal anal sphincter regains its tone until the passage of more contents into the rectum

84
Q

Describe the involuntary and voluntary actions of defacation.

A
  1. descending colon, sigmoid colon and rectum contract
  2. relaxation of both sphincters
  3. contraction of diaphragm and abdominal muscles
  4. relaxation of pelvic floor
85
Q

Stool incontinence is most often due to damage to what?

A

external sphincter

86
Q

Does contraction of the puborectalis muscle promote or inhibit defecation?

A

inhibit

87
Q

How does straining with the abdominal muscles help with defacation?

A

it lowers the pelvic flow 1-3 cm and allows the puborectalis to relax

this makes the rectum more straight up and down so stool can pass easier

88
Q

What is the pathophysiology/cause of megacolon?

A

Usually crohn’s disease or ulcerative colitis - you get release of inflammatory mediators, damage to epithelial barrier, increased inducible nitric oxide synthase and generation of excessive nitric oxide

the excess gas causes rapid dilation of the colon with diarrhea, pain, shock, potential for perforation

gotta remove the colon

89
Q

Describe the effects of IBS.

A

the itnestine just becomes more sensitive and contracts more frequently

you get abdominal pain, gas, bloating for at least 3 days per month

may switch back and forth between constipaiton and diarrhea

90
Q

What does IBS win the prize for?

A

It’s the most common chronic itnestinal problem

possibly 1/6 in the US

GI Week 4 (11 decks)

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