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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
Where in the small intestine is calcium actively absorbed? How?
in the duodenum thorugh a Ca++ channel on the brush border membrane
26
Again, what binds calcium intracellularly?
calbindin
27
How does the calcium exit the enterocyte?
via the basolateral CA ATPase pumps (exchanged with Na) or it's exocytosed
28
What vitamin enhances expression of the apical Ca++ channel and calbindin?
vitamin D
29
What percentage of ingested iron is absorbed? Where?
only 3-6% Primarily in the duodenum
30
What does excess absorption of iron lead to?
hemochromatosis
31
What about gastric physiology helps with iron absorption?
the acidity aids its reduction to the FE2+ form which is necessary for uptake
32
Teleologically, why does blood flow to the gut increase during a meal?
because active transport of solutes (esp Na) requires osygen and glucose so blood flow increases to increases delivery
33
What two neurotransmitters will stimulate Cl secretion in a long reflex?
ACh and VIP
34
What will be released by stroking the mucosa in a short reflex?
5-hydroxytrypatmine from local enterochromaffin cells
35
Any agent that elevates cAMP will cause the CFR to do what?
open, resulting in copious secretion in both the small and large intestine
36
What are some exacmples of substances that would do that?
prostaglandins, VIP, cholera toxin
37
What is guanylin? Secreted by what?
it's a gastrointestinal polypeptide that is secreted by goblet and ECL cells
38
What does guanylin bind to? In general, what does this trigger?
guanylyl cyclase type C (GC-C) receptors on the epithelial cells promotes secretion
39
More specifically, what does guanylin binding to the GC-C receptor trigger?
it raises concentration of intracellular cGMP, which increases Cl secretion through the CFTR into the lumen
40
What drug will similar activate the guanylate cyclase type C receptor (GC-C) to treat constipation?
linaclotide
41
How does this relate to diarrhea caused by E coli?
E coli has a heat-stable toxin that will also bind to the GC-C receptor and cause increased secretion
42
Desiccation of stool in the large intestine is facilitated largely by uptake of what ion?
Na+
43
What channel allows Na to enter the cell in the large intestine? Electroneutral or electrogenic?
an electrogenic ENaC (it's the same on that's found on the renal collecting duct epithelial cell)
44
How do we get increased expression of ENacs in the distal colon in response to a low-salt diet?
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
How does electroneutral NaCl absorption also occur in the colon?
the Na/H exchanger
46
What are some examples of secretagogues in the intestines?
``` parasympathetic activity with Ach VIP/NO Histamine Prostaglandins gastrin secretin motilin serotonin long-chain fatty acids bile salts bacterial toxins ```
47
What are some examples of absorbagogues in the itnestines?
``` sympathetic activity somatostatin aldosterone short chain fatty acids bile salts opioids ```
48
True or false: most diarrhea is osmotic.
false...sort of most diarrhea consists of a mix of secretion, osmotic and/or motility problems
49
About how long does it take for chyme to travel the 5 meter length of the small intestine?
2-4 hours under normal circumstances
50
About how long does chyme travel the 1 meter length of the large intestine?
2.5 days under normal circumstances
51
Mass peristalsis promote rapid forward propulsion. How often do they occur?
1-3 times/day
52
Besides mass peristalsis, what are three examples of motile processes?
1. segmental contractions 2. alterations in the surface configuration of the mucosa 3. tonic contraction of the sphincters
53
What two things does segmentation do to help digestion and absorption?
mixing to help enzymes get at the food and also slows transit so the food is exposed to absorptive surfaces longer
54
THe patterns of segmentation depend on the frequency of basal electrical ruythm and amplitude - initiated by focal increase in what ion?
Ca2+
55
How far do the segmental contractions usually propagate?
only a few centimeters
56
About how many BER cycles are there per minute in the jejunum? Ileum?
12 per minute in the proximal jejunum declines to 8 BER cycles/min in the distal ileum
57
The more action potentials, the higher the _____ of the BER wave and the higher the smooth muscle mechanical response.
amplitude remember that you can't alter the frequency of the BER - it's set
58
What are some substances that will increase small intestinal motility?
``` ACh from the vagus and enteric plexus motilin serotonin substance P prostaglandin gastrin CCK insulin ```
59
What are some substances that will decrease intestinal motility?
epinephrine secretin glucagon anything that actives opioid receptors
60
in general terms, what is the primary regulator of motility?
the enteric nervous system
61
When will a migrating motor complex occur?
4 hours after a meal (it will stop if you eat something)
62
WHy does erythromycin almost always cause diarrhea as a side effect?
it will bind motilin receptors, acting as a prokinetic
63
True or false: the sphincter of Oddi does not open during MMCs, so you don't get bile release
false - it does open and this may be important for preventing cholestasis
64
True or false: MMCs occur in both the small and large intestine.
false - only in the small
65
True or false: the ileocecal sphincter is tonically contracted.
True - to limit reflux of colonic contents into the ileum
66
DIstension of the ___ will cause a reduction in ileocecal sphincter tone while distention of the ))))) will increase tone.
distention of ileum = decreased tone distention of cecum = increased tone
67
What are the two reflexes involved in small intestinal motility?
1. peristaltis reflex 2. intestinointestinal reflex 3. ileal-gastric reflex 4. gastro-ileal reflex
68
What is the peristaltic reflex
we've already talked about it distension of the gut wall signals the enteric nervosus system to coordinate proximal contraction and distal relaxation
69
What is the intestinointestinal reflex?
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
Describe the ileal-gastric reflex.
distention of the ileum decreases gastric motility it's a long reflex involving the vagus nerve
71
What is the gastro-ileal reflex?
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
What is the frequency of the BER in the large intestine?
only 2/min - motility is very slow (that's why it takes 2.5 days to only go 1 meter)
73
What characteristic of the teniae coli makes proulsion less effective in the large intestine?
contraction is not well organized
74
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?
mass movements
75
How does emotional state alter reflex control of the large intestine?
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
Describe the colonocolonic reflex?
distension in one part of the colon relaxes other parts of the colon (enteric nervous system and modulation by sympathetics)
77
What are the two important mediators of the gastro-colic reflex?
5-HT and ACh
78
what group of nerves provide extrinsic input to the colon and inhibition of the internal anal sphincter?
pelvic nerves
79
What nerves stimulate the external anal sphincter?
somatic pudendal nerves
80
What anatomical aspect of the rectum will partially occlude and retard fecal flow?
transverse folds
81
Distention of the rectum will initiate what reflex?
the rectosphincteric reflex
82
What happens in the rectosphincteric reflex?
1. urge to defacate 2. relaxation of the internal anal sphincter 3. reflex contraction of external anal sphincter to prevent inadvertent expulsion
83
Then what happens after the distension occurs if you don't poop?
accomodation of the distension occurs and the internal anal sphincter regains its tone until the passage of more contents into the rectum
84
Describe the involuntary and voluntary actions of defacation.
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
Stool incontinence is most often due to damage to what?
external sphincter
86
Does contraction of the puborectalis muscle promote or inhibit defecation?
inhibit
87
How does straining with the abdominal muscles help with defacation?
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
What is the pathophysiology/cause of megacolon?
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
Describe the effects of IBS.
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
What does IBS win the prize for?
It's the most common chronic itnestinal problem possibly 1/6 in the US

GI Week 4 (11 decks)

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