Pathophys of Diarrhea and Absorption

Question 1

3 ways to not absorb enough water in gut?

Answer 1

Impaired electrolyte absorption.
Excessive electrolyte secretion.
Osmotic retention of water intraluminally.

Question 2

Are IBS and fecal incontinence diarrhea?

Answer 2

No.

Question 3

What’s the arbitrary cutoff between acute and chronic diarrhea? Is there a physiological difference between the two?

Answer 3

4 weeks.
No, there’s no physiological difference.
(but acute tend to be more caused by infections, chronic by… other things)

Question 4

What are 4 reasons that stuff could not be absorbed in the gut?

Answer 4

No breakdown.
Too fast of transit.
Too much input.
Cells can’t absorb.

Question 5

2 reasons for too much excretion?

Answer 5

Leaky gut.

Uncontrolled cellular exchange (e.g. Cholera).

Question 6

How does stool fluid osmolarity compare to that of the blood?

Answer 6

They’re equal. (Or rather, water will move to make them equal.)

Question 7

What’s osmolarity of the blood, normally?

Answer 7

290 mOsm

Question 8

How, mathematically, do you express the estimate of factors contributing to stool osmolarity?

Answer 8

290 mOsm = 2(Na + K) + (“other osmotically active stuff”)

Question 9

What’s osmolar gap? The formula?

What does the osmolar gap represent?

Answer 9

Osm Gap = measured stool Osm - calculated stool Osm.
Osm Gap = measured Osm - 2(Na + K)
The osmolar gap represents “other solutes,” such as undigested carbs.

Question 10

What is a normal Osm Gap value?

Answer 10

< 50 Osm.

Question 11

What does measured stool Osm that’s really low (much less than 290 mOsm) suggest?

Answer 11

Some sort of dilution of the stool sample - urine, fistula, malingering, lab error, etc.

Question 12

What do you conclude if the Osm gap is greater than 100 mOsm?

Answer 12

There’s some additional osmotically active stuff in the stool.

Question 13

3 different things that if not broken down can be osmotically active and cause diarrhea?
What’s a common cause of stuff not being broken down?

Answer 13

Carbs, protein, fat.

Defective brush border enzymes is a common cause (not for fat, though!).

Question 14

4 categories of things that can damage brush border of the small bowel?

Answer 14

Infections
Celiac
Loss of enzymes (eg. lactose intolerance)
Congenital (microvillous inclusion disease)

Question 15

How can short gut syndrome cause diarrhea?

Answer 15

Electrolytes aren’t pumped in, and the colon can’t make up for it.

Question 16

We’ll probably hear more about celiac… but what are some markers for it?

Answer 16

Villous atrophy
Crypt hyperplasia
Intraepithelial lymphocytosis
Anti-gliadin Abs

Question 17

3 things that cause fat not to be broken down?

Answer 17

Pancreatic insufficiency (not enough lipase)
Molecules can’t be cleaved (Olestra…)
Not enough bile acid to form micelles

Question 18

What do you call it when the colon has injured surface epithelium with lymphocytic infiltrate, but crypt cells look okay? What does this cause?

Answer 18

Lymphocytic colitis.

This results in net secretion of electrolytes -> watery diarrhea.

Question 19

How can stimulant laxatives cause diarrhea? (how can the colon mucosal surface look grossly?)

Answer 19

Increased motility, and chronic use can damage surface epithelium.
(damage can appear as melanosis coli - brown colon mucosa)

Question 20

2 organisms that cause unregulated ion secretion?

One non-infectious cause of unregulated ion secretion?

Answer 20

E. coli and V. cholera.

Non-infectious: Vasoactive hormones.

Question 21

What does E. coli enterotoxin do?

Answer 21

Works through PKG, increases Cl- and bicarb secretion.

Question 22

What does V. cholera enterotoxin do? (more specifics in the Infectious Diarrhea lecture)

Answer 22

Causes adenylate cyclase to be always active -> cAMP high all the time -> Cl- secreted nonstop -> watery diarrhea

Question 23

What’s the etiology of vasoactive hormones that cause diarrhea?

Answer 23

Neuroendocrine tumors

Question 24

Can the osmolality (…osmolarity too…?) of a stool sample change with time?

Answer 24

Yes. Bacteria can break down large molecules, disaccharides -> more small molecules, higher osmolarity.