Lecture 12: Pathophysiology of Acute Diarrhea and Absorption

Question 1

What is the pathophysiology of diarrhea?

Answer 1

1. incomplete absorption of water from lumen due to
   i. impaired electrolyte absorption
   ii. excessive electrolyte secretion
   iii. osmotic retention of water intraluminally
   iv. when maximum colonic absorptive capacity of 4 liters is exceeded
2. reduction of net water absorption by as little as 1% may cause diarrhea

Question 2

What is NOT diarrhea?

Answer 2

1. IBS (irritable bowel syndrome)
   
   • ab pain
   • constipation and diarrhea
   • absence of other causes
2. Fecal incontinence
   
   • when sphincters don’t do shit

Question 3

What is incontinence?

Answer 3

Involuntary urination or defecation

Question 4

What are the classifications of diarrhea?

Answer 4

1. acute vs chronic
2. bloody vs watery
3. malabsorptive vs secretory

Question 5

Can GI tube change osmolarity of luminal contents?

Answer 5

NO

Question 6

What is factitious diarrhea?

Answer 6

Patients may add water or urine purposefully to their fecal material to make it appear as diarrhea

Question 7

What is fistula diarrhea?

Answer 7

When there is a fistula connecting the bladder with the gut

Question 8

What is the significance of the fact that the gut cant concentrate the fluid?

Answer 8

That means the osmolarity of stool fluid must equal that of blood

Question 9

What is the osmolality?

Answer 9

2 X [Na+K]

Question 10

What is the osmolar gap?

Answer 10

Measured osmolality – 2(Na+K)

Exists because the calculated gap does not take into account other solutes

Question 11

What is a normal Osm gap?

Answer 11

<50mOsm

Question 12

What happens if you have a large osmolar gap?

Answer 12

It means that you have a large amount of soluble proteins within the diarrhea
Example: if patient is taking a Mg laxative or there are undigested carbohydrates
It means you have trouble taking in nutrient

Question 13

What is the osm of stool and blood?

Answer 13

290mOsm

Question 14

What happens if you have a low osm gap?

Answer 14

It means your ability to absorb nutrients is fine and is not the cause of diarrhea

Question 15

How does colon absorb water?

Answer 15

Electrolyte pumps

Question 16

How can you not absorb nutrients and have diarrhea as a result?

Answer 16

In the small intestine
1. there is a defect in the carbohydrate breakdown and absorption
2. protein breakdown and absorption defect
Defect in pancreatic enzymes and brush border
3. defect in fat absorption (pancreatic enzymes, micelle, brush border)

Question 17

What happens if stool Osm is 100 mOsm?

Answer 17

Fictitious (from urinating or water in there)

Question 18

What does the colon secrete?

Answer 18

K+ and HCO3-

Question 19

What does the colon absorb?

Answer 19

Na, Cl and H2O

Question 20

What can lead to brush border loss or injury?

Answer 20

1. Infections (virus, parasites, bacteria)
2. Celiac disease
3. Loss/non-expression of enzymes
   
   • lactase
4. congenital disorders
   
   • microvillous inclusion disease

Question 21

What does small bowel normal villous look like?

Answer 21

Goblet cells

Brush border

Question 22

What is celiac disease?

Answer 22

Gluten sensitive enteropathy
Causes malabsorption and diarrhea due to LOSS of small bowel surface area
A component of wheat (gladin) binds to the surface of enterocytes, a complex that is then attacked by the patients immune system
Lots of lymphocytes
Characterized by
	i. villous blunting
	ii. crypt hyperplasia
	iii. intra-epithelial lymphocytes

Question 23

What happens if you see anti-gladin antibodies?

Answer 23

Celiac disease

Question 24

What is secretory diarrhea?

Answer 24

The osm gap is low
That means nutrients are being absorbed fine
Too much being secreted

Question 25

What is osmotic diarrhea?

Answer 25

The osm gap is high
That means nutrients are not being absorbed
So higher osmolarity in stool

Question 26

What is C difficle colitis?

Answer 26

An example of a toxin mediated surface damage

Causes an explosion of mucin into the lumen of the bowel

Question 27

What is ulcerative colitis?

Answer 27

Inflammed colonic surface
Leads to a leaky gut
Leads to a bloody diarrhea

Question 28

What is the purpose of goblet cells?

Answer 28

To secrete mucin

Question 29

What is lymphocytic colitis?

Answer 29

1. watery diarrhea
2. surface damage due to intraepithelial lymphocytes
3. loss of water absorption
4. true cause unknown

Question 30

What causes brown bowel?

Answer 30

The use of certain laxatives
Damage of the surface will lead to melanin being absorbed by macrophages that leads to brown color
Laxatives can damage the surface of the colon

Question 31

What infectious agents lead to secretory diarrhea?

Answer 31

1. e. coli
2. cholera
   
   • upregulates cAMP to secrete more Cl- (goes into cell)

Question 32

What are two etiologies of secretory diarrhea?

Answer 32

1. cholera

2. E. coli

Question 33

What are two etiologies of osmotic diarrhea?

Answer 33

Lactose intolerance

Laxatives

Question 34

What can neuroendocrine tumors do?

Answer 34

Cause diarrhea because of hormones secreted

Hormone = vasoactive intestinal polypeptide (VIP)

Question 35

What is the function of VIP?

Answer 35

Stimulates secretion of water and electrolytes (many others but this is what is most pertinent to diarrhea)

Question 36

What does cholera toxin bind to?

Answer 36

The enterochromaffin cells to increase cAmP

Question 37

What is acute diarrhea?

Answer 37

Less than 4 weeks

Infections

Question 38

What is chronic diarrhea?

Answer 38

4 weeks or more

Lymphocytic colitis

Question 39

What determines acute vs. chronic diarrhea?

Answer 39

1. patient age
2. socioeconomics
3. geography

Question 40

What is diarrhea?

Answer 40

Increased volume AND weight of daily of stool

Question 41

Why do you have to measure diarrhea samples right away?

Answer 41

Because shit can change/get cleaved and you get a much higher osmolarity measurement than expected