Lecture 12: Pathophysiology of Acute Diarrhea and Absorption Flashcards
What is the pathophysiology of diarrhea?
- 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 - reduction of net water absorption by as little as 1% may cause diarrhea
What is NOT diarrhea?
- IBS (irritable bowel syndrome)
- ab pain
- constipation and diarrhea
- absence of other causes
- Fecal incontinence
- when sphincters don’t do shit
What is incontinence?
Involuntary urination or defecation
What are the classifications of diarrhea?
- acute vs chronic
- bloody vs watery
- malabsorptive vs secretory
Can GI tube change osmolarity of luminal contents?
NO
What is factitious diarrhea?
Patients may add water or urine purposefully to their fecal material to make it appear as diarrhea
What is fistula diarrhea?
When there is a fistula connecting the bladder with the gut
What is the significance of the fact that the gut cant concentrate the fluid?
That means the osmolarity of stool fluid must equal that of blood
What is the osmolality?
2 X [Na+K]
What is the osmolar gap?
Measured osmolality – 2(Na+K)
Exists because the calculated gap does not take into account other solutes
What is a normal Osm gap?
<50mOsm
What happens if you have a large osmolar gap?
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
What is the osm of stool and blood?
290mOsm
What happens if you have a low osm gap?
It means your ability to absorb nutrients is fine and is not the cause of diarrhea
How does colon absorb water?
Electrolyte pumps
How can you not absorb nutrients and have diarrhea as a result?
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)
What happens if stool Osm is 100 mOsm?
Fictitious (from urinating or water in there)
What does the colon secrete?
K+ and HCO3-
What does the colon absorb?
Na, Cl and H2O
What can lead to brush border loss or injury?
- Infections (virus, parasites, bacteria)
- Celiac disease
- Loss/non-expression of enzymes
- lactase
- congenital disorders
- microvillous inclusion disease
What does small bowel normal villous look like?
Goblet cells
Brush border
What is celiac disease?
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
What happens if you see anti-gladin antibodies?
Celiac disease
What is secretory diarrhea?
The osm gap is low
That means nutrients are being absorbed fine
Too much being secreted
What is osmotic diarrhea?
The osm gap is high
That means nutrients are not being absorbed
So higher osmolarity in stool
What is C difficle colitis?
An example of a toxin mediated surface damage
Causes an explosion of mucin into the lumen of the bowel
What is ulcerative colitis?
Inflammed colonic surface
Leads to a leaky gut
Leads to a bloody diarrhea
What is the purpose of goblet cells?
To secrete mucin
What is lymphocytic colitis?
- watery diarrhea
- surface damage due to intraepithelial lymphocytes
- loss of water absorption
- true cause unknown
What causes brown bowel?
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
What infectious agents lead to secretory diarrhea?
- e. coli
- cholera
- upregulates cAMP to secrete more Cl- (goes into cell)
What are two etiologies of secretory diarrhea?
- cholera
2. E. coli
What are two etiologies of osmotic diarrhea?
Lactose intolerance
Laxatives
What can neuroendocrine tumors do?
Cause diarrhea because of hormones secreted
Hormone = vasoactive intestinal polypeptide (VIP)
What is the function of VIP?
Stimulates secretion of water and electrolytes (many others but this is what is most pertinent to diarrhea)
What does cholera toxin bind to?
The enterochromaffin cells to increase cAmP
What is acute diarrhea?
Less than 4 weeks
Infections
What is chronic diarrhea?
4 weeks or more
Lymphocytic colitis
What determines acute vs. chronic diarrhea?
- patient age
- socioeconomics
- geography
What is diarrhea?
Increased volume AND weight of daily of stool
Why do you have to measure diarrhea samples right away?
Because shit can change/get cleaved and you get a much higher osmolarity measurement than expected
