Pathophys: Diarrhea

Question 0

What is the separation between acute and chronic diarrhea?

Answer 0

< 4 weeks duration is acute, else chronic.

Question 1

Simply, what are reasons for incomplete absorption of water from the GI lumen?

Answer 1

(1) impaired electrolyte absorption
(2) excessive electrolyte secretion
(3) osmotic retention of water intraluminally

Question 2

Which has higher osmolarity: stool fluid or blood?

Answer 2

They’re the same, 290 mOsm.

Question 3

What is the osmolar gap?

Answer 3

The difference between the actual osmolarity of a fluid and the calculated osmolarity (2[Na+K]).

Question 4

J: This intracellular parasite lives in surface epithelial cells of the small bowel and may produce diarrhea if sufficient surface area is affected.

Answer 4

What is cryptosporidium?

Question 5

When infected with cryptosporidium, what changes do surface epithelial cells undergo?

Answer 5

(1) loss of mucin
(2) loss of cytoplasm
(3) loss of brush border

Question 6

J: This disorder is characterized by villous blunting, crypt hyperplasia, and intraepithelial lymphocytes in the small bowel.

Answer 6

What is celiac disease?

Question 7

What is the initial insult in celiac disease?

Answer 7

An abnormal immune response to gliadin, a component of wheat, in the small bowel.

Question 8

How is celiac disease treated?

Answer 8

A gluten-free diet.

Question 9

What is the clinical presentation of celiac disease?

Answer 9

(1) malabsorption
(2) diarrhea
(3) iron-deficiency anemia

Question 10

Malabsorption of what nutrient is often associated with diarrhea?

Answer 10

Fat.

Question 11

What are mechanisms by which mild ulcerative colitis results in diarrhea?

Answer 11

(1) impaired reabsorption of bile acids in the colon leads to impaired absorption of fat in the small bowel.
(2) cytokines may affect secretion of electrolytes and motility.

Question 12

What intestinal infections cause bloody diarrhea? Mucoid, watery diarrhea? Toxin-mediated watery diarrhea?

Answer 12

(1) E. coli O 157, Shigella
(2) C. difficile
(3) E. coli, V. cholera

Question 13

What is the clinical presentation of lymphocytic colitis?

Answer 13

Watery diarrhea as a result of surface damage caused by intraepithelial lymphocytes (poor water absorption).

Question 14

J: This is a condition that presents with watery diarrhea with the use of certain laxatives. On endoscopy, the surface of the colon has a brown pigment.

Answer 14

What is melanosis coli?

Question 15

Where does melanosis coli get its name?

Answer 15

A melanin-like pigment accumulates inside macrophages in the lamina propia of the colon.

Question 16

Describe how E. coli enterotoxin causes diarrhea. How does this differ from V. cholera toxin?

Answer 16

(1) STa binds to the brush border enzyme gaunylyl cyclase C in the small bowel and proximal colon.
(2) increased cGMP activates protein kinase G.
(3) anion channels open, leading to increased secretion of Cl and HCO3.

The primary difference with V. cholera toxin is that a subunit enters the cell and adenylate cyclase is activated, increasing cAMP.

Question 17

What are 2 types of neuroendocrine tumors that cause diarrhea? What are the mechanisms?

Answer 17

(1) VIP-secreting tumors stimulate ion secretion into the GI lumen
(2) Gastrin-secreting tumors decrease pH in the duodenum, inactivating pancreatic enzymes, decreasing nutrient absorption

Question 18

What is suspected if the osmolarity of a stool sample is markedly low?

Answer 18

Factitious diarrhea, that is, the patient has added water, urine, etc. to the stool so as to give the appearance of diarrhea.