Intestinal Transport of Water & Electrolytes

Question 1

Histologically, where does secretion of water and electrolytes occur?

Answer 1

In the crypts

Question 2

State the approximate amounts of fluid absorbed in the different regions of the intestine

Answer 2

Duodenum/Jejunum: 5.5 L
Ileum: 2.0 L
Colon: 1.3 L

Maximum–
Small bowel: 12 L
Large bowel: 4-6 L

Question 3

Approximately how much fluid is secreted into the GIT? and where is it coming from?

Answer 3

TOTAL = 9L of fluid (8.8L is reabsorbed)

Dietary intake: 2000mL
Salivary: 1500mL

Bile: 500mL
Stomach: 2500mL
Pancreas: 1500mL

Intestine: 1000mL

Question 4

Histologically where does absorption take place?

Answer 4

On the villi

Question 5

Where in GIT does paracellular absorption occur?

Answer 5

Proximal portion of small bowel

Question 6

Where in GIT does transcellular absorption occur?

Answer 6

Throughout the intestines

Question 7

How does lactose intolerance cause diarrhea?

Answer 7

Lactose cannot be broken down (poorly absorbed), increases the concentration of osmotically active agents in the intestine, and therefore draws water in.

Question 8

What happens with heat stable E. coli?

Answer 8

Reduced absorption resulting from an inhibited transport system - can’t get Na+ in, and increase Cl- out via channel.

Question 9

What causes osmotic diarrhea?

Answer 9

Increased carbs or minerals (NaSO4 or MgCitrate) in the intestine set up an osmotic gradient – creates an osmotic gap which draws water into the intestine.

Question 10

What is the mechanism of diarrhea in IBS?

Answer 10

Pushes the water through too fast so that it cannot be absorbed.

Question 11

What are a couple mechanisms of secretory diarrhea?

Answer 11

1. Stimulated anion secretion
   
   • ->Bacterial (cholera) toxins
   • ->Carcinoid tumour (bradykinin hypersecretion)
2. Secretion from hyperplastic crypts
   
   • ->Chronic Inflam. (Celiac Sprue)

Question 12

What happens in Celiac disease?

Answer 12

1. Increased brush border hydrolysis –> increased osmolarity
2. Villous atrophy –> flattening of mucosa –> decreased absorption
3. Crypt hyperplasia –> hypersecretion (but can’t absorb)
4. Inflammation-induced hyper-secretion by crypt enterocytes

Question 13

What is the mechanism of cholera diarrhea?

Answer 13

Bacteria produce a toxin (multi-protein)

• -> binds apical membrane of enterocyte & enters cells
• -> activates secreteagogue production (produces cAMP–>PKA)
• -> stimulates CFTR to send Cl- into lumen
• -> inhibit NaCl absorption
• -> increased salt & water in lumen (hypersection)
• -> super watery diarrhea
• -> dehydration

Question 14

How would you treat kids with cholera diarrhea?

Answer 14

Give water with glucose

• Na+ gets absorbed with glucose via SGLT-1 transporter
• this occurs at proximal small intestine
• Na+ and water are dragged out of intestine near the beginning thus lessening the load later on