Electrolyte DSA

Question 1

compare and contrast the transport of electrolytes and H20 in small intestine and colon

Answer 1

*both: electrolytes and H20 can cross intestinal epithelial cells by cellular and paracellular transport

Colon

• lots of tight junctions so it is “tight” and more impermeable epithelia
• Na + channels allow passive diffusion of Na into cell from lumen and are stimulated by aldosterone
• active secretion of K+
• low H20 absorption so hypertonic feces

SI

• more “leaky” and permeable epithelia
• uses Na cotransporters for passive Na diffusion into cell from lumen
• passive absorption of K+ via paracellular route
• isoosmotic H20 absorption bc “leaky”

Question 2

How does the colon cause hypokalemia

Answer 2

diarrhea will cause increase K+ secretion by the colon

Question 3

secretory mechanisms of the GI are located in the ____ and absorptive mechanism is in the _____

Answer 3

1. crypts

2. vili

Question 4

what is the primary ion excreted into intestinal lumen

Answer 4

Cl-

• thru cAMP Cl- regulated channel
• Na and H20 will follow

Question 5

how does cholera toxin cause secretory diarrhea

Answer 5

-stimulates Cl- secretion

• cataylzes Gs receptor permanently active
• increased cAMP opens Cl-channels
• Na and H20 follow Cl- into lumen and leads to secretory diarrhea

Question 6

how does lactase def cause osmotic diarrhea

Answer 6

-unabsorbed lactose draws water into small bowel

because it increases osmotic pressure causing fluid to be secreted into lumen