Practice Exam Q for Membrane Dynamics

[terminalsanctuary]

Hi Everyone!

I hope everyone has been enjoying physiio so far.  Sorry for the late post...I ran into some Google groups problem with posting, but no more for me! Yay. :D  For most people, I know you guys have trouble posting right now, so ponder on this for a bit in the meantime.  Or you can email me your thoughts on the question and I can post them on this thread. 

This is a sample exam question that is really reflective of Dr. Herrera's tests.  Later in the week or maybe early next week, I will post hints or the answer. And for the few who can post right now, try to give it a shot.

Q: A rare genetic disease is caused by mutations in the SLC5A1 gene. This gene codes for the one of the most abundant forms of SGLUT protein. In persons with the disease, the SGLUT protein is non-functional. Briefly explain why persons with this disease

would be expected to show malnutrition, severe diarrhea, and dehydration.

Have fun!

-Danny Nguyen

[terminalsanctuary]

One student emailed me this answer, and I will post my response later, but I want to see what others think about this question before I say what the answer is.

"This is my tentative answer: With defective SGLT proteins, glucose cannot enter the epithelial cells from the lumen of the intestine, which means that glucose cannot enter the bloodstream and the person suffers from malnutrition. As for severe diarrhea and dehydration, this is caused by sodium ions remaining in the colon's mucus instead of being transported back into the epithelial cell through the SGLUT transporters in the apical membrane. Thus, the sodium ions create an osmotic gradient that also draws water into the mucus through aquaporins or through the tight junctions. This results in diarrhea and loss of fluid and salts from the body."

Feel free to email me if you got questions and/or if you think you know the answer!  :)

-Danny

[TerminalSanctuary]

"Hi Danny thanks for the practice question!

I believe that due to this mutation in the SGLUT transporters, there is an excess amount of glucose remaining in the lumen of the intestine. This glucose cannot go through the apical membrane and basolateral membrane to the blood stream so the body is unable to metabolism the glucose. The individual is not gaining the nutrition and is therefore malnourished. 

As for diarrhea and dehydration, besides glucose, ions such as sodium remain in the lumen as well because the dysfunction of SGLUT transporter. Water which will travel from hypotonic to hypertonic solutions, will diffuse through through the apical membrane into the lumen of the intestine. This water will be excreted with other wastes. The exceess water loss leads to dehydration. A significant water and salt loss will also lead to diarrhea.

Helen"

[TerminalSanctuary]

Because SGLUT is nonfunctional, sodium and glucose can't be reabsorbed from the lumen of the intestine through the epithelial cells into the blood. Because the person can't get glucose, they lack energy and are malnourished. Also, since sodium isn't being reabsorbed, water isn't being reabsorbed with it, so there are large amounts of water and sodium being excreted via diarrhea. Because the cells aren't getting water, the person is also dehydrated. 

-Sheena