810216 Prolab 1 rences Mailings Review View ormal the cell The disease cholera c

Question

810216 Prolab 1 rences Mailings Review View ormal the cell The disease cholera causes an imbalance in osmotic equilibrium and dehydration of the cholera victim. It is caused by the bacterium Vibrio cholerae. The bacteria produce an endotoxin that ativates cAMP umen of the small intestine. CAMP inhibits sodium production/activity in intestinal epithelial cells that line the I uptake and increases chloride secretion by the epithelial cells. This causes and electrolyte imbalance and the diarrhea observed with the disease. In terms of osmolarity/tonicity why would the intestinal cells' reabsorption of water decrease? (4 What then would happen to the interstitial fluid? Would other cells be affected too? Explain your answers. (6 MacBook Air 4 0

Explanation / Answer

Question) In terms of osmolarity/tonicity, why would the intestinal cell's reabsorption of water decrease?

Answer) Under normal circumstances, in the small intestine, an ion channel called the cystic fibrosis transmembrane conductance receptor (CFTR) allows the transport of Cl- ions out of the cells and is involved in adjusting the water levels. In case of cholera, the increased concentration of cAMP activates the CFTR to remain open. This causes Cl- ions to continuously move out of the cells and into the lumen. As a result, the Na+ ions get attracted by the chloride ions and also enter the lumen.

Because of this situation, the lumen has a very low water potential which causes water to leave the cells and enter the lumen (down the concentration gradient). The cells become severely dehydrated but the water does not get reabsorbed simply because, in the choleric state, the normal mechanism by which Na+ ions get absorbed by the intestinal wall is impaired. In order to maintain the osmotic balance, water cannot get reabsorbed unless the sodium ions are also taken up by the cells. As a result, excess release of sodium ions increases the secretion of water into the lumen.

Question) What then would happen to the interstitial fluid? Would other cells be affected too? Explain your answers.

Answer) The interstitial fluid constitutes the majority of the extracellular fluid that bathes the cells and makes up the internal environment of the body. As Na+ ions are mostly present in the extracellular fluid (135-150 mmol/litre) and play a major role in the movement of water, the secretion of these ions into the lumen causes a decrease of water from the interstitial fluid which moves into the lumen. The interstitial fluid volume will change.

Surrounding cells will be affected due to a change in the interstitial fluid volume, particularly the volume of the plasma. As plasma sodium concentrations will be low, the electrolyte balance will be affected and the movement of water across fluid compartments will also be hindered.

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