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11 Cards in this Set
- Front
- Back
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Identify the pathogen that causes cholera |
Vibrio Cholera |
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Describe why severe diarrhoea caused by cholera infection can be so dangerous if not treated quickly |
If not treated, the watery, painless, copious diarrrhoea can lead to severe dehydration, kidney failure and death (heart failure) within hours |
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Explain why ORS are more effective in treating the symptoms of cholera than water alone |
Drinking water doesn't replace lost electrolytes Water is not being absorbed from the intestine but actually being lost from cells ORS contain electrolytes to replace those lost ORS contain salts to help replenish fluids ORS contain glucose which enhances electrolyte absorption and provides energy |
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Why might a patient taking ORS with glucose feel that their symptoms were worsening and stop treatment? |
Presence of sugars in the gut e.g. the glucose in the ORS can increase the rate of diarrhoea so the patient might think their symptoms are worsening. |
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Explain how ORS cause water to reenter the cells & blood |
ORS contain high concentrations of glucose & sodium. They enter the gut lumen in high concs. & are transported into epithelial cells by sodium-glucose symport. Influx of sodium causes a +Ve charge within the cell & results in Cl- moving down its electrochemical gradient, and back into the cell. Water follows down its osmotic gradient to a region of more negative water potential. Water can then reenter the blood to restore blood volume |
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How is a knowledge of ion transport in the intestine important when devising a treatment for cholera? |
Water & ion fluxes in response to cholera infection need to be understood to deliver appropriate treatment First step is knowing that the cholera toxin affects chloride transport so that chloride ions enter the gut lumen at a higher rate than normal Knowing that sodium ions and then water will follow reveals the cause of the diarrhoea. A treatment that increases epithelial cell uptake of sodium & chloride to counter these losses can then be devised.
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Explain how the cholera toxin causes a loss of water into the gut lumen |
Cholera toxin = 2 subunits (A & B) which bind to receptors on the cell membrane
Subunit A enters the cell & causes the ion channels in the cell membrane to open, causing the loss of Chloride ions (Cl-) into the gut lumen
This means there is now a higher water potential in the cell than in the gut lumen, so water moves out of the cell, following down its osmotic gradient to a region of lower water potentail |
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What are some of the ethical issues involved with trialling new ORS formulations on humans? |
- Risk the new product may worsen the diarrhoea - risk of undesirable unexpected side effects - if new product is ineffective, risk that the inadequacy of the treatment could be life-threatening - is it fair to do a double-blind trial in this situation? |
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What does a solution used for oral rehydration contain? |
Water- to rehydrate the tissues Sodium - to replace the sodium ions lost from the epithelium of the intestine, and to make optimum use of the alternative sodium-glucose carrier proteins Glucose - to stimulate the uptake of sodium ions from the intestine and to provide energy Potassium - to replace lost potassium ions and to stimulate appetite Other electrolytes - such as chloride and citrate ions, to help prevent electrolyte imbalance |
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How is Cholera transmitted? |
- drinking water not properly purified, i.e. dirty drinking water - untreated sewage leaks into water courses - food is contaminated
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How does vibrio cholerae cause disease? |
- Ingested by humans 1)Travel to small intestine, use their flagella to propel themselves through the mucus lining of the intestinal wall
2) Then start to produce a toxic protein which has 2 parts. One binds to specific carbohydrate receptors on the cell-surface membrane. (Only the epithelial cells of the small intestine have these specific receptors which is why the cholera toxin only affects this region of the body). The other part, the toxic part, enters the epithelial cells
3) This causes the ion channels of the cell-surface membrane to open, so that the chloride ions that are normally contained within the epithelial cells flood into the lumen of the small intestine.
4) Loss of chloride ions from the epithelial cells raises the water potential of these cells, while the increase of chloride ions in the lumen of the intestine lowers its water potential. Water therefore flows from the cell into the lumen
5) loss of ions from the epithelial cells establishes a conc. gradient. Ions therefore move by diffusion into the epithelial cells from the surrounding tissues, including the blood. This in turn establishes a water potential gradient that causes water to move by osmosis from the blood and other tissues into the intestine
6) It is this loss of water from the blood and other tissues into the intestines that causes the symptoms of cholera, mainly diarrhoea and dehydration. |
