1. CHOLERA

2. Disease caused by infection with cholera bacterium – from? Symptoms = Diarrhoea and hence dehydration How the Cholera bacteria causes the disease 1.Firstly, most people infected don’t become ill, why not? 2.The bacteria that survive propel themselves through the thick mucus lining the intestine wall into the intestine wall. 3.The bacteria then produce a toxin which opens chloride ion channels in the intestine epithelial cells. 4.Chloride ions flow out into the lumen of the intestine. 5.This lowers the water potential of the intestine lumen (lower than the intestine cells). Water then moves by osmosis from the intestine cells into the lumen. Causing diarrhoea.

3. Extra 7. The loss of ions from the intestine epithelial cells creates a concentration gradient and hence ions diffuse into the epithelial cells from the blood and other tissues. This in turn establishes a water potential gradient causing water to move from the blood and tissues into the intestine lumen – this leads to severe diarrhoea and dehydration. 8. Six litres of water can be lost per day into the intestine lumen.

4. Diarrhoea and Oral Rehydration Solutions (ORS) Diarrhoea is the production of watery faeces (frequently). CAUSES 1.Damage to the intestine lumen 2.Loss of microvilli 3.Excessive secretion of water due to toxin (e.g. cholera) MAIN PROBLEM = excessive water loss from body and insufficient taken in can lead to dehydration, which can be fatal.

5. TREATMENT Rehydration of patient with Oral Rehydration Solutions (ORS) - not just water. These contain: 1.Water 2.Ions such as sodium, potassium and chloride 3.Glucose ORSs are often sold as a powder to be mixed with boiled water and taken regularly. There is usually a 1:1 ratio of glucose to sodium ions (Na + ) to give optimum conditions for the glucose/Na + co-transport. Once the glucose/Na + enter the epithelial cells of the intestine, water follows from the lumen by osmosis.

6. Development of ORS 1.Drug trailing – what do you remember from GCSE? Early problems with ORS Too high concentrations of glucose/ Na + led to increased water loss from cells. BUT – less glucose = less energy. Hence starch added to solution which can be steadily broken down to provide energy and does not lead to water loss by osmosis. Also eventually settled on a 1:1 ratio of Na + : glucose

7. Ethical Issues 1.Who should take part in the trials and how be recompensed? 2.Volunteers? 3.Fully aware of risks. 4.No chance of permanent damage?. 5.Only competent professionals to carry out trials. 6.All results to enter the public domain?