The use of oral rehydration solutions (ORS) in the treatment of diarrhoeal diseases. The applications and implications of science in developing improved oral rehydration solutions; ethical issues associated with trialling improved oral rehydration solutions on humans.

Diarrhoea leaves people dehydrated and with depleted amounts of necessary salts, as these things are lost in faeces. Cholera is an example of an illness that causes diarrhoea.

Oral rehydration solutions (ORS) are used to rehydrate and replenish key molecules.

ORS is a mixture of water, salts and sugars. A simplified ration is 1 litre of water to six teaspoons of sugar to half a teaspoon of salt. The water is often boiled to sterilise it.

• Sodium is needed because it goes into the cells and brings the water potential back down, this means water will move by osmosis back into the cells, and from there into the blood.
• Sodium has to enter the cells through co-transportation (because the normal carrier proteins are pumping sodium out) with glucose- this means that glucose is also needed.
• Other salts that make ORS isotonic; so that when people are drinking it their cells do not absorb all of the water and burst.

To work out the right proportions of salts and liquids, a lot of testing had to be done. This involved trialling early mixtures on humans to note the side effects and make appropriate changes. In the process many peoples conditions were worsened due to having too much of a certain molecule: too much glucose in one trial resulted in more water being drawn into the intestine and the diarrhoea was worsened.

Some claim that it is immoral to jeopardise peoples health by giving them un-trialled solutions; however, by trying out the solutions on people, scientists were able to refine ORS to create an effective treatment that saves many lives.

The specification wants you to say it contains glucose and:
Sodium (ions) / potassium (ions) / chloride (ions) / citrate (ions); 

Cholera bacteria produce toxins which increase secretion of chloride ions into the lumen of the intestine. This results in severe diarrhoea.

Toxins produced by the cholera bacteria effect the epithelial cells of the intestine- this is because it is complimentary to the receptors that only these cells have.

One half of the toxin binds to a receptor on the surface of the cell- this gives the other half access to the cell, so it can affect the producer of cAMP (that being a signal used within the cell).  The signal causes a protein channel to transport chloride ions out of the cell.

The effected cells are in the intestine, which chloride ions will now begin to flood into. The chloride ions lower the water potential in the intestine so water moves into it (along the gradient from high to low.) The intestines are where faeces is made, so when an effected person defecates it has a very high water content- diarrhoea. Because there is a lot of water in the intestine, molecules like salts will move into the intestine too (where they are in lower concentration) meaning that they too are lost in faeces.

The cholera bacterium as an example of a prokaryotic organism. The structure of prokaryotic cells to include cell wall cell-surface membrane, capsule, circular DNA, flagella and plasmid.

The bacterium that causes cholera is a prokaryotic organism as are all bacteria. 

These cells contain fewer organelles than an animal cell, and have some other features.

They have a cell-surface membrane, but they also have a cell wall like a plant: they have another layer outside of this to offer additional protection called a capsual.

The DNA in these cells is not contained within a nucleus- it is just a scrunched up ring called circular DNA.

A flagella helps bacteria move- often associated with sperm cells, but they are also important for cholera bacteria to get through the mucus lining to the epithelial cells in the small intestine.

Plasmids are small sections of DNA that are separate from the main circular DNA and replicate separately from it. They can carry genes that the bacteria didn’t always have and can be transferred between bacterium.