Whats the topic for today?

Well I talked about dogs urine last time so I couldn’t resist following that up with a talk about diarrhoea.
Bring it on, I’m sure our listeners can cope! So what causes diarrhoea?
Lots of things. I did a search on the web and came up with 281 causes of diarrhoea.
That’s a lot. Have we got time to talk about them all?
No but we can talk about the underlying physiological causes of diarrhoea. Basically we get diarrhoea when there is too much fluid in the faeces. The bowel absorbs water from the faeces so anything that prevents water absorption will cause diarrhoea. Similarly anything that causes water to enter the bowel will also cause diarrhoea.
So what sorts of things will make that happen
If the lining of the bowel is damaged its ability to absorb water will be reduced. All sorts of things can damage the lining of the bowel including bacteria, viruses, parasites, protozoa, toxins, a variety of specific bowel diseases like inflammatory bowel disease.
What would cause water to enter the bowel?
If food is not digested properly it actually draws water into the bowel by osmosis. There are all sorts of reasons why the food might not be digested but a common reason is simply that the gut becomes overactive and pushes food through the system far too fast for it to be digested.
Why would the bowel become overactive?
Its usually in response to an irritant substance or a toxin or infection. Its natures way of purging unwanted substances from the body  by shunting it through the system as quick as possible.
So does that mean diarrhoea is a good thing?
In some ways yes because the body is getting rid of the cause. There are drugs available that slow the activity of the gut to stop the diarrhoea but we don’t use these in the early stages of diarrhoea. We use them if the diarrhoea is severe or persistent and the patient is at risk of becoming dehydrated.
How do you set about diagnosing which of those 281 possibilities is causing the diarrhoea?
Most diarrhoeas only last a few days so initially we are more concerned about treating the symptoms and preventing dehydration than actually finding the cause. The first thing we do is to decide if the diarrhoea is from the small intestines or the large intestines as the causes and treatment for these will be different.
How can you tell the difference?
Generally small bowel diarrhoea is profuse and watery whereas large bowel diarrhoea is more often small pasty droppings often coated in fresh blood and a jelly like mucous.
If the diarrhoea doesn’t clear with initial treatment what do you do next?
If the diarrhoea persists or is unusually severe then we start off by sending a sample of diarrhoea to a pathology lab.
What sort of things will they do with it?
Firstly they will look down the microscope for any evidence of parasite eggs as worms is one of the biggest causes of diarrhoea. They will also be looking for protozoal infections like giardia or coccidiosis. Then they will culture the faeces to look for bacteria like salmonella or campylobacter. They can also test for viruses like parvovirus.
What if all these tests come back negative?
Then we will likely take blood and urine samples to look for signs of systemic disease as diarrhoea can be caused by all sorts of internal disease. Liver or pancreas diseases are a common cause of diarrhoea.
Are there any other tests available?
We can take x-rays and do ultrasound examinations but the ultimate test is to take bowel biopsies. For this we need to do open abdominal surgery and this also allows us to actually see the bowel and internal organs. The combination of all these tests usually comes up with a diagnosis.
So its seems that studying diarrhoea is quite useful then?
Yes you could say that and also possibly quite interesting