Very small tears in the delicate anal tissue are apparently a common problem in humans, obviously more so in certain groups than others. Whether they’re microscopic or severe enough to cause bleeding, why doesn’t the faecal matter enter the blood stream and make you very ill? If you ate faeces you’d get gastroenteritis I assume, so wouldn’t faecal matter in the blood be really dangerous?
In: Biology
It’s because your immune system attacks any small numbers of bacteria that enter. If someone is severely neutropenic (very very low immune system usually because of chemotherapy), then avoiding constipation is important not only for comfort but also for prevention of bloodstream infection.
Every time you brush your teeth, bacteria get into your blood stream. Every time you have a bowel movement, bacterial translocation through the colonic mucosa does the same. But you have a mighty fine immune system capable of wiping out those small bacterial incursions. Additionally, mucosal tears don’t violate large enough blood vessels to allow large amounts of fecal matter into circulation.
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Large amounts of faecal matter in the blood can be very dangerous, but remember, the tear is microscopic, so only very small amounts get through. The body has a number of defense mechanisms once it detects disruption to blood vessels to prevent them from becoming contaminated.
Clots don’t just help to stop bleeding, but also provide an extra boost of immune defense to help immediately shutdown any bugs that can get in.
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