Why do people with severe radiation sickness get that period where they suddenly get completely fine before getting worse again?

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Why do people with severe radiation sickness get that period where they suddenly get completely fine before getting worse again?

In: Biology

The cell life cycle exists in stages. Prior to cell division the cell does a self-check of the DNA to verify it’s all where it should be to ensure healthy cell division. If the DNA is damaged and cant be repaired then apoptosis occurs, programmed cell death.

When exposed to high levels of radiation some cells are severely damaged while others are only somewhat damaged. The severely damaged ones die off relatively quickly. Then healing occurs which triggers “healthy” cells to divide to replace the dead cells. Those “healthy” cells go through their checks to ensure successful division. This is when the DNA damage is discovered and the cells kill themselves, resulting in the delayed, more severe cell die off.

It has to do with the destruction of stem cells.

Stem cells are the cell factories of your body. Cells of various organs and tissues are constantly dying and needs replacement. Your stem cells are responsible for creating these new cells.

Now while most cells in your body are quite passive, the stem cells are constantly working very hard. This means that the stem cells are very sensitive to radiation damage, because they don’t have time to repair any DNA damage.

So at high doses of radiation, most, if not all, of your stem cells die. Many things start to happen, but most notably is the grinding of the [villi](https://image.shutterstock.com/image-vector/intestinal-villi-anatomy-small-intestine-260nw-502678183.jpg) in your intestine. These are in your gut and help with absorbing nutrients in food. But they are constantly physically grinded down by the same food. Unfortunately, the stem cells responsible for replacing these villus cells are dead, and now it’s a ticking bomb until the villi are all completely worn down. This takes roughly 1 week.

When this happens, chaos really starts to break loose, since your intestines are being physically damaged from the inside out. This may eventually lead to infections, and death.

Naturally, other parts of your body will also be affected by the lack of stem cells. Wherever regeneration of cells are necessary, damage will be inflicted in time. Notably your stem cells responsible for white cells die, leading to a submission of your immune system (this is why patients with radiation sickness are quarantined). The radiation burns also start deteriorating further. Even if you can halt off any infections and survive long enough, general organ failure (= death) may eventually occur as some organs start shutting down due to lack of new cells. Surviving radiation poisoning means hospitalization and attempting to hold off any infections. If the damage is bad enough, a transplant of new stem cells might be necessary (e.g. bone marrow transplant, skin drafts, etc). Doses high enough to shut down organs are not survivable.

This explains why the effects of radiation poisoning takes a week or so to really start manifesting. But you mention something very interesting in your question. The initial syndromes of radiation poisoning include nausea, fatigue, diarrhea, vomiting, sensory malfunction, etc. The real question is why *these* things happen. Why are there immediate effects at all? Unfortunately, we don’t exactly know. This is something that we can speculate about, and there are many theories (some of which are very likely true), but we don’t have any conclusive evidence for any explanations. It is of course something that’s very hard to do research on. While DNA damage occurs immediately upon radiation exposure, the effects shouldn’t really be noticeable until the next cell cycle. Some theories propose that it’s the nervous system which becomes over-saturated with inputs from electrical signals produced by the radiation. But for now, we don’t know.