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Now, what is the radiation effect at the next level, the cellular level?

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The cellular level, the issue here is the cellular effects of radiation can result

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any one of the following on the left-hand side.

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Again, on this slide, I've shown you a top diagram showing the cell cycle.

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Means any type of cells which is multiplying or dividing, they go through an

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interphase before they go to mitosis or meiosis stage to break up.

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So the radiation interaction depends at what cell level can result in a

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different cell damage. For example, here's an healthy normal cell, and now the

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radiation interacts, happen at the cellular level.

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That damaged cell can either repair itself,

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or it can have a neurotic, necrotic, or a mitotic catastrophe,

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autophagy, and mutated. Some of the cellular effect of irradiation is it is the

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instant death of the cells, it is reproductive death of the cell, or

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if it happen in the interphase stage, it's called the apoptosis or programmed cell

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death, that is the interphase death of the cell.

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The mitotic or genetic death, mitotic delay, interference of the function of the

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cell, or chromosomal damage. This is some of the things which we have understood

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depending on the timing of the radiation interaction with the cell.

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What do you mean by instant death?

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What we understand up till now is if you have a large volume of cells, if it is

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exposed to X-rays at gamma rays dose of about 100,000 rad or

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1,000 gray. This is a magnitude of order higher level than anything we see in

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medical imaging, so just want to clarify that.

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But I'm trying to understand the radiation biology at all different dose level.

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So if a cell's in a Petri dish, a large volume of cells are exposed to 1,000

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gray, which is really very high dose, that can result in a instant death

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of cells within few seconds or minutes due to gross disruption of the cellular

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form and structure. This is important to understand because we're going to come

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back and visit when you're talking about the acute radiation syndrome and so forth

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later. The second type of cellular effect is the reproductive death.

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Cells exposed to radiation doses of 100 to 1,000 rad, that is one to 10 gray,

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can permanently loses its ability to reproduce. That is called reproductive death.

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That is also we're going to talk on later stage about radiation effect with respect

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to sterility and so forth. The third effect of cellular effect of radiation is

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mitotic or genetic death. The mitotic or genetic death occurs due to

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exposure during the mitosis phase, as shown in this top diagram.

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The cell dies after one or more division, as they are most radiation-sensitive

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during the mitosis cell. Therefore, any radiation interaction at the mitosis

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divisions type phase can lead to cell death later.

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Even small quantity of radiation is enough to induce mitotic death.

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If the radiation level is still smaller, exposure as small as one rad, about 0.01

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milligray, you're talking now into the order of the medical imaging doses, there

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can be a mitotic delay, which means even exposure as small as one rad on

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cells entering mitosis can delay the start of the cell division.

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However, normal mitotic function resumes later.