Radiation death is caused by a combination of factors, however , the primary factors are the destruction of the hematopoietic and lymphatic tissues. For survival, the regeneration of these tissues must be initiated immediately after injury. Delay can frequently result in infection and consequent death.

(a) Hematopoietic tissues produces hemoglobin required for oxygen transport - its failure caused by irradiation will result in the inactivation of the energy cycle of the metabolic processes essential for survival.

(b) Lymphatic tissues produce the factors responsible for the immune (protective) functions of the body which suppress the bacteria and /or viruses which are normal body flora. If these tissues are destroyed by radiation injury these organisms will proliferate causing life-threatening infections.

I. General Effect of Radiation

Damage to rapidly proliferating tissues - basis for cancer therapy.

II. Specific effects:

1. Hematopoietic systems - are destroyed.
2. Lymphatic tissue - in spleen, thymus, lymph nodes - are destroyed.
3. Gastrointestinal cells - are destroyed loss of selective permeability.
4. Blood-tissue barriers - are damaged resulting in an increased permeability.

a. Hemorrhaging.
b. Susceptibility to bacterial and viral invasion.

5. Skin barrier breached - possible bacterial infection.
6. Formation of free radicals.

a. OH free radicals are formed which cause
b. DNA - mutation with the net result of:

i.  Cell death
ii. Chromosomal aberrations
iii. DNA strand breakage

III. Time Course

1. Five-ten days: death by infections.
2. After two weeks

a. Bone marrow deficiency - anemia
b. Lymphatic tissue deficiency - impaired immune system - death by
    infection.