Radiation Syndromes And Stages In Humans A syndrome is a combination of symptoms resulting from a single cause and occurring together so as to constitute a single clinical picture.Large acute whole-body exposures may result in one of three radiation syndromes.
a. 200 - 1,000 rads -- hematopoietic. Death, if it occurs, will primarily be a result of damage to the hematopoietic (blood forming) organs: red bone marrow, lymph nodes, spleen and thymus.
b. 1,000 - 5,000 rads -- gastrointestinal. Survival is impossible.Death occurs from both the damage to the lining of the GI tract (resulting in circulatory collapse) and damage to the hematopoietic system.
c. Above 5,000 rads -- central nervous system
What are the 4 stages of each syndrome?
Each syndrome can be considered to progress through the following four stages:
a. prodromal (initial) stage
b. latent phase
c. a period of illness
d. recovery or death
Symptoms of the Prodromal Stage?
The symptoms may include nausea, vomiting and diarrhea as well as anorexia (loss of appetite) and fatigue.
To some degree, the time of onset of these symptoms is indicative of the magnitude of the dose, however, the appearance of these symptoms, especially nausea and vomiting, can also be induced psychologically.
Describe the Latent Phase.
This is a period between the prodromal stage and the onset of symptoms of later stages.
The higher the dose the shorter the latent phase.
At sufficiently high doses the latent phase effectively disappears.
Describe the illness period.
Many of the characteristics of the prodromal stage reoccur along with a variety of additional symptoms, i.e.,ulcerations about the mouth, fever, etc.
Describe the Recovery of Death phase.
With an acute dose above 1,000 rads (10 gray), death is almost certain, even with the best of medical care.
Describe the Effects of Radiation on Blood Cells (Lymphocytes).
These are a type of leukocyte responsible for antibody production.
Lymphocytes are formed in the lymph nodes, the thymus and parts of the spleen.
Although mature lymphocytes do not divide, they are very radiosensitive and can be killed directly by radiation.
Within 15 minutes of a dose as low as 10 rads (0.1gray), the lymphocyte population can be seen to decrease.
This decrease in the number of lymphocytes can be used to estimate the dose.
Recovery of the lymphocyte population is slow.
Describe the Effects of Radiation on Blood Cells. (Granulocytes)
This type of leukocyte is produced in the red bone marrow and fights infection by engulfing foreign particles in the body.
Granulocytes are radioresistant but their lifespan is less than one day.Damage to their radiosensitive precursors results in a measurable decrease in the number of granulocytes within a few days of the exposure.Recovery of the granulocyte population is faster than that for lymphocytes.
Describe the Effects of Radiation on Blood Cells. (Platelets)
These cytoplasmic fragments are produced in red bone marrow.
They are not true cells but play an important role in coagulation.
Following acute whole body doses above 50 rads (0.5 gray), a decrease in the platelet population will occur in 2 - 5 days.They are radioresistant and any decrease in their number is due to damage to their precursor cells, the magakaryocytes. Their longer lifespan, approximately 4 days, means they disappear more slowly than granulocytes.
Describe the Effects of Radiation on Blood Cells. (Erythrocytes)
Erythrocytes are responsible for carrying oxygen from the lungs to the various tissues of the body.
They have an average life-span of 4 months.
Approximately one week after the exposure, a drop in the number of red blood cells will occur.
This decrease is a result of damage to their radiosensitive precursors, the stem cells of the red bone marrow.
The latter either stop dividing or die when they attempt to divide.
For the victim to have any chance at recovery, some of these stem cells must survive the exposure.
Progress of the Hematopoietic System Syndrome
Prodromal (Initial) Stage -- will occur within 1 to 5 days of the exposure.
Latent Phase -- will last 1 to 3 weeks after the prodromal stage.
Illness -- a period of extreme illness begins.
Death -- if it occurs, will be within a few days to 6 weeks of the exposure.
The most probable causes of death will be hemorrhaging and infection.
Description of Gastrointestinal Tract Lining
The lining of the gastrointestinal tract is covered with small finger-like projections called villi.
The cells on the surface of the villi are constantly migrating towards the tip of the projections where they are sloughed off.
Mitotically active cells (crypt cells) at the base of the villi replace those that are lost.
The turnover rate of these epithelial cells is high - they have an average life span from 1 to 3 days.
Effect of Radiation on GI Tract Lining
Sufficiently large acute exposures lead to the reproductive death of the crypt cells.
The cells covering the villi continue to be sloughed off but are no longer replaced.
This deterioration of the lining of the GI tract then leads to a loss of body fluid, inadequate absorption of nutrients and infection from the intestinal area.
Above 1,000 - 1,200 rads (10-12 gray) the crypt cells are completely destroyed, preventing any chance for recovery.
Progress of the GI Tract Syndrome
Prodromal (Initial) Stage – occurs within a couple of hours of the exposure, the individual will demonstrate a sharp loss of appetite, upset stomach and apathy. Several hours later NVD will occur.
Latent Phase -- By the third day after the exposure, the previous symptoms will have disappeared and the victim will appear healthy. The latent phase will last from 1 to 7 days.
Illness -- severe illness will follow the latent phase. This will include NVD, fever, apathy, anorexia and loss of weight.
Death -- within 3 to 12 days of the exposure
Progress of the GI Tract Syndrome
Once the cell renewal mechanism of the GI tract has been completely destroyed and cannot be replaced, death is inevitable.
The causes of death include fluid and electrolyte losses (circulatory collapse) brought about by the destruction of the lining of the GI tract.
Another contributing cause of death is infection.
Damage to the hematopoietic system simultaneously reduces the body's ability to cope with the infection.
Central Nervous System (CNS) Syndrome
Produced by acute whole body exposures above 5,000 rads (50 gray);
exposure of the head alone may have similar effects.
Survival is impossible.
Death results from respiratory failure and/or brain edema caused from direct or indirect effects on the CNS within 30 hours.
At these high doses, the individual stages of the central nervous system syndrome becomes so short that they cannot be distinguished.
Following exposure, the individual may function coherently for a short while or immediately go into shock.
Within hours the symptoms become very severe.
Symptoms include vomiting, diarrhea, apathy, disorientation, tremors and coma.
Radiosensitivity of tissue is directly proportional to its reproductive capacity and inversely proportional to the degree of differentiation.
Both experimental and clinical findings have shown that the human embryo is subject to severe radiation injury.
A few of the types of human abnormalities reported in the literature are blindness, cataracts, mental deficiency,coordination defects, deformed arms and legs, and general mental and physical subnormality.
The degree and kind of radiation damage is dependent on the stage of development of the embryo.
Most of the major organs in humans are developed during the period from the second to the sixth week post conception.
The majority of the gross abnormalities produced by irradiation of the embryo occur during this critical period.
Experimentally, doses as low as 25 rad (0.25 gray) have been shown to be effective in producing development changes if applied during this time.
Irradiation of the embryo after the period of major organ development produces delayed and less obvious effects, such as changes in mental abilities, sterility, etc.
A dose of 400 to 600 rad (4-6 gray) during the first trimester (excluding the first week) of pregnancy is sufficient to cause fetal death and abortion.
Human body cells normally contain 46 chromosomes, made up of two similar sets of 23 chromosomes each.
The 46 chromosomes of the human contain genes.
Genes occur in pairs with each pair determining a body characteristic.
For most gene pairs, one gene will dominate in producing a given characteristic.
Dominant genes are those which produce their effects even when only one of them is present in an individual, while recessive genes produce their effects only when an individual has two of them which are identical.
Consequently a recessive gene may be latent for a number of generations, until the union of sperm and egg cells which both contain the same recessive gene.
As the individual develops, the 23 chromosome pairs (half from each parent) are almost always duplicated without change.In some instances, the chromosome will fail to duplicate itself in every respect, a change occurring in one or more of the genes.
This change, called a mutation, is essentially permanent, for the mutant gene is reproduced in its altered form.
Body cells are called “somatic” cells.
Germ cells reside in the testes or the ovaries and are used to make sperm or ova.
If a change occurs in a somatic cell, there may be some effect on the individual, but the change is not passed onto the progeny.
If a change occurs in a germ cell, no visible injury will be sustained by the individual, but the effect may appear in future generations.
Changes in the germ cells are “heritable”, i.e., they can be inherited.
Somatic effects occur in the exposed individual, and heritable effects may occur in future generations.
Heritable Effects (Mutations)
It is generally believed that there is no threshold for genetic mutations resulting from exposure to ionizing radiations.
Most geneticists agree that the spontaneous mutation rate may be doubled without seriously endangering future generations.
The dose of radiation which will double the natural mutation rate (doubling dose) is estimated to be greater than 100 rem per generation.
Since the number of children conceived by an individual generally diminishes after the age of thirty, and since the number of persons occupationally exposed is only a small percentage of the total population, the current regulations are believed to be genetically safe.