1124 RADIATION BIOLOGY 



GASTROINTESTINAL SYSTEM 



There are marked variations in the radiosensitivity of the several 

 types of epithelium lining the various segments of the digestive canal, 

 reflecting differences in their histological constitution. The stratified 

 squamous epithelia lining hollow viscera are about as radiosensitive as 

 the stratified squamous epithelium of the skin (Lacassagne and Gricouroff, 

 1941). This is presumably due to injury of the cells in the germinative 

 layer of the epithelium with resulting failure to produce new cells to 

 replace those more superficial ones which will be desquamated with or 

 without previous cornification. Those covering epithelia of the digestive 

 system composed of columnar cells are decidedly more resistant than the 

 stratified squamous epithelia. However, this columnar epithelium is 

 provided with areas of less differentiated, germinative cells and these have 

 been found to be relatively radiosensitive. 



Associated with the digestive tract are the large salivary glands, the 

 liver, and the pancreas. These show contrasts in reactivity, the liver and 

 pancreas being very difficult to injure by radiation while the salivary 

 glands are somewhat more sensitive. 



Mouth, Nasopharynx, and Esophagus. Except in a few areas these 

 cavities are lined with stratified squamous epithelium, and they show, 

 after irradiation, changes similar to those shown by the epidermis. In 

 man complete desquamation and subsequent repair in these mucous 

 membranes occur somewhat earlier than in the skin after comparable 

 doses of radiation, and variations in sensitivity in the mouth, tongue, 

 inner surfaces of the cheeks, and nasopharynx have been described 

 (Coutard, 1922). With larger doses, necrosis of the epithelia and the 

 underlying tissues may result. As in the skin, fragility of the epithelium, 

 marked scarring, and permanently dilated vessels persist. There seem to 

 be no extensive studies on experimental animals. 



Stomach and Intestines. Destructive changes in the gastrointestinal 

 tract are noted as early as 3^ hour after exposure to a moderately large 

 dose (Pierce, 1948), the damage being greater in the small intestine than 

 in the stomach or colon, greatest in the crypts, most pronounced at 8 

 hours, and repaired within four weeks. With smaller doses the injury 

 is not so severe and repair is completed earlier, while with larger doses 

 (2000 r to the abdomen of dogs), the intestine may be so greatly damaged 

 as to lead to severe hemorrhages and ulceration with death of the animals 

 (Regaud, Nogier, and Lacassagne, 1912; Stafford L. Warren and Whipple, 

 1922). There are considerable species differences and unfortunately 

 many of the experiments are not comparable as to dosage and species. 



In contrast to the paucity of reports of studies on the upper portions of 

 the digestive tract, there is a voluminous literature on experimental and 

 therapeutic radiation of the stomach. The changes are of two main 



