There are two categories of nuclear radiation when it comes to its effects on human physiology: nonionizing and ionizing. Microwaves, radio waves, and ambient light are examples of nonionizing radiation that typically do not cause any physiological changes.  However, ionizing radiation, when exposed to in large doses, can cause radiation sickness or even certain death with radiation exposure upwards of 6 Gray unit (Gy).  In this paper, exposure to radiation will be studied more in detail in terms of its physiological effects on two parts of the body: bone marrow and the stomach.
The bone marrow is a tissue that functions as an organ to multiple skeletal systems in the body. It comprises haemopoietic cells, parenchyma cells, and the stroma. Haemopoietic stem cells give rise to blood cells with the aid of colony stimulating factors from parenchyma cells, while the stroma mostly provides the structural support.  When exposed to radiation that is less than 1 Gy for just over four months, the number of haemopoietic cells and the parenchyma cells begin to plummet.  The haemopoetic cell damage resulted in the lessening of the number of progenitor cells, which were estimated by measuring granulocyte-macrophage colonies.  In addition, Parenchymal cell damage invoked the inability for the progenitor/stem cells to produce differentiated blood cells, which clinically manifests itself as anemia.  Lastly, long-term exposure to radiation more than 2 Gy on the stroma can cause significant disabilities on the cell replication of supporting structures.  The stroma and parenchymal cells support haematopoiesis, the production of blood cells, and constant radiation may disrupt this replicating behavior.  Over all, damage to these three parts of the bone marrow may ultimately result in bone marrow cancer in the form of myelofibrosis and anemia.
Radiation on the abdomen may incur some damage on the digestive tract. The extent of the physiological changes in the stomach, especially, is dependent on the dose of the radiation and the sensitivity of the gut.  It is well known that chronic exposure to radiation can come from ongoing nuclear radiation therapy that patients have to go through, although it only uses trace amounts of radiation.  In the beginning, physiological changes manifest themselves through mucosal thinning and slight decrease in gastric acid production. [5,7] Unlike the bone marrow, the stomach is more resistant to radiation as it requires 40~50 Gray units of radiation at one sitting to cause major damage to chief gastric cells and parietal cells that aid in digestion with supplemental enzymes and acids.  The thinning of the mucosal lining and the death of digestion-aiding cells will ultimately result in gastric ulcerations.  Although the stomach may seem resistant to stronger doses of radiation than the bone marrow, constant chemotherapy and abdominal strategy will compound on the probability of slight ulcerations and antral stenosis. 
Diagnosis of injuries due to nuclear radiation exposure is difficult conduct without consulting a doctor. Whether it be in frequent low doses or periodic high doses, altogether, exposures to sensitive locations like the bone marrow and the gastrointestinal tract may causes irreversible physiological changes to their proper functions. [3,6]
© James Bai. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 C. H. Schultz and K. L. Koenig, "Weapons of Mass Destruction," in Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th Ed., by J. A. Marx et. al (Saunders, 2013), p. 2469.
 E. Zhao, et al., "Bone Marrow and the Control of Immunity," Cell. Mol. immunol. 9, 11 (2012).
 T. M. Fliedner, W. Nothdurft and W. Calvo, "The Development of Radiation Late Effects to the Bone Marrow After Single and Chronic Exposure," Int. J. Radiat. Biol. Re., 49, 35 (1985).
 Z. Zhang et al., "Effects of Gamma Radiation on Bone-Marrow Stromal Cells." J. Toxicol. Environ. Health A 73, 514 (2010).
 J. M. Novak et. al., "Effects of Radiation on the Human Gastrointestinal Tract," J. Clin. Gastroenterol. 1, 9 (1979).
 J. C. Harbert and J. S. Robertson, Nuclear Medicine Therapy (Thieme Medical Pub., 1987).
 H. M. Goldstein et al., "Radiological Manifestations of Radiation-Induced Injury to the Normal Upper Gastrointestinal Tract," Radiology 117, 135 (1975).