Effects of Radiation Exposure on Human Blood Forming Organs

          Radioactive are unstable atoms whose nucleus change or decay by spitting out radiation, which is in the form of particles or electromagnetic waves. Radiation can kill living cells or change the nature of living cells. Since all living things contain living cell, whether the radiation is large dose or low dose, naturally occur or manmade, it can be bring some biological effects to human body. Among all organs in the body, the organ mostly get affected by radiation from radioactive process is blood-forming organ. 

          Blood forming organ is an organ that synthesizes blood cell such as erythrocytes, leukocyte and platelets. The examples of blood forming organs are spleen and bone marrow. Blood forming organs are the most sensitive organs to radiation due to its rapid regeneration time. When blood forming organs are exposed to the radiation from radioactive component, early lethal effects that appear is hematopoietic syndrome. Hematopoietic syndrome presents due to ionizing radiation impairs hematopoiesis through a variety of mechanisms. Ionizing radiation exposures directly damages the hematopoietic stem cells and affects bone marrow in maintaining or supporting hematopoiesis in vivo and in vitro. Hematopoietic syndrome could cause death when body exposure at radiation doses <8 Gy (1 Gy = 1 Joule/Kg). Peak incidence of death occurs at about 30 day’s post- irradiation and also continues for up to 60 days. Exposure to ionizing radiation causes normal bone marrow and also spleen functions to be suppress with redistribution and apoptosis of mature formed elements of the blood. Symptoms that usually are associated with hematopoietic syndrome are fatigue, internal bleeding, bacterial infections, fever, ulceration or anaemia. Death normally occurs unless receive bone marrow transplant. 

         

          Disease that is associated with blood forming organs caused by ionizing radiation exposure is leukemia.  Leukemia is a cancer of white blood cells that begins in the bone marrow. When leukemia develops, it leads to an uncontrolled increase in the number of leukocytes. An increase in the number of leukocytes in human body can prevent healthy erythrocyte, platelets and mature leukocytes from being made. During the Second World War, two atomic bombs were dropped on Hiroshima and Nagasaki in Japan, there were 176 leukemia deaths among 50,113 survivors with significant exposures (>0.5 Gy). It was estimated that about 90 of these death are associated with radiation exposure. Symptoms that are associated with leukemia are anemia, bleeding, weight loss, night sweats, fever and easy bruising.

Radiation Damage on Skin

          Radiation skin damage can happen after a person receives radiation treatment for cancer. It can also occur when a person is accidentally come in contact with unsecured radiation sources such as food irradiators, radiotherapy equipment, x-ray machines, nuclear power or nuclear weapons. Skin damage can start to show within a few hours after exposure. However, some effects may not appear for months or even years. It depends on the amount of radiation and which part of the body was exposed.

          When the skin receives a significant dose of radiation, the symptoms occurred include swelling, erythema (skin redness like sunburn), dryness, itchiness, dry desquamation (peeling), increased pigmentation, epilation (hair loss) at the site, moist desquamation (blistering) and ulceration. Later effects may include thinning and hardening of the skin and difficulty with wound healing. When radiation damages cutaneous and subcutaneous tissue, the loss and damage of sweat glands, nerve tissue, hair follicles and blood vessels may be occurred.

Examples of radiation skin reactions:

Figure 1: Erythema (skin redness)

            

Figure 2: Dry Dequamation

 

Source: BC Cancer Agency, 2006.

          Skin effects are more likely to occur with exposure to low energy gamma, X-ray or beta radiation. It usually requires doses of about 300 rad (3 Gray) to produce a visible reddening of the skin. Hair loss can occur after acute doses of about 500 rad (5 Gray). The dose required for skin blistering to occur is relatively high, which in excess of 1,200 rad. Doses of about 1500 rad (15 Gray) produce serious burns with blistering. Doses reach 3000 rad (30 Gray) may result very serious burns which requiring skin grafts or amputation. More extensive skin damage involves deeper layers of the skin, such as tissue necrosis. In addition, skin cancers, tendon and joint degeneration may occur up to years after the dose.

          For the treatment of the radiation damaged skin, keeping the skin clean and excluding infection while the skin heals. Irritating substances such as brushes and soaps should be avoided.  Patients should be encouraged to wash the irradiated skin daily using gentle soaps and are discouraged from using any perfumed or alcohol contained products which may possess chemical irritants. Rubbing, scratching and massaging the skin should also be discouraged. On the other hand, direct application of heat or cold to the irradiated area such as ice or heating pads should be avoided. Protection from sun exposure is also required. Patients should be instructed to avoid direct sun exposure by cover the irradiated skin and by the use of sunscreen products.

          For serious radiation exposure, the key treatment includes immediate care and use of medications to inhibit infection, reduce inflammation and relieve pain. For itchiness, antihistamines and corticosteroids may be prescribed. Pentoxifylline, vitamin E and interferon gamma may be prescribed to stimulate blood circulation and to reduce fibrosis or thickening of skin tissues. In some cases, plastic surgery may be recommended by the doctors. Complete healing of the skin may take from several weeks up to a few years depending on the radiation dose of the skin received. In general, all of these injuries will recover, but may leave weakened skin. However, relatively high doses of radiation will result in skin that cannot be saved.

References: 

BC Cancer Agency, 2006. Care of radiation skin reactions.

Retrieved on July 2, 2011. Available from: http://www.bccancer.bc.ca/NR/rdonlyres/79E81484-6809-41CF-8CC2-0646DA6003F8/50912/CareofRadiationSkinReactions.pdf

Effects of Radioactivity towards Human Reproductive Organs

Radiation effects are varying with the dose, dose rate, sex and age. In males, spermatogonia are the most radiosensitive whereas for spermatozoa and spermatids are radioresistant. In general, radiation could cause sterility effect that warrants special attention. When the testis received a scattered dose from nearby abdominal and pelvic irradiation field, this may directly affect the gonads thus leading to infertility and impaired sex steroid production. In general, lethally irradiated cells die during division. A direct radiation dose as low as 0.15 Gray (Gy) is able to cause a significant depression in the sperm count and temporary azoospermia occurring after exposure to doses of 0.3 Gray. Furthermore, after exposing to doses as low as 1 Gy both of their numbers and that of their daughter cells, the preleptotene spermatocytes, are severely reduced. The doses of irradiation required to kill spermatocytes are higher than for spermatogonia whereby 2-3 Gy is able to result in an inability to complete maturation division, with a resultant decrease in spermatid numbers. However, spermatids show no overt damage, but after 4-6 Gy the resultant spermatozoa are significantly decreased in number, signifying covert spermatid damage (Amanda L. et al., 1993).Hence male sterility will have a reduced sperm count and low motility. Other than this, irradiation of the testis might occur during therapeutic, diagnostic procedures and occupational exposure. Irradiation of the testis during the radiotherapy treatment of cancer usually involves fractionated exposures. Under certain conditions, fractionation results more stem cell to be killed than single dose treatments, although this has not been proven in man (Hahn et al.). In addition, radiation might also result from accidental exposure. For instance during nuclear reactor accidents, this exposure may result in whole body exposure at doses below the threshold for lethality but above those capable of inducing long-term sperm count depression.

In females, ovarian follicles are the most radiosensitive. The radiosensitivity of the oocyte varies during the growth phase and is dependent on the age, the strain of the animal, and the species. In women, primordial oocytes are more resistant to the effects of radiation than oocytes in growing follicles. Other than this, permanent sterility which is manifested by the damage to the ovarian follicles occurs with 320 to 625cGy of the irradiation. However, follicles may recover in 5 to 6 months if the dose is lower. In younger women, relatively large dose are required to cause the damage than in older women. As radiation could cause a devastating effect in the embryo and fetus in expectant mothers, diagnostic radiological and nuclear medicine procedures are contraindicated for them. This is due to radiopharmaceuticals will reside in the body following a biological half-life, therefore it is more likely to cross the placenta thus cause fetal damage and may have a higher rate of miscarriage or stillborn baby. In those women whom the uterus has been involved in the radiation field, there is evidence that radiation changes to the uterus result in failure to carry a pregnancy, which has implications for in vitro fertilization in women with concomitant ovarian failure (Amanda L. et al., 1993).

Radiation Effects on Human Gastrointestinal Tract

           The gastrointestinal syndrome describes the effects of radiation poisoning on the stomach and intestine. Radiation with doses of 200 rems or more will cause gastrointestinal syndrome within first hour after exposure. The radiation will damage the gastrointestinal tract lining which leads to nausea, bloody vomiting, abdominal pain, diarrhea and poor appetite. This first phase may last for a few days and follow by a syndrome-free period. As the radiation continues to destroy the cells of the intestinal tract, the shedding of the dead cells will cause bloody diarrhea and severe dehydration. In addition, the blood vessels in the colon and rectum will bleed easily which also causing bloody stool. At this point, radiation begins to destroy the cells that multiply quickly. 

          The most radiation sensitive organ within the gastrointestinal tract is small intestine. It is the organ which will determine the survival of a person with an acute massive attack of radiation. In a healthy individual, the lining cells of the small intestine are constant replace by crypt cells. With acute dose of radiation, inflammation of the small intestine can occur along with scaring and blockage of the small intestine. The crypt cells are killed and the lining of the small intestine ruptures. The loss of cells leads to digestive tract vulnerable to bacteria which can cause life-threatening infections. Once the digestive system ceases to function, death can result within a few weeks due to loss of fluid and electrolytes or infection.

An Introduction to Radioactivity

              Radioactivity is the spontaneous emission of radiation which in the form of high energy photons or particles. Radiation occurs when unstable atomic nuclei decay and release particles.The unit used to measure radiation dosage applied to humans is the rem (roentgen equivalent in man). The rem is accounts for the effectiveness of the radiation to cause biological damage to living tissue. The dose of rems determines how much harm a person suffers. A rem is equal to 0.01 sievert in the International System of Units (SI). Radiation damage to the body cells can occur if a person is exposed to radiation through x-imaging, nuclear power or fallout from nuclear weapon. It can also occur after a person receives radiation therapy which used to treat cancer.

              Even radiation will cause biological damage to living cells but not all the cells are equally sensitive to radiation. Those cells which are actively reproducing are more sensitive compare to those cells which are not. This is due to dividing cells requiring correct DNA information for the cell’s offspring to survive. A direct interaction of radiation with the active cells might result in mutation or death of the cells. However, direct interaction of radiation with the DNA of a dormant cell would not have significant effect. Therefore, rate of production of the living cells indicates their sensitivity to radiation; different cells systems have different sensitivities.

Introduction of Anatomy and Physiology

Anatomy is the science of the structure of animal bodies, either living or dead.
Physiology is the science of the function, purpose, or action of living animal tissue. Both sciences usually study either humans alone or humans in relation to other animals.

Aristotle, the world's first meticulous biologist, conducted his own experiments and advocated that others likewise do so. Nevertheless, in a very un-Aristotelian way, his results and those of his school were enshrined in the centuries after his death while his rigorous empirical method was mostly ignored.