3. Physical agent’s effect to cell

•Radiation•Extreme thermal•Sudden change of air pressure•Electricity

1. radiation

• Radiation is the transmission of energy by electromagnetic waves and by certain charged particles (alpha and beta particles and neutrons) emitted by radioactive elements.

• Most of our information about whole-body irradiation has been derived from studies of Japanese atom bomb survivors and persons exposed during the Chernobyl nuclear power plant accident.

• 300 cGy: At this dose, a syndrome characterized by hematopoietic failure develops within 2 weeks, leading to bleeding, anemia, and infection. The last is often the cause of death, which occurs in about half of the people exposed.

• 10 Gy

In the vicinity of this dose, the main cause of death is related to the gastrointestinal system. At this dose, the entire epithelium of the gastrointestinal tract is destroyed within 3 days, which is the time of the normal life span of villous and crypt cells.

As a result, fluid homeostasis of the bowel is disrupted, and severe diarrhea and dehydration ensue. Moreover, the epithelial barrier to intestinal bacteria is breached; gut organisms invade and disseminate throughout the body. Septicemia and shock kill the victim.

• 20 Gy

With whole-body doses of 20 Gy and above, CNS damage causes death within hours. In most cases, cerebral edema and loss of the integrity of the blood brain barrier, owing to endothelial injury, predominate. With extreme doses, radiation necrosis of neurons can be expected. Convulsions, coma, and death follow.

2. Extreme thermal

• Extreme thermal can cause:a. Hypothermia is a Decrease in Body

Temperature Below 35°C (95°F)Hypothermia can result in systemic or focal injury. In localized hypothermia, actual tissue freezing does not occur. Frostbite, by contrast, involves the crystallization of tissue water.

• Acute immersion in water at 4°C to 10°C (39.2° to 50°F) reduces central blood flow. Coupled with decreased core body temperature and cooling of the blood perfusing the brain, this results in mental confusion. Tetany makes swimming impossible.

• Increased vagal discharge leads to premature ventricular contractions, ventricular arrhythmias, and even fibrillation. Within 30 minutes, heat loss exceeds heat production, and core temperature then begins to fall.

• Below 35°C, respiratory rate, heart rate, and blood pressure decline. If hypothermia is prolonged, decreased body temperature alters cerebrovascular function. When body core temperature reaches 32 °C (89.6°F), the person becomes lethargic, apathetic, and withdrawn. When it falls below 28°C (82.4°F), pulse and breathing weaken and coma supervenes.

• The most important factor in causing death is a cardiac arrhythmia or sudden cardiac arrest. These observations have been confirmed and extended, largely due to the indication of hypothermia in some patients undergoing open heart surgery. In fact, with careful pharmacologic control, prolonged periods of lower body temperature can be achieved with no residual harm.

b. hyperthermia

• Hyperthermia Means an Increase in Body Temperature

• Tissue responses to hyperthermia are similar in some respects to those caused by freezing injuries. In both instances, injury to the vascular endothelium results in altered vascular permeability, edema, and blisters. The degree of injury depends on the extent of temperature elevation and how quickly it is reached.

• Systemic Hyperthermia

• Fever is an elevation of body core temperature resulting from a change in the thermoregulatory center. It occurs because of (1) increased heat production, (2) decreased elimination of heat from the body (when reflecting an aberrant response of the thermal regulatory center), or (3) a disturbance of the thermal regulatory center itself.

• A body temperature above 42.5°C (108.5°F) leads to profound functional disturbances, including general vasodilation, inefficient cardiac function, altered respiration, and ultimately, death. Few, if any, defined pathologic changes are associated with fever alone.

3. Sudden change of air pressure• In high place such as in mountain (more than 4000m), it has a

low air pressure that increasing capillar permeability. And it can cause edema

• ExplosionAn explosion in the air can cause wave compression to the source so that can cause high pressure to abdominal, chest, and organ rupture.

• In lower place ( under the sea, underground or subway)Increasing oxigen, nitrogen and helium pressure so that make a ‘air bubble’ in blood and cause emboli

4. Electricity• Electricity can burn skin.• Cutaneous burns are the most common form

of localized hyperthermia. Both the degree and rate of temperature elevation determine the tissue response. A temperature of 50°C (120°F) may be sustained for 10 minutes or more without cell death, whereas a temperature of 70°C (158°F) or higher for even several seconds causes necrosis of the entire epidermis.

Cutaneous burns have been separated into three categories of severity: first-, second-, and third-degree burns.

• First-degree burns, such as mild sunburn, are recognized by congestion and pain but are not associated with necrosis. Mild endothelial injury produces vasodilation, increased vascular permeability, and slight edema.

• Second-degree burns cause epidermal necrosis but spare the dermis. Clinically, these burns are recognized by blisters, in which the epithelium separates from the dermis.

• Third-degree burns char both epidermis and dermis. Histologically, tissue is carbonized and cellular structure is lost.