Injury By Physical Agents Notes

Injury By Physical Agents

Thermal And Electrical Injury:

Thermal and electrical burns, fall in body temperature below 35°C (hypothermia) and elevation of body temperature above 41°C (hyperthermia), are all associated with tissue injury.

Read And Learn More: General Pathology Notes

1. Hypothermia: Hypothermia may cause focal injury as in frostbite, or systemic injury and death as occurs on immersion in cold water for varying time.
2. Hyperthermia: Hyperthermia likewise, may be localised as in cutaneous burns, and systemic as occurs in fevers.
3. Thermal burns: Thermal burns depending upon severity are categorised into full thickness (third degree) and partial thickness (first and second degree). The most serious complications of burns are haemoconcentration, infections and contractures on healing.
4. Electrical burns: Electrical burns may cause damage firstly, by electrical dysfunction of the conduction system of the heart and death by ventricular fibrillation, and secondly by heat produced by electrical
   energy.

Injury By Radiation

The most important form of radiation injury is ionising radiation which has three types of effects on cells:

1. Somatic effects cause acute cell killing.
2. Genetic damage by mutations and therefore, passes genetic defects in the next progeny of cells.
3. Malignant transformation of cells.

Ionising radiation is widely employed for diagnostic purposes as well as for radiotherapy of malignant tumours. Radiation-induced cell death is mediated by radiolysis of water in the cell with generation of toxic hydroxyl radicals.

During radiotherapy, some normal cells coming in the field of radiation are also damaged. In general, radiation-induced tissue injury predominantly affects endothelial cells of small arteries and arterioles, causing necrosis and ischaemia.

Ionising radiation causes damage to the following major organs:

• Skin: Radiation dermatitis, cancer
• Lungs: Interstitial pulmonary fibrosis
• Heart: Myocardial fibrosis, constrictive pericarditis
• Kidney: Radiation nephritis
• Gastrointestinal tract: Strictures of small bowel and oesophagus
• Gonads: Testicular atrophy in males and destruction of ovaries
• Haematopoietic tissue: Pancytopenia due to bone marrow depression
• Eyes: Cataract

Besides ionising radiation, another form of harmful radiation is solar (ultraviolet) radiation which may cause acute skin injury such as sunburns, chronic conditions such as solar keratosis and early onset of cataracts in the eyes.

It may, however, be mentioned in passing here that electromagnetic radiation produced by microwaves (ovens, radars, diathermy) or ultrasound waves used for diagnostic purposes do not produce ionisation and thus are not known to cause any tissue injury.

Injury by Physical Agents:

• Physical agents causing tissue injury are thermal and electrical burns, fall in body temperature below 35°C (hypothermia) and elevation of body temperature above 41°C (hyperthermia).
• Ionising radiation and solar radiation cause damage to somatic cells, genetic damage and malignant transformation