Environmental disease

Physical Injuries

1.Mechanical Trauma 2.Thermal injury 3.Electrical injury 4.Radiation injury

Mechanical Trauma

Mechanical forces may cause damage in several ways ,like compression ,stretching, torsion or penetration of tissues. The patterns of injury can be in the form of abrasion ,contusion, laceration. Abrasion is a wound produced by scraping or rubbing resulting in removal of the superficial layer. Skin abrasions may remove only the epidermal layer.


Contusion (bruise) : is a wound produced by a blunt object & characterized by damaged to blood vessels & extravasations of blood into tissues. Laceration : is a tear or disruptive stretching of tissue caused by application of force by a blunt object .Most lacerations have irregular edges . Incised wound caused by a sharp instrument . Puncture wound which is caused by a long narrow instrument & its termed (penetrating ). Gun shot wounds are special forms of puncture wounds.

One of the most common causes of mechanical injury is car accidents causing head injury, chest & knee injury .Chest injury include sternal & ribs fractures & less commonly lacerations of the spleen & liver.

Thermal injuries

1.Burns 2.Hyperthermia 3.Hypothermia

Burns


Children are mainly affected ,who are often scalded by hot liquids. The clinical significance of burn depend on the following factors: 1.Depth of burn 2.Percentage of body surface involved 3.Presence of internal injury from inhalation of hot & toxic fumes. 4. Efficacy of therapy specially fluid & electrolytes management & prevention or control of wound infection.


A full thickness burn involved destruction of epidermis & dermis with loss of dermal appendages .Both 3rd & 4th degree burns are in this category. Grossly the burns are white & anesthetic . In partial thickness burn, the deeper portions of the dermis are spared which include the first & second degree (both epidermis & superficial dermis). The partial thickness burns are pink with blister & painful .


Any burn exceeding 50% of the total body surface whether superficial or deep is grave & fatal. Hyperthermia : Prolonged exposure to elevated temp. can result in heat cramps, heat exhaustion & heat stroke


Heat Cramps: Result from loss of electrolyte by sweating, cramping of voluntary muscles usually in association with vigorous exercise . Heat exhaustion : Which is the most common. Its onset is sudden with prostration & collapse due to failure of CVS to compensate for hypovolaemia secondary to water depletion.


Heat stroke: Is associated with high temp. & high humidity with a failure of thermoregulatory mechanism , sweating ceases with a rise in body temp. The underlying mechanism is generalized peripheral vasodilatation with decreased blood volume. Necrosis of the muscles & myocardium may occur ,Arrhythmia ,DIC

Hypothermia

Electrical injury


Electrical injuries, which may result in death, can arise from low-voltage currents (i.e., in the home and workplace) or from high-voltage currents from high-power lines or lightning. Injuries are of two types: (1) burns and (2) ventricular fibrillation or cardiac and respiratory center failure, resulting from disruption of normal electrical impulses. The type of injury and the severity and extent of burning depend on the amperage and path of the electric current within the body.


Ionizing radiationThe various forms of ionizing radiation X-ray,α,β & γ rays can all induce cancer in animals and man, they injure the cells through which they pass with formation of ionized molecules highly reactive with nucleic acids proteins, thus cancer develop many years afer the first exposure, so the effect of repeated doses are cumulative


The carcinogenic effect of ionizing radiation and UV is due to damage to the DNA mainly, this includes : 1- changes in single bases ( point mutation) and consequent change of an amino acid in protein products of affected gene. 2- breaks in one or both strands of double helix (DNA) produce fragments which are liable to re-unite in the wrong order and this results in transfer of sequences of various lengths sometime visible microscopically as translocations and other chromosomal abnormalities


The effect of ionizing radiation on different tissues depend on the type of radiation and on the nature of tissue irradiated. Bone tissue absorbs and scatters ionizing radiation more than soft tissue because of its density, and as a consequence hemopoeitic tissue is severely damaged, thus leukemia are among the commoner type of cancer resulting from ionizing radiation


Thyroid, breast, and lung are relatively common sites of radiation induced carcinomas X-irradtion of the neck in infancy or childhood carries a significant risk of development of thyroid cancer in early adult life X-ray also increase incidence of CML in radiologists from exposure of hemopoietic marrow



Ultraviolet(UV) radiation In contrast to ionizing radiation UV penetrates tissue poorly and its effects are limited to the exposed skin and the main source of exposure is sun Carcinoma of the skin, like basal cell carcinoma ,squamous cell carcinoma, & melanoma occur in light skinned people


The dark skinned races are protected due to absorption of UV rays by melanin In xeroderma pigmentosa which is a rare precancerous inherited condition in which there is a defect of a repair enzyme which excise abnormal DNA segments