Thursday, May 15, 2014
CAUSES OF CELL INJURY
Causes of cell injury are summarized into three components. Injury of the cell occurs as a result of:
Causes of cell injury are summarized into three components. Injury of the cell occurs as a result of:
- A DEFICIENCY of substances that are vital to the cell
- A presence of substances that inhibit with cell function. This is noted in cases of POISONING or INTOXICATION
- The loss of the cell’s structural integrity such as in cases of physical injuries or also termed as TRAUMA.
DEFICIENCY
The life process of a cell is derived from a variety of chemical requirements, need for an energy supply and from its complex metabolism. Deficiency of these factors may contribute to inhibition of cell function hence, causing cell injury. Factors that may produce a deficiency of essential nutrients vital for the cell’s life process are the following:
- Primary nutrient deficiency
A lack of nutrients necessary for cell’s life process is called a primary nutrient deficiency. In cases where an individual is suffering from starvation a lack of dietary energy sources will result to cellular injury. Even in cases where an individual’s diet is adequate and even excessive in providing energy sources but when a certain nutrient is lacking cellular injury would still be the result. For instance, a person who lacks thiamine in his diet will result to damage on the nervous tissue as this vitamin is required for the normal carbohydrate metabolism in the tissue.
- Secondary Nutrient Deficiency
A secondary nutrient deficiency results from the inability of the body to absorb the substances that are present in the diet. In this case, the person’s diet is adequate not only in energy sources but also in vitamins and nutrients. However, there is a problem in the absorption of the substances that will still result to cell injury.
- Genetic defects
Injurious cell deficiencies can also arise as a result of genetic defects. The metabolic pathways of the cell contain substances that synthesized based on the encoded information from the genes that are present in the chromosomes. (See section on Anatomy and Physiology of Cells). Once chromosomes are damaged or injured a decline in metabolic intermediate occurs and the cell function is then compromised due to the lack or deficiency of these intermediates. Aside from that genetic control of metabolism is defective or inadequate when genetic defects are present. Thus, the resulting phenomenon is – CELL INJURY.
- Infection
Deficiency state leading to cellular injury can also be caused by viral actions. Following infection of a cell by a certain virus, the virus causes the cells to produce new virus particles that are then released from the infected cell. Aside from that, infectious agents utilize the needed nutrients that the cell must use for its processes. Some cells may survive this situation however, a disruption in the cell’s metabolism occurs when a heavy demand for key metabolites in the production of new viral particles that results to cellular injury.
INTOXICATION or POISONING
Cell injury also occurs as a result of poisoning. Toxins are injurious substances that produce cell intoxication. Toxins could either be exogenous or endogenous.
- Exogenous Toxins
Exogenous toxins are of external origins can be characterized as being of biological or non-biological origin.
- Biological exogenous toxins – these are produced by living organisms which are commonly microorganisms. These microorganisms serve as agents of infection and they gain access to body tissues and release injurious substances inside the body. Most commonly bacteria are sources of biologicaltoxins, however, other microorganisms such as the fungi and protozoa can also produce toxins that may cause an injury to the cells.
- Non-biological exogenous toxins – these are injurious chemicals that originate outside the body. When these substances (chemicals) are inhaled or swallowed they cause a massive cell injury and damage. Many therapeutic drugs are highly effective at prescribed doses. However, the same drugs can be fatal in higher doses.
- Endogenous Toxins
Endogenous toxins are injurious substances that arise inside the cells. These toxins are formed in two ways:
- Genetic defect which causes a toxic substance to be constantly produced. Intoxification in this way could either be direct or indirect. An example of direct intoxification due to a genetic defect is in case of Huntington’s disease, wherein a toxic substance causes a neurological dysfunction.
In indirect genetic intoxification the product of a genetic defect, which by itself not toxic, activates an alternative metabolite pathways wherein the products are toxic. For example in case of PKU toxic phenylketones are formed because of the interference in the normal neurological development.
- Impaired circulation that allows metabolic by-products to accumulate to toxic levels. Normally, cells produce substances at normal levels. For example, carbon dioxide and bilirubin. However, when these substances are not removed from the cells and excreted out of the body their levels rises and can cause extensive damage to the cells. Cell injury from these accumulated substances that are normally tolerated in normal levels is secondary to the impaired circulation that has interfered with their normal removal in the cell.
TRAUMA
Trauma is a physical injury. Physical disruption of cells is results to cellular injury or damage. Trauma can be caused by the following factors:
- Hypothermia
Hypothermia is defined as a decreased in the body temperature. Extreme cold injures the cells as a result of ice crystal formation in the water of the cytoplasm. Typically, this damage is noted on frostbite.
- Hyperthermia
Hyperthermia is the opposite of hypothermia wherein there is an increased in the body temperature. Extreme heat damages the cells by disrupting the cell proteins. Presence of excessive heat causes the proteins of the cells to denature. Normally, the function of a cell’s protein is linked to their structure, thus when denaturation occurs it is followed by a significant functional cell disruption. In very extreme heat such as in burn injury, protein is chemically transformed by combining with oxygen. The product of this transformation is the blackening and charring characteristic of a burned tissue.
- Ionizing radiation
Ionizing radiation is a high-energy radiation that is associated with x-rays and nuclear radioactivity. Very high exposures to ionizing radiation produce temperature elevation in the tissues that can result to burning. Aside from the mentioned information, ionizing injury can also cause injury through the production of free radicals. Free radicals are highly energetic ions that are produced and formed when ionizing radiation strips down the electrons from the cells.
- Mechanical pressure
Mechanical pressure can result to cellular trauma or injury. When cells are faced with increasing pressure, cells are physically overwhelmed and they cannot maintain their structural integrity. In cases where a pressure is applied to a certain body surface or a pressure is created due to the presence of a rapidly expanding tumors adjacent cells are subject to trauma or injury. Even without touching, cells can be injured mechanically. When loud noises are heard high pressures are generated to the fluid of the delicate inner ear that can cause injury.
- Infection
The action of microorganisms can cause not only intoxification or poisoning but also physical trauma. Viral proteins are formed when viral infection takes place. Viral proteins then bind to the cell membrane which results to gap formation that prevents normal cell operation causing cell rupture.
- Immune system defect
Antigen-antibody interactions at cell surfaces can lead to the physical disruption of the cell membrane. This occurs when the newly formed viruses are released from the cell without damaging it and some of their viral proteins are incorporated into the plasma membrane of a normal cell. Specialized cells in the immune system recognize the viral proteins attached to the cell membrane of a normal cell as foreign. The cells of the immune system then attack the foreign substances by binding with the viral proteins which results to membrane injury or damage and cellular death.
