Cell Injury

Cell injury A person’s state of wellness and disease is

reflected in the cells. Injury to any of the cell’s components can

lead to illness. Consider, for example, a patient with HIV.

The cells of the immune system may be altered, making the patient susceptible to infection.

Draw on your reserves, adapt, or die

When cell integrity is threatened (toxins, infection, physical injury, or deficit injury), the cell reacts in one of two ways:• by drawing on its reserves to keep functioning• by adapting through changes or cellular

dysfunction.If enough cellular reserve is available and the body

doesn’t detect abnormalities, the cell adapts. If there isn’t enough cellular reserve, cell death (necrosis) occurs.

Necrosis is usually localized and easily identifiable.

I. Toxic injury Causes may be endogenous or exogenous

factors Common endogenous factors include:

genetically determined metabolic errors, gross malformations, and hypersensitivity reactions. Exogenous factors include: alcohol, lead, carbon monoxide, and drugs that alter cellular function.

II. Infectious injury

Viral, fungal, protozoan, and bacterial agents can cause cell injury or

death. Infectious organisms affect cell integrity,

usually by :interfering with cell synthesis, producing

mutant cells.For example, human immunodeficiency virus

alters the cell when the virus is replicated in the cell’s RNA

III. Physical injuryResults from a disruption in the cell or in the

relationships of the intracellular organelles. Two major types of physical injury are:

thermal (electrical or radiation); include radiation therapy for cancer, X-rays, and ultraviolet radiation

mechanical (trauma or surgery); include motor vehicle crashes (RTA) and ischemia

IV. Deficit injury

When water, oxygen, or nutrients decrease , or if temperature changes and waste are accumulated, cellular synthesis can’t take place. A lack of just one of these basic requirements can cause cell disruption or death.

Conditions of Disease or Injury1-HypoxiaHypoxia is the decreased concentration of oxygen

in the tissues. What is the difference bwn hypoxia & hypoxemia?Cells and tissues become hypoxic when there is:

inadequate intake of oxygen by the respiratory system,

inadequate delivery of oxygen by the cardiovascular system,

or a lack of Hgb.Oxygen is required by the mitochondria for production of ATP.

Consequences of Hypoxiacell begins to swell and burst, because Na diffuses into the cell and withdraw water.

production of lactic acid, decreased pH causes damage to the nuclear structures.

The effects of hypoxia are reversible if oxygen is returned within a certain period of time, the amount of which varies and depends on the tissue.

Signs & Symptoms:- Tachycardia.- Tachypnea.- Muscle weakness.- Decreased level of consciousness.

Complications

- If cerebral hypoxia prolongs , consciousness may deteriorated to coma and death.

-Organ failure, including: ARDS, CF, or renal failure, may occur if hypoxia is prolonged.

Treatment: Increase oxygen in inspired air through a mask or mechanical ventilation.

2-Temperature Extremes- Very high temperatures can cause burn injuries (direct death) or

cause coagulation of blood vessels or cell membranes breakdown (indirect death) .

- Very cold temperatures can injure cell in two ways: vasoconstriction (inadequate nutrients and oxygen to the extremities), and the formation of ice crystals (directly damage the cells and can lead to cell lysis and bursting).

Prolonged exposure to the cold can lead to hypothermia.

Signs & symptoms: - Numbness or tingling of the skin or extremities.

- Pale or blue skin that is cool to the touch.

- Shivering early on, then lack of shivering as condition worsens. - Decreased level of consciousness, drowsiness, and confusion.

2-Temperature ExtremesComplications

- Blood clotting, characterized by pain and a

decrease in pulse downstream from the clot. If blood flow is inadequate for an extended

time, gangrene may result. - Frostbite.

- Ventricular dysrhythmia

3-Radiation Injury Radiation energy may be higher or low energy.

High-energy radiation (UV radiation) is called ionizing radiation, may injure or kill cells directly by destroying the cell membrane and causing intracellular swelling and cell lysis

As cells are killed or injured, the inflammatory response is stimulated; capillary leakiness, interstitial edema, WBCs accumulation, and tissue scarring.

It may also lead to mistakes in DNA replication or transcription which may cause programmed cell death or subsequent cancer .

Most susceptible cells are that undergo frequent divisions, gastrointestinal (GI) tract, the integument (skin and hair), and the blood-forming cells of the bone marrow.

Ionizing radiation is emitted by the sun, in x-rays, and in nuclear weapons.

3-Radiation InjuryLow-energy radiation is called non-ionizing radiation. Ionizing radiation.

Non-ionizing radiation includes microwave and US radiation.

The energy of this radiation is too low to break DNA bonds or damage the cell membrane.

3-Radiation InjuryS &Sx of Ionizing Radiation

- Skin redness or breakdown.

- With high doses, N & V caused by GI damage. - Cancer may develop years after the exposure . - Anemia if the bone marrow is destroyed.

Pediatric Consideration

Fetal cells rapidly undergo cellular division and are highly

susceptible to the damaging effects of ionizing radiation. Infants and young children also experience periods of rapid cellular growth and are at risk of genetic damage from ionizing radiation. Studies suggest that there are no apparent health risks to fetuses exposed to non-ionizing radiation .

4-Injury Caused by Microorganisms Cells of the body may be destroyed directly by the

MO or by a toxin released from the MO, or may be indirectly injured as a result of the immune and inflammatory reactions .

S & Sx: Infection by bacteria and viruses, often results in:

- Regional lymph node enlargement- Fever (usually low-grade with a viral infection)- Body aches- Skin rash or eruption, especially with viral infections- Site-specific responses, such as pharyngitis, cough,

otitis media

4-Injury Caused by Microorganisms Rx:- Bacteria and mycoplasmas are treated with

AB, preferably after C& S.- Certain viral infections may be treated with

antiviral agents. Other viral infections usually are left to resolve on their own, with care taken that a subsequent bacterial infection does not infect the original site or elsewhere.

Cell degenerationDegeneration; nonlethal damage of the cell , generally occurs in the cytoplasm of the cell, while the nucleus remains unaffected.

Degeneration usually affects organs with metabolically active cells, such as the liver, heart, and kidneys.

Causes:• increased water in the cell or cellular swelling• fatty infiltrates• atrophy• autophagocytosis, during which the cell absorbs some of its own

parts•pigmentation changesWhen changes within cells are identified, degeneration may be slowed or cell death prevented through prompt treatment. subclinical identification; a disease is diagnosed before the patient complains of any symptoms. Unfortunately, many cell changes remain unidentifiable even under a microscope, making early detection impossible.

Cell aging Normal process of cell aging; cells lose structure

and function. Lost cell structure may cause atrophy.

Two characteristics of lost cell function are:• Hypertrophy, an abnormal thickening or increase

in bulk• Hyperplasia, Cell aging may slow down or speed up,

depending on the number and extent of injuries and the amount of wear and tear on the cell

Warning: This cell will self-destruct

Cell aging Signs of aging occur in all body systems. Examples

of the effects of cell aging includedecreases in elasticity of blood vessels, bowel

motility, muscle mass, and subcutaneous fat. The cell aging process limits the human life span.

One theory says that cell aging is an inherent self destructive mechanism that increases with a person’s age.

Cell death may be caused by internal (intrinsic) factors that limit the cells’ life span or external (extrinsic) factors that contribute to cell damage and aging.

Cell DeathThere are two main categories of cell death:

1-Necrotic cell death, characterized by cell swelling and rupture of internal organelles.

Common causes of necrotic cell death include prolonged hypoxia and infection .

2- Apoptosis, is not characterized by swelling or inflammation, but rather the dying cell shrinks on itself and then is engulfed by neighboring cells.

Programmed cell death begins during embryogenesis and continues throughout the lifetime of an organism.

Viral infection of a cell will often turn on apoptosis, ultimately leading to the death of the virus and the host cell. Deficiencies in apoptosis have been implicated in the development of cancer .

Results of Cell Death

Dead cells are removed from the area or isolated from the rest of the tissue by immune cells in the process of phagocytosis.

If mitosis is possible and the area of necrosis is not too large, new cells of the same type fill in the empty space.

If cell division is impossible or if the area of necrosis is extensive, scar tissue will form in the vacated space

Gangrene refers to the death of a large mass of cells. Gangrene may be classified as dry or wet.

Dry gangrene spreads slowly with few symptoms and is frequently seen in the extremities, often as a result of prolonged hypoxia.

Results of Cell DeathWet gangrene is a rapidly spreading area of dead

tissue, often of internal organs, and is associated with bacterial invasion of the dead tissue. It exudes a strong odor and is usually accompanied by systemic manifestations

Gas gangrene is a special type of gangrene that occurs in response to an infection of the tissue by a type of anaerobic bacteria called clostridium.

It is seen most often after significant trauma. Gas gangrene rapidly spreads to neighboring tissue as the bacteria release deadly toxins that kill neighboring cells. This type of gangrene may prove fatal.

Wound Repair

Destroyed or injured tissues must be repaired by regeneration of the cells or the formation of scar tissue.

The goal is to fill in the areas of damage. Tissues that heal cleanly and quickly are said to

heal by primary intention. Large wounds that heal slowly and with a great deal of scar tissue heal by secondary intention. Several factors can delay healing, such as: malnutrition, systemic disease, poorly functioning immune system or if there is reduced blood flow to the injured tissue or if an infection develops.