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the smallest living unit of the body
When confronted with stress that endanger the normal structure and function it undergoes adaptive changes that permit survival and maintenance of function

When does cell injury, maladaptive changes, and cell death occur?

When stress is overwhelming or adaptation is overwhelming

Genes expressed in cells fall into 2 categories...

Genes that are necessary for the normal function of the cell
Genes that determine the differentiating characteristics of a particular cell type

Cellular Adaption

allows the stressed tissue to survive or maintain function


decrease in cell size
When confronted with a decrease in work demands or adverse environmental conditions, most cells are able to revert to a smaller size and a lower functioning level that is compatible with survival

Causes of Atrophy

-Disuse- reduction in skeletal muscle use
-Denervation-form of disuse that occurs in the muscles of a paralyzed limb
-Loss of endocrine stimulation- form of disuse
-Inadequate nutrition- cells decrease in size and energy requirements
-Ischemia or decrease blood flow- cells decrease in size and energy requirements


an increase in cell size and with it an increase in the amt of functioning tissue mass

Physiologic example of hypertrophy

increased growth of the uterus and mammary glands in pregnancy

Pathology example of hypertrophy

Myocardial hypertrophy secondary to HTN or disease heart valves


an increase in the # of cells in an organ or tissue
controlled process that occurs in response to an appropriate stimulus and ceases after the stimulus has been removed.

Physiologic example of hyperplasia

2 types: hormonal and compensatory

Pathologic example of hyperplasia

excessive estrogen production can cause endometrial hyperplasia and abnormal menstrual bleeding


Atypical hyperplasia


-deranged cell growth of a specific tissue that results in cells that vary in size, shape and organization
-minor degrees are associated with chronic irritation or inflammation
-it is abnormal, but it is adaptive and reversible
-may be a precursor to cancer


-a reversible change in which on adult cell type is replaced by another cell type

Injuries Damage Cells by:

-Direct damage to proteins, membranes, DNA
-ATP depletion
-Free radical Information
-increased intracellular calcium

Injurious Stimuli

-Chemical agents, hypoxia, free radicals, infectious agents, physical and mechanical factors, immunological reactions, genetic factors, nutritional imbalances

Hypoxic injury

-Cellular Responses ( the pathology of hypoxic injury:)
-decrease in ATP, causing failure of sodium-potassium pump and sodium-calcium exchange
- cell swelling (Na and H2) can enter freely)
- Ca accumulation activates multiple enzymes--> cell death
- Repurfusion Injury:
- results from the generation of highly reactive oxygen intermediates (oxidative stress)
- these radicals can all cause further membrane damage and mitochondrial calcium overload

Free radicals

-molecules with an unpaired electron in the outer electron shell
-extremely unstable and reactive
-normally removed from body by antioxidants

Injury from Physical Agents

-Extremes of Temperature
-Electrical forces

Blunt force injuries

-Application of mechanical injury to the body resulting in the tearing, shearing, or crushing of tissues
Examples: contusion vs. hematoma, abrasion, laceration, fractures

Sharp injuries

incised wounds, stab wounds, puncture wounds, chopping wounds

Gunshot wounds

-Entrance wounds
-Exit wounds

Asphyxial Injuries

-Caused by a failure of cells to receive or use oxygen
Examples: Suffocation, Strangulation, Chemical asphyxiates, drowning

Ionizing Radiation Injury

radiation injury with frequencies above the UV light range

Affects cells by causing ionization of molecules and atoms in the cell by directly hitting the target molecules in the cell or by producing free radicals that interact with critical cell components

UV radiation injury

portion of the spectrum of electromagnetic radiation just above the visible range

Contains increasingly energetic rays that are powerful enough to disrupt intracellular bonds and cause sunburn and increase the risk of skin cancers

Non-ionzing radiation injury

radiation energy at frequencies below those of visible light

exerts its effects by causing vibration and rotation of atoms and molecules

chemical injury

carbon tetrachloride, lead toxicity, carbon monoxide, ethanol, mercury toxicity, social or street drugs

Infectious injury

pathogenicity of a microorganisms

Disease producing potential depends on its ability to:
invasion and destruction
toxin production
production of hypersensitivity reactions

Immunologic and Inflammatory injury

-phagocytic cells
-immune and inflammatory substances
-membrane alterations

Injury from biologic agents

able to replicate and continue to produce their injurious effects

Injury from nutritional imbalances

nutritional excess and nutritional deficiencies predispose cells to injury

Pathologic Calcifications

the abnormal tissue deposition of calcium salts, together with smaller amounts of iron, magnesium and other minerals

Dystrophic Calcification

when it occurs in dead or dying tissue

Metastatic Calcification

when it occurs in normal tissue as a result of increased serum calcium levels.


cells usually maintain lower intracellular calcium
-acts as a 2nd messenger in the cell
turns on intracellular enzymes, some of which can damage the cell


Cell suicide

Necrotic Cell Death

-unregulated death caused by injuries to cells
-cells swell and rupture
-inflammation results


-Cell death and degradation
-Cells may undergo:
Caseous Necrosis

Infarction Necrosis

occurs when an artery supplying an organ or part of the body becomes occluded and no other source of blood supply exists

Coagulative Necrosis

-kidneys, heart, and adrenal glands
-protein denaturation

Liquefactive Necrosis

-Neurons and glial cells of the brain
-Hydrolytic enzymes
-Bacterial infection

Caseous Necrosis

-Tuberculous pulmonary infection
-Combination of coagulative and liquefactive necrosis

Fat Necrosis

breast, pancreas, and other abdominal organs
-action of lipases

Gangrenous Necrosis

-death of tissue from severe hypoxic injury
dry vs. wet gangrene
-Gas Gangrene


- a large area of necrotic tissue

Dry Gangrene

-lack of arterial blood supply but venous flow can carry fluid out of tissue
- the part becomes dry and shrinks, skin wrinkles, color change to dark brown or black
-spread is slow
-produces a line of demarcation

Wet Gangrene

-area is cold, swollen, pulseless
-skin is moist, black, under tension
-blebs form on the surface, liquefaction occurs, and a foul odor is produced
-death may occur

Gas Gangrene

-a serious and potentially fatal disease
-antibiotics are used to treat the infection and surgical methods are used to remove the infected tissue
- amputation may be required

Hypoxia causes ATP deletion or power failure

- Aerobic metabolism stops--> less ATP is produced
Na/K ATPase cannot run fast enough, cell swells up with water
- Anaerobic metabolism used--> lactic acid produced
- acid damages cell membranes, intracellular structures, and DNA

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