Cellular Injury And Abnormal And Normal Accumulation Of Intercellular Fluid
Abnormal and normal accumulation of intracellular substances
Intracellular accumulations often result from environmental changes or an inability of the cell to process materials (substances) that cannot be metabolized by the cells. These substances may accumulate in the cytoplasm. As a result common changes include:
1. Cellular swelling.
2. Lipid accumulation (Fatty change process in the cytoplasm of cells).
3. Glycogen depositions (Excess deposition of glycogen in organs).
4. Calcification (precipitation of calcium in dead or Chronic inflammation area)
5. Hyaline infiltration( characteristic alteration within cells or in the Extra-cellular spaces that appear as inclusion on stained histology).
Changes to cellular size or numbers Changes in size and numbers of the cells are usually
as a result of response to adapt to harmful agents.
The changes include:
I) Atrophy: Atrophy refers to a decrease in cell size.
Causes:
1. Decreased work load (Disuse atrophy)
2.Loss of nerve supply
3. Decreased blood supply
4. Inadequate nutrition
5. Loss of hormonal stimulation
Example: Uterine atrophy after menopause.
6. Physiologic Atrophy
Example: Loss of muscle bulk with ageing.
II) Dysplasia:
Dysplasia refers to the appearance of cells that have undergone some atypical changes in response to chronic irritation.
It is not a true adaptive process in that it serves no specific functions.
It is controlled reproduction of cells, but closely related to malignancy in that it may transform into uncontrolled, rapid reproduction.
It is complete loss of normal architectural orientation of one cell with the next both in shape and size.
Epithelial cells are common sites for dysplastic changes.
III) Hyperplasia: It is defined as increase of tissue mass due to an increase in the number of cells. It occurs in cells that are under increased physiologic workload or stimulations.
Types of Hyperplasia
a) Physiologic Hyperplasia: occurs when there hormonal stimulation Occurs in puberty and pregnancy
b) Compensatory-Hyperplasia : Occurs in organs that are capable of regenerating lost tissues.
Example: When part of liver is destroyed.
c) Pathologic Hyperplasia: Is seen in abnormal stimulation of organs with cells that are capable of regeneration
IV) Hypertrophy: Is an increase in the size of individual cells, resulting in increased tissue mass with out an increase in the number of cells.
It is usually response of a specific organ to an increased demand for work.
Example: Enlargement of muscles in Athletes
V) Metaplasia
• Metaplasia is a reversible change in which one type of adult cell is replaced by another type.
• It is an adaptive substitution of one cell type more suitable to the hostile environment for another.
CELLULAR INJURY (Cell Death)
Cell injury can be sub lethal or lethal. Sub lethal injury alters functions with out causing cell death. The changes caused by this type of injury are potentially reversible if the injuring stimuli are removed.
Causes of cell injury:
Causes of cell injury are the same causes of cellular adaptive changes as mentioned above.
Classification of cell injury: Cellular injury can be reversible or it may progress to irreversible change (Lethal change).
1. Reversible cell injury: Is cell injury which can be reversed when the stimulus or the cause of injury is removed.
Example: Ischemia:
Ischemia refers to a critical lack of blood supply to a localized area.
It is reversible in that tissues are restored to normal function when oxygen is again supplied to them, but if late progress to ischemic infraction.
It usually occurs in the presence of atherosclerosis in the major arteries.
The classic conditions resulting from ischemia is Angina pectoris.
2. Irreversible Cell injury : It is cellular injury that can not be corrected (reversed) after the stimulus or cause has been removed.
Example: Infarction: Is localized area of tissue death due to lack of blood supply. It is also called Ischemic Necrosis. It is due to occlusion of blood vessels by thrombus or embolus. Septic Infarction is added when there is evidence of infection in the area. It is irreversible cellular death due to lack of blood supply, when ischemia is persistent or late.
• Example: Acute myocardial infarction (AMI)
Necrosis: The term necrosis refers to cell or tissue death characterized by structural evidence of this death.
The structure change are mitochondrial swelling, rupture of cell membrane, shrinking of nucleus or fragmenting, and release of lysosomal enzymes.
classification of necrosis.
Coagulative-Necrosis: Usually results from lack of blood supply to an area.
• The cell structure and its architectural outline is preserved, but the nucleus is lost (structureless necrosis)
• Caseous Necrosis: is a good example of structureless necrosis. It is common in tuberculosis and is characterized by central area of necrosis which is soft, friable and surrounded by an area with a cheesy, crumbly appearance.
2. Colliquative- Necrosis (liquefactive- Necrosis) It frequently occurs in brain tissues and results from break down of neurons by released lysosomal enzymes resulting in formation of pockets of liquid, debris and cyst like structures in the brain tissue.