Summary of Pathology Knowledge Points
Chapter 1: Adaptation, Injury, and Repair of Cells and Tissues
Section 1: Adaptive Responses of Cells and Tissues
1. Adaptation: Refers to the non-damaging response of cells, tissues, or organs
to persistent internal or external stimuli. It manifests as changes in their
metabolism, function, and morphological structure to achieve a new balance
with the altered internal or external environment, thereby ensuring survival.
This process is called adaptation.
2. Main manifestations of adaptation:
o Atrophy
o Hypertrophy
o Hyperplasia
o Metaplasia
Atrophy: The reduction in volume of normally developed parenchymal cells, tissues,
or organs is termed atrophy. Atrophy of tissues or organs may also be accompanied by
a decrease in cell number.
(Note the distinction from hypoplasia and aplasia.)
Classification:
o Physiological atrophy: Often age-related, e.g., thymus atrophy during
puberty.
o Pathological atrophy.
Common types and examples of pathological atrophy:
Type Example
Malnutrition atrophy Cerebral atherosclerosis → cerebral atrophy
Malignancies, prolonged starvation → atrophy of organs
Local malnutrition
and tissues
Systemic malnutrition Atrophy
Pressure atrophy Hydronephrosis → renal atrophy
,Type Example
Disuse atrophy Immobilization after lower limb fracture → muscle atrophy
Poliomyelitis → anterior horn motor neuron damage →
Denervation atrophy
muscle atrophy
Endocrine atrophy Pituitary hypofunction → gonadal/adrenal atrophy
Damage-induced
Caused by viruses, bacteria, etc.
atrophy
3. Pathological changes:
o Gross view: The organ or tissue volume shrinks, weight decreases,
color darkens or turns brown, and texture becomes tough.
o Microscopic view: Cell volume decreases, sometimes with reduced
cell numbers, interstitial hyperplasia, and lipofuscin accumulation in
the cytoplasm.
Hypertrophy: An increase in the size of tissues or organs due to enlargement of
parenchymal cells. Hypertrophied cells contain more organelles and exhibit enhanced
function.
Classification:
Physiological hypertrophy:
o Example: Uterine smooth muscle hypertrophy during pregnancy due to
estrogen and progesterone stimulation.
o Example: Hypertrophy of skeletal muscles in weightlifters.
Pathological hypertrophy:
o Compensatory hypertrophy: Left ventricular myocardial hypertrophy
in hypertension, contralateral kidney hypertrophy after nephrectomy.
o Endocrine (hormonal) hypertrophy: Example: Acromegaly.
Hyperplasia: An increase in the number of parenchymal cells in an organ or tissue,
resulting from active mitosis.
Classification:
Physiological:
, o Example: Breast development during female puberty.
Pathological:
o Example: Hyperplasia due to excessive hormones or growth factors,
e.g., mammary gland hyperplasia.
Note: Hypertrophy and hyperplasia often coexist.
In tissues with active cell division, hypertrophy can result from both cell enlargement
and increased cell numbers. In tissues with limited proliferative capacity, hypertrophy
is solely due to cell enlargement.
Metaplasia: The replacement of one differentiated cell type by another differentiated
cell type. Metaplasia arises from the transdifferentiation of undifferentiated or stem
cells with proliferative and multipotent capabilities. It typically occurs between
homologous cells.
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Support for College Students.
Metaplasia:
Epithelial metaplasia:
o Squamous metaplasia (e.g., chronic cervicitis).
o Intestinal metaplasia (e.g., reflux esophagitis).
Mesenchymal metaplasia:
o Osseous or cartilaginous metaplasia (e.g., myositis ossificans).
Metaplasia usually occurs between homologous cells, i.e., between epithelial cells
(reversible) or mesenchymal cells (irreversible). The most common form is the
transformation of columnar or transitional epithelium into squamous epithelium,
termed squamous metaplasia. The replacement of gastric mucosal epithelium by
Paneth cells or goblet cells is called intestinal metaplasia. Metaplastic epithelium can
undergo malignant transformation, e.g., squamous cell carcinoma arising from
metaplastic epithelium.
Section 2: Injury to Cells and Tissues
Injury: When tissues and cells are exposed to harmful stimuli beyond their
compensatory capacity, they undergo abnormal changes in metabolism,
histochemistry, ultrastructure, and even gross or microscopic morphology. This is
termed injury.
Sublethal Cell Injury:
Chapter 1: Adaptation, Injury, and Repair of Cells and Tissues
Section 1: Adaptive Responses of Cells and Tissues
1. Adaptation: Refers to the non-damaging response of cells, tissues, or organs
to persistent internal or external stimuli. It manifests as changes in their
metabolism, function, and morphological structure to achieve a new balance
with the altered internal or external environment, thereby ensuring survival.
This process is called adaptation.
2. Main manifestations of adaptation:
o Atrophy
o Hypertrophy
o Hyperplasia
o Metaplasia
Atrophy: The reduction in volume of normally developed parenchymal cells, tissues,
or organs is termed atrophy. Atrophy of tissues or organs may also be accompanied by
a decrease in cell number.
(Note the distinction from hypoplasia and aplasia.)
Classification:
o Physiological atrophy: Often age-related, e.g., thymus atrophy during
puberty.
o Pathological atrophy.
Common types and examples of pathological atrophy:
Type Example
Malnutrition atrophy Cerebral atherosclerosis → cerebral atrophy
Malignancies, prolonged starvation → atrophy of organs
Local malnutrition
and tissues
Systemic malnutrition Atrophy
Pressure atrophy Hydronephrosis → renal atrophy
,Type Example
Disuse atrophy Immobilization after lower limb fracture → muscle atrophy
Poliomyelitis → anterior horn motor neuron damage →
Denervation atrophy
muscle atrophy
Endocrine atrophy Pituitary hypofunction → gonadal/adrenal atrophy
Damage-induced
Caused by viruses, bacteria, etc.
atrophy
3. Pathological changes:
o Gross view: The organ or tissue volume shrinks, weight decreases,
color darkens or turns brown, and texture becomes tough.
o Microscopic view: Cell volume decreases, sometimes with reduced
cell numbers, interstitial hyperplasia, and lipofuscin accumulation in
the cytoplasm.
Hypertrophy: An increase in the size of tissues or organs due to enlargement of
parenchymal cells. Hypertrophied cells contain more organelles and exhibit enhanced
function.
Classification:
Physiological hypertrophy:
o Example: Uterine smooth muscle hypertrophy during pregnancy due to
estrogen and progesterone stimulation.
o Example: Hypertrophy of skeletal muscles in weightlifters.
Pathological hypertrophy:
o Compensatory hypertrophy: Left ventricular myocardial hypertrophy
in hypertension, contralateral kidney hypertrophy after nephrectomy.
o Endocrine (hormonal) hypertrophy: Example: Acromegaly.
Hyperplasia: An increase in the number of parenchymal cells in an organ or tissue,
resulting from active mitosis.
Classification:
Physiological:
, o Example: Breast development during female puberty.
Pathological:
o Example: Hyperplasia due to excessive hormones or growth factors,
e.g., mammary gland hyperplasia.
Note: Hypertrophy and hyperplasia often coexist.
In tissues with active cell division, hypertrophy can result from both cell enlargement
and increased cell numbers. In tissues with limited proliferative capacity, hypertrophy
is solely due to cell enlargement.
Metaplasia: The replacement of one differentiated cell type by another differentiated
cell type. Metaplasia arises from the transdifferentiation of undifferentiated or stem
cells with proliferative and multipotent capabilities. It typically occurs between
homologous cells.
For more resources and PDF versions, visit the WeChat Official Account: Academic
Support for College Students.
Metaplasia:
Epithelial metaplasia:
o Squamous metaplasia (e.g., chronic cervicitis).
o Intestinal metaplasia (e.g., reflux esophagitis).
Mesenchymal metaplasia:
o Osseous or cartilaginous metaplasia (e.g., myositis ossificans).
Metaplasia usually occurs between homologous cells, i.e., between epithelial cells
(reversible) or mesenchymal cells (irreversible). The most common form is the
transformation of columnar or transitional epithelium into squamous epithelium,
termed squamous metaplasia. The replacement of gastric mucosal epithelium by
Paneth cells or goblet cells is called intestinal metaplasia. Metaplastic epithelium can
undergo malignant transformation, e.g., squamous cell carcinoma arising from
metaplastic epithelium.
Section 2: Injury to Cells and Tissues
Injury: When tissues and cells are exposed to harmful stimuli beyond their
compensatory capacity, they undergo abnormal changes in metabolism,
histochemistry, ultrastructure, and even gross or microscopic morphology. This is
termed injury.
Sublethal Cell Injury:
