Cellular Adaptations of Growth and Differentiation Dr. Abdulmalik Alsheikh,MD, FRCPC

Cellular Adaptations of Growth and Differentiation Introduction Adaptations Hyperplasia Hypertrophy Atrophy Metaplasia

Hyperplasia Definition : an increase in the number of cells in an organ or tissue. It is possible only if cells are capable of synthesizing DNA and mitotic division. Types : Physiologic pathologic

Hyperplasia Physiologic Hyperplasia: Hormonal Hyperplasia: increases the functional capacity of the tissue Breast during pregnancy and lactation Pregnant uterus Compensatory Hyperplasia: Increases tissue mass Liver after partial hepatectomy

growth factors acting on target cells Hyperplasia Pathologic Hyperplasia: caused by excessive : hormonal stimulation or growth factors acting on target cells

Hyperplasia Pathologic Hyperplasia: Hormonal : Endometrial hyperplasia: Increased Estrogen Progesterone/Estrogen imbalance Benign prostatic hyperplasia: Androgens

Hyperplasia Pathologic Hyperplasia Growth Factors Stimulation Skin wart due to viral effect : Human Papilloma Virus ( HPV ) .

Hyperplasia IS IT REVERSIBLE ? IS IT PREMALIGNANT ? YES NO…..BUT….PATIENT IS AT INCREASED RISK TO DEVELOP CANCER Good environment !! Endometrial hyperplasia

Hypertrophy Definition : an increase in the size of cells and consequently an increase in the size of the organ. Due to synthesis of more structural components NO NEW CELLS!! ONLY BIGGER

Hypertrophy Types : Causes : Physiologic Pathologic Hormonal Stimulation Increased functional demand

Hypertrophy Physiologic : Gravid uterus Muscle mass in athletes Both hypertrophy and hyperplasia of smooth muscle. Muscle mass in athletes hypertrophy

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Hypertrophy Pathologic : Cardiac muscle hypertrophy: due to chronic hemodynamic overload Hypertension - cardiac muscle hypertrophy due to increased resistance !! Cardiac valves diseases

Cardiac and skeletal muscle cannot divide Remember!! Cardiac and skeletal muscle cannot divide

Atrophy Remember ….atrophic cells are not dead !! Definition : Shrinkage in the size of the cell by the loss of cell substance. If sufficient number of cells is involved, the entire organ/tissue will decrease in size ….ATROPHIC. Remember ….atrophic cells are not dead !!

Atrophy Physiologic or Pathologic Physiologic: Pathologic: Some embryonic strucrures during fetal development Uterus after delivery Pathologic: Local generalized

Atrophy Causes : Decreased workload Loss of innervation Decreased blood supply Inadequate nutrition Loss of endocrine stimulation Aging Pressure

Atrophy Normally ….Synthesis = Degradation Atrophy…. Decreased synthesis and/or increased degradation

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Metaplasia Definition : a reversible change in which one adult cell type ( epithelial or mesenchymal ) is replaced by another adult cell type. Can occur in epithelial or mesenchymal tissues

Metaplasia WHY ?!! It is an adaptation process. Sensitive cells are replaced by other cells which more capable to withstand ( tolerate ) the adverse environment. Examples: Smoker lung Barrett’s esophagus

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Metaplasia Mechanism Is it good or bad ?!! Stem cells/ undifferentiated cells Reprogramming Is it good or bad ?!! Stimuli that predispose to metaplasia , if persistent, may induce malignant transformation in the metaplastic epithelium