Cell Growth, Adaptation, and Differentiation

Growth

The increase in size resulting from the synthesis of specific cellular or tissue components. Growth can occur at various levels—cellular, tissue, organ, organismal, or population.

Multiplicative Growth

Growth due to an increase in cell number through mitotic division.

Auxetic Growth

An increase in the size of an individual cell.

Accretionary Growth

Growth due to an increase in extracellular (intercellular) components.

Differentiation

The process by which an unspecialized (undifferentiated) cell becomes specialized in structure and function through selective gene expression.

Morphogenesis

The biological process that governs the development of the shape and structure of tissues and organs through cell growth, differentiation, and spatial organization.

G0 Phase (Quiescent/Resting Phase)

A state where cells exit the cell cycle and cease division, often temporarily or permanently, depending on the cell type.

G1 Phase (Growth/Presynthetic Phase)

A phase where cells grow in size, synthesize mRNA and proteins, and prepare for mitosis, with high biosynthetic activity.

Restriction (R) Point

A checkpoint in G1 phase ensuring sufficient growth factors and protein synthesis for cell cycle progression.

G1/S Checkpoint

A checkpoint clearing the cell for progression into the S phase, provided there is sufficient cell growth, no DNA damage, and all preparations are complete.

S Phase (Synthesis Phase)

The phase of the cell cycle during which DNA replication occurs.

G2 Phase (Pre-mitotic Phase)

A phase of rapid cell growth and protein synthesis following S phase, preparing the cell for mitosis.

G2/M Checkpoint

A checkpoint ensuring no DNA damage before cells proceed to cell division.

M (Mitotic) Phase

The phase where cell growth stops and all cellular activity focuses on producing two daughter cells, maintaining the chromosomal set.

Labile Cells

Cells that continuously divide throughout postnatal life, with a short lifespan and rapid turnover.

Stable Cells

Quiescent cells that divide infrequently under normal conditions but can be stimulated to differentiate or divide when lost.

Permanent Cells

Non-dividing cells throughout postnatal life.

Growth Factors

Polypeptides essential for cell proliferation, promoting cell survival, locomotion, contractility, differentiation, and angiogenesis.

Epidermal Growth Factor (EGF)

A growth factor that is mitogenic for keratinocytes and fibroblasts; stimulates keratinocyte migration and granulation tissue formation.

Transforming Growth Factor-α (TGF-α)

A growth factor similar to EGF, stimulating replication of hepatocytes and most epithelial cells.

Hepatocyte Growth Factor-α (HGF-α) / Scatter Factor (SF)

A growth factor enhancing proliferation of hepatocytes, epithelial cells, and endothelial cells; increases cell motility and keratinocyte replication.

Platelet-derived Growth Factor (PDGF)

A growth factor causing migration and proliferation of fibroblasts, smooth muscle cells, and monocytes; chemotactic and mitogenic for various cell types.

Vascular Endothelial Growth Factor (VEGF)

A dimeric glycoprotein promoting angiogenesis, increasing vascular permeability, and stimulating endothelial cell migration and proliferation.

Fibroblast Growth Factor (FGF)

A family of growth factors involved in wound repair, angiogenesis, hematopoiesis, and development of various tissues.

Transforming Growth Factor-β (TGF-β)

A growth factor with multiple isoforms that is chemotactic for immune and connective tissue cells, stimulates TIMP synthesis, and regulates inflammation and fibrosis.

Cytokines

Protein mediators of inflammation and immune response that also possess growth-promoting activities for various cells.

Autocrine Signaling

A mode of signaling where cells respond to signaling molecules they themselves secrete.

Paracrine Signaling

A mode of signaling where one cell produces a ligand that acts on adjacent target cells of a different type.

Endocrine Signaling

A mode of signaling where an endocrine gland produces hormones that target distant cells, typically via the bloodstream.

Cellular Adaptations

Reversible changes in the size, number, phenotype, metabolic activity, or functions of cells in response to environmental changes.

Homeostasis

A state of equilibrium or "steady state" in the body.

Hypertrophy

An increase in the size of cells, resulting in an increased size and weight of the organ, typically due to increased workload.

Physiologic Hypertrophy

Hypertrophy influenced by hormones and growth factors, such as skeletal muscles in bodybuilders.

Pathologic Hypertrophy

Hypertrophy influenced by existing medical conditions or chronic hemodynamic overload, such as myocardial hypertrophy secondary to hypertension.

Hyperplasia

An increase in the number of cells in an organ or tissue, usually leading to an increased mass, occurring in cells capable of dividing.

Physiologic Hyperplasia

Hyperplasia occurring as a normal bodily process, such as hormonal hyperplasia or compensatory hyperplasia.

Pathologic Hyperplasia

Hyperplasia caused by excesses of hormones or growth factors, or by viral infections.

Atrophy

Reduced cell size of an organ or tissue due to a decrease in cell size, mass, and number, mainly through the ubiquitin-proteasome pathway.

Physiologic Atrophy

Atrophy that occurs as a normal part of development, such as the thymus.

Pathologic Atrophy

Atrophy occurring due to disease or loss of trophic support, with causes including decreased workload, denervation, or inadequate nutrition.

Metaplasia

The replacement of one adult/differentiated cell type by another adult cell type, typically a response to chronic cellular injury and repair.

Dysplasia

An abnormal organization of cells characterized by increased cell proliferation with atypical morphology, often pre-neoplastic.