What Are Disturbances in Growth?
Disturbance in growth cover changes occurring from no growth to uncontrolled growth. Due to dynamic physiological and pathological changes, the cells fail to develop or adapt themselves to the changing environment. The cell's ability to respond to environmental changes is known as cellular adaptation. The various disturbances in growth are:
-
Aplasia - Complete failure of an organ to develop.
-
Agenesis - Absence of an organ or specific cells from an organ.
-
Atrophy - Decrease in organ, tissue, cell, or body part size.
-
Hypertrophy - Increase in the size of an organ, tissue, cell, or body part.
-
Hypoplasia - Decrease in the number of cells of an organ, tissue, cell, or body part. Due to this, the size decreases.
-
Hyperplasia - Increase in the number of cells of an organ, tissue, cell, or body part. Due to this, the size increases.
-
Metaplasia - Cellular adaptation is when one cell type of the same germinal layer replaces another.
-
Dysplasia - It is an abnormal growth or abnormal development of cells.
What Is Atrophy?
Atrophy is defined as a decrease in the size or number of cells after the cell, tissue, or organ has attained total average growth. The cells shrink due to loss or reduction in the number of cells. It is the adaptation of cells to decrease workload, nutrition deprivation, compression, and lack of hormonal stimulation. Histologically, the cells become small with little or no mitotic activities.
Classification of Atrophy
Atrophy can be classified as follows:
-
Physiological Atrophy:
-
Involution - It is defined as the decrease in the number of cells caused due to apoptosis. Involution of the organ is seen as age increases. For example, Thymus shrinks upon attaining puberty.
-
Senile Atrophy - It is due to the loss of cells and is seen with aging. Reproductive organs are the first organs to show such changes.
-
-
Pathological Atrophy:
-
Nutritional Atrophy - Malnutrition, malabsorption, neoplasia, and chronic infection are the causes of healthy atrophy in cells. If the organs lack nutrition, they start depleting their glycogen, fat, and protein reserve leading to muscle wasting.
-
Angiographic Atrophy - These atrophic changes are caused due to lack of blood supply. These changes are associated with anemia, ischemia, and chronic congestion.
-
Disuse Atrophy - It is due to reduced workload on the tissues and organs. For example, body mass decreases as a result of reduced work. In fractures, the fractured portion is stabilized using a plaster cast which causes the muscles to become inactive, and thus the size of myocytes (cells of the muscles) decreases.
-
Neurotrophic Atrophy - If a nerve is severely injured, the size of the muscle fibers decreases.
-
Pressure Atrophy - Cells and tissues adjacent to tumors and abscesses show loss of cells or changes in the cell size due to nutrition deprivation and decreased blood supply (ischemia).
-
Endocrine Atrophy - Steroid therapy for an extended period leads to the atrophy of the adrenal gland. Castration of the prostate leads to its atrophy.
-
What Are the Changes Seen in Atrophy?
Organs show fibrosis and are firm. Muscle tone is lost. Organs become soft and change color. Cells are small and decrease in number. For example, Adipocytes and myocytes become small.
What Is Hypertrophy?
Hypertrophy is an increase in cell size and organs without an increase in cell number. This phenomenon is seen in cells that cannot divide further, like the striated muscles. Muscular hypertrophy increases muscle capacity in a short period; however, excess of this can cause tissue fibrosis leading to organ damage.
Types of Hypertrophy
-
Physiologic Hypertrophy - It occurs as a result of exercise or hormone stimulation. For example, hypertrophy of the uterus during pregnancy and muscle build-up after working out.
-
Compensatory Hypertrophy - It occurs as a result of an organ or part of organ loss, as seen in kidney damage.
What Is Hyperplasia?
Hyperplasia is defined as an increase in the size of a tissue or an organ due to the rise in the number of cells. The cells which are capable of mitosis show the phenomenon of hyperplasia. It generally subsides when the stimulus is removed, whereas neoplastic proliferation does not.
What Causes Hyperplasia?
Hyperplasia is a cellular response to physical trauma, hormonal stimulation, and inflammation. However, striated muscles (muscles are attached to the limbs and body wall and help in movement and locomotion) and nervous tissue does not undergo hyperplasia.
What Are the Types of Hyperplasia?
-
Physiological Hyperplasia - Due to hormonal stimulation, glandular epithelial cells of the breast in females proliferate during puberty and lactation and increase the breast size.
-
Compensatory Hyperplasia - It is seen in liver cells and epithelial cells of the intestines and epidermis. For example, liver regeneration is due regeneration of hepatocytes (liver cells) after partial hepatectomy. Tissue regeneration in response to cuts is also an example of hyperplasia.
-
Pathological Hyperplasia - For example, excess androgen (male sex hormone) secretion results in prostate enlargement resulting in benign prostate hyperplasia (BPH). Excess estrogen (female sex hormone) secretion results in endometrial hyperplasia resulting in polycystic ovarian syndrome (PCOS).
What Is Metaplasia?
It is the transformation of one cell type into another cell type of the germinal layer. It involves both epithelial and mesenchymal tissue. If the stimulus causes metaplasia, the tissue may result in being normal. However, if the trigger is present, it can progress to dysplasia.
Mechanism of Metaplasia
Metaplastic changes can be caused due to chronic irritation, neoplastic changes, nutritional deficiencies, etc. Metaplastic changes are also seen in stem cells due to signals from various growth factors and cytokines.
-
Epithelial Metaplasia - It occurs due to nutritional deficiency like vitamin A deficiency causes squamous metaplasia. In addition, chronic irritation from chemicals and carcinogens causes metaplastic changes.
-
Mesenchymal Metaplasia - Metaplasia in mesenchymal cells cause extramedullary hematopoiesis in the adult liver due to bone marrow injury.
What Is Dysplasia?
It is the abnormal growth and development of cells and tissue. Dysplasia causes alteration in the size, shape, and orientation of cells. Dysplastic changes mainly affect the epithelium cell, as seen in the eyes, skin, brain, and skeletal system. In addition, dysplasia can cause neoplastic changes. Cells show various changes like variation in size (anisocytosis), shape (poikilocytosis), increased mitotic activities of the cell, and unarranged cells.
Conclusion
The research on various growth disturbances should focus on determining the different cell types and their origin. The pathways and mechanisms of growth disturbances should focus on prevention and treatment therapy for various diseases.
