Reversible Growth Disorder

Reversible Growth Disorders

Adaptive mechanisms by a cell that can change its form or functions in response to sublethal stress or injury in order to survive

Examples of Reversible Growth Disorders

Atrophy, hypertrophy, hyperplasia, and metaplasia

Cellular Adaptation

A change in cell size, number, or type that allows cells to adapt to stress or injury

Atrophy

A decrease in the size of an organ or tissue

Numerical Atrophy

Atrophy caused by a reduction in the number of cells

Quantitative Atrophy

Atrophy caused by a reduction in the size of individual cells

Physiological Atrophy

Atrophy that occurs as part of a normal involution process

Involution

A process in which an organ gradually decreases in size and activity after it is no longer needed as much

Examples of Physiological Atrophy

Involution of the thymus or Bursa of Fabricius, postpartum changes in the uterus, reduction of fetal structures, involution of the corpus luteum when the female is not pregnant, and senile atrophy

Umbilical Structure Atrophy

Reduction of fetal structures such as the umbilical vessels after birth

Ductus Arteriosus Atrophy

Reduction of the fetal ductus arteriosus, which becomes the ligamentum arteriosum

Corpus Luteum Involution

Normal regression of the corpus luteum when the female is not pregnant

Senile Atrophy

Physiological atrophy associated with aging

Pathological Atrophy

Atrophy caused by disease or abnormal conditions

Causes of Pathological Atrophy

Deficient nutrition, lack of innervation, necrosis of cells, and defective feedback mechanisms involving endocrine glands

Gross Appearance of Pathological Atrophy

The affected organ is smaller than normal

Microscopic Appearance of Pathological Atrophy

There are fewer or smaller cells

Disuse Atrophy

Pathological atrophy caused by decreased workload or use

Examples of Disuse Atrophy

Atrophy of an immobilized limb after fracture and muscle atrophy in an inactive racehorse kept in a stable

Vascular Atrophy

Atrophy caused by decreased blood supply

Causes of Vascular Atrophy

Long-standing ischemia, anemia, and chronic passive hyperemia

Endocrine Atrophy

Atrophy caused by loss of hormonal stimulation

Pressure Atrophy

Atrophy caused by prolonged pressure on tissue

Denervation Atrophy

Atrophy caused by loss of nerve stimulation

Neurotrophic Atrophy

Muscle atrophy caused by loss of nerve stimulation

Metabolic Atrophy

Atrophy associated with metabolic problems such as malabsorption syndromes

Starvation Atrophy

Atrophy occurring during starvation in which glycogen and fat disappear first, followed by proteins

Abiotrophy

Premature degeneration after normal development; it is irreversible

Example of Abiotrophy

Cerebellar abiotrophy in dogs

Hypertrophy

Increase in the size of an organ or individual cell, resulting in increased function

Cellular Hypertrophy

Increase in the size of individual cells

Organ Hypertrophy

Increase in the size of an organ due to cellular enlargement

Pure Hypertrophy

Hypertrophy seen in organs with increased activity, such as skeletal and cardiac muscle

Gross Appearance of Hypertrophy

The organ is larger and heavier than normal

Microscopic Appearance of Hypertrophy

Cells are increased in size, with possible increases in nuclear size

Compensatory Hypertrophy

Hypertrophy that develops when remaining tissue increases its workload after loss of another part

Example of Compensatory Hypertrophy

Enlargement of one kidney after removal of the other kidney

Skeletal Muscle Hypertrophy

Increase in skeletal muscle mass associated with increased physical activity

Diaphragm Compensatory Hypertrophy

Hypertrophy of the pig's diaphragm associated with chronic pneumonia

Physiological Hormonal Hypertrophy

Hypertrophy caused by normal hormonal stimulation

Example of Physiological Hormonal Hypertrophy

Hypertrophy of the uterus during pregnancy

Pathological Hypertrophy

Abnormal enlargement of cells or organs associated with disease

Example of Pathological Cardiac Hypertrophy

Thickening of a heart ventricle due to valvular stenosis

Pathological Intestinal Hypertrophy

Thickening of the muscular coat of the ileum associated with a defective ileocecal valve

Hyperplasia

Increase in the size of an organ or tissue due to an increase in the number of cells

Requirement for Hyperplasia

It occurs in organs or tissues that have retained mitotic activity

Gross Appearance of Hyperplasia

It may appear as an enlarged or hypertrophic organ

Microscopic Appearance of Hyperplasia

There is an increased number of cells

Reactive Hyperplasia

Hyperplasia caused by stimulation or irritation, resulting in increased cell proliferation

Lymph Node Reactive Hyperplasia

Enlargement of a lymph node due to proliferation of lymphocytes during antigenic stimulation

Reactive Hyperplasia in Sarcoptic Mange

Increased keratinized epithelial layer associated with sarcoptic mange

Acanthosis

Increased number of cells in the prickle cell layer of the skin

Hyperkeratosis

Increased keratinized layer of the epithelium

Callus Formation

Reactive hyperplasia associated with repeated contact or pressure from a rough surface

Mucosal Reactive Hyperplasia

Increase in mucous membrane epithelium caused by persistent irritation

Chronic Otitis Externa Hyperplasia

Hyperplasia of the ceruminous glands associated with chronic otitis externa

Chronic Bronchitis Hyperplasia

Hyperplasia of the bronchial epithelium associated with chronic bronchitis

Bile Duct Hyperplasia

Increase in bile duct cells associated with cholangitis caused by large gallstone obstruction

Endocrine Hyperplasia

Hyperplasia caused by hormonal stimulation

Mammary Gland Endocrine Hyperplasia

Cyclical changes in the mammary gland during lactation

Prostatic Hyperplasia

Enlargement of the prostate associated with increased testosterone levels in older men

Thyroid Hyperplasia

Hyperplasia caused by prolonged stimulation of the thyroid gland, such as with iodine deficiency

Compensatory Hyperplasia

Hyperplasia that occurs when remaining tissue compensates for loss of another part

Renal Compensatory Hyperplasia

After loss of one kidney, the remaining kidney undergoes hyperplasia and cellular hypertrophy

Renal and Pulmonary Compensation

Functional units of the kidneys and lungs can undergo hypertrophy and hyperplasia of individual cells

Regenerative Hyperplasia

Hyperplasia associated with loss of functional reserves in hepatocellular or hematopoietic tissue

Nodular Hyperplasia

A form of regenerative hyperplasia characterized by nodular growth

Cystic Endometrial Hyperplasia

Hyperplastic change occurring in the endometrium of the bitch

Metaplasia

A reversible change in which one adult cell type, epithelial or mesenchymal, is replaced by another adult cell type

Causes of Metaplasia

Chronic irritation, vitamin A deficiency, chlorinated hydrocarbon toxicity in sheep and cattle, and estrogen toxicity in the urinary tract of mink

Squamous Metaplasia

Conversion of specialized mucous membrane or glandular epithelium into squamous epithelium

Metaplasia and Differentiation

Metaplasia involves transformation into a new adult cell type through altered differentiation

Squamous Metaplasia in Cattle

Glandular epithelium may undergo squamous metaplasia during healing of necrotizing mastitis

Prostatic Metaplasia in Dogs

Estrogen secretion from a Sertoli cell tumor can transform secretory columnar prostatic epithelium into cornified squamous epithelium

Myeloid Metaplasia

Conversion of much of the adult spleen into hematopoietic tissue when the need for blood cell formation arises

Metaplasia in Smokers

Pseudostratified ciliated columnar epithelium can change into stratified squamous epithelium

Dysplasia

Disordered or abnormal development or growth of cells and tissues

Dysplastic Arrangement

Normal-looking cells may have an imperfect or disordered arrangement

Causes of Dysplasia

Infection, toxins, or physical agents may disturb stem cells

Reversibility of Dysplasia

Dysplasia may be reversible but can also become irreversible

Microscopic Features of Dysplasia

Pleomorphism, hyperchromasia, increased nucleocytoplasmic ratio, and increased mitotic activity in adults

Pleomorphism

Variation in cell size and shape

Hyperchromasia

Increased staining intensity of the nucleus

Increased Nucleocytoplasmic Ratio

An increased proportion of nuclear material relative to cytoplasm

Congenital Dysplasia

Dysplasia present from development, such as renal dysplasia in young dogs

Renal Dysplasia

Improper formation of nephrons, sometimes with abnormal tissues such as cartilage

Anaplasia

Reversion of cells to a more primitive and less differentiated type

Undifferentiation

Another term for anaplasia

Characteristics of Anaplasia

Loss of structural and functional characteristics of mature cells, hyperchromatic and enlarged nuclei, enlarged nucleoli, increased mitotic figures, tumor giant cells, and embryonal-type cells

Anaplasia and Malignancy

Anaplasia is a characteristic feature of malignancy and is irreversible

Normal Growth

Healthy, well-differentiated cells with normal growth and function

Hyperplasia vs Metaplasia

Hyperplasia involves an increase in cell number, while metaplasia involves a change from one adult cell type to another

Metaplasia vs Anaplasia

Metaplasia is a reversible substitution of one adult cell type for another, while anaplasia is an irreversible loss of differentiation toward a more primitive cell type

Hyperplasia vs Hypertrophy

Hyperplasia increases cell number, while hypertrophy increases cell size

Atrophy vs Hypertrophy

Atrophy decreases cell or organ size, while hypertrophy increases cell size or organ size