Hyperplasia, Metaplasia, Anaplasia & Dysplasia

Hyperplasia

Hyperplasia is the increase in number of cells leading to increase in size of organ/ tissue than normal.

Etiology

• Prolonged irritation e.g. fibrosis/ nodules in hands, pads.

• Nutritional disorders, e.g., Iodine deficiency

• Infections, e.g., Pox.

• Endocrine disorders, e.g., prostate hyperplasia.

Hyperplasia of connective tissue often surrounding a tumor is known as desmoplasia or desmoplastic reaction. It is common in mammary gland, stomach, uterus etc.

Macroscopic features

•      Size, weight and volume of the organ is increased.

•      Nodular enlargement of organ is present.

Microscopic features

•      Number of cells is increased,

•      Displacement of adjacent tissue,

•      Lumen of ducts/ tubules is obstructed.

Metaplasia

Metaplasia is defined as the transformation of one type of cells to another type of cells.

Etiology

• Prolonged irritation, e.g., gall stones cause metaplasia of columnar cells to stratified squamous epithelial cells in wall of gall bladder.

• Endocrine disturbances, e.g., in dog, columnar epithelium of prostate changes into squamous epithelium.

• Nutritional deficiency, e.g., nutritional roup. In poultry, cuboidal/ columnar epithelium of esophageal glands changed into stratified squamous epithelium.

• Infections, e.g., pulmonary adenomatosis.

Macroscopic features

      • Mucous membrane becomes dry in squamous metaplasia.

      • Presence of nodular glands on oesophageal mucous membrane due to vitamin A deficiency   

        in chickens also known as "Nutritional roup".

Microscopic features

      • Change of one type of cells to another type, In place of columnar cells, there are squamous   

        epithelial cells.

• In place of endothelial cells, cuboidal or columnar cells in alveoli e.g. pulmonary

        adenomatosis.

Dysplasia

Dysplasia is the disordered/ abnormal development of cells/ tissues which are improperly arranged. It is the malformation of tissue during maturation, e.g.,

1. Spermatozoa head and tailpiece are structurally abnormal or aligned in improper way.

2. Fibrous dysplasia in bones.

3. In gastrointestinal tract, disruption of cellular orientation, variation in size and shape of cells, increase nuclear cytoplasmic ratio and increased mitotic activity.

Anaplasia

Anaplasia is the reversion of cells to a more primitive and less differentiated type.

Anaplasia is characterized by extensive pleomorphism and/ or giant cell formation.