Aplasia & Hyperplasia

Aplasia/ Agenesis

Aplasia or agenesis is the complete failure of an organ or anatomic structure to form during embryogenesis. In short, it is the absence of any organ.

Pathologically, the organ or part is missing.

Examples involve absence of a gonad, a kidney, a limb or the tail.

Causes/ etiology:

1.      Inherited genetic defects, e.g., absence of tail.

2.      Poisoning by thalidomide causes absence of limb (amelia).

3.      Chemical agents or drugs, e.g., x-ray, γ-ray, isotope, chloramphenicol, sulfonamide may cause aplastic anemia.

4.      Prenatal viral infection, e.g., bovine viral diarrhea (BVD) may cause aplasia of cerebellum of calf.

Hypoplasia

Hypoplasia is the failure of an organ/ part to develop to its normal size.

It may occur either before or after birth.

Causes/ Etiology:

•      Congenital anomalies, e.g., hypoplasia of kidneys in calf.

•      Inadequate innervation,

•      Inadequate blood supply,

•      Malnutrition,

•      Hormonal deficiency,

•      Infections.

Macroscopic features

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

Microscopic features

•      Size of cells is reduced.

•      Number of cells is decreased.

•      More fat and connective tissue is present.