Mechanisms and Morphological Basis
The volume increase of any organ is always based on hyperplasia—an increase in the number of structural elements. Depending on the anatomical features of the tissue, this process can occur predominantly through the division of the cells themselves or by increasing the number of intracellular structures (or a combination thereof).
Marked biochemical shifts occur at the subcellular level:
- Proteins are synthesized intensively, leading to an increase in fibrous structures.
- RNA concentration increases in the cytoplasm, and DNA concentration increases in the nuclei.
- The activity of oxidation-reduction cycle enzymes rises.
Organelles are forced to adapt to high energy demands. For example, mitochondria can fuse with each other, forming giant shapes with an increased number of cristae.
Physiological and Compensatory Hypertrophy
Based on the conditions of development, the process is divided into two major groups: adaptive (under healthy conditions) and compensatory (in disease).
- Physiological (working) hypertrophy occurs in completely healthy individuals as an adequate response to increased function. A classic example is the increase in skeletal muscle mass and myocardium in professional athletes. Organ function remains within homeostatic limits.
- Compensatory hypertrophy develops in pathologies. Its main goal is to compensate for the lost functions of a damaged organ. It is important to note that the enlarging tissue itself is not affected by the pathological process. A typical example is myocardial thickening in arterial hypertension.
Types of Hypertrophy in Disease
If an organ or its part is damaged, the body attempts to compensate for the loss of function. Depending on the nature of the damage, several types of compensation are distinguished:
- Regenerative. Triggered in the surviving areas of a damaged organ. For example, heart muscle tissue enlarges around the scar after myocardial infarction (large-focal cardiosclerosis), and healthy kidney tissue proliferates in nephrosclerosis.
- Vicarious (replacement). Characteristic exclusively of paired organs. If one organ is destroyed or surgically removed, the remaining one takes on a double workload and increases in size.
- Idiopathic. Arises for unclear reasons and is often hereditary and familial in nature (e.g., hypertrophic cardiomyopathy).
Pathological Hypertrophy
Unlike compensatory hypertrophy, true pathological hypertrophy carries no adaptive meaning. It does not restore lost function and often distorts it, acting as a direct symptom of disease that requires treatment.
Pathological forms include:
- Neurohumoral. Associated with impaired neuroendocrine gland function. A striking example is acromegaly, in which pituitary and hypothalamic lesions lead to enlargement of facial bones, hands, feet, and internal organs (splanchnomegaly).
- Hormonal. Occurs during endocrine imbalances. This includes glandular endometrial hyperplasia in ovarian dysfunction, gynecomastia in men, and prostatic hyperplasia in elderly individuals.
- Hypertrophic overgrowths. Formed in zones of prolonged chronic inflammation or impaired lymph circulation (e.g., lymphedema/elephantiasis of the lower extremities).
- False (Pseudohypertrophia). The organ visually enlarges, but not at the expense of working cells. This occurs when adipose and connective tissue proliferate in place of the atrophying functional parenchyma.