ETIOLOGY AND MECHANISM OF ATROPHY

Atrophy: Shrinkage in the cell size with the loss of cell material is well-known as atrophy. It characterises a form of adaption and finally causes cell death. There are two types of atrophy:

·       Physiologic atrophy (occurs during fetal development)

·       Pathologic atrophy (occurs during adult life)

Etiologies of atrophy

The common etiologies of atrophy are as follows:

Ø      Decreased workload: When a broken limb is immobilized in a plaster cast as well as the patient is restricted to complete bed rest, skeletal muscle atrophy occurs.

Ø      Loss of innervations: Damage of nerves lead to rapid atrophy of cell fibres.

Ø      Reduced blood supply: A decrease in blood supply to a tissue because of arterial occlusive disease causes atrophy of tissue.

Ø      Inadequate nutrition:Marasmus is a form of PEM which results from a severe scarcity, or impaired absorption of vitamins, proteins and minerals., eg. adipose stores have been washed-out resulting in marked muscle wasting.

Ø      Loss of endocrine stimulation: Loss of stimulation of estrogen after menopause resulting in physiologic atrophy of the endometrium, vaginal epithelium and breast.

Ø      Aging: The aging process is associated with loss of brain cell and heart cell.

Ø      Pressure: Tissue compression for any length of time can cause atrophy. Example: An enlarging benign tumor can cause atrophy in the surrounding compressed tissues.

Mechanism of atrophy

Ø      Increased protein degradation plays a key role in atrophy. Mammalian cells contains multiple proteolytic system that serve distinct function. Acid hydrolase, e.g. cathepsin and other enzymes of lysosomes degrade the endocytosed proteins from the

·        Extracellular environment and

·        Cell surface

The ubiquitin-proteasome pathway is responsible for this.

Mechanism

Protein conjugated with ubiquitin                       Degredation of protein with proteasome           

Ø      Increasing amount of autophagic vacuoles also play a vital role in atrophy. These membrane bound vacuoles which are found within the cell containing cell components (e.g. mitochondria, endoplasmic reticulum), that are designed for destruction, into which lysosomes discharge their hydrolytic contents. The cell components are then digested.

Cell debris contained by the autophagic vacuole may possibly resist digestion and persist as a residual bodies in cytoplasm. Example of residual body is lipofuein granule. Presence of lipofuein granule in cytoplasm in sufficient amount, imparts a brown staining to the tissue. This condition is called brown atrophy.
CLASSIFICATIONOF ANTIHYPERTENSIVE DRUGS