Adaptations: atrophy. Types of atrophy. Microscopic and gross pathomorphology
Cellular atrophy is a decrease in cell size. If enough cells decrease in size then the whole organ will decrease. Some examples include the natural process in the thymus, skeletal muscle atrophy as well as the brain.
Types of atrophy are:
- Muscle atrophies
- Disuse
- Dystrophies and motor neuron conditions
- Atrophy of muscles caused by damage to motor nerves, or muscle tissue itself. Examples include Charcot-Marie-Tooth, all other Muscular Dystrophies. Atrophies of the brain tissue is a common disease which affects the brain, it can be generalised or localised, and while some degree of atrophy is natural with age, severe atrophy is seen in disorders such as Alzheimer's.
- Gland atrophies
- Adrenal gland atrophy occurs during prolonged steroid abuse, atrophy of breasts can occur following estrogen reduction.
- Vaginal atrophy
- In postmenopausal women, walls of the vagina become thinner
Gross brain atrophy: a brain with Alzheimer disease (top) has narrow gyri and widened sulci, especially frontally and temporally, compared with a healthy brain (bottom).
Image: “AD versus CO” by Hersenbank, CC BY-SA 3.0, via Wikimedia Commons.
Some types of atrophy are physiologically normal, such as the shrinking of the thymus throughout one's life. Additionally, atrophy can be full body atrophy in cases of severe malnutrition.
Remember: the classic causes of atrophy, with an example of each:
- Decreased workload: a leg immobilised in a plaster cast
- Loss of innervation: muscles after nerve injury or poliomyelitis
- Reduced blood supply: the brain in atherosclerosis
- Poor nutrition: cachexia in cancer, marasmus
- Loss of hormonal stimulation: endometrium after menopause
- Pressure: tissue next to an expanding benign tumour
The mechanism of atrophy is a combination of decreased protein synthesis and increased protein degradation. In many circumstances, atrophy is combined with autophagy, decreasing cell size (cell number falls by apoptosis).