MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 1. ORGAN. ORGAN SYSTEM. ORGANISM

INJURY

2. Atrophy

Atrophy refers to a decrease in organ volume and a decline in its function occurring during normal life or As a result of disease. Congenital underdevelopment of an organ is termed hypoplasia, whereas the complete Congenital absence of an organ is called agenesis. Aplasia denotes the underdevelopment of an organ that persists as an early rudiment. In hypoplasia, Organs are not only reduced in size but also retain an embryonic Structure. Occasionally, humans exhibit a lobulated Kidney ("bear kidney"), a lobulated Spleen, or a bicornuate Uterus. The congenital absence or hypoplasia of one of the paired organs typically does not affect the function of the entire system, as the contralateral organ compensates for it. Sometimes, hypoplasia of an entire system occurs, such as the Reproductive System. The absence or underdevelopment of an unpaired organ is accompanied by severe disruption of the Organism's vital activity and may sometimes lead to death. For instance, cerebral hypoplasia is invariably associated with intellectual disability, while severe hypoplasia or Aplasia of the Brain is incompatible with life.

Signs of atrophy. In atrophy, organs are reduced in volume primarily due to a decrease in the volume of parenchymal Cells. The cells exhibit a reduction in both the number and size of Cell/35.html">Mitochondria, as well as ultrastructures performing specialized Functions (myofibrils in myocytes); cytoplasmic volume decreases. Atrophied cells may contain inclusions in the form of lipofuscin granules, imparting a brown color to the organ. In such cases, the condition is referred to as Brown atrophy of the organ, such as The Heart or Liver. Concurrently with cellular atrophy, the organ stroma proliferates, and adipose tissue frequently expands as well. The latter replaces the atrophied organ parenchyma, creating the impression that the organ has increased in volume (false hypertrophy).

As a rule, an atrophied organ appears reduced in volume and firm due to stromal proliferation, rendering its surface finely granular.

Atrophy can be physiological or pathological. Physiological atrophy of organs accompanies normal human life. For example, the umbilical Arteries atrophy after birth; the Thymus atrophies upon the attainment of Puberty. In elderly individuals, Muscles and Gonads gradually undergo atrophy.

Pathological atrophy is associated with disease and develops at any age. Pathological atrophy may involve the entire organism (generalized atrophy) or its individual parts (local atrophy).

Generalized atrophy, or wasting, may develop in starvation (alimentary cachexia) or in malignant tumors, particularly of the digestive tract (Cancer cachexia). Cachexia is defined as the extreme degree of bodily wasting accompanied by the atrophy of multiple organs.

The causes of wasting may include Disorders of the central nervous and endocrine systems, cerebral and pituitary cachexia, and chronic infectious diseases (tuberculosis, chronic dysentery).

The cause of local atrophy (atrophy of individual organs or body parts) is most frequently disorders of

Blood Circulation (anemia) or innervation. Disuse atrophy develops most commonly. It arises within an organ as a result of decreased function; for instance, immobilization of a limb following a fracture leads to Muscle atrophy, and tooth extraction leads to alveolar bone resorption. In disuse atrophy, Tissues receive a reduced blood supply, Cellular METABOLISM is depressed, and cells decrease in volume.

Atrophy resulting from inadequate blood supply is most frequently observed in elderly individuals with vascular atherosclerosis.

Neurotic atrophy develops when innervation is impaired, most commonly affecting skeletal muscles. Examples include Spinal Cord damage resulting from poliomyelitis or trauma.

Atrophy caused by Physical and Chemical factors occurs under The Influence of ionizing radiation in the Bone Marrow and gonads. Radioactive iodine induces Thyroid Gland atrophy. Prolonged corticosteroid therapy leads to Atrophy of the adrenal cortex.

If atrophy is moderately expressed, The structure of the affected organ is restored upon the elimination of its underlying cause.