Adipose tissue: anatomy and metabolism

Types and patterns of distribution of adipose tissue

According to its location and metabolic characteristics, adipose tissue is divided into three main types: 1) subcutaneous adipose tissue; 2) deep (subfascial) adipose layer; and 3) internal (visceral) fat, located mainly in the abdominal cavity. The thickness and ratio of these three layers are extremely diverse, differ significantly in different parts of the body, and largely determine the contours of the human figure.

The location and architecture of fat deposits depend on many factors (heredity, gender, age, average metabolic rate, etc.) and are characterized by the following basic patterns.

• The subcutaneous layer of fatty tissue exists in all anatomical zones and determines, first of all, the smoothness of the contours of the human body. Its thickness is largely determined by the individual ratio of energy intake and energy expenditure and, in the vast majority of cases, is relatively easily reduced by physical exercise and/or by reducing the overall energy value of the diet.
• The deep subfascial fat layer is expressed only in some anatomical zones (abdomen, thighs, submental area) and determines individual differences in the contours of the figure, as well as the volume and contours of various areas of the human body. Fat deposits of the deep layer have a special tissue metabolism, and their localization and volume are largely fixed genetically and change relatively little when a person loses weight.
• Excess fat deposits of the male type are characterized by:
  • a relatively uniform increase in the thickness of the subcutaneous fat layer of the limbs and chest;
  • a more significant increase in abdominal volume, mainly due to visceral fat deposits with a relatively small thickness of the superficial and deep layers of the anterior abdominal wall;
  • frequent presence of fat "traps" in the flanks and submental area.
• Excess fat deposits of the female type are characterized by a local increase in the volume of predominantly the deep layer of adipose tissue in the thighs, inner surface of the knees, abdomen and - more rarely - on the face, arms and shins.

Types and forms of fat deposits

The basis for the increase in the volume of adipose tissue is the hypertrophy of fat cells (adipocytes). This process can occur in adipose tissue of any localization and leads to the development of two main forms of fat deposits: 1) local and 2) general (generalized).

Localized forms of fat deposits

Local hypertrophy of fat cells can occur due to their genetically determined increased sensitivity to glucose entering the body. There are three main forms of local distribution of fat deposits:

• fat "traps" (limited form);
• diffuse-local form;
• finely tuberculate contour disturbances.

Fat "traps" are characterized by relatively clear boundaries of changes in body contours due to hypertrophy of adipocytes of the deep or superficial layers of adipose tissue. The hypertrophy of the deep layer is of the greatest importance.

The diffuse-local form of fat deposits is characterized by a pronounced increase in the predominantly superficial layer of adipose tissue in a certain anatomical area. In this case, the contours of this area are not clearly outlined and smoothly transition into neighboring areas with a normal thickness of the fat layer.

Most often, areas of diffuse increase in the thickness of the fat layer are located on the anterior surface of the thigh and in the epigastric region, less often - on the posterior surface of the thigh and on the shin.

Small-tuberous contour disorders are caused by pronounced hypertrophy of adipocytes of the subdermal layer and are found in both local and generalized forms of fat deposits. The development of this condition is largely associated with congenital features of the metabolism of adipocytes of the superficial fat layer, and is also due to the anatomical structure of the subcutaneous fat. In particular, the subdermal layer contains connective tissue bridges that connect the dermal layer of the skin with the superficial fascia and provide both fixation and mobility of the skin in relation to deep tissues. In some people with a low elasticity threshold of connective tissue bridges, adipocyte hypertrophy leads to bulging of adipose tissue towards the skin with the formation of an uneven contour in the form of small tubercles on the skin surface. This condition is often called cellulite, which, from the point of view of medical terminology, is incorrect, since the ending "it" is used to denote an inflammatory process. It is more appropriate in this case to use the term "small-tuberous lipodystrophy".

A characteristic feature of all local forms of obesity is the relative stability of their volume and shape, which can be maintained even with significant weight loss.

Generalized form of fatty deposits (obesity)

According to modern concepts, general obesity is the result of an energy imbalance that occurs when the amount of incoming energy exceeds the energy expenditure of the body. Excess energy leads to the deposition of additional volume of adipose tissue. In this case, hypertrophy of fat cells of both the superficial and deep layers occurs. With severe obesity, the thickness of the adipose tissue becomes significant, and the contours of the fat "traps" are no longer clearly defined.

Such changes in adipose tissue often occur in adulthood and are subject to predominantly conservative treatment. At the same time, according to the research of N. Greenwood (1985), fat cells can form throughout life. The increase in fat mass due to both hypertrophic processes and an increase in the number of cells is unfavorable for the prognosis of conservative treatment.

Effective body contouring for these patients is possible with the help of liposuction, which removes excess fat cells.

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