Corpus: Adipose tissue

Adipose tissue is a specialised, metabolically active tissue consisting mainly of fat cells (adipocytes).

...according to tissue type[Bearbeiten]

Histologically, there are three different types of adipose tissue:

• white adipose tissue
• brown adipose tissue
• beige adipose tissue

When we talk about fatty tissue, we usually mean white fatty tissue, as brown fatty tissue is only found in a few parts of the body in adults.

...according to function[Bearbeiten]

A distinction is made according to the function of white adipose tissue:

• Construction fat: mechanically important filling tissue; serves as padding and displacement layer in the so-called fat bodies.
• Storage fat: storage of triglycerides

Brown adipose tissue can produce heat by oxidising fatty acids.

...according to localisation[Bearbeiten]

• Subcutaneous fatty tissue (SFT): Located directly under the skin and serves as protection against the cold
• perivascular adipose tissue (PVAT): Surrounds the blood vessels and has secretory functions
• Visceral adipose tissue (VFT): Is localised in the free abdominal cavity, where it surrounds the internal organs
• Adipose marrow: Is located in the medullary cavity of the bones

Adipose tissue that occurs in certain anatomical positions as a structural element is also referred to as the adipose body (corpus adiposum). These include, among others:

• Corpus adiposum infrapatellare
• Corpus adiposum subacromiale
• Corpus adiposum orbitae
• Corpus adiposum buccae

Adipose tissue develops from mesenchymal cells, particularly in the vicinity of blood vessels. The first adipocytes develop in the embryonic period (4th-8th week), whereby predominantly brown adipose tissue develops. White adipose tissue develops during the foetal period and postnatally until puberty. Postnatally, the brown adipose tissue predominantly disappears and only persists in selected areas of the body (e.g. in the mediastinum, around the aorta).

Fat cells also develop permanently from preadipocytes in adults. A crucial transcription factor for adipogenic differentiation is PPAR-γ.

The adipose tissue consists of adipocytes that are incorporated into a loose reticular fibre scaffold. Their cell diameter is up to 100 µm. Depending on the type of adipose tissue, the fat cells have one large lipid-filled vacuole or several smaller vacuoles. Accordingly, a distinction is made between univacuolar and plurivacuolar adipocytes. The fat droplets are freely present in the cytosol, i.e. they are not surrounded by a biomembrane like secretory vesicles.

The cell nucleus is displaced to the periphery by the vacuoles and appears flattened ("signet ring cell"), other cell organelles are only sparsely recognisable.

Adipose tissue serves a multitude of functions within the organism:

• Storage of lipids, fat-soluble vitamins and water
• Thermal insulation (e.g. Panniculus adiposus)
• Structure maintenance (e.g. Bichat fat plug)
• Pressure cushion (e.g. gluteal fat)

Adipose tissue is now perceived as an endocrine organ in its own right because it produces and secretes a large number of signalling molecules, also known as adipokines. These include hormones such as leptin and adiponectin, which are involved in the regulation of hunger and blood sugar levels. Visceral fat has a particularly high endocrine activity.

The distribution of fatty tissue in the body, the so-called fat distribution pattern, is determined by gender, among other factors. A distinction is made between an android and a gynoid fat distribution pattern.

With age, the ability of adipocytes to eliminate lipids by metabolising them decreases. Lipid uptake, on the other hand, remains largely constant. This effect is considered to be one cause of the easier weight gain in old age.^[1]

The loss of adipose tissue is known as adipose tissue necrosis. It is based on the destruction (necrosis) of the adipocytes. Adipose tissue necrosis is a special form of colliquative necrosis.

Overeating leads to a pathological increase in fatty tissue, which is known as obesity. Obesity increases the risk of metabolic diseases (especially diabetes mellitus), cardiovascular diseases and diseases of the musculoskeletal system.

Adipose tissue contains numerous mesenchymal stem cells. These adipose-derived stem cells (ADSCs) can be obtained and processed relatively easily by liposuction. As multipotent stem cells, they can then differentiate into different cell types, e.g. cartilage, bone, nerve and muscle cells. Adipose stem cells are used in regenerative medicine and tissue engineering.