Fettvev

Fettvev, or adipose tissue, is a specialized connective tissue consisting predominantly of adipocytes that stores energy as triglycerides and serves protective and insulating roles. It is distributed throughout the body, most notably as subcutaneous fat under the skin and as visceral fat around internal organs, with smaller depots in bone marrow and other sites.

Two principal types are recognized: white adipose tissue (WAT) and brown adipose tissue (BAT). WAT stores excess energy as triglycerides and functions as an endocrine organ, secreting adipokines such as leptin, adiponectin, and resistin, which influence appetite, insulin sensitivity, and inflammation. BAT contains many mitochondria rich in UCP1 and can generate heat through non-shivering thermogenesis. Beige (brite) adipocytes can emerge within WAT under certain stimuli and acquire thermogenic capacity.

Anatomically, adipose tissue comprises adipocytes, precursor cells, immune cells, fibroblasts, and a vascular network. The tissue expands primarily by hypertrophy of existing adipocytes, with hyperplasia occurring during developmental growth and some metabolic conditions. Adipocytes release fatty acids via lipolysis in response to hormonal signals; insulin inhibits lipolysis, while catecholamines promote it.

Functionally, fettvev provides energy storage, cushioning, and thermal insulation. It also plays a key endocrine role, influencing energy balance, appetite, glucose metabolism, and inflammation. Pathologically, excess visceral fat is associated with metabolic syndrome, insulin resistance, and cardiovascular risk, while healthy adipose tissue supports metabolic homeostasis. Brown and beige fat in humans are of interest for potential obesity therapies through stimulation of thermogenesis.