Adipose tissue performs important functions in the human body. A distinction is made between white and brown adipose tissue; with the brown portion being much smaller than the white portion.
What is adipose tissue?
Adipose tissue is formed from reticular connective tissue and occurs in various parts of the human body. There are two types, brown and white, or yellow, adipose tissue. The brown fat is needed for heat production, the white one has different tasks. The components of body fat are fat cells, adipocytes. Brown adipose tissue is found in adult humans only in small quantities and in very few places, for example under the armpits, in the thoracic cavity in the mediastinum or on the kidneys. An infant, on the other hand, has a much higher proportion of brown adipose tissue because it is much more susceptible to cold. In newborns, brown fat is mainly located in the region around the chest and neck. White adipose tissue is divided according to its function into insulating fat, storage fat (also depot fat) and building fat. Furthermore, it serves as a metabolic organ, as it is involved in energy metabolism. The distribution of white adipose tissue is different in women and men. In women, it is mainly accumulated under the skin on the hips, abdomen and thighs; in men, it largely coats internal organs and the digestive system as visceral fat.
Anatomy and structure
Both white and brown adipose tissue are composed of fat cells. Brown fat cells are plurivacuolar; that is, they are filled with multiple small lipid droplets. They have many mitochondria, which in turn contain numerous cytochromes (colored proteins). These proteins are responsible for the brown color. White adipose tissue, on the other hand, has univacuolar fat cells that contain only a single large lipid droplet and are much larger than the cells of brown adipose tissue. This large lipid droplet (vacuole) pushes the nucleus of the cell flat against the edge of the cell. To keep the vacuole in shape, it is surrounded by stabilizing protein structures called intermediate filaments. Each fat cell is enveloped by a protein layer called the basal lamina. Numerous blood vessels run through the white adipose tissue. The fat of the human body contains a lot of oleic acid and has an intense yellow color. The name “white adipose tissue” comes from the fact that fat is extracted by default from fat cells prepared for examination purposes, and these empty cells look white under the microscope.
Function and tasks
Brown adipose tissue has the task of generating heat. Especially in infancy, this function is needed because the thermoregulation of newborns is not yet developed. The generation of heat is triggered by nerves of the sympathetic nervous system, which release the hormone norepinephrine. This releases fatty acids, which oxidize through a special process. This oxidation generates heat, which is transmitted through the blood vessels to the circulatory system and eventually to the organs. The white adipose tissue has various functions. On the one hand, it serves as an energy reserve in the form of storage or depot fat. This reserve allows a person to survive for up to 40 days without eating. Storage fat is mostly found in the subcutis of the buttocks and abdomen, but also in the peritoneum, the skin lining the abdominal cavity. The fatty tissue, known as building fat, has a protective function. It acts like a cushion for the body and prevents mechanically caused injuries. This fat is located, for example, under the skin on the soles of the feet, around the eye, on the cheeks and on joints, but also on organs such as the kidneys and heart. In the case of inadequate food intake, this fat is also used to supply the body, virtually as the last available source of energy. If the abdominal fat is also depleted, this results in the sunken cheeks and eye sockets typical of extremely malnourished people. Finally, the insulating fat, which is mainly located in the subcutaneous tissue, protects the body from releasing too much heat to the outside. White adipose tissue additionally plays an important role in the metabolism of the human body.
Diseases and ailments
Lipoma represents a common change in adipose tissue. It is a benign growth that forms in the subcutaneous fatty tissue. Lipomas grow very slowly, usually on the back or abdomen, arms or legs. But they also occur on the face.They usually do not cause any discomfort and, from a medical point of view, removal is not necessary unless the lipoma presses on nerves or vessels. In the face, a lipoma is often removed for cosmetic reasons. Malignant, on the other hand, is the less common liposarcoma, a lump that grows very quickly and causes pain. It is more likely to develop in older people; men are more often affected than women. Liposarcomas are caused by the degeneration of fat cells. Liposarcoma must be surgically removed. Another possible disease in fat tissue is necrosis. In this case, fat cells die and the lipid droplets contained in the cells penetrate into the surrounding connective tissue. This results in the formation of so-called false cysts. This disease frequently occurs in the fatty tissue of the female breast. These false cysts are benign and are sometimes mistaken for malignant lumps during palpation examinations. Ultimately, only surgical removal and histological examination of the lumps provides certainty. Necrosis is caused by injury or bruising of the breast tissue.
