If you look at it with the eyes of an old physiologist, leaving aesthetic canons, fashions and so on for a moment, adipose tissue is a connective tissue made up of cells, called adipocytes, mainly responsible for the accumulation of fat in the form of triglycerides . If, on the other hand, it is observed on the basis of the most recent scientific findings, adipose tissue is a real organ, consisting of two types of cells (white and brown), capable of producing real hormones, such as leptin, which influence the activity of the whole organism (see also: adipose tissue and obesity - visceral fat).
White adipose tissue and brown adipose tissue
In mammals there are two different types of adipose tissue: white and brown.
The other type of adipose tissue, called brown, is abundant in hibernating mammals and in puppies.
In humans, the brown adipose tissue is present in small quantities in the newborn (axillary and interscapular area). With the growth, a large part of this tissue is transformed into white adipose tissue; for this reason in the adult we find only traces of brown adipose tissue , distributed in the form of small cellular islands scattered among the numerous white adipocytes. Therefore there are no exclusive deposits of white adipose tissue or brown adipose tissue, but always and in any case mixed deposits, where the relative percentages differ according to the topographical location.
Characteristics of white adipose tissue
These are very large cells, capable of accumulating large quantities of triglycerides within them, which come together to form a large oily drop. The fluidity of this drop is guaranteed by the internal temperature of the organism, which is higher than the melting point of the lipids contained in it. Due to the considerable size of this drop, the cytoplasm and the nucleus are relegated to the periphery.
White adipocytes are not simple reservoirs of fat, but metabolically active cells, capable of synthesizing triglycerides and storing them. The same cells are also able to hydrolyze these triglycerides and pour the obtained glycerol and fatty acids into the blood. Adipocytes also have the ability to convert excess glucose into reserve triglycerides.
MAIN FUNCTIONS OF WHITE ADIPOSE TISSUE
- Synthesize triglycerides and store them as an energy reserve (1Kg = 7000 Cal approximately).
- Hydrolyze the deposited triglycerides and introduce free fatty acids into the blood.
- Synthesize triglycerides from glucose.
- Mechanical shock absorber, thermal insulator and producer of hormones and biologically active substances (adipokines), including leptin, adiponectin, interleukin 6 (IL-6) and tumor necrosis factor-α. The most endocrineally active is the abdominal adipose tissue.
Adipokines - which play an important role in energy metabolisms - are also the basis of the pathophysiology of widespread diseases (arterial hypertension, obesity, atherosclerosis, type 2 diabetes). These substances are associated with others with a pro-inflammatory and pro-insulin-resistance action, produced by macrophages responsible for the digestion of those dead fat cells, because they are made too bulky by excessive lipid accumulation (typical of obesity). Not surprisingly, it has been shown that the number of macrophages present in the adipose tissue is proportional to the degree of obesity. Their migration here seems to be related to the hypoxic state that is created in the adipocytes following the excessive hypertrophy, which determines their death.
Brown adipose tissue "
