Food gives energy and constantly causes many biological processes in our body. If eaten food is too much part of its energy, whatever its origin could be, (alcohol, carbohydrates, fats and proteins) is stored as energetic supply. The tryglicerides are 65% of adipose tissue, the white tissue is about 90% of the adipose mass (the adipocytes are the specific fat cells of adipose tissue). In humans there are two types of adipose tissue, the white tissue (WAT: White Adipose Tissue) and the Brown Tissue (BAT: Brown Adipose Tissue).

White Adipose Tissue

White Adipose Tissue derives its name from the colour we can see in the microscope. It is a white-yellow mass because of the carotenoids. Of the two types of tissues the WAT is the most scattered in our body and its main function is to produce as well as to store energy.

The white adipose tissue is made up of unilocular cells which contain a large lipid droplet with little cytosol. The nucleus and the little organs are flattened and located on the cellular periphery. All these cells are divided into small groups named ‘lobules’ which are separated from the connective tissue. The WAT is located in the hypodermis, in the mesentery and mediastinum. It plays not only an energetic role but also a mechanical role (support and protection) and it also has a heat-insulating function. In the plasmatic membrane of the white adipocytes there are some enzymes, called LYPOPROTEINLIPASES, whose function is the fission of the link between the tryglicerides and the proteins which take them throughout the blood. In this way the tryglicerides and the free fatty acids can enter the adipocytes. Then they can be used as energy and stored as a reserve.

The WAT can control the appetite whose intensity is directly proportional to the number of adipocytes which have a small quantity of lipids because of their production of leptin.

Brown adipose tissue

The second type of adipose tissue (BAT) has a brownish colour because of the large quantity of mitochondria. Unlike white adipose tissue it is less scattered throughout our body.

BAT is made up of multilocular cells which contain many vesicles of fat. Besides being full of mitochondria, these cells have considerable cytoplasm more than the white adipocytes.

In the inner mitochondrial membrane there are some proteins calledUPC–1 (also known as uncoupling or thermogenic proteins. These proteins are activated by the release of fatty acids and they can dissolve the gradient of protons in the inner mitochondrial membrane. This gradient (with less protons inside than outside) is very important for the production of ATP. When this gradient is dissolved by the thermogenesis the energy from this process is released as heat rather than being used to generate ATP. This process is called ADAPTIVE THERMOGENESIS.

In conclusion, the UCP-1 aims at producing heat when the body is exposed to the lowest temperatures. The brown adipose tissue can start with the excess of calories in the diet. In theory this process based on the dispersion of the energetic surplus that releases heat might assure the homeostasis of the body weight apart from food excesses.

In overfeeded mice there is an evident increasing of thermogenesis which has a preventive effect on the development of obesity. Brown adipose tissue has reacted to this with the same metabolic and structural modifications as during the thermogenesis originating from cold.

In mice that are genetically obese brown adipose tissue has a low thermogenesis.

So the small quantity of brown adipocytes in an adult seems to be one of the pathogenic mechanisms which are fundamental for developing obesity.

Adipose Tissue Function

The adipose tissue has to get and to release fat for the energetic activity, but it is a real organ that can secret various proteins (leptin, GLUT4, TNF-alfa, PPARgamma, UCPs) which influence the whole body metabolism. Researchers’ attention is concentrating on these biochemical agents and their therapeutic ability.

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