Adipose tissue is a special connective tissue that functions as the main storage for fat in the form of triglycerides. In humans, it is present in two different forms: white and brown. Its quantity and distribution are individual for each.
White adipose tissue performs three functions: thermal insulation, mechanical cushion and, most importantly, a source of energy. Basically, it is located directly under the skin and is the main heat insulator of the human body, because it conducts heat three times worse than other tissues. The degree of insulation depends on the thickness of this layer. For example, a person with 2 mm of subcutaneous fat will feel most comfortable at 15 ° C, while with 1 mm - 16 ° C. In addition, adipose tissue surrounds the internal organs and provides them with shock protection.
For example, it is located:
- around the heart;
- in the kidney area;
- filling around joints;
- inside the eye socket, behind the eyeball, etc.
As the main energy store, it provides a reserve in case of excess consumption. Therefore, more energy canbe obtained from a gram of fat (9 Kcal) than from a gram of carbohydrates (4 Kcal) or protein (4 Kcal). In addition, if a person stored excess energy in the form of carbohydrates, the increase in mass would interfere with his mobility.
However, there are some restrictions on the use of fat as "fuel". Thus, tissues that function primarily due to anaerobic processes (for example, red blood cells) must receive energy from carbohydrates and must have an adequate supply of them. In addition, under normal conditions, the brain depends on glucose and does not use fatty acids. Under unusual metabolic circumstances, he can use ketone bodies (a by-product of incomplete fat metabolism) if they are present in high enough amounts.
Brown adipose tissue gets its name from the color caused by the rich vascularity and densely packed mitochondria found in various locations.
Instead of serving as a substrate, the lipids in it release energy directly in the form of heat. The mechanism of its generation is associated with metabolism in mitochondria.
The biochemical process of releasing energy in the form of heat is activated when the overall body temperature begins to decrease. In response to hypothermia, the human body releases hormones that stimulate the release of fatty acids from triglycerides, which in turn activate thermogenin.
In humans, the formation of brown adipose tissue begins at 20 weeks of fetal development. Duringbirth, it is approximately 1% of body weight. Its layer is located around the blood vessels that supply oxygen to the brain and abdominal organs, and also surrounds the pancreas, adrenal glands and kidneys. Thanks to brown adipose tissue, the vital organs of the newborn do not get supercooled in a low temperature environment.
After birth, the baby begins to develop white adipose tissue, and brown begins to disappear. In an adult, there are no places for its accumulation at all, although it is present (about 1% of the mass of fat), but randomly mixed with white.
