Where is the fat?
Fat or fat is in several places in your body. First of all, the fat is located under your skin (subcutaneous fat). Some of it is also found at each of your kidneys. Where the rest of the fat is located depends on whether you are a man or a woman
* In adult men, places where fat tissue is mainly accumulated is the chest, abdomen and buttocks, which gives the appearance of “apples”
* In adult women places where mainly fat tissue accumulates are breasts, hips and buttocks, giving the appearance of a “pear”
* The differences in the location of fat come from sex hormones such as estrogen and testosterone.
There are two types of body fat in your body
White fat tissue – source of energy, thermal insulation, shock absorption by mechanical hazards
Brown fat tissue – is found mainly in newborns, between the shoulders (under the shoulder blades); important in thermogenesis.
Adipose tissue is composed of fat cells. Fat cells are a unique type of cells. You may think that fat cells are small formable stores that store droplets of fat
The cells of white adipose tissue are large and contain not large amounts of cytoplasm, only 15% of the volume, not the large nucleus and one large lump of fat, which constitutes as much as 85% of the volume.
Fatty cells brown tissues are slightly smaller, are equipped with mitochondria and slightly less fat. Mitochondria are used to generate energy. Fat cells are formed during the development of the embryo in the 3rd trimester of pregnancy and later during puberty, when the concentration of sex hormones is strongly elevated. It is during adolescence that there is a difference in the distribution of adipose tissue in men and women. One amazing fact is that fat cells do not multiply after puberty – if your body contains more fat, the amount of fat cells (adipocides) does not change. Each cell becomes larger (to some extent, after which new adipocytes are produced). As an addition, probably amounts of fat are stored in the liver and in small amounts in the muscles.
How fat enters your body
When you eat food containing fats, mainly triglycerides, they move through the stomach and intestines. What’s happening in the gut
1. Large fat drops are mixed by bile salts derived from the gall bladder in a process called emulsification. After a mix of large drops of fat, I create smaller ones that are called micelles that increase the surface of fats. Fats are hydrophobic, enzymes have access only to ‘internal’ parts of fat droplets, so breaking them on micelles enables better digestion of them.
2. Pancreatic enzymes called lipase “attack the surface of each micelle and break it down into every part of the fat – glycerol and fatty acids.
3. Glycerol and fatty acids are absorbed by the intestinal epithelial cells.
4. In intestinal cells, glycerol and fatty acids are re-packed into molecules (triglycerides – glycerol + 3-fat) surrounded by a protein coating. These molecules are called chylomicrons. The protein coating increases the lipid solubility in water.
5. Chylomicrons go to the lymphatic system – they are not transported directly into the bloodstream because they are too big to pass through the capillary walls.
6. The lymphatic system eventually connects to the veins, and in this place only the chylomicrons enter the bloodstream.
You may wonder why fat molecules are broken down into smaller particles, i.e. glycerol and fatty acids, and then re-combined into triglycerides. The reason for this is that the fat molecules are too large to pass through the cell membranes. So when they pass from the intestine through the intestinal epithelial cells to the lymph, or when they pass through the cell membranes, the fat must be broken down. But when fat is already transported in the bloodstream or lymph, it is more beneficial for the body to transport larger molecules, because triglycerides do not attract such excess of water molecules through osmosis as smaller molecules.
How fat is stored in your body
Chylomicrons stay in the blood for a long time – only about 8 minutes – because the enzyme called lipoprotein lipase, LPL breaks down fat into fatty acids. LPL is found in the walls of the blood vessels in adipose tissue, muscle tissue and cardiac muscle. LPL activity depends on the insulin concentration. If its concentration is high, LPL will be active; otherwise, if the insulin concentration is low, LPL will not show activity.
The fatty acids from the bloodstream are absorbed into adipocytes, muscle cells and liver cells. In cells, under the stimulation of insulin, fatty acids are processed into fatty molecules (triglycerides) and stored in tissue.
It is also possible for adipocytes to absorb glucose and amino acids, which are absorbed into the bloodstream after a meal, and are converted into triglycerides. Processing of carbohydrates or proteins for fats is 10 times less effective than fat in adipocyte, but the body can perform such reactions. If you have 100 kcal surplus in fat (about 11grams) floating in the bloodstream, adipocytes can accumulate only 2.5 kcal. On the other hand, if you have 100 kcal of glucose surplus (about 25grams) floating in the bloodstream, it takes 23 kcal to process glucose into fat and store it. By choosing, adipocytes will more easily catch fat and store it than compared to carbohydrates because fat is much easier to collect.
It is important to note that your body is storing more fat and does not increase the amount of adipocytes; each adipocyte increases in volume (as I wrote earlier – to some extent).
Insulin antagonistic hormones
When you do not eat a meal, your body does not absorb nutrients. If your body does not absorb nutrients, insulin levels are low. However, your body always uses energy; and if you do not absorb nutrients, this energy must come from internal sources of carbohydrates, fat and proteins.
Under these circumstances, various organs secrete hormones
Pancreas – glucagon
Pituitary gland – growth hormone
Pituitary gland – ACTH (adrenocorticotropic hormone)
Adrenal glands – adrenaline (epinephrine)
Thyroid – thyroid hormones
These hormones affect liver, muscle and adipose tissue and show antagonistic action to insulin.
How your body breaks down fats
When you are not eating, exercising, the body must take energy from sources of carbohydrates, fats and proteins.
The most important source of energy for your body is glucose. …
The first line of defense in maintaining energy homeostasis is the breaking down of glycogen into individual glucose molecules – this process is called glycogenolysis. Then, your body breaks down fat into glycerols and fatty acids in a process called lipolysis. Fatty acids can be immediately burned to produce energy, or they can be used to create glucose in a process called glycogenesis. In glycogenesis, amino acids can also be converted to glucose.
In adipocytes, another type of lipase breaks down fat to fatty acids and glycerol. This lipase is activated by various hormones, such as glucagon, adrenaline and growth hormone. As a result, glycerol and fatty acids are released into the blood and transported to the liver. Then they can be further decomposed or used for glycogenesis.
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