Adipose tissue: what it is, types and characteristics

Let's see what adipose tissue is, what the cells that form it are like, and its relation to overweight.

From a biochemical point of view, fat includes several types of lipids, organic molecules made up mainly of carbon and hydrogen, whose function is usually the storage of energy in living beings. Lipids, generally in the form of triacylglycerols, have a very high caloric content (10 kcalAdipose tissue: what it is, types and characteristics

Let's see what adipose tissue is, what the cells that form it are like, and its relation to overweight.

From a biochemical point of view, fat includes several types of lipids, organic molecules made up mainly of carbon and hydrogen, whose function is usually the storage of energy in living beings. Lipids, generally in the form of triacylglycerols, have a very high caloric content (10 kcal/gram). They are therefore a compact and excellent way of storing energy for stress and exercise. According to the World Health Organization (WHO), dietary fat intake should not exceed 30% of the total amount of organic matter ingested. On the other hand, the percentage of carbohydrates should be around 55-60% and proteins 15%. Contrary to what is said in popular culture, fats are not bad: on the contrary, they help us to function in times when resources are scarce, both humans and other animals.Moving away a little from dietary conceptions, today we come to show you

• some of the most important characteristics of human adipose tissue. . We advance you that these go far beyond energy storage, so better not to take anything for granted.

What is adipose tissue?Adipose tissue is

a type of tissue made up of cells called adipocytes, where a large amount of energy is stored in the form of fat.. This cellular organization is responsible for many functions, however, an excess of this tissue can cause serious health problems. It is generally associated with the work of energy storage, but, in addition, it produces a large amount of peptides and factors of both endocrine and paracrine function.

In healthy individuals, adipose tissue accounts for 10 to 30% of the total mass, depending on the Body Mass Index (BMI).

depending on Body Mass Index (BMI), ethnicity, gender and other factors. In morbidly obese patients, the percentage of fat can be as high as 80% of their weight. When a person moves in these values, the risks of ischemic Heart disease, gastric cancer, accelerated cellular aging and many other pathologies multiply.

Adipose tissue is composed of many cells. Adipocytes are the dominant and main bodies, accounting for 80-90% of the total tissue volume and 60-70% of the total number of cells (in terms of numbers). Looking at the ultrastructure of this tissue, we see that adipose tissue is approximately 18% water, 80% triglycerides (fats) and 2% proteins. In obese subjects, the water content decreases and fats occupy a larger fraction of the total. Adipocytes and their relationship with weight.

As their name suggests, adipocytes are the cell types that characterize adipose tissue. Before continuing with more complex terminology, it is necessary to dedicate a few lines to these characteristic cell bodies. We are dealing with rounded cells about 10-200 microns in diameter, 95% of whose internal content is represented by lipid components.Very interesting studies have explored the idea that, after the age of 20, the number of adipocytes in humans remains practically constant even if we lose weight.

Obesity and overweight are due to 2 main events at the cellular level

• The prevalence of one or the other process is highly age-dependent. The prevalence of one process or the other is highly age-dependent. Until 2008, it was believed that adipocytes newly synthesized during weight gain were lost during weight loss. However, it seems that the cell number is constant during adulthood: what varies is the diameter and the amount of fat stored in each adipocyte, not the number of them. Interesting, isn't it?

The types of adipose tissue in humans

In the human body, lipids are stored in 2 types of adipose tissue: white and brown. We will tell you about its particularities in the following lines. 1. White adipose tissue (WAT)Its main location is in the subcutaneous, abdominal, inguinal, perirenal (around the kidneys), retroperitoneal, gonadal, around the organs and in other physiological places in a dispersed way.

The TAB is the main energy reserve tissue of the organism. and is also attributed with the function of protecting many vital organs and structures from mechanical injury.

This type of tissue is called "unilocular" because each adipocyte has a single fat droplet, which occupies the vast majority of its cytoplasm.

. However, this characteristic is not fixed, since sometimes very well nourished animals may present multilocular white adipocytes during their development, although the fat droplets will fuse into a single one when they mature. Both the nucleus and the rest of the cytoplasmic components occupy a thin peripheral space, close to the plasma membrane.Historically it was believed that the TAB was a not very active tissue, but research has shown in recent decades that it is a highly dynamic cellular conglomerate, since it secretes numerous factors, not only lipids but also proteins. Without going any further, white adipose tissue has been found to secrete steroid hormones, so it is considered an essential component of the human endocrine system.

The molecules synthesized in this tissue are called adipokines.

. An example of these is leptin, which is synthesized almost exclusively in adipocytes, although it is also expressed in the hypothalamus, ovary and placenta. Among many other functions, this hormone affects food intake in humans, acting on the central nervous system (CNS). Other adipokines, less known but equally important, are resistin and adiponectin. 2. Brown adipose tissue (BAT)Biology buffs may be familiar with this type of tissue, as it is abundant in hibernating mammals. During this delicate period of physiological "standstill", brown fat is responsible for thermogenesis, or in other words,

the production of heat in response to abnormally cold temperatures.. As the rest of the animal's metabolism is at a standstill (except for vital functions), energy has to come out of specialized tissues, such as this one, in drips and drabs.

The human being also presents it, but mainly in the neonatal stage, during lactation and in infants.

during lactation and in very young children. The proportion of this tissue decreases markedly after 8 weeks of life, to 1% of the total mass of the individual. Brown adipose tissue is found in the axillary, perineal, paravertebral, cervical areas, scattered in arteries and around organs. Brown fat is formed by adipocytes containing several lipid droplets, i.e., it is multilocular. These are smaller than those that make up white fat and, in addition, have a dry brownish tone (hence its name). It is interesting to know that this tone is due to the abundant presence of mitochondria in the cytoplasm, which is in line with their function of burning energy and producing heat.It is also curious to report that, in mammals studied,

the appearance of brown adipose tissue varies based on environmental conditions.

. When specimens are at temperate temperatures and have ample food availability, the adipocytes closely resemble those present in white fat. On the other hand, when the animal is deprived of food and the weather becomes inclement, they revert to their natural "cluster" form, with multiple distinct fat droplets inside.

Summary

As you have seen, adipose tissue goes far beyond the storage of energy in the form of fat, both in humans and in other animals. It also has an important endocrine function (as it synthesizes and releases hormones that act on other organs), promotes thermogenesis and survival in times of need (the case of brown fat in mammals) and protects organs from mechanical damage, among many other things. Fat is not bad in itself, because without it, mammals could not live. The problem comes when many more calories than necessary are ingested and, therefore, adipocytes increase in size and generate overweight or obesity.

• Bibliographic references:
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• Atlas of plant and animal histology: adipose tissue. Retrieved February 12 from https://mmegias.webs.uvigo.es/guiada_a_adiposo.php.
• Hernández, H. D. B., Guillen, L. F. M., Guillen, M. F. M., Lemus, L. F. M., Ferrufino, G. J. Q., & Vidaur, N. A. (2019). Adipose tissue and its endocrine function. Scientific Journal of the University School of Health Sciences, 6(2), 49-60.
• Hita, M. G., Ramírez, B. E. B., Madrigal, B. R., Godínez, S., & Panduro, A. (2002). Endocrine functions of the adipose cell. Revista de endocrinologia y nutricion, 10(3), 140-146.
• Marcano, Y., Torcat, J., Ayala, L., Verdi, B., Lairet, C., Maldonado, M., & de Vegas, J. (2006). Endocrine functions of adipose tissue. Venezuelan Journal of Endocrinology and Metabolism, 4(1), 15-21.