According to this theory, particular physiologic conditions, such as cold exposure, are able to induce the differentiation of white adipocytes into brown cells. Adipose tissue contains several cell types, with the highest percentage of cells being adipocytes, which contain fat droplets. Adipogenesis, i.e., the development of adipose tissue, varies according to sex and age. Activation of UCP1 stimulates uptake of lipids and glucose from circulation to process of thermogenesis. (2017); Betz and Enerback (2017); Buscemi et al. In addition, adipose progenitors (AP), Adipose tissue is mainly composed of adipocytes and a stromal vascular fraction (SVF) consisting of pericytes, endothelial cells, monocytes, macrophages, and ASCs [61]. White adipose tissue is the most common and is the fat that so many of us complain of acquiring. Brown fat does, however, release energy in the form of heat. Figure 1. Adipocyte is a large, spherical or oval shaped cell, with large fat droplet causing shifting of nucleus to periphery of the cell Bone is firm and used for protection and support. Copyright © 2021 Elsevier B.V. or its licensors or contributors. Figure 4. Adipose tissue is known to secrete a large number of proteins which regulate metabolism, energy intake and fat storage. AT possesses a relatively dense network of blood capillaries, with almost every adipocyte surrounded by one capillary, ensuring adequate exposure to nutrients and oxygen. Central abdominal fat causes insulin resistance. Their color is derived from the abundance of blood vessels and mitochondria in the tissue. Leptin plays also a role in reproduction. Other roles of leptin are increase of cytokine production and macrophage adhesion and phagocytosis, modulation of blood pressure, influence on insulin sensitivity of peripheral, hepatic and skeletal muscle, and modulation of pancreatic β-cell function [3]. In patients with type 2 diabetes, obese with insulin resistance, and in patients with coronary heart disease, adiponectin is not expressed [2]. BMAT expansion coincides with insulin resistance (Walji et al., 2016) and BMAT is increased in animal models of diabetes (Kim and Schafer, 2016). Thereafter, the rate of cell proliferation slows down during adolescence and, in weight stable individuals, remains fairly constant throughout adulthood. A number of excellent reviews were published on this topic in recent years, and the interested reader will find detailed descriptions of the biology and function of brite, Aldiss et al. Rens L.J. This cytokine influences on inflammation, apoptosis, cytotoxicity, synthesis of interleukin-1 and interleukin-6, and on adipocyte metabolism. Brown adipose tissue (BAT) is found in fetuses and newborn. In visceral adipose tissue, its secretion is three times higher as compared to subcutaneous adipose tissue. Freshly dissociated ASCs are also usually associated with different types of cells such as endothelial cells, fibroblasts, preadipocytes, mast cells, and cells from the smooth muscle. Factors exerting a direct effect on adipose mass. It was observed that hypothalamic hypogonadism in humans and in rodents is due to deficiencies or insensitivity to leptin. Activation of brown fat leads to increased energy expenditure, reduced obesity, and lower plasma glucose and lipid levels and exerts a prominent beneficial effect on metabolic homeostasis. (2017); Fernandez-Quintela et al. (2017a); Chu and Gawronska-Kozak (2017); Chu and Tao (2017); Cinti (2017); Contreras et al. Epicardial adipose tissue (EAT) is defined as the adipose tissue adjacent to the epicardium surrounding the heart, located inside the pericardial sac; pericardial adipose tissue, also named pericardial fat (PCF), delineated by the pericardial sac, is a local fat depot that surrounds the heart in which the coronary arteries are embedded [ 7, 8 The secondary fat formation takes place later in fetal life (after the 23rd week of gestation) as well as in the early postnatal period, whereby the differentiation of other fusiform precursor cells that accumulate lipid to ultimately coalesce into a single large drop per cell leads to the dissemination of fat depots formed by unilocular white adipocytes in many areas of connective tissue. In contrast, mice lacking the insulin receptor in bone have fewer BMAds in the proximal tibia (Irwin et al., 2006), whereas mice with adipose tissue-specific insulin receptor knockout have smaller BMAds (Qiang et al., 2016). In humans, there are two main sites of adipose tissue accumulation: Visceral and subcutaneous. (2017); Fernandez-Quintela et al. Adipose tissue is a highly dynamic, metabolically active organ involved in a multitude of physiological processes. Many experimental evidences have shown the presence of both white and brown adipocytes in the same depot. Browning of white adipose tissue is an adaptive and reversible response of WAT to stimuli. It was observed the link between IL-6 and obesity, inflammation, and coronary heart disease. In this case, adipocytes may be four times their normal size. Many types of human organs express leptin, such as placenta, gastric fundus mucosa, and skeletal muscle, but subcutaneous adipocytes are responsible for 80% of total leptin production [2]. Adipose Tissue. While these depots exhibit heterogeneity with respect to their molecular, morphological, and metabolic profiles,8 and differences exist between men and women, the metabolic functions of adipose tissue are retained in some capacity at each site. Adipose cells are the main structures in the body that store fat. Most of it disappears in adult humans. In newborns, brown adipose tissue is mainly located on the back, along the upper half of the spine, in between the shoulders, and surrounding the kidneys. In the process, the cells become rounder. Cinti and coworkers proposed the transdifferentiation theory to explain why white and brown adipocytes are present within the same depot (Cinti, 2009). In women, as compared to men, functional brown adipocyte is more common. (2017); Chen et al. Smaller depots with unique functions have been addressed earlier in this chapter. We will address the brown fat secretome and its specific properties in the following subsections. We share our knowledge and peer-reveiwed research papers with libraries, scientific and engineering societies, and also work with corporate R&D departments and government entities. These include thermal isolation, cushioning the organs, an endocrine role, and production of numerous bioactive factors. Indeed, in vitro studies revealed that differentiating adipocytes and AT explants trigger blood vessel formation [52, 53] and that, in turn, AT endothelial cells (ECs) promote preadipocyte differentiation [54]. Then, using the flow cytometry approach on freshly harvested human AT-SVF, we reported that AT-ECs percentage remained constant whatever the degree of obesity. (2017); Betz and Enerback (2017); Buscemi et al. Brown fat has thermogenic properties. As described earlier, it is primarily located in the subcutaneous and visceral depots and is able to store energy as triglycerides and to modulate energy homeostasis through its own secretory activity. During normal embryonic development, primitive fat organs are known to be associated with vascular structures [2, 46, 47]. The cellular components in the isolation of ASCs vary based on the influence of multiple factors such as age, tissue type, isolation procedures, culture and experimental conditions, passage number of the dissociated cells, and storage of cells. Adipocytes, i.e., cells presenting lipid droplets where lipids are stored as triglycerides, represent the major cell type. The former directly interferes with the transcriptional machinery, while the latter is based on the binding of negative regulators to yield inactive forms of known activators. Figure 16.2. The mass of BAT depends on overweight, obesity, and age. We identify multiple types of adipocyte progenitors that are common across depots, including a subtype enriched in individuals with type 2 diabetes. We use cookies to help provide and enhance our service and tailor content and ads. In addition to the thermogenic effect that helps to dissipate an excess of calories, brown fat is now considered to exert thermogenesis-independent effects, most likely by a host of specifically secreted factors. The white adipose cells are spherical with a variable size, which depends on the size of the lipid droplet (unilocular lipid droplet). There are many other cell types present in the adipose tissue. Brown and beige adipose tissue burn energy and generate heat. The reticulum cells store fat droplets that later coalesce to form one large drop. Recently, the potential role of brown AT as a secretory organ in the protection against obesity has been also recognized. Cartilage is flexible, yet resistant to being torn, and is found in body structures like the nose and ears and also forms a cushion for the bones in many joints. Both types include adipocytes, cells which are designed for the storage of fat, and the cells can store different types of lipids in varying concentrations, with brown adipose tissue varying considerably in color and lipid composition. (A) White and brown adipose tissue is located in various anatomical locations in humans. A small amount of fat in your body is brown adipose tissue (BAT). After a few early passages of cells, the ASCs in culture survive leading to homogeneity of the population. Adipose tissue (AT) is considered one of the largest endocrine organs in the body as well as an active tissue for cellular reactions and metabolic homeostasis rather than an inert tissue for energy storage. The most prominent types of cells in the adipose tissue are the adipocytes. In the following pages of this lab unit, you will have an opportunity to examine a few (of the many) types of animal tissue. 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