Adipose Tissue (Fatty Tissue)
Adipose tissue, or fat is an anatomical term for loose connective tissue composed of adipocytes (fat cells). Best known for its role in fat storage, in mammals, three types of adipose tissue exist:
- White adipose Tissue (WAT)
- Brown adipose Tissue (BAT)
- Beige or brite adipose.
Brown adipose tissue, is present in small mammals (e.g., mice) & in new-born humans. Anatomically located around the major organs in a neonate & known to dissipate with age. Its distinct colour is due to its high vascularization & contain large numbers of intracellular mitochondria. It releases heat via oxidation of fatty acids. Classical BAT is specialized to dissipate chemical energy serving a protection function against hypothermia (Giralt & Villrroya (2013); Wu et al. (2012)). It can suppress weight gain & metabolic disease through its action as specialized, heat-producing adipocytes, most of it decrease with human aging.
Beige or brite adipose tissue; has morphological & molecular characteristics of classical thermogenic brown adipocytes.
Adipocytes of white adipose tissue WAT, is the most common & is the fat that so many of us complain of acquiring. Mainly consist of one vacuole for storage of triglycerides. Adipose tissue is primarily located beneath the skin, but is also found around internal organs. In the integumentary system, which includes the skin, it accumulates in the deepest level, the subcutaneous layer which providing insulation from heat & cold also, around organs as it provides protection padding. It also functions to reserve of nutrients. WAT, developing in multiple anatomical sites, stores chemical energy and demonstrated known structural, functional, metabolic and endocrine differences between different WAT deposits.
Adipose tissue can further be classified according macroscopic tissues type, anatomical location & structural /functional characteristics.
Although both WAT & BAT are of mesodermal origin, they are believed to originate from different mesenchymal stem cells lineages.
Recent studies have described adipose tissue as a metabolic & endocrine organ producing various substances including adipocyte-derived hormones such as liptin & adipsin; bioactive peptides known as adipokines such as adiponectin, visfatin, omentin, & resistin to name a few; as well as cortisol & various sex and steroid hormones. These substances act both locally (paracrine/autocrine) & systemically (endocrine), exerting various physiological effects (Gimble et al. 2007; Harwood 2012; Kershaw & Flier 2004).
The adipose tissue contains multipotent stem cells, which can differentiate into fat, bone, cartilage, & types of tissue.
Characteristic of Tissue According to Age & Gender
Marked differences have been observed between genders in both the metabolism and endocrine function of adipose tissue. Women are known to have a higher percentage of body fat & mainly store adipose tissue in the gluteal-femoral region. Adiposity in this region is associated with larger fat cell size with increased stimulated lipolysis & triglyceride synthesis. Adipose tissue storage in men is primarily in the visceral and abdominal regions. obesity in men is associated with increased lipoprotein lipase activity and with decrease stimulated lipolysis & triglycerides synthesis, Blaak (2001); Edens et al. (1993); Fried et al. (1993). Several studies have shown that the differences in visceral adipocytes metabolism between genders disappear with menopause. It was further suggest that female sex hormones may play a role in this gender-specific adipose deposition; this includes, for example, weight gain in the abdominal region of postmenopausal women as well as associated metabolic changes, Rebuffe-Scrive et al. (1989); Trujillo and Scherer (2006)
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