## 4 The Anatomy of Obesity
### Histological Aspects  
The adipocyte is the fundamental cellular unit of adipose tissue. Beyond the role of a mere energetic depository, adipocytes act as a part of a system similar to a standalone endocrine organ by secreting a large variety of peptides and metabolites involved in weight regulation. In addition to the metabolic functions exerted by means of the enzyme pathways involved in beta-oxidation and free fatty acid metabolism, many of the adipokines secreted by these cells have a proinflammatory and procoagulant influence. Other peptides are implicated in insulin resistance and hunger regulation, with a significant effect on body weight and cardiovascular obesity-associated risk. Many of the substances secreted by adipocytes have a still unknown role and are a key interest for medical research [74].  
Adipose tissue is highly cellular in nature. The adipocytes that conglomerate in order to form this tissue can respond to external stimuli that determine the increase in adipose mass, either by increasing their individual dimensions or by increasing the physical number of cells. The increase in adipocyte size defines adipocyte hypertrophy. This type of response is typically found in android obesity, with a high proportion of visceral fat. Hypercellular obesity, on the other hand, has a more variable character, frequently identified in individuals that become overweight since childhood. It is however almost always present in severely obese patients, regardless of age. Hypertrophic obesity generally develops during adulthood and has a strong connection with cardiovascular risk. This type of obesity usually responds well to body weight interventions, which are generally inefficient in hypercellular adiposity. This particular resistance to treatment is one of the main aspects that drives the imperative need for assertive preventive action during childhood [75]. Figures 1 and 2 were taken with permission from the pathology laboratory of the Pediatric Clinical Hospital Sibiu, Lucian Blaga University of Sibiu, and display the different histological appearances of hypertrophic and hypercellular adipose tissue.  
Figure 1: Adipose tissue stained with hematoxylin and eosin (H&E); (**a**) original magnification \(\times\)10, adipose hyperplasia tissue with thickened fibrous septae and increased vascular network. (**b**) original magnification \(\times\)40, adipose tissue demonstrating enlarged (hypertrophic) adipocytes. Prepared by the authors. Courtesy of the Pediatric Clinical Hospital Sibiu, Lucian Blaga University of Sibiu.  
A further aspect to be considered upon examining the cellular foundation of adiposity is regarding the maturation of adipocytes, as they differentiate from preadipocytes. Characterizing the stimuli responsible for the initiation of this process and identifying the factors that lead to preadipocyte recruitment, differentiation, hypertrophy, and/or apoptosis could play a key role in defining the mechanisms behind weight excess. Research in this field could provide potential targets for weight reduction by means of controlling the process of adipocyte proliferation, thus avoiding the development of hypertrophic, metabolically dysfunctional adipocytes responsible for increasing cardiovascular risk, insulin resistance, and the risk of recurrence after weight loss [76].