Adipose Tissue:Gene, Lifestyle and Gender Differences
Adipose tissue are supporting tissues which contain cells that functions as a major storage site for fat (Albright and stern, 1998) these cells are called adipocytes.
Developmentally, they are derived from primitive mesenchyme where they develop as lipoblast.
Histologically, the major bulk of adipose tissue is a loose association of lipid-filled cells (adipocytes), which are held in a framework of collagen fibres (Albright and stern, 1998).
Stored fats within adiposytes are derived from three main sources: dietary fat circulating in the bloodstream as chylomicrons, tryglycerides synthesized in the liver and transported in blood, and triglycerides synthesized from glucose within adipocytes. Adipose tissue therefore generally has a rich supply of blood supply and rate of fat deposition and utilization within adipose tissue is largely determined by dietary intake and energy expenditure.
Triglycerides is made up of 90% cell volume in matured adipocytes (Lessen and lesson, 1976).in addition to adipocytes, adipose tissue contains stromal-vascular cells including fibroblastic connective tissue cells leukocyte, macrophages and preadipocytes (not yet filled with lipid), which contribute to their structural integrity (Johnson and Greenwood, 1998).
The size of adipose tissue mass is a function of both adipocyte number and sizes: hyperplastic growth for increase in the number of adipocytes and hypertrophic growth for increase in size of adipocytes (Albright and sterm, 1998)
Adipose tissue has various anatomical locations in the body, subctaneous Adipose Tissue (SAT) is found directly beneath the skin, intramuscular Adipose tissue which is found interspaced in skeletal muscle and intra-abdominal Adipose Tissue (IAT) (Visceral) surrounds the internal organs and provides some protection of those organs from jarring.
Visceral fat is composed of several adipose depots including mesenteric, epididymal white adipose tissue (EWAT) and perirenal fat.
The largest fat depot is subcutaneous fat (Marin et al., 1992). On the average, subcutaneous fat mass is approximately 50% in man and 70% in woman of total adipose tissue mass (HaHori et al., 1991). Visceral fat is approximately 18% in man (Ross et al., 1992) and 6% in women (Ross et al., 1993). The total adipose tissue mass and visceral adipose tissue mass increases with age (Goodman- Gruen & Barrett-connor, 1996).
Adipocyte density is higher in visceral fat and visceral adipocytes are smaller in subcutaneous fat (Bjontorp, 1996). The primary factors that determine the presence, amount and distribution of adipose tissue are genetic makeup, gender and lifestyle (Wirth and Stermetz, 1998; Greenwood and Johnson, 1993).
Gender Differences: Nature has made it that women deposit fat on the thighs and buttocks while men deposit fat around the middle. Researchers have shown that it is a direct function of an enzyme called lipoprotein lipase which is necessary for fat storage in those regions. Women have higher concentrations of lipoprotein lipase in the thighs and buttocks while men have higher concentrations in the abdomen. Because lipoprotein lipase is produced by fat cells, it preserves one’s fat distribution in times of weight gain generally rendering women into pears and men into :apples”
There is a maintain of evidence that men may gain weight around the hips and thigh and the women may gain weight around the middle since fat distribution is related to a person’s hormonal levels (Albright and stern 1998). Estrogen for female and testosterone for male. When the reverse becomes the case on the gender.
Lifestyle: It has been implicated as one of the factors that determined the amount and distribution of fat in individuals. (Ross et al. 1996). One’s lifestyle can increases or decrease the distribution of body fats.
There is increasing evidence that smoking is conducive to greater accumulation of visceral fat and greater insulin resistance and that smoking increases the risk of metabolic syndrome and type 2 diabetes (mokdad at al; 2000). Waist circumference or waist-to-hip ratio (WHR) is an indicator of the amount of visceral adipose tissue (VAT).
A greater amount of VAT is related to the metabolic syndrome, diabetes, and cardiovascular diseases (71). Cross-sectional studies indicate that WHR is higher in smokers than in nonsmokers (Bamia at al; 2004). Waist circumference is strongly associated with VAT mass (71), and VAT is influenced by the cortisol concentration (Pasquiali et al; 2000).
Smokers were shown to have higher fasting plasma cortisol concentration than did nonsmokers (Cryer et al.,1976, Friedma et al., 1987). Higher cortisol concentration could be a consequence of the stimulation of sympathetic nervous system activity that is induced by smoking (Willianson et al., 1991; Bamia et al., 2004).
The amount of food intake and the rate of exercise as observed by Rose et al (1996) is a determining factor of fat distribution since dietary intake and energy expenditure determines the rate of fat deposition and utilization within adipose tissue. People of sedentary lifestyle are at risk of developing obesity.
Genes: Play important roles on fat distribution (Albright & Sterm, 1998). Work from experimental animals shows clear genetic anomalies as one of the basic cause of obesity. Genes for obesity can be recessive, dominant, or polygenic. Recessive alleles that influence the development of obesity have been identified in various rodents (Albright and Sterm, 1998). Studies of human candidate genes are being performed in an attempt to identify genes that contribute to obesity.
One of the molecule that may be involved in such signaling is the Oblib (ob) gene product. Mutation in ob gene result in profound obesity and typeII diabetes in mice (Friedman et al. 1991; Coleman 1978). The mouse ob gene and its human homologue have been cloned and sequenced (Zang et al. 1986) and the gene is expressed in adipose tissue. It was found through in situ hybridization histochemistry that there is over expression of ob genes in obese subjects (Lonnquist