Physiology
Free fatty acids are liberated from lipoproteins by lipoprotein lipase (LPL) and enter the adipocyte, where they are reassembled into triglycerides by esterifying it onto glycerol. Human fat tissue contains about 87% lipids.
There is a constant flux of FFA(Free Fatty Acids) entering and leaving adipose tissue. The net direction of this flux is controlled by insulin and leptin - if insulin is elevated there is a net inward flux of FFA and only when insulin is low can FFA leave adipose tissue. Insulin secretion is stimulated by high blood sugar which results from consuming carbohydrates.
In humans, lipolysis (hydrolysis of triglycerides into free fatty acids) is controlled through the balanced control of lipolytic B-adrenergic receptors and a2A-adrenergic receptor-mediated antilipolysis.
Fat cells have an important physiological role in maintaining triglyceride and free fatty acid levels, as well as determining insulin resistance. Abdominal fat has a different metabolic profile—being more prone to induce insulin resistance. This explains to a large degree why central obesity is a marker of impaired glucose tolerance and is an independent risk factor for cardiovascular disease (even in the absence of diabetes mellitus and hypertension). Studies of female monkeys at Wake Forest University (2009) discovered individuals suffering from higher stress have higher levels of visceral fat in their bodies. This suggests a possible cause-and-effect link between the two, wherein stress promotes the accumulation of visceral fat, which in turn causes hormonal and metabolic changes that contribute to heart disease and other health problems.
Recent advances in biotechnology have allowed for the harvesting of adult stem cells from adipose tissue, allowing stimulation of tissue regrowth using a patient's own cells. In addition, adipose-derived stem cells from both human and animals reportedly can be efficiently reprogrammed into induced pluripotent stem cells without the need for feeder cells. The use of a patient's own cells reduces the chance of tissue rejection and avoids the ethical issues associated with the use of human embryonic stem cells.
Adipose tissue is the greatest peripheral source of aromatase in both males and females, contributing to the production of estradiol.
Adipose derived hormones include:
- Adiponectin
- Resistin
- Plasminogen activator inhibitor-1 (PAI-1)
- TNFα
- IL-6
- Leptin
- Estradiol (E2)
Adipose tissues also secrete a type of cytokines (cell-to-cell signalling proteins) called adipokines (adipocytokines), which play a role in obesity-associated complications.
Read more about this topic: Adipose Tissue
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