What it is, part 2
Free fatty acid is "liberated" from lipoproteins by lipoprotein lipase (LPL) and
enters the adipocyte, where it is reassembled into triglycerides by esterifying
it onto glycerol. Human fat tissue contains about 87% lipids.
In humans, lipolysis is controlled though the balanced control of lipolytic
B-adrenergic receptors and a2A-andronergic receptor mediated antilipolysis.
Fat is not laid down when there is a surplus available and stored passively
until it is needed; rather it is constantly being stored in and released from
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 profileóbeing 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).
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. 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:
- Plasminogen activator inhibitor-1 (PAI-1)
- Estradiol (E2)
Adipose tissues also secrete a type of cytokines (cell-to-cell signaling
proteins) called adipokines (adipocytokines) which play a role in
A specialized form of adipose tissue in human infants, and some animals, is
brown fat or brown adipose tissue. It is located mainly around the neck and
large blood vessels of the thorax. This specialized tissue can generate heat by
"uncoupling" the respiratory chain of oxidative phosphorylation within
mitochondria, leading to the breakdown of fatty acids. This thermogenic process
may be vital in neonates exposed to the cold, who then require this
thermogenesis to keep warm as they are unable to shiver, or take other actions
to keep themselves warm.
Attempts to stimulate this process pharmacologically have so far been
unsuccessful, but might in the future be a target of weight loss therapy.
In 2007, researchers isolated the adipose gene, which ap≠par≠ently serves to
keep animals lean dur≠ing times of plen≠ty. Increased adipose gene activity was
associated with slimmer individuals.
Adipose tissue has a density of ~0.9g/ml. Thus, a person with much adipose
tissue will float easier than a person with lot of muscular tissue, since
muscular tissue has a density of 1.06 g/ml.
Cultural and social role
Excess adipose tissue on a human can lead to medical problems; however, a
round or large figure does not of itself imply a medical problem, and is
sometimes not primarily caused by adipose tissue. For a discussion of the
aesthetic and medical significance of body shape, see dieting and obesity.
The term "adipose" was also used as the name of a monster in a 2008 episode
of the British science fiction series Doctor Who , Partners in Crime. Aliens
called "the Adipose" are part of a plan involving diet pills, hence the link
with fat tissue.