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Structure and Function of Adipose Cells
Adipose tissue is made up of lipid-filled cells called adipocytes. The
denseness of this tissue relates to both the size and number of these cells.
Once new ones are formed, they are permanent. They can be reduced in size,
but not eliminated. There are two chemical mechanisms for releasing fat from
adipose tissue: lipolysis and thermogenesis. Lipolysis involves the chemical
decomposition of fat within adipose tissue and its movement into the blood
as an energy source. Phosphatidylcholine, found in soy lecithin, can
stimulate lipolysis. Thermogenesis means increasing the metabolic rate by
burning fat to produce body heat. Ephedrine, caffeine and aspirin stimulate
the rate of thermogenesis. You can find a number of diet supplements
containing these ingredients as the basis for their weight reduction claims.
Adipose tissue is stored differently in men and women. Generally, but not
always, men’s adipose tissue is stored in the upper body. Women tend to
store theirs in their lower bodies. You may hear the terms apple- and
pear-shaped to describe this phenomenon. Genetics plays a large part in this
distribution. Children tend to have the same fat distribution as their
same-sex parents. As we age, our bodies store fat differently. After
menopause, women accumulate fat in their upper bodies. Extreme weight gain
and "yo-yo dieting" can also increase upper body fat. Surplus upper body fat
is related to cardiovascular disease, hypertension, and non-insulin
dependent diabetes. Older men store their fat in their lower bodies.
If you eat more energy (fats, carbohydrates and proteins) than you expend,
it is converted into fat and stored in adipose tissue. This increases the
denseness of the tissue. That is why, ideally, you should eat only the
energy you use. You lose weight by eating less energy than you need and
decreasing the fat which is stored in the adipose tissue. You can also lose
weight with a regular exercise program. The benefit of exercise during
weight loss is that it preserves fat-free body mass and your fat loss will
be equal or greater than your weight loss.
White Adipose Tissue
Slide Courtesy of Department of Biological
Sciences, University of Delaware.
Within the body are white and brown types of
adipose tissue. The white adipose tissue (WAT) found beneath the skin acts
as a heat insulator in the body by conducting two-thirds less heat than
other tissue. It surrounds internal organs and protects them from jarring.
WAT is also found in the lymph nodes and the skeletal muscle. It stores
triglycerides as energy for use as needed. The number of white adipose cells
and the amount of fat in a cell are regulated by various factors, including
diet, physical activity, hormones and pregnancy.
In 1994, researchers discovered the hormone leptin in WAT. This meant that
it was more than just a layer of fatty tissue beneath the skin. It was
considered to be part of the endocrine system of organs, such as the
thyroid, which secrete hormones that control many body functions. WAT
secretes the hormones leptin, adiponectin and other proteins called
adipokines, which are involved in lipid metabolism, insulin sensitivity,
vascular function and blood pressure regulation. This is the key to the
understanding of the ounderlying cause of obesity, which medical researchers
refer to as a state of chronic mild inflammation. As WAT increases,
adipokines (which have inflammatory properties) increases and adiponectin
(which has anti-inflammatory properties) decreases. This increase may cause
Type II diabetes, heart disease and cancers of the breast and colon in
obesity.
Brown Adipose Tissue
Slide Courtesy of Department
of Biological Sciences, University of Delaware.
Brown adipose tissue (BAT) gets its name from
the rich blood vessels and densely packed mitochondria in it. It is located
near or around critical organs and supplies blood to the brain, spinal cord,
heart, lungs, and kidneys during cold stress. In infants, BAT comprises 5%
of the total body mass. BAT decreases in humans as they age and virtually
disappears by adulthood.
References
Albright, Ann L. and Stern, Judith S. (1998). Adipose Tissue. In:
Encyclopedia of Sports Medicine and Science. URL:
http://www.sportsci.org/encyc/adipose/adipose.html
Answers Corporation. (2008) Health Dictionary: Adipose Tissue. Answers.Com
Health. URL:
http://www.answers.com/topic/adipose-tissue?cat=health
--------------------------. (2008). Health Dictionary: Brown Fat.
Answers.Com Health. URL:
http://www.answers.com/topic/brown-adipose-tissue?cat=health
Austgen, Laura. (2002) Brown Adipose Tissue. Colorado State University
Biomedical Hypertexts. URL:
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/misc_topics/brownfat.html
NuGo (The European Nutrigenomics Organization). (2006). The Nutrigenomics
Information Portal. URL:
http://www.nugo.org/nip/26003
Trayhum, P and Wood, I.S. Signalling role of adipose tissue: adipokines and
inflammation in obesity. Biochemical Society Transactions. URL:
http://www.biochemsoctrans.org/bst/033/1078/bst0331078.htm
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