White Adipose Tissue
White adipose tissue (white fat) is what most people call "body fat". It is
loose (soft) connective tissue composed mostly of "fat cells" called
adipocytes held together by strands of protein fibers and a few blood
vessels. Fat cells are huge when compared to most other human cells and
the largest can measure up to one-fifth of a milimeter in diameter making
them, at least in theory, barely visible to the naked eye. White fat cells are
basically giant living balloons filled with fat. The normal machinery of a living
cell is present in fat cells, but it gets squeezed into a thin outer shell that is
hard to see under a microscope. Below is a photograph of white adipose
tissue under a microscope at relatively low power. The tissue has been
carefully prepared to preserve the structure of the individual adipocytes
which are the structures that look like soap bubbles in the photo.
White adipose tissue has a number of functions the most obvious of which
is energy storage. It also acts as a cushion for delicate organs,
particularly in the abdomen where a large 'curtain' of adipose tissue called
the greater omentum overlays the spleen, pancreas and intestines.
Fat also acts as a thermal insulator protecting people against severe
cold and fat cells produce hormones including leptin described in greater
detail on another page and which reduces appetite in proportion to the
size and number of fat cells in the body.
The interior clear fat globules of adipocytes are almost pure fat;
generally triglycerides and cholesterol.
It is estimated that the average human has about thirty billion fat cells.
When a non-pregnant adult person gains weight, his or her fat cells will
increase in size until they are about four times bigger (heavier) than
normal and only then will they begin to divide to produce more fat cells.
The first condition, having bigger but not more fat cells is termed
"hypertrophic obesity" whereas the latter condition is known as
"hyperplastic obesity" and is considered harder to treat.
White adipose tissue is the material most people call "body fat" and
plays a number of roles in human health the most important of which is
energy storage. There is however another kind of fat that plays a
totally different role: it burns fat. This is known as brown fat and is the
subject of the next page.
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