The Purpose and Composition of Adipose Tissue

Adipose Tissue
Adipose Tissue. Credit: STEVE GSCHMEISSNER/Science Photo Library/Getty Images

Adipose tissue is a lipid storing type of loose connective tissue. Also called fat tissue, adipose is composed primarily of adipose cells or adipocytes. While adipose tissue can be found in a number of places in the body, it is found primarily beneath the skin. Adipose is also located between muscles and around internal organs, particularly those in the abdominal cavity. The energy stored as fat in adipose tissue is used as a fuel source by the body after the available energy acquired from carbohydrates is used up.

In addition to storing fat, adipose tissue also produces endocrine hormones which regulate adipocyte activity and are necessary for the regulation of other vital bodily processes. Adipose tissue helps to cushion and protect organs, as well as insulate the body from heat loss.

Adipose Tissue Composition

The majority of cells found in adipose tissue are adipocytes. Adipocytes contain droplets of stored fat (triglycerides) that can be used for energy. These cells swell or shrink depending on whether fat is being stored or used. Other types of cells that comprise adipose tissue include fibroblasts, white blood cells, nerves, and endothelial cells.

Adipocytes are derived from precursor cells that develop into one of three types of adipose tissue: white adipose tissue, brown adipose tissue, or beige adipose tissue. The majority of adipose tissue in the body is white. White adipose tissue stores energy and helps to insulate the body, while brown adipose burns energy and generates heat.

 Beige adipose is genetically different from both brown and white adipose, but burns calories to release energy like brown adipose. Beige fat cells also have the ability to boost their energy-burning capabilities in response to cold. Both brown and beige fat get their color from the abundance of blood vessels and presence of iron-containing mitochondria throughout the tissue.

Mitochondria are cell organelles that convert energy into forms that are usable by the cell. Beige adipose can also be produced from white adipose cells.

Adipose Tissue Location

Adipose tissue is found in various places in the body. Some of these locations include the subcutaneous layer under the skin; around the heart, kidneys, and nerve tissue; in yellow bone marrow and breast tissue; and within the buttocks, thighs, and abdominal cavity. While white fat accumulates in these areas, brown fat is located in more specific areas of the body. In adults, small deposits of brown fat are found on the upper back, the side of the neck, the shoulder area, and along the spine. Infants have a greater percentage of brown fat than do adults. This fat can be found on most of the back region and is important for generating heat.

Adipose Tissue Endocrine Function

Adipose tissue acts as an endocrine system organ by generating hormones that influence metabolic activity in other organ systems. Some of the hormones produced by adipose cells influence sex hormone metabolism, blood pressure regulation, insulin sensitivity, fat storage and use, blood clotting, and cell signaling. A major function of adipose cells is to increase the body's sensitivity to insulin, thereby protecting against obesity.

Fat tissue produces the hormone adiponectin which acts on the brain to increase metabolism, promote the breakdown of fat, and increase energy use in muscles without affecting appetite. All of these actions help to reduce body weight and reduce the risk of developing conditions such as diabetes and cardiovascular disease.
Sources:

  • Adipose Tissue, Glands, Society for Endocrinology. Updated March 2011 (http://www.yourhormones.info/glands/adipose_tissue.aspx)
  • Stephens JM (2012) The Fat Controller: Adipocyte Development. PLoS Biol 10(11): e1001436. doi:10.1371/journal.pbio.1001436. Published November 27, 2012 (http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001436)