Biochemistry of the Metabolism

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Adipose Tissue

Adipose tissue can be classified into two prominent types:

  1. White adipose tissue (WAT)
  2. Brown adipose tissue (BAT)

Another, recently discovered subtype known as “beige“, serves as an intermediate between the two — the term is still not widely used, but it is gaining attention.

Adipose tissue can transition from white into brown (with beige being the intermediate step) when being exposed to cold.

Figure 1. Comparison of white (left) and brown (right) adipose tissue

White adipose tissue (WAT)

In white adipose tissue, the primary role in the production of ATP by the degradation of fatty acids and to store and the excess amount of energy in the form of TAG.

  • An adipocyte typically consists of a single lipid droplet, few mitochondria and cell nucleus (Figure 2)
  • The white adipose tissue is found all over the body in different amount and volume
  • In case of prolonged periods of excessive amounts of energy, both the volume and number of adipocytes will increase
  • In the case of deficient amounts of energy (dieting, for example), only the volume will decrease (it’s impossible to get rid of them!)
Figure 2. White adipose tissue

Brown adipose tissue (BAT)

In brown adipose tissue, there are far more mitochondria, and the lipid content is split into several small lipid droplets. A major role of BAT is the heat production by the UCP1 (uncoupling protein-1), which uses the high amount of fatty acids (Figure 3).

Figure 3. Brown adipose tissue

BAT is typically found newborns in the following locations:

  • Thymus
  • Back
  • Kidneys
Figure 4. Brown adipose tissue distribution in a fetus

In adulthood, the number and volume of BAT cells decrease.

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