Specialized Connective Tissues
Recall that cartilage, tendons, ligaments, bone, and blood are all considered specialized connective tissues. These will be described in later modules. Here we will look at both white and brown adipose tissue as specialized CTs.

Adipose tissue
Connective tissue in which fat storing cells or adipocytes predominate is called adipose tissue. Due to extraction of the lipids in these cells in most H&E stained paraffin preparations, you will notice a lack of stain where lipid droplets were once stored.

White adipose tissue: This tissue is primarily made up of white or unilocular adipocytes, which are so named because they have a single large droplet of lipid that almost entirely fills the cell. The lipid droplet displaces the flattened nucleus and organelles to the periphery. This tissue plays a key role in energy storage, insulation (prevents heat loss), and cushioning of vital organs. It also produces hormones, growth factors, and inflammatory mediators and is now considered a key endocrine organ that regulates nutritional homeostasis. Examine example 1  and example 2.

Brown adipose tissue: In humans, this tissue is found principally in newborns and comprises 2 to 5% of adipose tissue on the back, neck, and shoulders, where it plays a crucial role in thermogenesis. Brown adipose tissue is composed of smaller multilocular adipocytes, which are so named because they have many lipid droplets. They also contain numerous mitochondria that give the unstained tissue a brown color. Nuclei tend to be more centrally located and spherical. The small amount of brown fat in adults is found in adipose tissue around the kidneys, adrenals, aorta, and mediastinum.

Compare the differences between white (left image) and brown (right image) adipose tissue.

Now let's examine the cells that are associated with CT.