White vs Brown Adipose Tissue
Adipose tissue is composed of densely packed adipose cells known as adipocytes. Depending on the nature of the adipocytes, there are two types of adipose tissues present in the body, namely; white adipose tissue and brown adipose tissue. The adipose tissues are mainly responsible for the lipid storage and the metabolic activities of the body. The two types of adipose tissues differ in many ways including their physiological features, cell types, functions and locations they found in the body.
What is White Adipose Tissue (WAT)?
White adipose tissue (WAT) is most common adipose tissue type that is composed of densely packed mature adipocytes and stromal-vascular cells, which include endothelial and immune cells. Each adipocyte of WAT contains a large single droplet of fat, hence called unilocular. In addition, the cytoplasm of adipose cell is sheet-like with a flattened nucleus. Between the cells of WAT, there are capillaries and a very few connective tissues. The lipid type found in WAT is mainly triglycerides, which are derived from the lipoproteins. The tissue accounts for 20% of total body weight in an adult male and up to 25% in an adult female. The distribution of WAT highly varies with age and gender of the individual. However, it is widely distributed throughout the body, unlike the brown adipose tissue. The tissue is mainly found under the skin with the exception of eyelid, penis and scrotum, and also present abundantly in the mesenteries, hypodermis, omenta, and around the kidneys.
The WAT’s main function is the energy storage (as fat) and mobilization. In addition, the WAT also acts as an insulator, which controls the heat conduction through the skin, and a cushion against mechanical stress.
What is Brown Adipose Tissue (BAT)?
Brown adipose tissues (BAT) are composed of cells, which contain a number of small lipid droplets of various sizes, thus called multilocular. In addition, the cytoplasm of cells of BAT contains a large amount of mitochondria and lysosomes, which is responsible for the brown color of the tissue. The spherical nucleus of BAT cell is located centrally or eccentrically. BAT is largely found in hibernating animals and the human fetus, and it almost absent in human adults. There is a rich supply of capillaries present between the cells of BAT. This tissue is very important especially for newborn humans exposed to cold conditions and animals emerging from hibernation; because BAT can increase the heat of the body during critical cold conditions. During the heat generation, the hydrolysis of lipid is taken place to form fatty acid and glycerol. This reaction is regulated by norepinephrine, which is released by sympathetic nervous system. Unlike the WAT, this tissue is not widely distributed and mainly found around the great vessels, adrenal glands and in the neck region.
What is the difference between White and Brown Adipose Tissues?
• White Adipose Tissue (WAT) is widely distributed and is the most common type of adipose tissue, unlike the Brown Adipose Tissue (BAT).
• The cells of BAT are smaller than those of WAT.
• A large single lipid droplet is present in the cytoplasm of the cells of WAT, thus called unilocular. Whereas few small lipid droplets are found in the cytoplasm of the BAT, hence called multilocular.
• Unlike the WAT, BAT is best developed in hibernating animals and human fetus.
• WAT serves as the main energy storage, insulation, and provides protection against mechanical shocks, whereas BAT is important for heat generation inside the body.
• WAT has numerous receptors for several hormones that regulate the accumulation and release of fat, whereas norepinephrine promotes the hydrolysis of lipid in BAT.
• WAT has sheet-like cytoplasm with flattened nucleus while BAT has a spherical nucleus.
• Unlike in the WAT, the cells of BAT have a large amount of mitochondria and lysosomes.
• As the names imply, BAT is brown color, whereas WAT is white.
• In BAT, the cell numbers are increased in cold conditions unlike in WAT.