Adipose Tissue

Original Editor - lucinda hampton

Top Contributors - Lucinda hampton, Kim Jackson, Vidya Acharya and Sai Kripa  

Introduction

The more technical term for body fat is adipose tissue. It is a loose connective tissue composed of fat cells, with individual cells being called adipocytes.

Image 1: Adipose tissue

Adipocytes contain lipid droplets of stored triglycerides. These cells swell as they store fat and shrink when the fat is used for energy.

Adipose tissue helps to store energy in the form of fat, cushion internal organs, and insulate the body.

There are three types of adipose tissue: white, brown, and beige adipose.

1. White adipose stores energy and helps to insulate the body.
2. Brown and beige adipose tissue burn energy and generate heat.

Adipose tissue also produces hormones, eg adiponectin, which help to burn fat and reduce body weight.Image 2: White adipose distribution in the body.

Location

Adipose tissue can be found in a number of different places throughout the body.

1.White adipose tissue is the most abundant type of fat in humans. It is distributed within subcutaneous fat, visceral fat, and bone marrow fat.

• Subcutaneous fat is found throughout the whole body, in the spaces between the skin and underlying muscles.
• Visceral fat is predominantly found around the organs in the abdominal cavity, such as the liver, intestines and kidneys, as well as in the peritoneum.
• White adipose tissue is also present in the bone marrow and can be found in the pericardium surrounding the heart, or cushioning other parts of the body, like the soles of the feet, eyeballs, and certain blood vessels.

2. Brown adipose tissue is mostly present during fetal life and in infants. With age, the amount of brown fat decreases progressively. In adults, remaining brown fat deposits can be found surrounding the vertebrae, above the clavicles, in the upper back, and in the mediastinum. Their colour is derived from the abundance of blood vessels and mitochondria in the tissue.

Normal Adipose Amounts

In healthy adults, adipose tissue usually comprises 20–25% of the total body weight. See Body Composition

• Specific body fat percentage varies considerably amongst individuals, ranging from less than 10% to over 40% of the total body weight.
• Increased levels of adipose tissue has been associated with several health problems, including obesity, diabetes mellitus, and heart disease, among others.

Main Function

The main function of:

1. White adipocytes: store excess energy in the form of fatty molecules, mainly triglycerides. Fat storage is regulated by several hormones, including insulin, glucagon, catecholamines (adrenaline and noradrenaline), and cortisol. Depending on the body’s immediate energy requirements, these hormones can either stimulate adipose tissue formation and storage (i.e. lipogenesis) or initiate the release of fat from adipose tissue (i.e. lipolysis). White adipose tissue also helps cushion and protect parts of the body, and insulates the body from extreme temperatures.
2. Brown fat is to use energy to generate heat through a process called non-shivering thermogenesis, which serves as an important defence mechanism to protect newborns against hypothermia. In adults, non-shivering thermogenesis becomes secondary to shivering thermogenesis, which is achieved by the contraction of skeletal muscles.

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. Adipose tissue performs these vital roles by secreting several biologically-active factors known as adipokines. These molecules contribute to a variety of different functions, including regulation of energy balance, food intake and satiety, inflammatory response, and metabolism of steroid hormones.

• A major function of adipose cells is to increase the body's sensitivity to insulin, thereby protecting against obesity.
• Adipocytes are also responsible for the production of the hormone leptin. Leptin is important in regulation of appetite and acts as a satiety factor.

Image 3: Leptin (produced by adipocyctes) and Ghrelin, hunger hormones.

Interesting Facts

1. Your body fat level may be influenced by your microbiome: Researchers studying a new realm of therapies known as postbiotics (the by-products that bacteria leave behind) which help the body synthesize insulin more effectively. A new study discovered that administering postbiotics to mice with obesity reduced their insulin sensitivity (without any need for weight loss) heralding promising potential treatments for obesity with type 2 diabetes.
2. Excess Fat promotes cancer: Adipose tissue also secrets hormones that make cancer cells grow quicker. In fact, when adipose tissue expands, it also allows more immune cells to enter the tissue. These B and T immune cells secrete pro-inflammatory molecules eg adipokines [PDF]peptides signal other organs (and cytokines), which create the perfect microenvironment for tumor growth.
3. You have a fixed number of fat cells as an adult: new fat cells are constantly created and destroyed, but the body always remains below a fixed limit, which is set during adolescence. This is a key reason why it's so important to prevent childhood obesity.
4. Too much or too little fat can increase your risk of diabetes 2. Obesity can predispose a person to type 2 diabetes, too little fat has a similar effect, according to the American Diabetes Association.
5. Epigenetics is a new frontier for fat research ( ie all the other factors that control how and when each gene is expressed).Researchers studying fat to better understand metabolic disorders recently focused on the field of epigenetics, as these changes are likely to play a critical role in the development of chronic disorders like metabolic syndrome and type 2 diabetes. Unlike the genetic code, it is possible to reverse and alter these elements, which means we can potentially develop new ways to prevent and treat these common disorders.