An Introduction
Adipose tissue is a complex, essential, and highly active metabolic and endocrine organ. It is a source of several hormones, including leptin, estrogen and resistin. Adipose tissue is composed primarily of adipocytes or fat cells. These comprise lipid storage droplets, which contain triacylglycerol and vary in size depending on the amount of stored fat. The following article covers various aspects of adipose tissue, such as its types, structure, location, and function. So, let us start with what the adipose tissue in the coming section:
What is Adipose Tissue?
The group of cells which have a similar structure and function that acts together to perform the desired function are called tissues. There are four different kinds of tissues in animals, they are:
Connective tissue
Muscular tissue
Epithelial tissue
Nervous tissue
The connective tissue has two different subclasses, they are loose connective tissue and dense connective tissue. These subclasses can further be divided as follows:
Loose Connective Tissue:
Areolar connective tissue
Adipose connective tissue
Reticular connective tissue
Dense Connective Tissue:
Dense regular connective tissue
Dense irregular connective tissue
Elastic
Adipose Connective Tissue
The specialized type of connective tissue consists of fat or lipid cells called adipocytes. In a healthy person, 20 to 25% of total body weight is composed of fat tissue. The adipose tissue’s main function is to store energy in the form of fat. Adipose tissue comprises multiple nerve cells and blood vessels in addition to fat cells, storing and releasing energy to fuel the body as well as releasing critical hormones essential to the body's needs.
Types of Adipose Tissue
Based on the location they are present, it is divided into two types, they are visceral fat and parietal fat.
Based on the structure, it can be divided into, white adipose tissue and brown adipose tissue.
Adipose Tissue Function
Along with the storage of fat cells, these cells help to perform different functions such as:
It is a metabolic organ that helps in the regulation of homeostasis.
Thermal isolation.
Production of a great number of bioactive factors.
Acts as an endocrine gland that is responsible for the production of hormones.
Helps in cushioning the organs.
Adipose Tissue Location and Structure
The tissue that stores fat in our body is adipose tissue, this fat is distributed all over in two ways, they are:
Parietal fat is also called subcutaneous fat that is found present under the skin.
Visceral fat is found surrounding the internal organs such as eyeballs or kidneys.
The adipose tissue consists of cells and an extracellular matrix. These cells are the most abundant and structural elements that are distributed throughout the small amount of the cellular matrix. The main type of cells that are found are adipocytes. Including this there are other different kinds of cells, are fibroblasts, preadipocytes, capillary endothelial cells, macrophages, and stem cells. These cells are commonly called non-adipocyte cells. The non-adipocytes combine to form a stromal vascular fraction. The adipocytes function is to support and protect the adipose tissue.
The adipocytes and the stromal cells help in the production of the extracellular matrix. The matrix consists of reticular fibers that are connected as a fine network that helps to hold and place the cells. The adipose tissue has a rich supply of blood vessels and unmyelinated nerve fibers.
Adipocytes
Adipocytes are the building blocks of adipose tissue. They are also known as fat cells or adipose cells. The adipocytes are divided into two types depending on the distribution of two types of adipose tissue.
White Adipocytes: It consists of the main cells of the white adipose tissue. The shape can vary from spherical to oval or polyhedral. It consists of a single lipid droplet that pushes the nucleus to the peripheral side of the cell. The cytoplasm is present around the lipid droplet and contains fewer mitochondria.
Brown Adipocytes: It consists of chief cells of brown adipose tissue. They are very small in size and consist of multiple lipid droplets. These droplets surround the nucleus that is present in the centre. It has numerous mitochondria that are found dispersed among the droplets which give them a brown colour. Golgi apparatus, a small number of ribosomes, and endoplasmic reticulum can also be found in the cytoplasm.
Beige Adipocytes: It is found dispersed in the white fat tissue. A small portion of it can also be found in visceral fat.
Adipose can perform different functions depending on the location it is present.
The abdominal fat has a different kind of metabolic function compared to all other fat in the body, and it can also influence the inducing insulin resistance.
Parietal fat helps in thermoregulation.
Visceral fat provides cushion-like support to the internal organs by protecting them from mechanical injuries.
The adipose tissue is very crucial for health, it is not only important for the storage of fat cells it also contains plenty of nerve cells and blood vessels that help in the storage and releasing of the energy to the body. The excess of fat content in the body can lead to medical conditions such as obesity and the loss of healthy body fat can lead to a condition called lipodystrophies.
Important facts about Adipose Tissues
Adipose tissue is a special and different type of connective tissue, mainly composed of fat cells called adipocytes. Adipocytes are classified into three types: white adipocytes, brown adipocytes, and beige adipocytes. Their structure, location, and function are different. Therefore, adipose tissue can be divided into white adipose tissue mainly composed of white and beige fat cells and brown adipose tissue composed of brown fat cells. White adipose tissue is the main type of fat in the human body. It can be found under the skin (subcutaneous fat), around the internal organs (visceral fat) and in the central cavity of the bones (marrowfat), and can cushion various parts of the body. Its main work is to act as an energy store, but it also protects the body from extreme temperatures, provides a buffer for vital organs, and secretes hormones and biological factors. Brown adipose tissue mainly exists in the fetus and infancy. It is mostly seen in the upper back, above the clavicles, in the mediastinum, and surrounding the vertebrae. Brown adipose tissue's major function is to generate heat through non-shivering thermogenesis, which is particularly important in preventing hypothermia in newborns.
FAQs on Adipose Tissue
1. Define adipose tissue. Write the difference between white adipose tissue and brown adipose tissue.
The adipose tissue definition is as follows - it is a specialized connective tissue that helps in the storage of fat.
The difference between white adipose tissue and brown adipose tissue is:
White Adipose Tissue | Brown Adipose Tissue |
These tissues are located in subcutaneous, intraabdominal, epicardial, and gonadal. | These tissues are located in interscapular, perirenal, cervical, paravertebral and supraclavicular. |
These are spherical in shape. | These are elliptical and smaller compared to white adipose. |
It consists of a single lipid droplet, few mitochondria, a flattened nucleus, and endoplasmic reticulum. | It consists of multiple lipid droplets, numerous mitochondria, and an oval-shaped nucleus. |
They help in the storage of fat. | They help in heat production. |
2. What is the function of perirenal fat?
The adipose capsule of the kidney or the perinephric fat or perirenal fat is a structure found between the renal fascia and renal capsule. It receives blood from the abdominal aorta. It is composed of white adipose tissue. It performs different physiological functions such as the storage of fat and the synthesis of the proinflammatory adipokines.
3. What is adipose tissue composed of?
Adipose tissue is made of a loose collection of specialized cells called adipocytes embedded in a web of collagen fibers that lies in three layers under the skin.
4. What are adipose tissues involved in?
Body fat cells produce and store fat, which is released for metabolism during fasting. White adipose tissue is used to distinguish it from more active brown adipose tissue, which is involved in the production of heat and maintaining body temperature. Subcutaneous fat makes up the majority of the body fat reserve. Furthermore, adipose tissue surrounds organs, serving as a shield to protect them from physical harm. The fat content of this tissue is 82-88%, the protein content is 2-2.6%, and the water content is around 10-14%.
5. Where is the adipose tissue found?
Adipose tissue can be found throughout the body in many locations. White adipose tissue is the most common kind of fat in humans. Subcutaneous fat, visceral fat, and bone marrow fat all come under it. Subcutaneous fat is present throughout the body, in the gaps between the skin and the muscles beneath it. Visceral fat is present predominantly around the liver, intestines, and kidneys, as well as in the peritoneum, in the abdominal cavity. White adipose tissue is also present in bone marrow. White adipose tissue is also present in the pericardium, which encompasses the heart, and in the soles of the feet, eyeballs, and specific blood vessels, among other places.
Brown adipose tissue, also known as brown fat, is mostly present during fetal life and in infants, unlike white adipose tissue. Brown adipose tissue is mostly present on the back of newborns, running along the top half of the spine, between the shoulders, and around the kidneys. The amount of brown fat in your body decreases as you become older. Brown fat deposits can still be removed around the vertebrae, above the clavicles, in the upper back, and the mediastinum in adulthood (the central compartment of the thoracic cavity).
Adipose tissue comprises 20–25 per cent of total body weight in healthy persons. Nonetheless, individual body fat percentages vary, ranging from less than 10% to over 40% of total body weight. Increased adipose tissue levels have been associated with many health issues, including obesity, diabetes, and heart disease.
