What Is Subcutaneous Tissue?

Subcutaneous tissue is an insulating layer of fat that helps protect bones and muscles in the body. It also performs a variety of other important functions, including shock absorption and energy storage.

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Contusion trauma to the subcutaneous tissue may result in a focal discontinuity of fat lobules (pictured). US can demonstrate this injury as hypoechoic foci within normal tissue layers.

Insulation

Like the pads a football player wears, subcutaneous tissue acts as protective padding to cushion muscles and organs against shock and changes in temperature. This layer, which is primarily composed of fat cells (adipocytes), serves as an insulator and also provides a reserve energy supply.

Adipose tissue is a good insulator because its fat molecules are poor conductors of heat. These tissues also serve the purpose of insulation by absorbing and holding the body’s heat, keeping the internal organs warm.

When subcutaneous tissue thins out due to aging, the body becomes more sensitive to cold weather. The loss of this insulating layer is responsible for why you are more likely to get hypothermia as you age. The fatty layer also provides a buffer between the skin and fascia, protecting deeper structures from acute trauma.

Thermoregulation

The subcutaneous layer covers specialized heat-exchange organs and contains fat cells (see the image). These structures help regulate body temperature by dumping and constraining thermal energy. For example, when the skin is cold, cutaneous blood flow increases to shed more heat into the environment; conversely, when the skin is warm, the system slows or stops this flow.

Thermoreceptors in the skin detect these changes. The signals they generate are auxiliary and provide feedback; this reduces the load on the main control system, thus decreasing its response time and error.

Normally, the body maintains its temperature by dumping excess thermal energy into the environment and by regulating its metabolism. The former is achieved by shivering; the latter is achieved through brown adipose tissue’s ability to produce heat.

When a person receives frequent injections at one location, the fat under the skin may expand to form an abscess (see the image). In traumatic situations, foreign bodies such as wood splinters and thorns and metal fragments can get into the subcutaneous tissue. These can lead to secondary soft-tissue infection resulting in granulomas and abscesses.

Shock Absorption

A large portion of the subcutaneous layer consists of fat, which insulates the body from cold and absorbs shock when you fall or experience an impact. The layer also connects the skin to the muscles and bones beneath it, limiting contact friction between them. The body stores this fat in specialized cells called adipose tissue and can convert it to energy if necessary.

The subcutaneous layer also plays a role in blood flow and circulation. It contains a network of blood vessels and nerves that carry nutrients and oxygen to the rest of the body. It is also a site for the production of hormones, such as leptin, which regulates hunger and satiety.

The subcutaneous layer also helps to distribute injected medications. Its fatty tissue allows the needle to penetrate the skin easily without puncturing the deeper dermis layer. This is important for patients with poor perfusion, such as those in shock or respiratory distress. For this reason, it is important to use a technique known as the six rights of injection safety when administering IM or SC medication.

Structural Support

The subcutaneous layer of skin provides a framework for the muscles, tendons and nerves that attach it to bones and joints. It also provides a cushion for the deep structures of the body that need to be protected from changes in temperature and shock.

It contains adipose tissue that varies in thickness depending on a person’s diet and genetics. In some areas, such as the eyelids and genitals, it may not contain fat, while in other places, such as the abdomen or buttocks, it can be more than an inch thick.

Light microscopy of the epidermis, dermis and subcutaneous adipose reveals an undulating pattern of epidermal papillae and rete ridges that are reinforced by the tough, fibrous septa of the dermis. These septa are supported by a protein called laminin. Heparan sulfate and dystroglycan bind to laminin at the C-termini. These proteins are part of a complex that helps the tissue glide smoothly over the overlying skin and connect to tissues underneath, such as bone and muscle. Damage to this structure leads to abnormal shear stress that can result in a scar defect or recurrent infections.

Energy Storage

The fat cells of the subcutaneous tissue (adipocytes) are arranged in clusters that vary by site, body type and nutritional status. The fat cells store energy in the form of triglycerides (esters of fatty acids and glycerol). They also secrete the hormone leptin to help control appetite and signal when the body has enough energy.

The large proportion of fat in the subcutaneous layer provides insulation, shock absorption and structural support. It also acts as a reserve of energy. When the body metabolizes carbohydrates, triglycerides are converted to glucose in muscle and liver cells. The resulting glycogen is then transported to the adipose tissue and other storage depots.

Just like the armor that a medieval knight might wear, the spongy and resilient fat of the subcutaneous layer protects bones and internal organs against injury. It works around the clock to limit damage incurred by falls or other traumas.