Subcutaneous Tissue Composition
The skin is composed of three layers: the epidermis, the dermis, and subcutaneous tissue.2
There are several structures and specialized cells that exist within subcutaneous tissue,
including:
Collagen and elastin fibers (these attach the dermis to muscles and bones)
Fat cells
Blood vessels
Sebaceous glands
Nerve endings
Hair follicle roots
The hypodermis is largely composed of adipose tissue (fat tissue), which is made up of
adipocytes, or fat cells.3 The amount of adipose tissue varies throughout the body. It is
thickest in the buttocks, the palms of the hands, and the soles of the feet. The size of
adipocytes is determined by an individual's nutritional habits. Generally speaking, a
person who maintains a healthy diet and exercise habits has smaller adipocytes and is less
likely to be overweight.
The location and thickness of subcutaneous tissue differ by gender.4 Men tend to
accumulate more around the abdomen and the shoulders, while women tend to
accumulate it around the thighs, hips, and buttocks.
Functions of Subcutaneous Tissue
The epidermis' adipose tissue acts as an energy reserve.5 Once the body uses up energy
that's acquired from consuming carbohydrates, it turns to adipose tissue as a fuel source,
which can lead to weight loss. Adipocytes can swell or shrink depending on whether the
fat is being stored or used. The hormone leptin is secreted by fat cells to help control
appetite and signal when you are full.
Additionally, this fat acts as "armor" that protects muscles, bones, organs, and more
delicate tissues. Think of subcutaneous tissue as the protective gear that athletes such as
football and ice hockey players wear. It's the body's natural padding, cushioning and
protecting your bones and muscles if you fall or take a hit.
Subcutaneous tissue also regulates body temperature by making sure that your internal
temperature isn't too high or too low.6 The hypodermis essentially insulates the body,
allowing you to go outside on a cold day without getting hypothermia (a dangerous
condition that, if allowed to go on for too long, can result in freezing to death).
Subcutaneous Injection
Since the subcutaneous tissue contains a limited network of blood vessels, medications
injected here are absorbed gradually over time.7 This makes them an ideal route for many
drugs. That's why may medications are injected into the hypodermis. Examples of
medications that may be given by subcutaneous injection include epinephrine for allergic
reactions, some vaccinations, insulin, some fertility drugs, some chemotherapy
medications, morphine, growth hormone, and anti-arthritis drugs.8 The parts of the body
that have greater concentrations of subcutaneous tissue make them ideal injection sites.
These include:
The outer part of the upper arm
The middle part of the abdomen
The front of the thigh
The upper back
The upper part of the buttocks
The Effect of Age on Subcutaneous
Tissue
As you age, subcutaneous tissue starts to thin out. This weakened layer of insulation
makes the body more sensitive to the cold because less tissue makes it harder to stay
warm.
The loss of subcutaneous tissue due to aging also causes the body to sweat less, which, in
turn, makes it harder to stay cool in warm weather.9 It can also affect the body's reaction
to certain medications that are absorbed by subcutaneous tissue.
While the hypodermis is not visible, it can have a dramatic effect on the appearance of
the skin and the way aging impacts the skin, specifically in the area of the face and neck.
With aging, the volume of facial fat decreases, and there is less supportive tissue to
support the normal elasticity of the skin.10 The facial skin begins to droop and sag; the
bones and muscles of the face also lose volume. Some people may choose to receive
chemical cosmetic fillers to "plump up" the skin in these areas.
