The Integumentary System : A Dual Defense Against Pathogens and Injury

The integumentary system functions as the body’s outer layer. It is made up of the skin, nails, hair, and glands. The organs of the integumentary system act as the first line of defense against pathogens and also keep you safe from injury and sunlight. The integumentary system works together with other bodily systems to keep the body in balance and maintain its well-being. The skin, being the largest organ of the body, works round the clock to protect the body from various external factors. Here we take an in-depth look at the integumentary system and its immune function and how the skin defends the body.

One of the most important roles of the integumentary system is to keep the body safe from injuries and infections. It acts like the body’s coat or armor and it is also your first line of defense against all kinds of pathogens. The integumentary system also protects your body from the harmful ultraviolet (UV) rays of the sun, while also regulating your body temperature. The integumentary system is also responsible for storing fat, glucose, water, producing vitamin D, and providing support to your immune system, and keeping you safe from diseases.^{(1, 2, 3, 4)}

Some of the important functions of the integumentary system are as follows:

• Provide physical protection against pathogens and foreign invaders that can harm the body.
• It helps absorb and heal abrasions, wounds, cuts, and other injuries.
• It cushions and protects the body from infections.
• It keeps the body safe from the sun’s UV rays.
• It protects the body from sunburn.
• It excretes sweat, sebum, and other wastes from the body.
• It maintains the body temperature and helps you stay cool.
• It helps you detect/feel the heat, cold, and other sensations.
• It synthesizes vitamin D. ^(5, 6)

The defense of the body from all types of pathogens is carried out by two bodily systems – the integumentary system and of course, the immune system. These systems work closely together to defend and protect your body.

The skin is the first barrier and line of defense between your body and the external environment. It helps retain body fluids and defends against the entry of viruses, bacteria, parasites, and other such pathogens. It also protects the body by regulating body temperature.

Research has shown that the skin plays a critical role in the body’s immunity.^(7, 8)

The skin is the body’s first line of defense against any harmful pathogens. The skin has specialized immune cells within the tissues to help it fight off the invading pathogens. The skin is also home to a wide variety of beneficial bacteria, known as the skin microbiota, which fight disease-causing microbes.⁽⁹⁾

The skin serves as a wall-like barrier that protects the inside of the body from environmental factors and microbes. This is your primary defense against infection. The layers of the skin also provide protection from external forces, while being home to the beneficial bacteria that protect you.

The skin is made up of two primary layers that work together both functionally and anatomically. The outermost layer, known as the epidermis, forms the thin overlying protective cover that gets easily regenerated after an injury. The epidermis also functions to trap the moisture inside the body while also protecting against any kind of external chemical corrosion.

The second layer of the skin, known as the dermis, is a thick, fibrous layer that provides the skin with strength and elasticity. It is home to the blood vessels, nerves, and other adnexal structures like the sweat glands, hair follicles, and sebaceous (oil) glands. These layers of the skin rest on subcutaneous tissue that also helps provide padding and support to the skin.^(10, 11)

The dermis contains the sebaceous glands, which secrete oil or sebum. The sebum helps in creating a skin surface that is hostile to many types of microbes. This also encourages harmless bacteria to grow and thus compete with and push out the harmful pathogens. The dermis is also home to many other crucial components of the immune system that are known as skin-associated lymphoid tissue. This comes in handy when and if the skin barrier gets breached by harmful microbes. If this happens, the immune system gets alerted immediately by cells known as Langerhan cells, which detect and collect antigens. Antigens are substances that trigger your immune system into action to start producing antibodies against the harmful microbes attacking the body.^{(12, 13, 14, 15)}

There are certain internal cavities of the body that are a continuation of your skin itself. These include the gut, eyes, and the urinary and reproductive systems. The defense mechanisms of these body cavities are also considered to be a part of the skin itself. These include:

Saliva, tears, and urine contain a bactericidal enzyme known as lysozyme which kills off components of the bacterial cell walls.⁽¹⁶⁾

Vaginal secretions are transformed into lactate by the beneficial bacteria, thus creating an acidic environment, and inhibiting many harmful pathogens.⁽¹⁷⁾

Urine is also acidic, preventing the growth of bacteria and also flushing the urethra regularly.

The mucus present in the respiratory tract works to trap any inhaled bacteria or microbes, while the cilia send the mucus to the pharynx to get swallowed. In the stomach also, most pathogen that makes it that far get killed by the stomach acid or the enzymes present in gastric juices.

The lymphoid tissue present in the intestines also contains lymphocytes that identify and kill microbes.

An injury can cause damage to the skin and the underlying blood vessels. This could lead to loss of blood and also allow pathogens to enter the body. The process of healing following an injury begins immediately after you suffer an injury. Right after an injury, the blood vessels start to constrict and the formation of blood clots begins to stop the bleeding. After the bleeding stops, the first stage of healing begins with the integumentary system and is known as the inflammatory stage. In this stage, the body already starts to heal itself and attempts to eliminate any kind of microbes that may have entered through the site of injury.

After this, the second stage of healing begins, known as the proliferative stage. During this stage, the blood flow increases to the site of injury and you will start seeing many visible signs of healing including swelling, pain, redness, and warmth at the injury site. The cells further begin to divide rapidly in order to increase in numbers and start repairing the damage caused by the injury. Collagen, which is a type of structural protein, is also sent to the injury site in order to strengthen the tissues and help in repair.^(18, 19)

In the last stage of healing, known as the maturation stage, this collagen starts becoming more organized and stronger. The wound keeps maturing and eventually, a scab develops at the site of the injury.^(20, 21) This is how the skin and the integumentary system together with the immune system help defend the body against external factors and pathogens.

All the organs and systems of the body work together to keep things working as they should. One of the integral bodily systems that play a role in your immunity and keeping the body safe is the integumentary system. Comprising of the skin, hair, nails, and glands, the integumentary systems act as the first line of defense against pathogens and environmental factors. The skin is a critical part of the integumentary system, responsible not only for defending the body against harmful microorganisms but also for the healing process. Taking care of your skin will ensure that your body’s first line of defense remains in good condition to carry out its functions properly.

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