Although we do many things, such as washing our hands and using hand sanitizer, to reduce our chance of catching an infection, it is impossible to avoid germs. It is our own body's immune system that does the most to protect us from infectious disease. Our innate, or specific, immune system is like an army of cellular assassins and the tools of their trade, which have the sole purpose of recognizing and eliminating specific pathogens, microbes that can harm us by causing disease.
But there are many physical and chemical components of the body that provide more general protection; those parts of the immune system that do not recognize or battle specific pathogens. If the specific immune function is the body's army of pathogen assassins, the nonspecific immune system can be thought of as the front line fortress and elements of defense that prevent microbes from getting into our body and establishing infection.
What are the Physical Components of the Skin’s Defense?
Our body’s first line of defense is nonspecific (doesn’t fight specific antigenic invaders), and includes structures, chemicals, and processes that work to prevent pathogens entering the body. These first line defenders include the skin and mucous membranes of the respiratory, digestive, urinary, and reproductive systems.
Did you know your skin is comprised of two main layers?
- epidermis
- dermis
The Epidermis
The epidermis is composed of multiple layers of tightly packed cells, which few pathogens can penetrate on their own. In addition to this structural barrier, the natural shedding of dead skin cells removes many attached microorganisms. Then there are other cells called epidermal dendritic cells that actively patrol the skin to phagocytize (engulf and digest) pathogens.
The Dermis
The dermis is situated beneath the epidermis and contains protein fibers called collagen. Collagen is a tough fibrous protein which gives skin the strength and pliability to resist abrasions that could introduce microorganisms.
What are the Chemical Components of the Skin's Defense?
Perspiration
Secreted by the skin’s sweat glands, perspiration contains salt and enzymes. Few microbes can live in a highly saline environment, like that of the skin’s surface. The lysozymes in sweat are a type of enzyme that can destroy the cell walls of bacteria.
Sebum
Sebusm is secreted by skins sebaceous (oil) glands. The oil helps keep skin pliable and less likely to break or tear and also lowers the pH of the skin to a more acidic level that inhibits the growth of many types of bacteria.
What about the Role of Mucous Membranes?
Mucous-secreting membranes line all of our body cavities that are open to the outside environment. Unlike the skin’s surface epidermal cells, the epithelial cells on the outermost layer of mucous membranes are living.
But like epidermal cells, epithelial cells are tightly packed together, preventing entry of pathogens into the body. Epithelial cells are also continually shedding, the discarded cells carrying away any attached microorganisms.
Come visit the science and nature forums and where we can talk about the mad skills of the human body! For more information on immunology and the body’s first line of immune defense, see:
- University of South Carolina School of Medicine, Microbiology and Immunology Online
- Science Prof Online - Human Immunology
