We’re always taught that the skin is the largest organ of the human body.

But besides that, what else do we know about our skin? Why do we have it? What does it do? How does it work?

 

THE SCIENCE OF WHY

 

Skin is a part of our integumentary system and consists of all our outer protective body coverings, which all work together to create a barrier from debris, disease, pollution, and even damaging UV rays that exist in our everyday environments. Hair, nails, and secretion glands are a few of the other components of our integumentary system.

 

Keeping our bodies together and protecting us from the threats around us are the most basic functions of our skin. But our skin also holds our excretion mechanisms, which do things like emit pheromones when we’re in love, and regulate our body temperature by sweating. It provides us with a nerve system structure to house one of our most essential senses: touch. And lastly, when skin is exposed to UV radiation it produces vitamin D, which is an important step in developing strong bones and teeth. 

 

THE SCIENCE OF HOW

 

To get a better understanding of how our skin works, we have to get down to a cellular level. Since we’re only talking about skin we won’t get into the cells for glands or muscles, but they each have their own type of cells too. Skin has three basic layers that break down into many, many, many sublayers. However, our first basic layer is a stratified squamous epithelium layer, aka the epidermis, which is our outermost layer of skin. The majority of cells that make up this layer are keratinocytes, but there are other dendritic cells including L-cells, Merkel cells, and melanocytes, to name drop a few. This epithelium layer is compiled of several sublayers, but for now I’ll spare you that level of detail. The beginning and first layer of the epidermis is the basal cell layer. This layer uses stem cells to create the keratinocytes that morph over a month’s time into what we see on our skin’s surface. While these cells age, they migrate out from the inside layer and soak up a protein called keratin that eventually kills the cell. No joke. These dead cells harden and flatten as they move to the outermost layer. They pack tightly together to form the first line of protection and defense that we have against microorganisms or drying out our deeper tissues. The hardened cells shed and fall off as we go about our lives, but the inner layer continues to generate new cells to take their place. 

 

 The epidermis skin layer is joined together with the dermis by a porous membrane zone called the dermal-epidermal junction. This is what supports the epidermis, allows cell and fluid transfers and sensory exchanges, and provides the orientation and direction for cells to grow. 

 

Under the dermal-epidermal junction is the dermis layer. It’s a thick, dense layer of amorphous, fibrous, connective tissue and the reason our skin has stretch, feeling, and even fingerprints. The dermis layer is the bulk of our skin. It houses a variety of cells, as well as massive networks of fibers, blood vessels, glands, hair follicles, motor nerves, sensory nerves, and includes the muscle fibers that cause the little hairs on your body to stand up, what we call goosebumps. Collagen is a family of proteins that fundamentally build the dermis layer, about 70% of our skin’s non-water weight, to structure and strengthen the integumentary system.  There are 15 different types of collagen fibers but mostly type 1 collagen makes up the dermis. The most enriching amino acids for collagen are glycine, hydroxyproline, and hydroxylysine. Although elastic fibers are not as populus or nearly as damage-resistant as collagen, they are what gives our skin its forgiving stretch. Elastic fibers are basically made of protein filaments and an amorphous protein, elastin, and bind to a matrix of glycosaminoglycans. As we age to adulthood, the collagen fibers in our dermis layer get thicker and we seem to lose fibroblasts. 

 

Finally, the deepest layer of our skin is the subcutaneous layer, or panniculus. This layer has little pockets of fat cells and holds our skin to the muscles underneath. Among connective tissues throughout the body, mast cells are also found in our subcutaneous fat and derive themselves from bone marrow. Mast cells are traditionally tied to our body’s allergic and inflammatory responses. Once activated from its receptors, these cells give off an array of responses including histamine, leukotrienes, prostanoids, proteases, cytokines, and chemokines. The subcutaneous fat layer also is our body’s energy storage space, and provides us buoyancy. Can you believe it? This is our natural, built-in floatation device. However, I remain firm that humans should rely on a lifejacket instead of our subcutaneous layer to stay afloat. 

 

Well, that’s the basic overview of our biggest organ in the human body and arguably the most important player of our integumentary system. The cycle of a skin cell serves a very intricate role in a complex system. We rely on our skin to regulate, protect, and defend us from so many things we encounter every day- even the invisible things like pollution and UV rays. Now that we understand how much endless hard work our skin does, let’s try to thank it by taking a few extra minutes for some well-deserved care.