The Integumentary System

The integumentary system is one of the main protective systems of the human body. It’s not a commonly known system. It contains your skin, hair, nails, and several glands. Did you know your skin is the largest organ in your body? It makes up approximately 7% of your body weight! The skin is also known as your integument or covering. Have you ever heard the expression that “beauty is only skin deep”? It’s an interesting statement because everything you see on another person’s appearance is dead! The layer of skin and hairs that are visible are actually dead epithelial cells!

The skin is actually formed from two layers: the superficial epidermis layer which is composed of epithelial tissue and the deeper connective tissue layer known as the dermis. The hypodermis is below the dermis and composed of loose connective tissue. When you give a subcutaneous (or sub-Q) injection you inject the drug into the hypodermis layer. Subcutaneous means below the cutaneous membrane which is another term for your skin. One medication commonly given via this method is insulin.

The Integumentary System and Homeostasis

Let’s check out the integumentary system in action in the following case study.

You and your friend, Tori, are baking cookies. It’s the end of the semester and you both have been craving chocolate chip goodness. While the cookies are in the oven, you and Tori decide to study your anatomy and physiology. You are currently studying the integumentary system. The timer goes off and Tori jumps up, very excited, grabs a dish towel and pulls the cookie sheet out of the over. “OW!” Tori yells – as she drops the cookie sheet onto the table. “I just burned my hand on the cookie sheet”.

You reply, “Quick, rinse it under cold water, I think that is supposed to stop the burn.”

“It really hurts!” Tori exclaims while running her hand under the cool water from the faucet.

“Let me see your hand” you tell Tori.

When she shows you, you notice a couple blisters beginning to form on her fingers and palm. “I think you burned through your epidermis layer and maybe to the dermis. Don’t blisters mean you have a second degree burn?” you ask her.

“What does that mean?” Tori asks. “Should I go to that prompt care place?”

“Let’s look it up, I think if you keep it clean you will be ok. There are several layers of cells in the epidermis, aren’t there?” you ask. “Our textbook says if the skin blisters it is a sign of a second degree burn. These burns don’t typically damage the lower layer, the dermis.”

“It’s a good thing it didn’t burn through the dermis, then I would be more prone to other infections, wouldn’t I? Didn’t we read about the skin protecting us from microbes around us?” Tori asks?

The integumentary system is vital for our body’s homeostasis. As we saw with Tori, the skin is an important barrier for protection. If the skin is damaged from a burn, or torn, it opens up an entry point for microbes to enter our body. This is why we always wear protective gloves when handling body fluids. The gloves protect us in case there are any openings in our skin. It’s better to be extra cautious about this. Our epidermis is multi-layered to make it better suited for protection. If Tori’s burn had penetrated deeper it also would have increased fluid loss and dehydration. The skin functions as a cover to keep interstitial fluids inside rather than seeping out. Every day we lose a small amount of water through our skin and our lungs from breathing. This water loss is termed insensible perspiration and is accelerated when in dry air. Our cells in the epidermis produce a protein known as keratin that helps to decrease water loss from our skin. If skin becomes dry, it cracks and creates an opening in our defenses. When you think of maintaining homeostasis, protection is probably one of the first processes you think of and the skin is vital for this.

The integumentary system is also crucial for body temperature regulation. When we are too warm, blood vessels going to the skin open up (vasodilate) and more blood flows to the surface of the skin to release heat to cool the body. Our skin turns pink or red when this happens. If body temperature continues to rise, our sweat glands become active and we sweat to cool off (this is termed sensible perspiration). When we are cold, the blood vessels shrink (vasoconstrict) to decrease blood flow, and consequently heat loss, from our skin. Our skin might turn blue from the decrease in blood flow. We also have a layer of body hair covering our body which insulates and helps us retain heat. It’s a good idea to wear a hat when in cold weather to reduce heat loss from our head!

Another function of the skin, isn’t commonly known. The skin produces vitamin D in response to sunlight or UV radiation. Vitamin D is a very important vitamin, it’s crucial for calcium absorption from our food, and has recently been shown to have anti-cancer properties. If our vitamin D levels fall, this could impact our skeletal system by decreasing the absorption of calcium, and consequently the amount that gets to our bones.

Our skin is also tied into our nervous system. One of our main senses – touch is dependent on numerous receptors located in our skin. We can feel and process information regarding pressure, temperature, light touch, and pain through our skin. If Tori didn’t feel pain when she touched the hot cookie sheet, she wouldn’t have dropped it to reduce the damage from the heat.

Clearly, the integumentary system is more involved in our functioning than a clear skin and gorgeous hair!

The Components of the Integumentary System

The integumentary system is composed not only of the skin, but also nails, glands, and hair. The most numerous component of the integumentary system is the integument or skin. The skin contains the superficial epidermis, which consists of epithelial tissue, and the deeper dermis which is formed from dense irregular connective tissue. The epidermis contains nerve endings for pain, which is why Tori felt the pain of the burn. The epidermis is avascular, which means it doesn’t have blood capillaries. Nutrients get to the epidermis from the vascular dermal layer. Only those cells closest to the dermis are able to receive the nutrients and these cells have rapid mitotic rates. The cells in the epidermis migrate to the surface, and then are shed daily. They are constantly being replaced by the cells deeper. The dermis contains the blood vessels, sweat and oil glands. The dermis also has receptors for touch. Below the dermis is the hypodermis layer. This is the fatty layer that anchors the skin to your body. The hypodermis is technically not part of the integumentary system.

The skin also contains sweat and oil (sebaceous) glands. Sweat glands release sensible perspiration to cool us when we overheat. Sweat is mostly water but also contains electrolytes and a waste product known as urea. Urea is one of the main components of urine too! Sebaceous glands produce oil, otherwise known as sebum. Sebum and sweat form a chemical barrier on our skin to decrease bacterial growth on our skin.

Hair and nails are additional structures associated with the integumentary system. Body hair takes up space to compete with pathogens for room on our skin. Body hair also insulates us. Did you know that there are approximately 100,000 hairs on your head and 30,000 in a man’s beard? Fingernails and toenails provide leverage and protection when we grab and manipulate objects.

The epidermis contains the pigment melanin, which protects our cells from UV radiation. Melanin is also responsible for our hair, skin and eye color. Keratin was previously mentioned and is important for decreasing water loss from our skin. Many skin lotions contain keratin to prevent dry skin. Another important protein is collagen. Collagen provides strength to our skin. Collagen has a white appearance and often when the skin heals extra collagen is placed at the site. Sometimes this results in a white scar.

When you study the integumentary system, you will learn about the chemical and cellular components which work together to maintain the integrity of the system. As consumers, we spend a lot of money on products meant to make our skin and hair look better, younger, and healthier. As you read through this topic, think about whether those products really can make a difference or if they are just the result of well-played marketing campaigns!