A few years ago, I got into a heated debate.
The topic was: what is the largest organ in the body?
My “opponent”, a very bright student studying human health and disease, insisted that the liver was the largest, while I contended that it was the skin.
I was sure I was right (although this young gentleman’s self-assured smirk was making me doubt myself more and more every minute).
He pontificated that the skin couldn’t even correctly be called an organ.
I countered that it was an organ and asked what evidence did he have that it wasn’t.
To this, he recited that an organ was a self-contained group of tissues that cooperated to perform a particular function in the body, like a kidney or the heart. He proclaimed that a tissue was a group of similar cells with similar functions and thus the skin was a tissue, not an organ.
Defiantly, and a little more defensively than the situation warranted, I replied that he was wrong and whether he liked it or not the skin was an organ. (Not the most persuasive argument I’ve ever used but it’s one that’s infuriating to counter!)
We ended up Googling the answer and to my pride’s relief, I had remembered my biology 101 course correctly, the skin is indeed an organ.
When people think of organs, they, like my sparring buddy, usually think of the brain, heart, liver, lungs, kidneys, and other internal organs. But the definition of an organ as a group of distinct tissues working together towards a common goal applies to more than just these. It also includes the nose, the anus, the thyroid, the head and neck, the eyes, and even the bronchi! In fact by this definition of an organ, we have 78 in total.
But how is the skin an organ?
The skin is an organ because it is composed of tissues working together. The main three tissues are:
- The epidermis, the outermost layer of skin.
- The dermis, under the epidermis.
- The subcutaneous or fat layer, under the dermis.
Each layer has its own distinct form and functions and is composed of a unique profile of cells. Let’s look at each of the skin’s tissues in more detail.
Guarding Against Bad Guys: The Epidermis | |
Introduction: |
The tough outermost layer of the skin that can be very thin, like on your eyelids, or thicker, like on the soles of your feet. Keratinocytes make up 90% of the cells of this layer. They originate in the bottom of this layer and are slowly pushed outward by newer cells until they’re shed off. In this way, the skin is constantly replenishing itself. |
Main Roles: |
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Components: |
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Sublayers: |
The stratum basale (innermost sublayer, also called the stratum germinativum), stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum (outermost sublayer). |
Fun Fact: |
This layer has no blood supply! This is why you can shave and, assuming you don’t cut yourself, not end up writhing in pain. |
Where the Party Is: The Dermis | |
Introduction: |
The strong and elastic layer that comprises comprises around 90% of the thickness of the skin. |
Main Roles: |
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Components: |
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Sublayers: |
Papillary (upper) and reticular (lower) layers. |
Fun Fact: |
The blood vessels in this layer transport the vitamin D made by this layer to other parts of the body! |
Bringing Us Together: The Subcutaneous Tissue | |
Introduction: |
The layer comprising a network of fat and collagen cells that protecting the body from excessive heat loss. It also acts as a shock absorber protecting the inner components of the body, particularly the inner organs. |
Other names: |
Subcutis (cutis = skin), hypodermis (hypo = beneath, dermis = skin), hypoderm, and superficial fascia (fibrous tissue). |
Main Roles: |
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Components: |
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Fun Fact: |
The thickness of this layer varies throughout the body and from person to person! |
So there you have it! Conclusive proof that the skin is indeed an organ. You can now whip out this fact at parties but, unlike my younger self, be able to articulate that the skin is an organ because it is composed of distinct types of tissues working together to protect and support your body.
![Diagram of human skin](http://www.tempobioscience.com/blog/wp-content/uploads/2016/06/640px-Diagram_of_human_skin.jpg)
CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=507467
Helpful Sources:
American Academy of Dermatology
Merck Manual
National Cancer Institute
National Geographic