Skin Cells and Functions
Skin serves as a protective barrier, a way to sense the world, and a layer that keeps nutrients and water inside the body. Four types of cells make up the skin, and they are produced mainly in the epidermis near the basement membrane.
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Skin: The Body's Barrier
The largest organ you have in your body isn't your stomach, although it sometimes seems that way. It isn't your brain, your intestines, or your liver. Your skin is your largest organ, and it's the main barrier between you and the outside world.
It's soft, but your skin does a great job of protecting you from a number of external dangers like the viruses and bacteria that make you sick, as well as other types of physical harm. Several different types of cells make up your skin, and each provides a different, important function.
Skin's Functions and Layers
Protection is a major function of skin, but there are others. Your skin is full of nerve endings that help you sense the world around you. Your skin emits sweat when you're hot. Sweat evaporating from your skin cools you. Your skin is also like a sack that holds in your important fluids and nutrients.
To the naked eye, your skin seems like a pretty simple organ, but if you dig deeper, you'll find out that it's actually made up of a few different layers and different kinds of skin cells. The outer layer of your skin that you see and feel and with which you sense the world is called the epidermis. Within the epidermis are layers of four different kinds of skin cells: keratinocytes, melanocytes, Merkel cells, and Langerhans cells.
A thin layer called the basement membrane separates the epidermis from the lower layer of the skin, called the dermis. The dermis is composed of proteins, like collagen and elastin, which support the skin and make it strong and flexible. Under the dermis is the hypodermis, which is largely made of fat for insulation and support of the upper layers.
You started life as a single cell that divided into two cells. Those divided into four, and so on, until you grew into an adult. Once we reach adulthood, most of our cells stop growing and dividing. We're done at that point. There are a few exceptions, however, and one of those is skin cells.
You may have noticed that when your skin is dry, it gets flaky and pieces fall off. Don't be alarmed and think that you're eventually going to lose all of your skin. Skin cells die, slough off, and are replaced by new skin cells. The process slows down as you get older, but it never stops.
Skin cells grow and divide in the basement membrane. From here, the new cells get pushed up into the epidermis. Once in the epidermis, the cells no longer receive blood or nutrients. They begin the slow process of dying and sloughing off to be replaced by yet more new cells. Your outermost layer of skin is nothing but dead cells.
Keratinocytes are the most common among skin cells. They account for between 90% and 95% of your skin. The primary function of these cells is to create the barrier between you and the rest of the world.
Keratinocytes produce the protein called keratin, and by the time the cells have been pushed up from the basement membrane, they are mostly sacks filled with keratin. This protein is structural and provides your outer skin with its strength and helps it act as a barrier. Hair and nails are made of keratin, which is why you might see beauty products advertise it as an ingredient.