Do you know? Skin is the largest organ of the human body. Your skin is a crucial barrier between the outside world and your inner organs and tissues. It is much more than a simple covering, and it carries out many functions that help maintain health:
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Skin act as a defensive barrier, protecting your inner organs from foreign invaders such as bacteria and viruses.
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Skin is a sensory organ. Nerve endings near its surface pick up and relay information about the surrounding environment to your brain. It translates these nerve impulses into messages like heat, cold, touch, pressure, and pain.
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Skin as a temperature controller. When you’re too hot, it helps cool you down by sweating and dilating your blood vessels. In contrast, those blood vessels constrict to conserve heat deep inside your body when you're cold.
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Skin as a manufacturing plant. The skin makes vitamin D using the sun’s energy for many body functions.
What is Skin Made Up Of?
For the skin to carry out all the functions, it relies on the specialized structures in its 3 layers:
- the epidermis
- the dermis
- the subcutaneous layer (sometimes called the hypodermis or fat layer)
#1 The Outermost Layer - Epidermis
The outermost layer is called the epidermis - the part you can see and touch. It is a protective, physical barrier against the outside environment—fun fact: it is just about as thick as a piece of paper.
The very top portion of the epidermis is known as the stratum corneum. It’s composed of cells called keratinocytes, which produce a protein called keratin. As the older cells on the surface slough off, younger cells rise to form a new layer. This continuous cycle completely renews the skin surface about once a month.
The epidermis also plays a key role in protecting you from the sun’s radiation. There are pigmented cells called melanocytes located at the bottom of the epidermis. These cells produce melanin that color skin and help protect against ultraviolet (UV) protection. When exposed to sunlight, melanocytes make more melanin, and the skin darkens to help protect against further damage.
#2 The Middle Layer - Dermis
The dermis layer lies directly beneath the epidermis. It is a thicker layer that contains collagen, blood vessels, nerves, hair follicles, and sweat and oil glands. The dermis is also where we sense pain, touch, heat, and cold. It helps regulate body temperature by expanding and contracting blood vessels to maintain a constant body temperature.
Fibroblasts in the dermis layer secrete collagen, which gives the skin its strength and firmness. Elastin fibers made of protein in the dermis give skin its elasticity.
#3 The Deepest Layer - Hypodermis
The deepest layer of the skin is called the hypodermis (the subcutaneous layer). It mainly consists of connective tissues and fats between the dermis and muscles or bones. Fat in the subcutaneous layer stores nutrients and insulates and cushions muscles and bone.
How about Hair and Nails?
Your hair and nails are skin too. Your hair produced in a hair follicle is generally a thin fiber made of many overlapping layers of keratin. By contract, your nails are thickened and hardened form of the epidermis (top layer). Nail cells originating from the nail bed base are composed of a much stronger form of keratin. They aren’t sloughed off like the epidermis layer of the skin on every other part of the body. Thus, a nail is simply a sheet of keratin like the topmost layer of skin, but much harder and thicker.