The skin is the human body’s largest organ.
It covers approximately 22 square feet (2 square meters) and weighs about 20 pounds or more.
This organ is essential to our human survival, since it acts as a protective barrier against environmental agents such as bacteria and virus. Besides that, skin is responsible for some crucial functions, such as thermal regulation or sensory functions (tact, pressure, cold, heat, pain…). Our skin also has an excretory function, since it removes unnecessary substances.
Skin has three different layers
The epidermis, the outermost layer, is composed of multiple flattened cells with particular functions. The keratinocytes, the main cells of the epidermis, are in constant renewal; therefore the “oldest” outer cells are being constantly removed. In the outermost layers, the keratinocytes become corneocytes (almost dead cells) and are soaked in liquid cement, forming the “corneal layer”. This layer, which resembles “brick walls” (the corneocytes represent the bricks and the fat between the cells represents the cement), is responsible for the protection against external aggressions and for the skin waterproofing, keeping the water on the surface of the skin, providing it elasticity and softness.
In this superficial layer we can also find the melanocytes: cells that are responsible for the pigment that provides color to our skin (melanin). There are also cells that have an immune defense function, which are called Langerhans cells; and others with neurosensory activity (Merkel cells).
It is also in the epidermis that cutaneous attachments are placed: nails, body hair, sweat glands and sebaceous glands. Our nails are full of keratin and protect our fingertips. Body hair is practically spread all over our bodies, except on the palm of our hands and the bottom of our feet. In average, on our scalp there are 100 to 150 thousand hairs, of which we lose about 70 to 100 per day, that are then renovated cyclically.
Our sweat and sebaceous glands are, respectively, responsible for regulating body temperature (they get rid of substances that give rise to sweat) and for producing and eliminating oil or sebum in the skin.
In depth, the next layer is the dermis, which is responsible for providing strength and elasticity to the skin. The dermis consists of a connective tissue rich in collagen fibers, elastic fibers and others. This layer contains different cells: some residents (fibroblasts) and some that come from blood circulation (white blood cells) to collaborate in the defense against microorganisms. In the dermis there are: several structures related to the epidermis (body hair and sweat and sebaceous glands), blood and lymphatic vessels, nerves and nerve endings, which establish communication between the skin and the rest of the organism.
The deepest layer is the hypodermis. Composed of fat cells (adipocytes), it protects the human body against physical trauma and it also acts as a calorie deposit.
Did you know that…?
In a single inch of skin there are:
65 small muscles connected to other hairs;
70 heat receivers;
15 cold receivers;
100 sebaceous glands;
More than 500 sweat glands;
Tens of millions of cells;
The skin is the heavier organ of the human body: an adult’s skin weighs between 4 and 9 kg.