The Skin

The skin is the largest organ in the human body

It measures almost 2 m2 and weighs approximately 4 kg.

It is an essential organ for human survival as it acts as a protective barrier against environmental agents such as bacteria or viruses, and is also responsible for essential functions such as thermal regulation or sensory functions (touch, pressure, cold, heat, pain…) . The skin still has the excretory function of substances that need to be eliminated by the body.

The skin is made up of three layers

The epidermis, the most superficial layer, is made up of several types of cells, each with its own function. Keratinocytes, the main cells of the epidermis, are in constant renewal, with the “older” external cells being continually eliminated, imperceptibly. In the outermost layers, keratinocytes transform into corneocytes (almost dead cells) and are embedded in a lipid cement, forming the so-called “horny layer”. This layer, which resembles a “brick wall” (the corneocytes represent the bricks and the fat between the cells the cement), is responsible for protecting against external aggressions and for waterproofing the skin, keeping water on the surface of the skin, giving it elasticity and softness to the touch.

This most superficial layer also contains melanocytes, cells responsible for the pigment that gives the skin its color (melanin). There are also cells whose function is immunological defense and which are called Langerhans cells, and others with neurosensory activity (Merkel cells).

It is also in the epidermis that cutaneous appendages originate: nails, hair, sweat glands and sebaceous glands. Nails are structures rich in keratin and act as protectors for the ends of the fingers and toes. Hair exists practically all over the body, except on the palms of the hands and soles of the feet. On the scalp, for example, there are an average of 100 to 150 thousand hairs, of which we lose 70 to 100 per day, being renewed cyclically.

Sweat glands and sebaceous glands are, respectively, responsible for regulating body temperature (by eliminating substances that give rise to sweat) and for producing and excreting oil or sebum in the skin.

In depth, the next layer is the dermis, responsible for giving resistance and elasticity to the skin. The dermis is made up of connective tissue rich in collagen fibers, elastic fibers and others and contains different cells, some resident (fibroblasts) others that arrive from the blood circulation (white blood cells) to collaborate in the different tasks of the skin, namely in defense against the microorganisms. In the dermis there are several structures related to the epidermis (hair and sweat and sebaceous glands) and to blood and lymphatic vessels and nerves and nerve endings, which establish communication between the skin and the rest of the body.

The deepest layer is the hypodermis. Composed of fat cells (adipocytes), it protects against physical trauma and acts as a store of calories.

 

Did you know…?

in a single centimeter of skin there are:

65 small muscles linked to as many hairs;
70 heat receptors;
15 cold receptors;
100 sebaceous glands;
More than 500 sweat glands;
Tens of millions of cells.

The skin is the heaviest organ in the body: an adult’s skin weighs between 4 and 9 kg!