Structure and functions of Your Skin

 

 

We are constantly talking about skincare, buying expensive products to care for our skin, concerned about skin problems, ageing and how to avoid it. However, only few people know about skin structure, functions, and why we have a certain skin type. Knowledge on this type of information can help in how to build your skincare routine more effectively, to choose what to apply for a specific problem, how each molecule works, and how to layer different products.

In this part of the Skin Series, we are going to talk about skin, its structures and functionalities and what are the factors affect it.

Let’s start.

 

What is the skin?

The skin is one of the body organs, just as heart, kidneys, or stomach. It is actually the biggest organ of our body and the most visible one. If you extend your skin completely, you can cover two square meter surface, which represents 1/6 of the overall body weight. It is not surprising that the appearance of our skin can play an important role in how we feel and in our self-stem.

 

Basic diagram of the skin layers

 

Skin Structure

The skin has three different layers: epidermis, dermis and hypodermis, each one of them having different sub-layers.

Epidermis

The epidermis is the outer layer of the skin. This layer protects us against external factors and loss of internal fluids. The epidermis has five layers of one special cell type called keratinocytes. The keratinocytes suffer a differentiation process (the process in which a cell changes from one type to another) going through different stages. Each one of the stages is a layer of the epidermis. Three are no blood vessels or structures in the epidermis.

The epidermis composition is basically, 95% keratinocytes and 5% melanocytes. The epidermis layers (from inside to outside) are:

Steucture of the epidermis

 

☀ Stratum Basale. This layer is where keratinocytes production takes place.

☀ Stratum Spinosum. The keratinocytes start to produce keratin.

☀ Stratum Granulosum. The keratinocytes become hard and form a structure type called granules.

☀ Stratum Lucidum. Cells become flat and form a high-density layer. This layer is only present in some of the body parts, as the palms of the hands, the soles of the feet, and the digits.

☀ Stratum Corneum. It is the most outer layer and the visible one. At that stage, the keratinocytes are dead cells that have lost the nucleus and are called corneocytes. There are around 20 layers of corneocytes in the stratum corneum. These cells are responsible for the desquamation process.

 

All the processes, from keratinocytes production in the stratum basale to the desquamation process or loss of corneocytes in the stratum corneum, takes 28 days. That is the reason why it is so important to exfoliate the skin, to help the elimination of the corneocytes.

Desquamation Process

 

There are some lipids between the corneocytes which, by an enzymatic reaction, produce a mixture of ceramides, fatty acids, and cholesterol. This mixture of compounds forms the Skin Lipid Barrier, which protects us against water loss and harmful external molecules.

We mentioned that 5% of the epidermis is formed by melanocytes. They are in the stratum basale and are responsible for melanin production. Melanin is very important for our body. It absorbs UV radiation and, therefore, protects us from its harmful effects.

It is common to think that the skin colour depends on the amount of melanin we have, but that is not fully true. The skin colour depends on the number of melanosomes, which are a type of vesicle or bag full of a mixture of melanin, carotene and hemoglobin. I guess you know that carrots help you to get tanner, that it for its high carotene content.

 

Between the epidermis and the next layer, the dermis, there is a separation layer called Basement Membrane or Dermo-epidermal Junction.

 

Skin layers showing the different sub-layers

 

Dermis

It is the medium layer of the skin and it is much thicker than the epidermis (1-5 mm). It sustains and supports the dermis.

The major component of the dermis is the connective tissue, made of a mixture of collagen and elastin. These components give strength and elasticity to the skin and are vital in healthy, young-looking skin.

The dermis contains also specialised cells (as mast cells or mastocytes and fibroblasts) and structures such as blood vessels, lymphatics, sweat glands, and nerves.

The dermis presents two sub-layers, the most superficial Papillary Dermis and the deeper Reticular Dermis.

 

Hypodermis

This is the most inner layer of the skin and it is below the dermis. It is basically composed of fat, which provides support and insulates the body from cold. It also contains blood vessels and nerves.

 

What are the skin functions?

The skin has different functions. The main functions are: 

 

☀ Protection. The skin acts as a barrier protecting us from external aggressions such as mechanical impact, micro-organism, and harmful chemicals.

☀ Sensation. The skin contains a lot of receptors for different feelings as heat, cold, touch, or pain, among others that allows us to take actions and communicate.

☀ Storage. The skin acts as a storage place for different molecules such as lipids, water, or vitamin D.

☀ Control Water Loss. The lipid barrier prevents water loss and keeps us hydrated.

☀ Prevents nutrients to be washed off from the skin.

☀ Thermoregulation. The fat layer on the hypodermis together with the sweat glands on the dermis help us to regulate the body temperature.

☀ Protects against UV radiation. The melanin produced by the skin protects us from the harmful UV-A and UV-B radiation, which can cause DNA damage.