Skin Biology - Layers, Functions, and Protection

Introduction:

One of the five and largest sense organs of our body. It covers the entire external surface of the body. It protects the internal organs from the external environment using a multilayered network of cushioning, a cellular barrier, and protective oils. It is a barrier against germs, sunlight, chemicals, and mechanical injury. It also controls the temperature and quantity of water released into the surroundings. It also produces vitamin D from sunlight, which is necessary for bone health.

What Is Skin?

Skin is the largest organ in the body, made of water, protein, fats, and minerals. Skin is a part of the body’s integumentary system, including hair, nails, oil glands, and sweat glands. The term integumentary means the outer covering of the body. It serves various bodily functions, including protection from the outside environment, regulating body temperature by sweating and flushing when it is hot, and raising goosebumps when it is cold.

What Are the Layers of the Skin?

The skin comprises three tissue layers:

1. Epidermis, the outermost layer.

2. The dermis is the middle layer.

3. The hypodermis is the bottom layer.

What Is Epidermis?

The outermost layer of the skin, the epidermis, comprises millions of skin cells joined by lipids (a natural mortar-like substance), which strengthen the barrier, control the volume of water expelled from the body, and prevent organisms' entry into the body. The thickness of the epidermis varies according to the body site.

What Are the Layers in the Epidermis?

The layers in the epidermis are as follows:

• Stratum Corneum (Horny Layer): The stratum corneum, the epidermis' topmost layer, comprises 20 to 30 cell layers made up of keratin (a protein) and horny scales made up of dead keratinocytes (cells in the epidermis). It is the layer responsible for variation in thickness. Dead keratinocytes produce a substance called defensins, the body’s first immune response.

• Stratum Granulosum (Granular Layer): This layer contains diamond-shaped cells. The cells in this layer produce waxy material, which acts as glue and helps cells get stuck together.

• Stratum Spinosum (Spinous or Prickle Cell Layer): It comprises 8 to 10 cell layers and contains polyhedral-shaped cells with a spine-like process. Intercellular bridges called desmosomes (a structure that holds the epidermal cells together) are present in this layer.

• Stratum Basale (Basal Layer): The deepest part of the epidermis comprises columnar cells, and proteins arranged in columns make new skin cells. That’s because this layer is only one of the four epidermis layers that undergo mitosis (a division of the cellular nucleus). Thus, as the topmost layer of the skin flakes off, younger skin cells push up from the basal layer to take its place.

What Are the Cells in the Epidermis?

There are four different types of cells in the epidermis. They are as follows.

• Keratinocytes - It is a major cell type in the epidermis. It forms a waterproof and protective barrier by producing lipids. The cells are produced in the basal layer and move towards the outermost layer.

• Melanocytes - These cells are found in the basal cell layer and secrete a pigment called melanin that the new cells absorb to guard against the sun's damaging rays. The amount of melanin in a person's body is governed by their genes and the amount of sun exposure.

• Langerhans Cells - These cells are part of the immune system since they are designed to shield the body from foreign particles.

• Merkel Cells - These cells are responsible for touch sensation.

What Is Dermis?

The middle layer of the skin is called the dermis. It lies below the epidermis and performs various functions. It comprises hair roots, blood vessels, nerve endings, and sweat glands that help control body temperature and eliminate waste products. It also consists of oil-producing glands called the sebaceous glands, which help the skin remain soft, smooth, and waterproof. The oil prevents the skin from absorbing too much water while swimming.

What Are the Layers in the Dermis?

The dermis has two layers, namely papillary and reticular.

• Papillary Dermis: The papillary dermis contains interlocking connections that allow the epidermis to receive blood and nutrients.

• Reticular Dermis: The reticular dermis is the thicker and deeper portion of the dermis. It contains structural components like collagen and elastin. Collagen is a protein that makes cells stronger and more resilient. Elastin is another protein that keeps the skin flexible. Hair follicles and oil-producing glands are also present in this dermis layer.

What Is Hypodermis?

The hypodermis is the bottom layer of the skin. It is a fatty layer. Fat helps protect against injuries to muscles and bones during an accident. It has connective tissue which attaches the dermis to the muscle and bone. Nerves and blood vessels in the dermis get bigger in the hypodermis and help connect to the rest of the body.

What Is a Basement Membrane?

It is a thin sheet of fibers between the outer layer and middle layer of the skin. It regulates what is allowed to move back and forth between the two, acting as an extra barrier against intruders and an extra safeguard against the loss of water and other essential resources. When skin needs to grow or heal, the basement membrane becomes permissive, allowing water and nutrients to reach the wounded epidermis and help it heal.

What Are the Functions of the Skin?

The few important functions of the skin in the body are as follows:

1. Protection From the Environment: This is the skin's most important function. It keeps the pathogens such as bacteria and viruses away and causes no harm to the body.

2. Preventing Water Loss: In desert areas, skin becomes thicker to prevent water loss due to dry air. Human beings have thick skin that loses less water.

3. Sensation: It is the main sense organ that can sense touch, heat, pain, cold, and pressure. These sensations are transmitted to the brain by a network of nerves and help to respond according to the particular sensation.

4. Regulation of Temperature: Human skin can purposefully shed water through sweating and cool itself. This attribute helps in removing heat from the body. The body can also promote heat loss by flushing, which causes hot blood from deep within to move to the skin's surface, radiating heat into the surrounding area.

5. Storage: Water and lipids can be stored in the skin's tissues. These give the body additional insulation.

What Else Is Included in the Skin?

The skin has 60,000 melanocytes (cells that make melanin or skin pigment) and about 19 million skin cells per square inch, and also contains 1000 nerve endings and 20 blood vessels.

What Are the Conditions or Disorders Associated With Skin?

Skin is susceptible to various conditions because it is the body’s external protective barrier. Some of the skin disorders or conditions are as follows:

• Allergies.

• Bug bites.

• Blisters.

• Skin infections.

• Skin rashes and dry skin.

• Skin lesions such as moles and skin tags.

How to Protect the Skin?

Elastin and collagen get depleted as age progress, which causes the skin’s middle layer to be thin, resulting in skin sagginess and wrinkles.

Skin aging cannot be stopped by any means, but some steps can help maintain healthier skin. They are as follows.

• Sunscreen: Apply sunscreen every day, even indoors. Use a broad-spectrum sun protection factor of at least 30.

• Avoid Tanning: Tanning damages the skin and may cause skin cancer.

• Avoid Smoking and Using Tobacco Products: Nicotine damages the skin and makes skin age faster.

• Cleanser: Use gentle cleansers to wash the face in the morning and evening.

Conclusion:

Skin, the body’s largest organ, protects the body from germs and other factors. It regulates the body's temperature, and nerves under the skin surface provide a sense of touch. The protective covering may experience more and less severe problems. It is always better to have a physician’s opinion when there is any problem.