Layers of Skin : Learn Importance and How Do They Work

Skin is the largest organ of the body and along the nails, hair, nerves, glands is the part of the integumentary system. It acts as a protective barrier against harmful bacteria, viruses and other foriegn substances. It is the connective tissue that consists of fibres, cells and extracellular matrix. 

Our skin consists of three main layers :

• Epidermis 
• Dermis 
• Hypodermis 

Let's discuss the function of skin layers 

Epidermis 

Epidermis is the visible and the outermost layer of the skin which acts as a protective barrier against foreign substances like bacteria and viruses, thereby preventing their entry into the deeper layers of the skin.

This layer is constantly renewed as it sheds away the dead skin cells on a daily basis.It is evident that we shed around 500 million skin cells each day. Also, the outermost parts of the epidermis consist of 25–30 layers of dead cells. It prevents water loss from the skin and the presence of cells called melanocytes are responsible for its color. 

The epidermis further comprises of five distinct layers namely, Stratum Basale,Stratum Spinosum, Stratum Granulosum, Stratum Lucidum, Stratum Corneum

Lets discuss the layers of epidermis one by one:

1. Stratum Basale 

Stratum basale is also known as stratum germinativum. It is the lowest layer of epidermis and is composed of keratinocytes, melanocytes and tactile cells. Keratinocytes, also referred to as skin cells, are produced in this layer and undergo cell division constantly. 

Keratinocytes are composed of a fibrous protein called keratin which gives a hard texture to skin, hair and nails. In addition, between the epidermis and the dermis is a thin sheet of fibers called the basement membrane.

2. Stratum Spinosum

Stratum spinosum consists of 8-10 cell layers of daughter keratinocytes and dendritic cells. These fight against infections in the body. The protruding structures called desmosomes are responsible for the shiny appearance of stratum spinosum.  

3. Stratum Granulosum 

Stratum Granulosum consists of 3-5 layers of cell, particularly diamond shaped cells along with keratohyalin granules and lamellar granules. This layer appears grainy due to the changes in keratinocytes.   

Keratohyalin granules contain keratin precursors that aggregate, crosslink, and eventually form bundles. The lamellar granules contain the glycolipids that get secreted to the surface of the cells and function as a glue, keeping the cells stuck together.

4. Stratum lucidum 

Stratum lucidum has 2-3 layer cells. This layer has closely packed keratinocyte cells with seleiden, a clear protein rich in lipids. This is the thick skin that is found in your palms, feet and soles, its transparency is due to seleiden. 

5. Stratum Corneum

This layer consists of 15-30 layers of dead keratinized cells. They are shed every four weeks. The layer derives its name from the process of keratinization or cornification that happens.

Dermis

Dermis is present below epidermis and is known as the second layer of the skin. This layer contains collagen, blood vessels, elastin and hair follicles. Sweat is produced from this layer as sweat glands present in this layer which help flush out toxins through the body. The nerve endings in the dermal layer are responsible for the sense of touch in your body.

Sebum, a natural oil produced to keep the skin lubricated is produced in this layer by glands named as sebaceous glands. 

Dermis has two sublayers- 

• Papillary Dermis 
• Reticular Dermis 

Papillary Dermis

In this layer a loose mesh is formed by the collagen fibres. The papillary layer contains blood vessels, fat cells also known as adipocytes and phagocytes which are known as defensive cells. This layer contains nerve fibres, lymphatic capillaries and touch receptors. 

Reticular Dermis

This layer contains irregular, dense and vascularized connective tissue. It also contains collagen and elastin fibers. 

Collagen is a fibrous protein that is made of long and thin fibrils that keep the skin cells intact. They give strength to the skin. Elastin is a fibrous protein that gives skin its elastic nature.

Hypodermis 

The hypodermis or subcutaneous tissue consists of well-vascularized, loose adipose tissue and connective tissue. The deeper tissues including muscle, tendon, ligament, joint capsule and bone that lie beneath the hypodermis.

The main function of this layer is to attach dermis to the body, control body temperature, and store fat. This layer maintains the temperature and acts like a cushion or shock absorber.  The fat in this layer protects your muscles, bones and internal organs from injuries. The layer also helps attach dermis to the bones and muscles.

Skin color

The skin colour varies from extreme white to extreme dark. The variation in skin color is due to the presence of a pigment called melanin. It is evident that the coloration of light skin is mostly determined by the whitish-blue color of connective tissue below the dermis and hemoglobin in the veins of the dermis.

The key role of melanin is to protect the skin from damaging UV light from the sun which is the major cause of skin cancer. Melanin is produced by cells called melanocytes, which is followed by sunburn from exposure to the harmful UV rays.

Function of skin

Some of the main roles of skin are -

• It Protects against foreign substances or pathogens. Langerhans cells in the skin are part of the immune system.
• It stores lipids (fats) and water.
• Sensation can be sensed as nerve endings detect temperature, pressure, vibration, touch, and injury.
• It controls water loss by preventing water from escaping through evaporation.
• It prevents nutrients from being washed from the skin 
• It produces sweat and dilates blood vessels, the skin helps keep the body cool. 

In a nutshell, skin is the largest external organ which plays a vital role. Skin is of paramount importance it protects the body from harmful radiations, and maintains the appropriate temperature.