Layers of the skin 

The skin is the largest organ in the body. It acts as protection against environmental agents. It acts as a barrier against bacteria and other harmful agents. It also helps in regulating body temperature. It also helps in keeping our bodies hydrated. There are three layers of skin namely the epidermis, the dermis and the hypodermis.

The epidermis is the outermost layer of the skin. It makes up about 1-2 mm of the skin. The epidermis is mostly made up of dead cells that form a tough outer layer that protects our bodies from injury and infection. The epidermis also helps to regulate our body temperature.

The dermis is the second layer of the skin. It is located below the epidermis and contains blood vessels, hair follicles, glands, and nerve endings. Its functions include protecting underlying muscles and bones from injury, regulating body temperature, and producing sweat so that the skin can release heat.

The hypodermis is the third and deepest layer of the skin. It is composed mainly of fat and connective tissue. The hypodermis helps to store energy and insulate the body from cold temperatures.

Basically, the epidermis is composed of dead cells or keratinocytes. The keratinocytes are continuously replaced by new ones that are generated from the basal cells found in the epidermis. These basal cells multiply faster than the cells that are found upon the surface of the epidermis.

The new cells that are generated from the basal layer of the epidermis form a layer which is called stratum germinativum (stratum basale). This layer continues to secrete enzymes that are used in the breakdown of the keratinocytes.

The stratum germinativum is overlaid by other layers or strata of cells called stratum spinosum, stratum granulosum, and stratum lucidum.

These layers are composed of connective tissue fibres which are embedded in an extracellular matrix.

What is the Function of the Epidermis? 

The epidermis is the outermost layer of skin in humans. It is made up of stratified squamous epithelium with underlying connective tissue. Its main functions are protection, absorption of nutrients, and secretion.

Contrary to popular belief, the epidermis itself has no real ability to regenerate or heal itself. The epidermis acts as a barrier between your body and the environment. It prevents many harmful substances from entering the body. The epidermis also contains nerve endings that allow you to feel pain, respond to touch, and regulate body temperature.

The epidermis is further subdivided into five layers: The stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum and stratum basale

The most superficial layer, the stratum corneum, is composed of 15 to 20 layers of flattened dead cells. The purpose of the stratum corneum is to prevent water loss with an effective waterproofing system, protect underlying tissues from injury by physical, chemical, and biological insults, promote absorption of topical products, and provide a barrier to microorganisms.

The second layer of the epidermis, stratum lucidum protects the skin in areas most common to damage, such as the palms of the hands, the side of the fingers.

The next layer is the stratum granulosum. The purpose of this layer is to produce new cells, which migrate from this layer to the outermost layer. The cells of this layer are filled with keratohyalin granules.

The second last layer is the stratum spinosum. It is partly responsible for the skin's strength and flexibility. 

Lastly, the innermost layer of the epidermis, stratum basale contains column-shaped basal cells that are constantly dividing and being pushed toward the surface. This layer is also home to many melanocytes that produce melanin (the pigment responsible for the colour of our skin.

What is the Function of the Dermis? 

The dermis is the vascular layer of the skin and provides texture and colour to the skin. The dermis is composed of connective tissue and cushions the body against stress and strain. Growth and repair of connective tissue occur in the dermis and is the reason that scarring takes place. There are four different layers in the dermis: papillary layer, reticular layer, arrector pili muscle and adipose layer.

The dermis is also responsible for distributing water and oxygen to keep it alive, as well as providing structural support.

The dermis is about twice as thick as the epidermis, but most of its volume is interstitial fluid, with only 20% of its substance composed of collagen and elastin fibers. 

This matrix contains two types of fibers: collagen (responsible for biomechanical strength) and elastic fibers (responsible for skin elasticity). 

The dermis is not devoid of blood vessels; in fact, it has more blood vessels than any other system in the human body. There are approximately 100 capillaries per square millimeter. Blood, along with oxygen and nutrients, reaches the upper layer of the dermis through these capillaries.

The dermis is divided into two parts: the papillary region and the reticular region. The papillary region has a relatively thin connective tissue prismatic layer over a lamina densa made of dense irregular connective tissue. In contrast, the reticular region has a thicker layer of connective tissue with an abundance of collagenous, elastic and reticular fibers. Underneath all these layers and fibers is a layer of fat and aponeuroses.

What is the Function of the Hypodermis? 

The hypodermis is the layer of fat and connective tissue that exists underneath your skin. It acts as a protective shield between you and the outside world. The hypodermis consists of a bundle of connective tissues that helps in the formation of blood vessels and nerves. It is this layer that prevents you from experiencing pain from the outside world.

The hypodermis is a layer of fat tissue that acts as a shock absorber and also acts as a source of additional energy. This layer sits between the skin and muscles. In other parts of the body, it may be called by other names such as intermuscular fat, subcutaneous fat, superficial fatty tissue, hypodermal or mesodermal tissue.

The hypodermis is a layer of fat and fibrous tissue below the dermis and above the subcutaneous tissue, which lies between the dermis and muscle or bone. Body fat is found throughout the hypodermis and is the main component of this layer. The hypodermis contains blood and lymph vessels as well as nerves that provide sensory perception to the body. The fat found in this layer plays an important role in digestion and metabolism as well as provides insulation for the body.

Take Away

The skin is an organ and in layman's terms, it can be divided into three layers.

The epidermis is the outermost layer of the skin. The epidermis has five layers namely, the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum and stratum basale.

The dermis is the layer beneath the epidermis. The dermis contains blood vessels, nerves, hair follicles, sweat glands and oil glands that are arranged in layers.

The hypodermis is the deepest layer of the skin where fat cells are present. Beneath this layer, there are muscles, bones, cartilage, blood vessels and lymph nodes.