Beauty Note | Structure of Skin

Amani Zolkarnaini Saturday, March 02, 2019

Beauty Note | Structure of Skin

Although at the thickest point, skin is only a few millimeters thick, but in fact, it is the largest and the most complex organ in the body. Skin carries a lot of different function including as protective barrier, as signal of medical condition, as body temperature regulator, as sensor for touch, pain, pressure, temperature and as storeroom for body.

All of these functions are carried out by different layers of skin. So, do you know haw many layers does your skin has actually?

Skin in fact made of three different layers namely:

Epidermis
Dermis
Hypodermis

3 main layers of skin.

📌 Epidermis

Epidermis is the thinnest and the uppermost layer of the skin and classified as keratinized (cornified) stratified squamous epithelium. This layer is mainly made of keratinocytes, cells that are highly responsible in forming a skin barrier against external harms such as bacteria, virus, fungi, parasites, heat damage and UV radiation.

Simple epithelial tissue.

Stratified epithelial tissue.

Two major works that take place in epidermis layer are:

Production of new keratinocytes (skin cells) replacing the old cells via keratinization process.
Production of melanin pigment by melanosomes secreted by melanocytes to gives the skin its tone and colour.

Keratinocytes, melanocytes and melanosomes in epidermis layer.

Epidermis layer can be divided into several sublayers of keratinocyte cells from the deepest to the most superficial layer known as:

1) Stratum Germinativum / Stratum Basale / Basal Layer

This sublayer is where the keratinocytes are originated before moving up to the surface of epidermis and being shed as dead skin cells when it mature.
This layer is also where melanocytes is located, the cells which are responsible in producing melanosomes for determination of skin tone and colour.
Merkel cells are also found in this sublayer, it acts as a receptor which is responsible in stimulating sensory nerves that the brains perceives as touch.

2) Stratum Spinosum / Prickle Layer

This sublayer is where the keratinocytes fight against foreign substances from entering themselves with the helps of special immune cells called Langerhans cells.
Langerhans cells involve in epidermal immune system where it are able to engulf foreign substances and damaged cells that occur in this layer.

3) Stratum Granulosum / Granular Layer

This sublayer is where part of keratin and lipid production occurs which play important roles in the formation of Stratum Corneum later.

4) Stratum Lucidum / Clear Layer

This sublayer is only present in thicker skin of hand palms and feet soles. Its main function is to reduce friction between the Stratum Corneum and Stratum Granulosum. Keratinocyte.

5) Stratum Corneum / Cornified Layer

This sublayer is composed of many dead keratinocytes (dead skin cell) filled with keratin which eventually will shed off the surface of epidermis to be replaced by new keratinocytes.

Sublayers of epidermis.

📌 Dermis

Dermis is the thickest layer of the skin and it is located in the middle of skin layers. It is known as a layer of connective tissues which is mainly fibrous, consisting both collagen and elastic fibres. Between these fibrous components, lies and amorphous extracellular “ground substances” containing glycosaminoglycans such as hyaluronic acid, proteoglycans and glycoproteins.

Collagen fibres are one of the most durable proteins that gives the skin strength, waterproofing, and elasticity. Another function of collagen is to heal the wound. It forms a mesh-like scaffold in the damaged tissue and seals off the wound by forming a scar.

Elastic fibres are primarily composed of protein elastin which is very important in keeping the skin flexible but tight. It provides a bounce-back reaction to the skin when pulled. It also helps in keeping the skin smooth as it stretches.

The main role of dermis layer is to sustain, support the epidermis layer and enable the skin to thrive by feeding the surface of epidermis from within. Roughly, dermis layer is said to have two sublayers of connective tissue that merge together without clear demarcation.

Those two layers are:

1) Papillary layer (Upper layer)

It is thinner, composed of loose connective tissues that is highly vascular.

2) Reticular layer (Deeper Layer)

It is thicker, composed of dense connective tissue that constitutes the bulk of dermis.

Papillary and Reticular layes of dermis.

Dermis houses many cell types founded within the connective tissues including:

1. Fibroblasts

To handle the synthesis of collagen, elastic and reticular fibres and extracellular matrix material.

2. Macrophages

To detect, engulf and destroy pathogens and apoptotic cells.

3. Adipocytes

To provide insulation and energy storage.
To assist in hair follicle regeneration and wound healing.

4. Mastocytes

To mediate inflammatory responses, collagen remodelling and wound healing.

5. Schawann cells

To keep peripheral nerve fibres (both myelinated and unmyelinated) alive.

6. Stem cells

To provide new cells and replace the old cells that are damaged or lost.

It also contains other structures that carry their own function which are:

1. Sensory Nerves

To sense pain (nociceptor).
To sense pressure, vibration, texture (mechanoreceptor).
To sense temperature (thermoreceptor).
To sense changes in muscle length and muscle tension.

2. Blood Vessels (vein & artery)

To bring oxygen and nutrients to the uppermost layer of skin.
To regulate body temperature as when cold, it constricts while when hot, it enlarges.

3. Arrector Pili Muacles

Responsible in stimulating the autonomic nervous system and cause contraction making the hair stand perpendicular to the surface of epidermis when trigerred by cold and fear.

4. Gland (sebaceous)

To produce an oily/viscid substance containing proteins and fatty acids into hair follicle in order to lubricate the surface of epidermis and waterproof hairs.
Secretion are mainly responsible for body odour.

5. Eccrine/Merocrine Gland (sweat)

To produce a watery substance containing water and sodium chloride directly onto the surface of epidermis via sweat duct.
Secretion are mainly responsible for cooling of the body.

6. Hair Follicles

To develop hair which helps in regulating body temperature, protecting against injury and enhancing sensation.
The above part of hair is called as shaft while the below part is known as root. Its colour depends on the amount of pigment produced by melanocytes.

Structures in dermis layer of skin.

📌 Hypodermis

Hypodermis is the deepest layer of the skin and serves to connect the skin to the underlying fibrous tissues of the bones and muscles. This layer mostly rich in fat (adipose tissue) and connective tissue that carry various kinds of functions which are: