Epidermis

Skin is the largest organ of the body and one of the most complex. While it plays many roles in sustaining life and health, it also has many potential problems. The epidermis is the outermost layer of skin on your body. It protects your body from damage, keeps your body hydrated, and produces new skin cells. There are three main layers around the skin.

Epidermis:

The epidermis is the outermost layer that makes up the skin, with the inner layers being the dermis and the hypodermis. The epidermal layer provides a barrier against harm and infection by environmental pathogens and regulates the amount of water lost from the body to the atmosphere by transepidermal water loss.

The epidermis comprises several layers of flat cells above the basal layer, which is formed of vertically arranged columnar cells. 

Structure of Epidermis:

The epidermis is a layered epithelial structure composed of keratinocytes that produce the structural protein keratin. The epidermis is mainly composed of four attachment layers of squamous epithelium organised into separate vertical zones according to the stage of differentiation. The epidermis resembles a brick wall, keratinocytes represent bricks, and the extracellular matrix represents mortar. The layers are the stratum basal layer, the stratum spinosum, the stratum granulosum, and the stratum corneum from the innermost to the outermost.

Stratum Basal Layer:

The basal layer is the deepest layer of the epidermis, connecting the epidermis to the basal layer, below which is the dermis layer.

Stratum Spinosum Layer:

The stratum spinosum has a pointed appearance due to the protruding cellular processes that connect cells through structures called desmosomes. The stratum spinosum is composed of 8-10 layers of keratinocytes that form due to cell division in the basal layer.

Stratum Granulosum:

The stratum granulosum has a granular appearance due to further changes in keratinocytes when extruded from the stratum spinosum.

Stratum Corneum:

The stratum corneum is the most superficial layer of the epidermis, exposed to the external environment. The stratum corneum usually has 15 to 30 layers of cells.

The functions of the epidermis:

All layers of the skin, including the skeletal system, organs, muscles, and tissues, work together to protect the body. There are many other functions of the epidermis:

• Hydration: The outermost layer of the epidermis retains moisture and keeps the skin moisturised and healthy.

• Protection: The epidermis acts like armour to protect the body from damage such as ultraviolet radiation, pathogens and chemicals.

• Skin Colour: The epidermis contains cells called melanocytes, which produce melanin. Melanin is the pigment that gives colour to the skin.

Now that you know the epidermis, let’s move on to the epidermis notes and their types.

Epithelial Tissue

Epithelial tissues are spread throughout the body. These tissues cover all body surfaces, body cavity lines, and hollow organs and are the primary tissue of the glands. They perform various functions, including protection, secretion, absorption, excretion, filtration, diffusion, and sensory uptake.

Types of Epithelial Tissue

There are nine types of epithelial tissue:

1. Squamous Epithelium:

These are tightly packed, thin, flat cells. Squamous epithelial cells cover the cavities of the mouth, oesophagus, alveoli, and blood vessels. This fabric protects against mechanical damage and keeps out bacterial invasion.

2. Stratified Squamous Epithelium

When the squamous epithelium is located in many layers, it becomes a complex squamous epithelium called stratified squamous epithelium. This type of tissue is also found on the skin and the inner walls of the oesophagus.

3. Simple Cuboidal Epithelium

These cells are rectangular parallelepipeds. These tissues are found in salivary glands, tubules, sweat glands etc. These tissues help in absorption, secretion and excretion.

4. Stratified Cuboidal Epithelium

When the cuboidal epithelium is placed in many layers, it forms a stratified cuboidal epithelium. It is inside the pancreatic duct and salivary glands. These tissues generally help in protection.

5. Simple Columnar Epithelium

The columnar epithelium cells are in the shape of a column. These are found in the mucous membranes of the stomach and intestines. It helps in absorption and secretion.

6. Ciliated Epithelium

If the columnar epithelial tissue has cilia, it is known as the ciliated epithelium. They are located in the inner layers of the trachea, tubules, etc. Their primary function is to help move material in a single direction.

7. Glandular Epithelium

These are modified columnar epithelial tissues. These are large cells found in the lacrimal glands, sweat glands etc. This tissue helps in secretion.

8. Pseudostratified Columnar Epithelium

These tissues are present in the respiratory passage and ducts of many glands, and their primary function is to help in protection, secretion and mucous movement.

9. Transitional Epithelium

These tissues are present in the urinary bladder, urethra and ureter and help in protection against abrasion and erosion.

Conclusion

The epidermis is an outer protective layer that acts as an essential barrier to environmental pathogens, chemicals and UV light and plays an important structural role. It has many vital functions, such as protecting the body from the outside world, moisturising the skin, creating new skin cells, and adjusting the colour of the skin. 

The epidermis and its waxy cuticle form a protective barrier against mechanical damage, water loss and infection.