Epidermis- Structure and Function

Introduction

Skin is the organ that covers the entire human body. The skin consists of three layers-epidermis, dermis, and hypodermis. The outermost covering layer of the skin is the epidermis. Skin is a natural barrier to various pathogens and protects the body from chemical and mechanical injury.

What Is Epidermis?

The epidermis is the outermost layer covering the skin. It acts as a barrier to the human body. The epidermis protects humans from environmental pathogens and also helps in the regulation of temperature. In addition, the epidermis protects the body from natural ultraviolet rays. The epidermis has various layers. The thickness of the epidermis varies with the layers.

What Are the Layers of the Epidermis?

The epidermis has five layers.The five layers of epidermis are stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. The stratum basale is the deepest layer, and the superficial layer is the stratum corneum. The layers of the epidermis are mentioned below.

• Stratum basale.

• Stratum spinosum.

• Stratum granulosum.

• Stratum lucidum.

• Stratum corneum.

Stratum Basale: stratum basale, the deepest layer, is also known as stratum germinativum. The epidermis and dermis are separated by a basement membrane. The stratum basale is attached to the basement membrane by hemidesmosomes. The cells found in this layer are keratinocytes and melanocytes.

Stratum Spinosum: Stratum spinosum, known as the prickle cell layer, has 8 to 10 layers in the epidermis. It has polyhedral cells containing cytoplasmic processes, which give a spine-like appearance. In addition, dendritic cells are present in this player.

Stratum Granulosum: It is about 3 to 5 layers. Diamond-shaped cells in this layer contain keratohyalin and lamellar granules. Keratohyalin granules secrete keratin. Lamellar granules contain glycolipids .glycolipids secreted from lamellar granules are secreted to the cell surface and act as a glue, thereby keeping cells intact.

Stratum Lucidum: It is of 2 to 3 layers in the epidermis. Stratum lucidum is seen in the thick skin areas like palms and soles. Eleidin is present in this layer. Eleidin is the transformation product of keratohyalin.

Stratum Corneum: The superficial layer of the epidermis is composed of 20 to 30 layers of stratum corneum, also known as anucleate squamous cells. It is made up of keratin. Dead keratinocytes secrete defensins(defensins are part of our first defense mechanism).

What Are the Cells in the Epidermis?

Major cells seen in the epidermis are keratinocytes, melanocytes, Langerhans cells, and Merkel's cells.

Cells in the epidermis are listed below.

• Keratinocytes.

• Melanocytes.

• Langerhans cells.

• Merkel's cells.

Keratinocytes:

Keratinocytes are predominantly seen in the stratum basale layer of the epidermis. Keratinocytes play a significant role in the activation of cholesterol in synthesizing vitamin D.

Melanocytes:

Melanocytes primarily produce melanin pigment. Melanocytes are derived from the neural crest cells. Melanin pigment made in the skin acts as a sunscreen. Melanin is seen in the stratum basale layer.

Langerhan Cells or Dendritic Cells:

Langerhans or dendritic cells are the first skin defensive cells that play an essential role in the presentation of antigens. These cells are seen in the layer of stratum spinosum, and they originated from mesenchymal cells. Langerhans cells contain Birbeck granules containing cytoplasmic organelles in tennis-shaped form.

Merkel's Cells:

Merkel cells are seen in the stratum basale layer, which is present directly above the basement membrane. Merkel cells are oval-shaped and act as mechanoreceptors to touch. In addition, Merkel cells are seen in palms, soles, genital and oral mucosa.

What Is the Function of the Epidermis?

The function of the epidermis is as follows;

• The epidermis acts as a physical barrier by protecting it from mechanical trauma and chemical injuries

• It also protects the body from invading microorganisms

• Helps in immune defense mechanism

• Maintains homeostasis

• Exocrine functions by sweat and sebaceous glands

• Endocrine functions -synthesis of vitamin D

• Sensation to tactile, temperature, and pain

• Sometimes appearance, texture, and color of the skin act as the marker of some systemic conditions.

How Is Vitamin D Synthesized in the Epidermis?

The keratinocytes in the stratum basale layer help convert the 7 dehydrocholesterol to vitamin D during sun exposure. In addition, enzymes and vitamin D receptors in the keratinocytes help convert vitamin D to its active form called 1,25 dihydroxy vitamin D. Vitamin D receptors have a significant role in the proliferation and differentiation of keratinocytes.

What Is the Embryology of the Epidermis?

The epidermis is of ectodermal origin. The sensory nerve endings are derived from the neural crest cells. Langerhans cells are mesodermal tissue origin.

What Are the Disorders That Affect the Epidermis?

• Squamous cell carcinoma.

• Basal cell carcinoma.

• Malignant melanoma.

• Langerhan cells histiocytosis.

• Merkel cell carcinoma.

• Pemphigus vulgaris.

• Bullous pemphigoid.

• Infections like scalded skin syndrome.

• Drug reactions like DRESS are called Drug reactions with Eosinophilia and Systemic Symptoms syndrome.

• Steven Johnson syndrome.

• Erythema multiforme.

• Toxic epidermal necrolysis is associated with certain medications like sulfa-containing drugs and nonsteroidal anti-inflammatory drugs or NSAIDs.

• Anti-seizure medications.

What Are the Signs of an Unhealthy Epidermis?

• Change in color.

• Dry skin.

• Peeled and eroded skin.

• Scaly skin.

• Other conditions-acne blisters and dandruff.

What Are the Tips for a Healthy Epidermis?

• Regularly bathe in warm water with non-irritant cleansers.

• Use sunscreen to avoid sun damage.

• Drink plenty of water and be hydrated.

• Use gentle moisturizers, lotions, and creams.

• Reduce stress.

• Good sleep also nourishes the skin.

• Visit a doctor if you find any problem.

What Are the Foods to Eat for Healthy Skin?

Some foods are beneficial to the epidermis. Healthy epidermis is achieved from hydrated foods, foods rich in essential free fatty acids, vitamins, and certain minerals. Some of the foods to consume for healthy skin are listed below.

• Fish rich in omega-3 fats -salmon, herring, and mackerel

• Avocados.

• Walnuts are -a source of omega3 and omega-6 fatty acids.

• Sunflower seeds-source of antioxidant vitamin E.

• Sweet potatoes.

• Kiwi fruits.

• Beta carotene is rich in carotenoids, vegetables-carrot, and spinach.

• Red or yellow bell peppers.

• Broccoli - contains zinc, vitamin A and vitamin C.

• Tomatoes-source of vitamin c and carotenoids lie in lycopene.

• Soybeans increase skin elasticity.

• Dark chocolates.

• Green tea protects from cell damage and aging.

• Red grapes.

• Pomegranates.

• Collagen peptides.

Conclusion

The epidermis, the outermost layer of skin, has numerous vital roles in protecting the human body. Always protect your skin from skin damage. Hydration of the skin is maintained by drinking excess water, and healthy skin is kept.