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, which is of ectodermal origin. The sensory nerve endings of this layer are derived from the neural crest cells. Langerhans cells are mesodermal tissue origin.

Skin is a natural barrier to various pathogens and protects the body from chemical and mechanical injury. All the layers of the skin vary in their significant function and anatomy. The article mainly talks about the outer covering of the skin, the epidermis.

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 regulate 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.

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: The deepest layer, stratum basale, is also known as stratum germinativum. A basement membrane separates the epidermis and dermis. 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 eight to ten layers in the epidermis. It has polyhedral cells containing cytoplasmic processes, which give it a spine-like appearance. Dendritic cells are also present in this player.

• Stratum Granulosum: It is about three to five layers. Diamond-shaped cells in this layer contain keratohyalin and lamellar granules. Keratohyalin granules secrete keratin. Glycolipids can be found in lamellar granules. Lamellar granules release glycolipids, which are secreted to the cell surface where they function as a glue to hold cells together.

• Stratum Lucidum: It is of two to three 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?

Cells in the epidermis are as follows:

• Keratinocytes: They 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: They 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: They 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 Are the Blood Supply and Lymphatics of the Epidermis?

The epidermis has no direct blood supply. Blood vessels and lymphatic vessels are mainly found in the dermis layer of the skin and are arranged into two plexuses. The first one is located between the papillary and reticular layers of the dermis, and the other one is present between the dermis and subcutaneous tissues. The epidermis is supplied by the superficial arteriovenous plexus, such as the subepidermal or papillary plexus, which are important for temperature regulation. The temperature of the body is regulated through the skin by an effective mechanism that works by increasing the skin’s blood flow and transferring heat from the body to the environment. The autonomic nervous system controls the changes in blood flow, and the sympathetic stimulation results in heat retention (vasoconstriction), and vasodilation causes heat loss. An increased body temperature leads to vasodilation of the blood vessels and occurs due to the inhibition of the sympathetic centers in the posterior hypothalamus, and a decrease in the body temperature causes vasoconstriction of skin blood vessels.

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

How Does the Epidermis Synthesize Vitamin D?

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 Are the Various Conditions That Affect the Epidermis?

• Squamous cell carcinoma (skin cancer).

• Basal cell carcinoma (skin cancer due to sun exposure).

• Malignant melanoma (occurs when melanoma or skin pigment-producing cells become cancerous).

• Langerhans cells histiocytosis (occurs due to the excessive build of Langerhans cells).

• Merkel cell carcinoma (neuroendocrine tumor of the skin).

• Pemphigus vulgaris (an autoimmune disease).

• Bullous pemphigoid (a skin disease that causes blisters on the skin).

• Infections like scalded skin syndrome.

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

• Steven Johnson syndrome (a disorder of mucus membrane and skin).

• Erythema multiforme (caused by some allergic reaction to an infection or medicine).

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

• Some anti-seizure medications may also affect the epidermis.

What Are the Signs of an Unhealthy Epidermis?

• Change in color.

• Dry skin.

• Peeled and eroded skin.

• Scaly skin.

• Other conditions include 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.

One must visit a doctor if one experiences any problems or symptoms.

What Are the Foods to Eat for Healthy Skin?

Some foods are beneficial to the epidermis. A 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 omega-3 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 are a source of vitamin C and carotenoids that 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. Therefore, one must always put effort into protecting the skin from skin damage. It can be done with the hydration of the skin regularly by maintaining water intake regularly, nourishing the skin with proper food intake, and using sunscreens to avoid sun damage.