Epidermis Structure and Functions Quiz

Introduction

• Skin is the largest organ in the body, typically accounting for 15%-20% of total body weight.
• In adults, it presents a surface area of 1.5-2 m² to the external environment.
• Also known as the integument or cutaneous layer.

Layers of Skin

• Skin is composed of two main parts:
  • Epidermis: an epithelial layer originating from ectoderm.
  • Dermis: a layer of mesodermal connective tissue.

Epidermal Derivatives

• Hair
• Nails
• Sebaceous glands
• Sweat glands

Functions of Skin

• Protective: Acts as a physical barrier against thermal and mechanical insults (like friction), and most pathogens.
  • Skin alerts resident lymphocytes and antigen-presenting cells (APCs) in the skin when encountering microorganisms, initiating an immune response.
• Permeability Barrier: Regulates water loss/uptake to allow terrestrial life.
  • Allows certain lipophilic (fat-loving) drugs to be delivered via skin patches.
• Sensory: Contains various mechanoreceptors that monitor the environment and regulate the body's interactions with physical objects.
• Thermoregulatory: Maintains constant body temperature through insulating components (fatty layer, hair on the head) and mechanisms that accelerate heat loss (like sweat production and a dense superficial microvasculature).
• Metabolic: Synthesizes vitamin D3, essential for calcium metabolism and bone formation, through UV light's action on its precursor.
• Sexual Signaling: Skin features (pigmentation, hair) are visual indicators of health involved in attraction between sexes in vertebrates, including humans.

Cells of the Epidermis

• The epidermis consists mainly of keratinocytes (about 90%).
• Pigment-producing melanocytes
• Antigen-presenting Langerhans cells
• Tactile epithelial cells called Merkel cells

Importance of SSKE

• Not covered in the provided text.

Layers of the Epidermis

• Stratum corneum
• Stratum lucidum
• Stratum granulosum
• Stratum spinosum
• Stratum basale

Medical Application

• Albinism: A congenital skin condition of low pigmentation, resulting from defects in tyrosinase or melanin-producing pathways.
• Vitiligo: An acquired condition with skin depigmentation in patches due to loss or reduced activity of melanocytes.
• Causes of melanocyte loss can include environmental, genetic, or autoimmune conditions.
• Alopecia areata/totalis/universalis: Conditions causing hair loss, often attributed to immune system attacks on hair follicles.
• Melanocyte proliferation can lead to moles (benign) and potential development of malignant melanoma (changes in mole size/appearance can indicate dysplasia).
• Psoriasis is a chronic skin condition where keratinocytes are produced and differentiate at accelerated rates, leading to epidermal thickening, increased keratinization, and frequent desquamation (shedding). Psoriasis is caused by overactive T lymphocytes, causing an autoimmune reaction with redness, irritation, itching, and scaling.
• Merkel cell carcinoma: A rare and aggressive skin cancer originating from Merkel cells, associated with a high mortality rate relative to other skin cancers.
• Friction blisters: Fluid-filled spaces between the dermis and epidermis caused by excessive rubbing, leading to protective thickening/hardening in the form of corns or calluses, if persistent.

Questions about wound healing and keratinization

• The importance of epithelialization in wound healing is not specified in the provided document.
• Keratinization is the process where cells differentiate into a hard, protective layer, often found in the epidermis.
• Desquamation is the process of shedding superficial layers of keratinized cells.

Other notes

• The epidermis in thick skin (e.g., palms and soles) has five layers, not four, compared to thin skin regions.
• The dermis has two sublayers: the papillary (thinner, with projections known as papillae) and the reticular (thicker, with extensive collagen fibers).
• The basement membrane separates the stratum basale of the epidermis from the dermis, facilitating nutrient diffusion to the epidermis.