Integumentary System in Histology - Junqueira’s Basic Histology 13th Ed

Integumentary System

• The integumentary system is the largest single organ of the body.
• It consists of two main layers: the epidermis (epithelial layer of ectodermal origin) and the dermis (layer of mesodermal connective tissue).

Epidermis

• The epidermis is a stratified squamous keratinized epithelium composed of cells called keratinocytes.
• It lacks microvasculature, and its cells receive nutrients and oxygen by diffusion from the dermis.
• Epidermal cell types include:
  • Keratinocytes
  • Langerhan cells (antigen-presenting)
  • Melanocytes (pigment-producing)
  • Merkel cells (tactile epithelial cells)

Layers of the Epidermis

• Stratum basale (basal layer):
  • Single layer of basophilic cuboidal or columnar cells
  • Characterized by intense mitotic activity
  • Contains progenitor cells for all epidermal layers
  • Important feature: cytoskeletal keratins
  • Source of alive skin cells
• Stratum spinosum (spinous layer):
  • Thickest layer, especially in epidermal ridges
  • Synthesis of keratin and other proteins takes place
  • Characteristically exhibit spinous processes
  • Prickle cells
  • Synthesis of keratin would give the cell a spiny extension

Derivatives of the Skin

• Structures that are embedded on the skin but are otherwise considered as separate organs or tissues:
  • Hair follicles and hair
  • Sweat (sudoriferous) glands
  • Sebaceous glands
  • Nails

Functions of the Skin

• Protective:
  • Provides a physical barrier against thermal and mechanical insults
  • Protects against most potential pathogens and other materials
• Sensory:
  • Allows us to feel tactile objects
• Thermoregulatory:
  • Mechanisms for accelerating heat loss (sweat production)
• Metabolic:
  • Cells of the skin synthesize vitamin D3, needed for calcium metabolism and proper bone formation
• Sexual Signaling:
  • The effects of sex pheromones produced by apocrine sweat glands and other skin glands are important in attraction between sexes in all vertebrates

Subcutaneous Tissue (Hypodermis)

• Located beneath the dermis
• A loose connective tissue layer usually containing pads of adipocytes
• Adipocytes vary in number in different body regions and in size according to nutritional state
• Extensive vascular supply promotes rapid uptake of insulin or drugs injected into this tissue

Sensory Receptors

• Unencapsulated:
  • Merkel cells
  • Free nerve endings
  • Root hair plexuses
• Encapsulated:
  • Meissner corpuscles
  • Lamellated (pacinian) corpuscles
  • Krause end bulbs
  • Ruffini corpuscles

Dermis

• The surface of the dermis is very irregular and has many projections (dermal papillae) that interdigitate with projections (epidermal pegs or ridges) of the epidermis.
• Especially in skin subject to frequent pressure, where they reinforce the dermal-epidermal junction.
• Epidermal ridges are extensions of the epidermis to the dermis.
• Dermal papillae connect the dermis to the epidermis.