The Integument

The Integument

Overview of the Integument

  • The integument is composed of the epidermis and dermis, forming the protective outer layer of the body.

Epidermis

  • Definition: Outermost layer of the integument, classified as keratinized stratified squamous epithelium.
  • Characteristics:
    • Lacks blood vessels, relying on diffusion for nutrition and gas exchange.
    • Composed of specialized cells:
      • Keratinocytes: Produce keratin, an insoluble protein that provides strength and waterproofing.
      • Melanocytes: Produce melanin, which gives skin its pigment and helps protect against UV radiation.
      • Merkel Cells: Function in sensory perception by stimulating nerve endings.

Layers of the Epidermis

  • Stratum Basale:
    • Location: Deepest layer of the epidermis.
    • Structure: One-cell thick with large cells and round nuclei undergoing mitosis. Contains many melanin granules.
  • Stratum Spinosum:
    • Structure: Composed of several layers of cells that may appear “spiny” due to desmosomes and cytoskeletal components.
  • Stratum Granulosum:
    • Comprises 3 to 5 layers of cells that have a grainy appearance. The cells in this layer are dying.
  • Stratum Lucidum:
    • Occurrence: Present only in thick skin (like palms of hands and soles of feet).
    • Structure: Contains 2 to 3 layers of dead cells, which may stain darker than the stratum corneum.
  • Stratum Corneum:
    • Structure: Thickest layer, containing 20-30 layers of dead, scaly, interlocking keratinocytes that undergo desquamation at the apical surface.

Dermis

  • Divided into two layers:
    • Papillary Layer:
      • Characteristics: Contains dermal papillae, which are projections into the epidermis.
      • Composition: Made of areolar connective tissue.
    • Reticular Layer:
      • Characteristics: Dense irregular connective tissue lacking reticular fibers.
      • Content: Contains hair follicles, sweat glands (sudoriferous), sebaceous glands, blood vessels, and nerves.

Exocrine Glands of the Skin

Types of Exocrine Glands in the Dermis

  • Apocrine Sweat Glands:

    • Location: Found in axilla, areola of the breast, pubic, and anal regions.
    • Description: Coiled tubular glands located next to hair follicles, opening into the hair follicle.
    • Mode of Secretion: Merocrine via exocytosis of vesicles into the duct of the gland.
    • Function: Produce a thick, slightly oily sweat that may have pheromone-like properties.
    • Word Origin: "apo-" means away from, and "krino" means to separate or secrete.

  • Merocrine (Eccrine) Sweat Glands:

    • Location: Most of the surface of the body.
    • Description: Coiled tubular glands with main secretory portions found deep within the reticular layer of the dermis, opening to the skin's surface.
    • Mode of Secretion: Merocrine via exocytosis of vesicles into the duct of the gland.
    • Function: Produce thin, watery sweat that cools the body.
    • Word Origin: "meros" means share, and "krino" means to separate or secrete.

  • Sebaceous Glands:

    • Description: Glands next to hair follicles with ducts opening into them.
    • Mode of Secretion: Holocrine - disintegrated whole cells filled with product discharged into the duct of the gland.
    • Function: Produce sebum (an oily substance) that lubricates the skin and inhibits bacterial growth.
    • Word Origin: "sebaceous" relates to sebum and "holos" means whole, combined with "krino" meaning to separate or secrete.

Sensory Receptors in the Dermis

Types of Sensory Receptors and Their Functions

  1. Free Nerve Ending:

    • Location: At epidermal/dermal junction.
    • Function: Senses light touch, temperature, pain, and pressure.

  2. Lamellated (Pacinian) Corpuscle:

    • Location: Deep in the dermis and hypodermis.
    • Function: Senses deep pressure and high-frequency vibration.

  3. Tactile (Merkel) Cell:

    • Location: At the epidermal/dermal junction.
    • Function: Senses fine touch, textures, and shapes.

  4. Tactile (Meissner) Corpuscle:

    • Location: In dermal papillae.
    • Function: Senses fine, light touch and texture.

Structure of Hair Follicles

Parts of a Hair Follicle
  • Connective Tissue (Dermal) Root Sheath:
    • Description and Function: Surrounds the entire hair follicle, mainly composed of dense collagen fibers.
  • Cortex:
    • Description: Constitutes the bulk of the hair, composed predominantly of keratin.
  • Cuticle Layer:
    • Description: The outer portion of the hair composed of several layers of hard plates of keratin surrounding the cortex.
  • External Root Sheath:
    • Description: Outer layers of the hair follicle continuous with the stratum basale and stratum spinosum of the epidermis.
  • Glassy Membrane:
    • Description: Specialized basement membrane external to the external root sheath and internal to the connective tissue surrounding the hair follicle.
  • Internal Root Sheath:
    • Description: A sheath derived from epithelial tissue lying between the external root sheath and the hair itself.
  • Hair Shaft and Bulb:
    • The growth and visible parts of hair.

Integument Lab Report Instructions

  • Use PowerPoint to present data regarding the integument, following an outline format.
  • Ensure all anatomical structures are labeled accurately based on a master list including:
    • Epidermis structure (stratum basale, spinosum, granulosum, lucidum, corneum)
    • Dermis layers (papillary and reticular)
    • Sweat glands
    • Hypodermis
    • Hair structures (root, shaft, papillae, arrector pili)
  • Include sections and details about Meissner’s corpuscles, Pacinian corpuscles, and skin structures.