Integumentary system

• Dermis


  Below epidermis
• INTEGUMENTARY SYSTEM


  • Comprises the skin and its derivatives
  • Protects against mechanical damage
  • Protects against invasion of microorganisms
  • Provides flexibility in motion
  • Prevents desiccation
  • Prevents damage from ultraviolet radiation
  • Helps maintain body temperature
  • Aids in the excretion of body wastes
  • Synthesizes vitamin D (ergosterol)
  • Maintenance of homeostasis
  • Sensation – nerve endings sensitive for heat, cold, touch, pleasure, pressure, and pain
  • Secretion – sebaceous glands secrete oil to lubricate and maintain the health of the skin
  • Gives rise to a variety of differentiated structures (feathers, nails, horns, claws, glands, hair)
  • Respiration – amphibians
  • Locomotion/Defense – adhesive pads, claws, horns, scutes, & feathers
• Hypodermis


  Subcutaneous region made up of loose connective & adipose tissue
• Skin of Cartilaginous Fishes is multilayered and contains mucus and sensory cells
• General Features of the Integument - DERMIS

  • Thicker than epidermis
  • Collagen fibers which are woven into distinct layers
  • Bundles of collagen fibers like “cloth” for shark skin which can be stretched if pulled
• Skin of Amphibians consists of stratified epidermis and dermis that contains mucus and poison glands
• Dermis develops from mesoderm and mesenchyme and produces the reticular lamina
• Skin of Birds has a thin epidermis with feathers derived from reptilian ancestors, providing insulation and lightweight surface area needed for flight
• Epidermis is derived from ectoderm and produces the basal lamina
• Basement membrane


  Between epidermis & dermis (basal lamina and reticular lamina)
• Integument

  Skin + derivatives = Integument
• Epidermis


  Surface
• General Features of the Integument - EPIDERMIS

  • Produce mucus to moisten the skin surface
  • In terrestrial vertebrates: keratinized or cornified layer
  • Stratum corneum: cornified epidermis (differentiate into hair, hooves, horn, sheathes, or other specialized cornified structures)
  • Keratinization: keratinized callus
• Skin of Bony Fishes contains scales and a thin layer of dermal tissue overlaid the superficial epidermis normally covers the scales
• Skin of Jawless Fishes has relatively thick skin and contains epidermal glandular cells that secrete the protective cuticle
• Skin of Reptiles reflects their adaptation to terrestrial habitat with a thick and hard outer layer of epidermis (stratum corneum)
• Layers of the Epidermis

  1. Stratum corneum (horny layer) - outermost layer, made up of stratified squamous, consist of dead, keratinized cells, continually shed off by molting

  2. Stratum lucidum (clear layer) - present in thick skin surfaces, cells consist of flattened dead keratinocytes, absent in face

  3. Stratum granulosum (granular layer) - middle layer where epithelial cells gradually die and become keratinized, contain abundant granules

  4. Stratum spinosum (spiny layer) - consists of several layers of cells next to the basal layer, cells receive nourishment from dermis, die as they move away from nutrients

  5. Stratum basale (stratum germinativum) - deepest layer, constantly producing new cells
• Different Sensory Nerve Endings

  • Pacinian corpuscles - pressure
  • Krause’s end bulb (Frigidoreceptors) - cold sensation
  • End bulbs of Ruffini (Caloreceptors) - heat sensation
  • Free nerve endings (Algesireceptors) - pain sensation
  • Meissner’s corpuscle - light touch
  • Merkel’s corpuscles - pressure, used in Braille script
  • Ruffini’s corpuscles - vibrations and stretching
• Skin of Mammals

  • Hairs
  • Quills
  • Variety of epidermal glands
  • Highly stratified and cornified epidermis
  • Dermis thicker than epidermis
  • Cornified epidermis prevents dehydration, aiding in terrestrial colonization
• Skin of Reptiles Outer layer of epidermis (stratum corneum)

  • Thick and hard, dry, lacks glands, modified into keratinized scales, scutes, and beaks
  • Prevents abrasion, dehydration, and provides protection
• Skin of Birds

  • Epidermis usually thin, only 2 or 3 layers
  • Feathers derived from reptilian ancestors, complex skin derivatives
  • Provides strong yet lightweight surface for flight
  • Serves as insulation to conserve body heat
• Layers of Dermis

  1. Stratum spongiosum - borders epidermis, made up of loose connective tissue, collagen, glands, and chromatophores

  2. Stratum compactum - more compact collagenous connective tissue, nerves, blood vessels, tactile corpuscles, provides structural strength and protection against puncture and laceration
• Layers of the Skin

  1. Epidermis (scalp) - outer and thinner layer, derived from ectoderm

  2. Dermis - inner and thicker layer, derived from mesoderm, richly supplied with blood vessels, nerves, sense organs, sweat glands, oil glands, and hair follicles

  3. Hypodermis - made up of fats and connective tissue
• Frog skin consists of Stratum spongiosum and Stratum compactum
• Epidermal Scales are a continuous layer of repetitious thickenings of the stratum corneum found only in amniotes
• Mucous gland is smaller with big secretory cells
• Snake skin is shed
• Scales of most mammals are confined to legs and tail, e.g., rats & beavers
• Ganoid or rhomboid scales are covered with ganoin, a shiny substance, and are armor-like scales found in fishes like garpike
• Epidermal Scales develop in areas where feathers are absent, e.g., facial area, legs, feet in birds
• Ctenoid scales are found in bony fishes and arrange in diagonal rows with free edges
• Plastron is made of nine dermal plates covered with epidermal scales
• Claws, Hoofs & Nails are modifications of stratum corneum at the ends of digits, with claws being curved, laterally compressed keratinized projections from the tips of digits
• Armadillos have hair & scales interspersed over entire body
• Sensory receptors

  • Frigidoreceptors - for cold sensation
  • End bulbs of Ruffini (Caloreceptors) - for heat sensation
  • Free nerve endings (Algesireceptors) - for pain sensation
  • Meissner’s corpuscle - light touch
  • Merkel’s corpuscles - pressure, used in Braille script
  • Ruffini’s corpuscles - vibrations and stretching
• Dermal Scales are located in the dermis of the skin and mostly found in fishes
• Production of structures involving keratinization includes Epidermal Scales, Dermal scales, Claws and Talons, Hooves, Nails, Baleen, Feathers, Beak, Hair, and Horns
• Sturgeon scute is a type of scale
• Poison gland is big in size but the secretory cells are smaller
• Animals with epidermal scales

  • Lizards, snakes (overlapping), crocodiles (nonoverlapping), birds (confined to legs and feet)