Verr lec 3

• The Integument

  • Epidermis
  • Dermis
  • Hypodermis/Subcutaneous

  Variations

  • The relative number and complexity of skin glands
  • The extent of differentiation and specialization of the most superficial layer of the epidermis .
  • The extent to which the bone develops in the dermis. Amphioxus – with epidermis and dermis, but epidermis is one cell thick. Human – with epidermis and dermis, but epidermis is 4-5 cell thick.
• The Integument : Embryonic origin

  • It develops from the ectoderm, mesoderm, and neural crest cells.
  • The ectoderm gives rise to the epidermis and the nails and hair follicles.
  • The mesoderm gives rise to the dermis and the hair follicles.
  • Neural crest cells gives rise to the melanocytes, the melanin-producing cells in the skin
• The Integument: Functions

  1. Skin derivatives may be waterproof, abrasion-resistant covering that can be used for insulation, protection, defense, locomotion
  2. The skin of the derivatives may be colored for camouflage, thermoregulation, or communication
  3. The skin contains receptors for cutaneous sensation
  4. Maintains water balance, vit D synthesis
• The Epidermis

  • Superficial layer that may be divided into several regions; avascular
  • Contains numerous types of glands that may secrete mucus, slime, poisons, enamels, pheromones, photophores, etc.
  • Various kinds of derivatives arise from cornified layer of tetrapod epidermis.
  • In general, keratin is a feature of the skin of terrestrial craniates, not of fishes and aquatic amphibians
• FISHES

  • Mostly unicellular goblet and granular cells that secrete mucus and other substances like alkaloids, toxins, or nutritious mucus (eaten by hatchling)
  • Abundance of epidermal glands, scales are beneath the epidermis
  • Most fishes and synthesize little or no keratin at all
• Teleost have PHOTOPHORES or light-emitting multicellular glands

  • Luciferase, Luciferin
  • Species and sex recognition
  • Lure, warning, concealment by countershading
• TETRAPODS

  • 2 primary epidermal features : Integumentary glands and Stratum corneum
  • Morphologically varied integumentary glands: Simple or Compound, Saccular or Tubular , or both
• TETRAPODS : Glands vary in their ways cells liberate the substances

  1. Merocrine- secrete products via cell membrane; cell remains intact ; human sweat gland
  2. Holocrine – cells themselves constitute the secretion; bird oil gland, mammal sebaceous gland
  3. Apocrine – accumulates in the apical portion, then pinches off along with some cytoplasm; self-repair ; Mammary glands
• Mucous glands:

  • Loss may be due to thick stratum corneum
  • Retained only in lubricated surfaces of mammals
• Granular glands:

  • Secrete toxic or irritating alkaloids for defense
  • Chiefly located on back and feet (ex. femoral glands of male lizards form temporary spines to hold female)
  • Absent in birds and mammals
  • Source of most pheromones
  • Parotid glands in toads
• Oil glands:

  • Water-repellant secretion of avian uropygial glands is transferred to feathers during preening
• Sebaceous glands:

  • Alveolar glands that secrete the oily sebum, usually exuded into hair follicles
  • Ceruminous glands of ear canal secrete cerumen
  • Meibomian glands moisten eye conjunctiva
• Sudoriferous glands:

  • Coiled tubular glands that extend deep into the dermis
  • Secrete sweat
  • Function as thermoregulators
• Scent glands:

  • Pheromones secreted by sebaceous and sudoriferous glands
  • Goat feet use scent trail for species recognition
  • Anal glands of skunk drive away enemies
  • Anal glands of male musk deer signal sex
  • Temporal glands in elephants swell during breeding season
• MAMMARY GLANDS

  • Compound alveolar glands arising from milk lines that spread beneath the dermis, with supernumerary nipples forming above patches
  • Milk letdown is under neuro-hormonal control
  • Monotremes secrete milk from modified sweat glands on surface of hair tufts in the absence of nipples.
• Stratum Corneum

  • Keratinized outer layer, rare in aquatic forms, except for cornified spines and teeth in buccal cavity of cyclostomes and anuran tadpoles
  • Mostly found in skin derivatives of tetrapods that help prevent desiccation
• EPIDERMAL SCALES

  • Found only in amniotes; overlapping folds in squamates; large polygonal scales called scutes are found on snake belly and turtle's plastron.
  • Horny scales of birds are overlapping plates of keratinized epidermis.
• CLAWS, HOOFS, NAILS

  • Claws first appeared in basal amniotes and persisted in birds and in most mammals.
  • Claws evolved into nails in primates, and into hoofs in ungulates; usually worn down by abrasion, except squamates which shed them.
  • Claws and nails are local modifications of skin, as can be seen in their retention of epidermal, dermal and subcutis layers.
  • Claws serve primarily to protect underlying tissues, but are also used for scratching, digging or as a weapon.
• FEATHERS

  • Are highly specialized epidermal structures that have evolved from the scales of reptiles.
  • The color of feathers serve as camouflage and to protect birds from predators.
  • The color of feathers serve to communicate sex type. This is called sexual dimorphism when the male and female of a species display different plumages.
  • Feathers repel water with the aid of the uropygial glands' oily secretions rubbed over the body during preening.
  • This is particularly important in waterfowl, where oil spills saturate the feathers and destroy the bird's delicate protective covering.
• HAIR

  • Consists of dense keratin from cornified cells, trapped air vacuoles, and varying quantities of melanin.
  • Cells are produced by the germinal epidermis at the bulb of the hair follicle
• • Bulb – encloses the dermal papilla; at its root, hair cells cornify
  • Shaft – remainder of hair
  • Cuticle – a membranous cover, composed of thin, transparent cornified squamous cells arranged like shingles
  • Medulla – course hair; irregular shrunken cornified cells
  • Arrectores pilorum – when contracted, the hairs are elevated and the skin is pulled into tiny mounds (goose bumps). ferocious appearance in carnivores . For thermoregulation
• • Guard hairs –outer coats; associated with the sebaceous glands; waterproofing
  • Wool hairs / underfur –good insulators
  • Vibrissae – tactile; root is surrounded by basketlike network of sensory endings
• Horns – keratinized surface for offense, defense and display in ungulates

  • Bovine horns (cow, sheep, oxen)
  • Pronghorn (antelopes) - Core dermal bone covered by a sheath of horn; antelopes annually shed their branched and horny covering
  • Hair horns (rhinoceros) - Agglutinated keratinized hair like epidermal fibers that form a solid horn on roughened area of the nasal bone
• ANTLERS

  • Deer family, males only (except in caribou and reindeer). For territorial defense; affected by testosterone concentration
  • Dermal bone attached to the frontal bone
  • New growing antlers are “in velvet”, covered with a soft vascular skin and velvety hair; shed annually
• GIRAFFE HORNS

  • Stunted antlers that remain in velvet throughout life
  • Paired, protrude from the frontals
  • Permanent, unbranched
• BALEEN

  • Whales; whalebone plates in oral epithelium, with fringes that strain food out of the water passing through them

  RATTLES

  • Rattlesnakes; rings of horny stratum corneum attached to tail after each molt

  COMBS

  • Roosters; covered with thick, warty stratum corneum

  BEAKS – horny sheaths; functional counterparts of the lips and teeth of mammals
• • Monkeys and apes – sit on ISCHIALC CALLOSITIES
  • Camels – kneel on KNEE PADS
  • Most mammals (cats) – walk on TORI, an epidermal pads; at the end of digits, tori are called APICAL PADS
  • CORNS and CALLUSES – temporary thickening of the stratum corneum that develop where the skin has been subjected to unusual friction
• The Dermis

  • Consists of collagenous connective tissue, blood vessels, small nerves, pigment cells, lymphatics, naked and encapsulated exteroceptors, bases of multicellular glands, hairs or feathers and their erector muscles, chromatophores
  • Vascular
• The Dermis

  • Has an ancient and persistent potential to form bone
  • Bone is a constituent of the dermis (except birds)
  • Early fishes- armored fishes
  • Cowhide and pigskin, dermis of leatherback turtles, lamprey skin. Extremely tough due to the densely packed collagen bundle . When bone is lacking in the dermis, it is because bone salts were not deposited on the collagenous matrix
• BONY DERMIS OF FISH

  • Bony armor –broad bony plates or smaller bony scales, just beneath the epidermis
  • Dermal armor – protection; reservoir of calcium and phosphates
  • Generalized pattern consist of lamellar bone, spongy bone, dentine (with spiny elevations, denticles) and an enamel-like substance on the surface
  • Large plates gave rise to thinner fish scales, or parts of the skull and pectoral girdle skeleton
• The Dermis: Tetrapod Osteoderms

  • Minute-bony scales
  • ARMADILLOS- small polygonal bones united and extending to midventral line.
  • CROCODILIANS- oval osteoderms at the back, with cornified crests
  • TURTLES-scales compose the carapace and plastron
• The Dermis: Dermal Pigments

  • CHROMATOPHORES- permanently branched dermal pigment cells; all are derived from neural crest.
  • Physiologic color changes are reflexive and result from movement of pigment granules into or out of the processes.
  • Dispersal of pigment granules is under control of neurotransmitters or hormones (intermedin and melatonin).
  • Morphologic color changes are slow and depend chiefly on seasonal pigment synthesis.
• Chromatophores

  1. Melanophores- melanin (brown) granules in cytoplasmic organelles called melanosomes; melanocytes contain melanin granules in striated muscle and meninges
  2. Lipophores-lipid-soluble; consist of: xanthopores (yellow) and erythropores (red)
  3. Iridophores- contains guanine, a prismatic substance