lec 4,5,6

Cards (44)

  • Amphioxus
    • Represents chordate integument reduced to its simplest form
    • Epidermis consists of a single layer of columnar epithelial cells covered by a thin cuticle
    • Dermis is thin and composed of soft connective tissue
    • Subcutaneous layer is a thin gelatinous layer with few fibres
    • Pigment is lacking
    • No exoskeleton
  • Cyclostomes
    • Epidermis is stratified
    • Deepest layer is the active Malpighian layer, no dead stratum corneum
    • Outer cells are living, have nuclei and secrete a thin cuticle
    • Epidermis contains pigment cells, unicellular glands and sensory cells
    • Pigment cells may be present in the dermis
    • Dermis is even thinner than the epidermis
    • No integumentary scales, skin is smooth
    • Horny teeth or epidermal teeth in the buccal cavity and on the tongue are modified epidermal scales
  • Fishes
    • Epidermis is stratified and covered with cuticle
    • Unicellular glands are present, multicellular glands may be present
    • Dermis consists of a loose outer and a deeper more compact layer
    • Dermis has chromatophore cells giving fishes their changeable colors
    • Characteristic dermal derivative is the scale
    • Fishes are generally covered with scales which constitute the exoskeleton
    • Some fishes lack scales like catfish, electric ray, chimaeras
  • Exoskeleton in vertebrates
    • Derived from the epidermis of the skin, dermis or both
    • Epidermal exoskeleton is made of flat horny epidermal cells
    • Dermal exoskeleton is made of bone or bone-related substance
    • Epidermal exoskeleton is ectodermal in origin, dermal exoskeleton is mesodermal in origin
  • Cartilaginous Fishes
    • Well-developed exoskeleton composed of placoid scales
    • Each placoid scale has a basal plate embedded in the dermis and a spine projecting through the epidermis
    • Basal plate is made of bone-like dentine, spine is made of dentine covered in vitrodentine (enamel-like substance)
  • Development of Placoid Scale
    1. Dermal cells aggregate and form a dermal papilla
    2. Papilla pushes up the epidermis
    3. Malpighian layer cells over the papilla elongate and help shape the spine
    4. Outer dermal papilla cells secrete dentine of the scale
    5. More dentine secretion increases scale size and pushes it through the epidermis
    6. Basal plate forms enclosing the dermal papilla leaving passage for blood vessels and nerves
  • Placoid scale is totally dermal in origin
  • Placoid scales grow to a certain size, then shed and new scales replace the old ones
  • Teeth of Cartilaginous Fishes
    • Modified placoid scales
    • Not firmly united with the jaws, attached by connective tissue
    • Formed at the bottom of a dental groove, continuously replaced as new teeth form
  • Teeth of Vertebrates
    • Two types: epidermal teeth (e.g. horny teeth of Petromyzon) and true teeth
    • True teeth have a crown (like placoid scale spine), root (like basal plate) and pulp cavity
    • Crowns are covered in enamel (epidermal origin), rest is dentine (dermal origin)
  • Teeth are derived from modified bony dermal plates, homologous to placoid scales
  • Tooth Replacement Types
    • Monophyodont (no replacement)
    • Diphyodont (first set replaced by second permanent set)
    • Polyphyodont (indefinite replacement)
  • Tooth Location
    • May be located anywhere in the oral or pharyngeal regions with stomodaeal ectoderm and supporting cartilage/bone
    • In addition to jaws, may be found on vomer, palatine, pterygoid, parasphenoid and splenial bones
    • In some fishes, teeth are located on the tongue and attached to the hyoid arch
  • Tooth Shape Types
    • Homodont (similar shape)
    • Heterodont (differentiated into incisors, canines, premolars and molars)
  • Tooth Attachment Types
    • Acrodont (attachment on rim only)
    • Pleurodont (attachment on inner margin of bone)
    • Thecodont (in sockets, fixed by cement)
  • Bony Fishes
    • Well-developed exoskeleton of bony scales
    • Bony scales are permanent structures, not shed
    • Scale growth rings can be used to determine fish age
  • Bony Scale Types
    • Cosmoid (extinct, composed of dentine, middle vascular bone and inner lamellate bone)
    • Ganoid (layers of enamel-like ganoine covering lamellate bone)
    • Ctenoid (thin, translucent plates with comb-like projections on free edge, growth rings indicate seasons)
  • Ganoid scales
    • Found in ganoid fishes, e.g. Polypterus
    • Amia has modified ganoid scales on the head
    • Sturgeons have similar scales in the tail region
  • Ctenoid scales
    • Common type found in most teleost fishes
    • Thin, translucent plates composed of underlying layer of fibrous material covered by a layer which resembles bone
    • Each scale is embedded in a small pocket in the dermis
    • The scales are obliquely arranged so that the posterior free end of one scale overlaps the anterior fixed edge of the scale behind it
    • The free edge bears numerous comb-like projections
    • Lines of growth are present
  • Cycloid scales
    • Roughly circular in outline
    • Located in pockets in the dermis and have lines of growth similar to those of ctenoid scales
    • The posterior edges are free but smooth
    • Found in Holostei (Amia), Dipnoi and some Teleostei
  • In certain fishes, the ctenoid and cycloid scales may be present, those on the underside being cycloid and those on the upper side being ctenoid
  • The scales covering the lateral line are frequently perforated
  • Development of cycloid or ctenoid scales
    1. Dermal cells accumulate and form scleroblasts
    2. Scleroblasts arrange into a dermal papilla
    3. Dermal papilla pushes the epidermis and secretes bone to form the scale rudiment
    4. Scale increases in thickness and dimension as more bone is secreted
    5. Anterior edge grows inward, posterior edge grows outward pushing the epidermis
    6. Epidermis either remains as a thin membrane or ruptures leaving the posterior edges exposed
    7. The bony scale is entirely dermal in origin
  • Amphibian skin
    • Epidermis composed of several layers with a dead stratum corneum
    • Dermis is relatively thin with a stratum spongiosum and stratum compactum
    • Important organ of respiration
    • Blood vessels, lymph spaces, glands, and nerves abundant in the stratum spongiosum
    • Chromatophores found beneath the epidermis
    • Anura and Urodela possess naked skin without exoskeleton
    • Extinct Stegocephalia had bony dermal plates
    • Some living caecillians possess minute dermal bony scales
  • Teeth in frogs (Rana)

    Formed in the same manner as in cartilaginous fishes
  • Claws in Amphibia
    • First appear in Amphibia, on the posterior extremities of a few genera
    • Modifications of the corneal layer, just as the hoof and nail
  • Reptilian skin
    • Epidermis characterized by extremely well-developed corneal layer
    • Scales derived from the horny stratum corneum
    • Ecdysis occurs at intervals for removal of dead outer layers
    • Dermis consists of superficial and deep layers
    • Many lizards and snakes have abundant chromatophores in the superficial dermis
    • Skin considered 'dry' due to absence of skin glands
  • Types of reptilian scales
    • Epidermal scales in snakes and lizards
    • Epidermal scales in turtles and crocodiles
  • Epidermal scales in snakes and lizards
    • Each scale projects backward and overlaps the scales behind
    • Scales are continuous with each other at their bases
    • Snakes and lizards undergo periodic ecdysis
  • Epidermal scales in turtles
    • Cover the plastron and carapace
    • Each scale develops separately
    • Epidermis under each scale grows peripherally, increasing the scale area
    • New cornified layer pushes older scales away, resulting in irregular concentric rings
    • Pigment located in the epidermis
  • Epidermal scales in crocodiles
    • Do not undergo ecdysis
    • Wear away and are gradually replaced
  • Claws in reptiles
    • Consist of a dorsal convex horny plate (unguis) and a ventral concave subunguis
    • Epidermal structures
  • Horny beaks in Chelonia
    Epidermal structures encasing the jaws
  • Dermal scales in turtles
    • Bony plates (osteoscutes) form a rigid dermal skeleton fused to the endoskeleton
    • Epidermal scales cover the dermal plates
  • Dermal scales in crocodiles
    • Small, not fused to one another
    • Possess dermal ribs (gastralia) in the ventral abdominal region
  • Dermal scales in some lizards and snakes
    • Small
  • Development of epidermal scales
    1. Dermal cells accumulate to form dermal papilla
    2. Malpighian layer becomes active and divides, forming flattened, cornified cells that compress into scales
    3. Scales are thickened parts of a continuous horny layer, not separated like fish scales
  • Development of dermal scales
    Develop in a similar manner to the ctenoid scales of bony fishes
  • Avian skin
    • Epidermis thin and delicate, except on legs and feet where corneal scales are present
    • Feathers cover and protect the body, modified from corneal scales
    • Dermis thin, but muscle fibers abundant to raise and lower feathers
    • Chromatophores absent
  • Avian exoskeleton

    • Feathers
    • Horny scales on feet
    • Horny claws on digits
    • Horny beak