CHAPTER 6 INTEGUMENT Integument aka the skin has 3 layers Dermis Epidermis Basement membrane Arises from the ectodermal and mesodermal layers of the embryo. The Dermis Can perform intramembraneous ossification which results in dermal bones RE OSTRACODERMS Mostly fibrous connective tissue made from collagen. This tissue gives the skin its shape and prevents sagging. Important feature of shark skin. Prevents the skin from wrinkling which would slow swimming and cause the sharks to sink. The Epidermis The epidermis is specialized depending on the needs and habitat of any giving organism* Example: Mucus glands Importance to aquatic animals? Fish and frogs Importance to terrestrial animals? Instead of a mucus layer they rely on keratinization. Keratinization?! An important tetrapod innovation to allow them to move away from the water. Keratinization is when skin cells begin to die and form a thick protein layer of keratin. The dead cells plus the proteins that produce function to retain water and protect the living epidermal cells. Keratinization cont. 2 types of keratin proteins > alpha and beta Sauropsids have both types Synapsids have only alpha Alphas are softer RE finger nails, callouses Betas are harder RE beaks, claws, some scales Further specialization of the keratin layer = horns, hooves, hair, etc. Integument by Phylogeny FISH PRIMITIVE FISHES No keratin in fishes despite the presence of scales > Instead the epidermis is very glandular > Mucus layer aka mucus cuticle. Ostracoderms and placodermi with dermal bony plates CHORNDRICHTHYES Protection from predators, hydrodynamics, protection from bacteria and parasities. The fishes scales actually arise from the dermis and are considered dermal scales. No dermal bone but similar dermal origin placoid scales BONY FISH Three main scale types with various amounts of dermal bone, dentin, and enamel. Shark skin Ostracoderm scale Ganoid scale Cycloid scale Cosmoid scale Ctenoid scale Amphibians HAVE MOSTLY LOST THE DERMAL SCALES SEEN IN FISHES (EXCEPTION SOME APODA) EPIDERMIS PERFORMS Cutaneous respiration So no keratinization Capillary beds are restricted to the dermal layer in all animals except amphibians with their cutaneous respiration. Very glandular epidermis Mucous glands Poison glands Reptiles Scales are folded epidermis without dermal origin bone to support it. Extra thick shell components are called scutes. Keratinized. Some have keratinized horns (alpha keratin), claws (beta keratin). Some species do have dermal bone in other parts of body usually the belly for protection. Molting Most extensive in members of Squamata. White blood cells infiltrate between the layers of epidermis and help separate the out layer in a shed. Birds Uropygial gland Waterproof feathers Not found in some water birds Relation to reptiles Covered in epidermal scales Feathers are modified scales of keratin Initial evolutionary steps unknown Warm-blooded vs Cold-blooded Birds Feathers start in the embryo as a feather follicle. This is an invagination of the epidermis into the dermis where the root of the feather begins to form. The shaft is vascular and forms a framework upon which avascular keratinized cells grow. Functions of feathers Contour feathers = aerodynamics Flight feathers Down feathers = warmth Filoplumes = display Mammals Hair types Pelage (fur) Guard hairs & Underfur Vibrissae (whiskers) Quills Evolution: from scales or sensory hairs? Cynodonts Mammals Glands Sebaceous glands Sebum Wax glands Meibomian glands Sweat glands Eccrine glands Apocrine glands monotremes Mammary glands Produce milk Differences in monotremes, marsupials, placental mammals marsupials Placental mammals Specializations of the integument Nails Tightly compacted cornified epithelial cells Found only in primates Claws (talons) Curved, compressed epithelial cells Found in amphibians, birds, reptiles, mammals Hooves Found in horse, cows, deer The Equine Hoof Horns and antlers True horns Found in family Bovidae Occur in both sexes Living bony projection surrounded by skin and keratin Horns and antlers True antlers Found in family Cervidae Also made of bone but bone that is not part of the skull Shed and regrown each year Vascular epidermal covering to speed growth. Driven by hormones. Horns and antlers False horns and antlers Rhinoceros horn Giraffe horn Fish tubercles Horned lizard Baleen Found in whales Extract krill from water Contains no bone Dermal armor Found in ostracoderms and placoderms Armadillo Turtle shells Color Pigment contained in chromatophores Melanophores = melanin Iridophores = guanine Erythrophores = red Xanthophores = yellow Blue rarely seen Color change
