Comparative Vertebrate Anatomy: Integument Lecture Notes PDF

Comparative Vertebrate Anatomy: Integument Embryonic Origin  Integument ⚫ Epidermis – derive from the ectoderm ⚫ Dermis - develops from the mesoderm ⚫ Basement Membrane – between the epidermis and dermis ⚫ Hypodermis – transitional subcutaneous region made up of very loose connect...

Comparative Vertebrate Anatomy: Integument Embryonic Origin  Integument ⚫ Epidermis – derive from the ectoderm ⚫ Dermis - develops from the mesoderm ⚫ Basement Membrane – between the epidermis and dermis ⚫ Hypodermis – transitional subcutaneous region made up of very loose connective tissue ⚫ One of the largest organs of the body making up some of the 15% of the body weight ⚫ Epidermis and dermis may rise up to special forms Function ⚫ Provides as a border between the organism and its environment ⚫ Parts of the exoskeleton and thickens to resist mechanical injury ⚫ Maintenance of suitable water ⚫ Barriers that prevents the entrance of pathogens ⚫ Thermoregulation and respiration ⚫ Protection from harmful sun rays ⚫Storage of calcium and synthesis of Vitamin D ⚫ Production of pheromones ⚫ Receptions ⚫ The multilayered epidermis arises from the single-layered ectoderm ⚫ The deep layer of epidermis, the stratum basale stays on the basement membrane and replenishes the outer Periderm through active cell division ⚫ The epidermis further differentiates into a stratified layer with a mucous coat on the surface ⚫ The dermis arises from several origin: ⚫ Dermatome, an embryonic skin segment derived from the outer wall of the dermomyotome of the segmental epimeres ⚫ The dermatome settles in under the epidermis to differentiate into the connective tissue layer of the dermis ⚫ Some migrating neural crest cells settle between the dermis and the epidermis contributing to bony armor and to skin pigment cells called chromatophores General Feature EPIDERMIS Avascular layer composed of epithelial cells ⚫ Produces mucus ⚫ Keratinized or cornified layer DERMIS ⚫ Vascular inner layer of the integument ⚫ Composed of collagenous connective tissue derived from the mesoderm ⚫ Holds the blood vessels, nerve cells, pigment cells, bases of multicellular glands, and bases of hairs or feathers in place ⚫ Provides tensile strength, and physiological support for the interfacing epidermis Integumentary Structure/Function ⚫ The Structure of the Epidermis Figure 5-2 Integumentary Structure/Function ⚫ Components of the Integumentary System Figure 5-1 Chromatophores - Pr o v i d e c o nc e a l i ng c o l o r a t i o n t o t h e integument Types: Melanophore – melanin Iridophore – which contains light reflecting crystalline guanine platelets Xanthophore – yellow pigments Erythrophore - red pigment ⚫ Melanocytes Figure 5-3 Glands ⚫ Formed from the stratum germinativum of the epidermis ⚫ All are exocrine Types of glands 1. Unicellular glands ⚫ Single specialized, and interspersed among the epidermal cells in fishes Types: 1. Club cells – elongated, binucleated unicellular gland - contains chemicals that excite, alarm or fear 2. Granular cells- in Lampreys and other fishes - contribute to mucus cuticle 3. Goblet Cells – in bony and cartilaginous fishes 4. Sacciform cells – hold a large, membrane- bound toxic secretory products used to repel enemies 2.Multicellular glands ⚫ Formed by ingrowths of the stratum germinativum into the dermis ⚫ The branches of multicellular glands are connected to a single duct which opens onto the outer surface  Types 1. Tubular Glands ⚫ Simple tubular glands – ceruminous glands ⚫ Simple coiled tubular glands – sweat glands ⚫ Simple branched tubular glands – sweat in the axillae ⚫ Compound tubular glands- mammary glands of Monotremes 2. Saccular glands ⚫ Simple saccular glands – mucous and poison glands in the skin of amphibians ⚫ Simple branched saccular glands- sebaceous or oil glands ⚫ Compound saccular glands- mammary glands of metatherians and eutherians Scales ⚫ Serve as exoskeleton of vertebrates for protection of the body ⚫ Epidermal (turtles and snakes) ⚫ Dermal scales (fishes) Dermal Scales ⚫ Cosmoid scale is a small, thick scales consisting of a dentine-like material known as cosmine ⚫ in sarcopterygians resides in a double layer of bone, one layer is vascularized and the other is lamellar ⚫ Placoid scale- consists of basal plate embedded in the dermis with a caudally directed spine projecting through the epidermis (Elasmobranchs) ⚫ Rhomboid/ Ganoid scale – rhomboidal in shape and composed of bones ⚫ thick surface coat of enamel, without dentin ⚫ Sturgeons, Paddle fish and Gars ⚫ Cycloid and Ctenoid scale – closely resemble with each other that may occur both on one fish ⚫ Consists of an outer layer of bone and a thin layer of connective tissue ⚫ The bony layer is characterized by concentric ridges representing the growth increments in the fish Feathers ⚫ Are modified reptilian scales formed from the beta keratin layer of the epidermis ⚫ Distinguish birds from all other vertebrates Types 1. Filoplumes or hair feathers consists of long, slender shaft which may bear a few barbs at its distal ends 2. Down feathers/ Plumulae Composed of a short basal hollow quill, embedded in the skin and numerous barbs which arise from the free end of the quill 3. Contour Feathers - arise in pterylae, consists of long shaft and a broad, flat portion called the vane Hairs ⚫ Mammals, composed primarily of alpha keratin of the epidermis ⚫ Consists of a base or root and a shaft ⚫ Fur/ Pelage composed of guard hairs and underfur ⚫ Vibrissae or whiskers – hairs with sensitive nerves ⚫ Hairs – root, shaft (cuticle, cortex, medulla) ⚫ Arrector Pili Fishes: ⚫ Primitive fishes contains bony plates of dermal armor ⚫ Nonkeratinized and covered by a mucus ⚫ Most living fishes there is no prominent superficial layer of dead, keratinized cells ⚫ Microridges – surface cells increases surface area for communication ⚫ Mucous cuticle ⚫ Epidermal cells and specialized unicellular glands Development of Fish Skin Scales Chondrichthyes ⚫ Dermal bone is absent but contains placoid scales ⚫ Numerous secretory cells and stratified epidermis cells are present in the epidermis ⚫ Chromatophores occur in the lower part of epidermis and upper region of the dermis ⚫ Dermis is composed of fibrous CT especially elastic and collagen ⚫ Placoid scales develop from the dermis Osteichthyes ⚫ Larger number of mucous glands especially among Lungfishes and modern fishes ⚫ Epidermal glands (Unicellular glands) and Multicellular glands in few fishes ⚫ Dermis is subdivided into a superficial layer of loose CT and a deeper layer of dense fibrous CT with cycloid or ctenoid scales ⚫ Chromatophores within the dermis ⚫ Scales are located near close to the epidermis Tetrapods - Amphibians ⚫ Scales are absent, multicellular glands (epidermal glands) and epidermis with stratum corneum ⚫ Skin is specialized as respiratory surface across which gas exchange occurs ⚫ Salamanders – Cutaneous respiration ⚫ Leydig cells within the epidermis of larval salamanders secrete substances that resist in entry of bacteria and pathogens ⚫ Nuptial pads in males ⚫ Two multicellular glands: Mucous glands – smaller made up of little cluster of cells Poison glands – larger with stored secretions ⚫ Chromatophores – occasionally in the epidermis but common in the dermis  Reptiles ⚫ Keratinization is much more extensive and skin glands are fewer ⚫ Epidermal origin of scales ⚫ Hinge – junction between the adjacent epidermal scale ⚫ Large scales are termed scutes ⚫ Osteoderms – dermal bones support the epidermis ⚫ The dermis is composed of fibrous connective tissues ⚫ Epidermis is divided into three layers ⚫ Stratum basale ⚫ Stratum granulosum ⚫ Stratum corneum ⚫ Molting or Ecdysis ⚫ Stratum basale duplicates the deeper layers of granulosum ⚫ Stratum intermedium is formed ⚫ WBC promote separation and loss of the old superficial layer of the skin ⚫ Femoral glands – in many lizards, along the underside of the hindlimb in the thigh region ⚫ Scent Glands in turtles and crocodiles  Birds ⚫ Feathers is considered as an elaborate reptilian scales ⚫ Dermis of bird skin is richly supplied with blood vessels – Brood patch, sensory nerve endings and smooth muscles ⚫ Epidermis comprises the stratum basale and the stratum corneum ⚫ Skin is almost entirely free of glands except for Uropygial Gland and Salt Gland ⚫ Feathers as a distinguishable traits of birds among the other vertebrates ⚫ Pterylae vs Apteria ⚫ Feathers follicles Mammals ⚫ Epidermis – specialized as hair, nails or glands ⚫ Keratinocytes that forms the dead, superficial cornified layer of the skin ⚫ Langerhans cells in the stratum spinosum ⚫ Merkel cells ⚫ Chromatophores Dermis ⚫ Double layered – outer papillary layer and inner reticular layer ⚫ Communication with other organ systems ⚫ Cardiovascular ⚫ Lymphatic ⚫ Nervous ⚫ Sensation ⚫ Control of blood flow and secretion Specialization of the Integument ⚫ Nails – tightly, compacted, cornified on the surface on hands ands toes -protection and stabilize the skin at the tips of the fingers and toes ⚫ Claws or Talons – curved, laterally compressed keratinized projections from the tips of digits ⚫ Hooves – enlarged keratinized plates on the tips of the ungulate digits ⚫ Horns and Antlers ⚫ Baleen – strainers to extract krill from the water gulped in the distended mouth ⚫ Scales – for protection