lec 2,3

• Integumentary System


  Commonly referred to as the skin together with its derivatives. Cover and protect the tissues lying beneath it. Abundantly supplied with sensory nerve endings which are affected by environmental stimuli. Type of environment, whether aquatic or terrestrial, is of importance in variations in structure and derivatives.
• Integumentary System


  • Outer layer, the epidermis, composed of cells derived from ectoderm
  • Underlying mesodermal layer known as the dermis or corium
  • In tetrapods, ecdysis consists of shedding the outer layer of the epidermis
  • The epidermis is made up entirely of cells with the deepest layer, known as Malpighian layer, the middle is transitional later and the outer layer of flattened cells is the stratum corneum or homy layer
  • The dermis consists mostly of connective tissue
  • From the skin, arise the external appendages such as scales , feathers, hairs, horns, claws, nails and hooves, as well as, the internal appendages as the glands
• Skin Colour


  • Results from pigment found either in the skin itself or in its products
  • Lower vertebrates have pigment found in chromatophores; melanophores ,xanthophores and guanophores
  • In mammals, pigments found in the lowest layer of epidermal cells
  • In true albinos, there is a total lack of pigments
  • In man, additional branched pigment cells, melanoblasts at the point of junction between epidermis and dermis
• Skin Glands


  • All are exocrine
  • Not different from those found in other parts
  • Malpighian layer alone is concerned with their formation
  • According to structure, unicellular or multicellular
  • The unicellular glands, in Amphioxus, cyclostomes, fishes and amphibian larvae, mucous cells
  • The multicellular glands are formed by ingrowths of the Malpighian layer into dermis
  • It may be hollow, or solid and a lumen appears later
  • It may be compound gland

  
• Methods of Secretion


  • Merocrine glands
  • Holocrine glands
  • Apocrine glands

  
• Amphioxus


  • Only unicellular merocrine mucous glands (goblet cells )
• Cyclostomes


  • Only unicellular merocrine mucous glands (club shaped and granulated)
• Fishes


  • Unicellular mucous glands are characteristic
  • African lung-fish Protopterus, there are both unicellular and multicellular mucous glands
  • A few elasmobranch and teleost fishes have multicellualar poison glands, may at the base of a spine on each pectoral fin (catfish) or spines on the operculum
  • Some deep-sea elasmobranchs and teleosts living in total darkness have luminous phosphorescent organs, called photophores, arranged in longitudinal lines and they are modified integumentary glands
  • Another type of multicellular mucous glands is associated with the clasping organs of certain sketes and rays
• Amphibians


  • Large numbers of the multicellular mucous glands
  • Multicellular poison glands are also present
  • Warts and parotoid glands are actually masses of Poison glands
  • Toads usually have more poison glands than frogs
  • Other specialized multicellular glands, such as those on the feet of certain tree-welling frogs and toads and the glandular thumb pads of male frogs and toads
• Reptiles


  • Rough and scaly skins primarily adapted for life on land
  • Total lack of integumentary glands so the skin is dry
  • To prevent evaporation of water
  • Scent glands associated with sexual activity
  • Crocodilians have two pairs of skin glands which secrete musk, lower jaw and the cloacal orifice
  • Femoral glands in the males of some lizards and vestigial in the females
  • Some snakes have glands in the cloacal region
  • In certain turtels musk glands are present
• Birds


  • The skin of birds, like that of reptiles, is practically devoid of glands
  • Uropygial gland found above the uropygium of the tail in aquatic birds
  • Secretes oil which lubricates the feathers, making them quite impervious to water
  • The only other skin glands found in birds are certain modified oil glands in the region of the ear opening. They are found only in few birds such as the American turkey
• Mammalian Skin Glands


  • Sebaceous glands
  • Sweat glands
  • Wax glands
  • Scent glands
  • Mammary glands
• Sebaceous Glands


  Oil glands, absent from the palms and soles. the duct of the gland opens into a hair follicle. Keep the hair and skin smooth and soft. Imparts to the animal its individual odor
• Sweat Glands


  Simple coiled tubular glands. Function to getting rid of metabolic wastes and helping to maintain body temperature. Most numerous in regions devoid of hair, and may even open into hair follicles. Several mammal: however, have no sweat glands e.g., moles, the spiny ant-eater ,sirenians. cetaceans and the scaly an-eater. In many mammals, sweat glands a confined to certain regions
• Wax Glands


  Glands in the external ear passages and consist of coiled tubes like those of the sweat glands. The secretion is fatty. They are larger than ordinary sweat glands, and their ducts often join those of sebaceous glands opening into hair follicles. The mixture of the two kinds of secretion form ear wax
• Scent Glands


  They are either modified sweat or sebaceous glands, but the nature of their secretion is known only in few cases. They may be useful in attracting members of the same species or of the opposite sex. They varies greatly in locations
• Mammary Glands


  Milk producing glands, apocrine, modified sweat glands. Active only at certain times: immediately after the youngs are born and generally as long as active sucking continues. In general, the actively secreting mammary gland is made up of many small masses called lobules; each of which consists of large number of alveoli composed of secretory cells. The small ducts leading from the alveoli converge to from a larger duct. This unites with similar ducts from other lobules, and the common duct or ducts-thus formed lead to the outside. Since fatty or adipose tissue usually surrounds the ducts and alveoli, it contributes much to the size of the breasts