integument

• Integument - the outer covering of the body, a protective wrapping that includes the skin and all structures derived from or associated with skin
• Molluscan epidermis is delicate and soft and contains mucous glands, some of which secret the calcium carbonate of the shell
• Epidermal cells are typically columnar in shape and can be ciliated, non-ciliated, or glandular. Their external surface is composed of a microvillous layer which assists in retaining mucoid secretions in place.
• Mucus is mostly water. It functions as a slippery lubricant and an adhesive. It is vital in feeding, reproduction, and locomotion and adhesion. It also insulates the mollusk from the surrounding environment.
• some molluscan mucus has antimicrobial properties and can also protect against predators
• Arthropods integuments provide not only protection but also skeletal support. Exoskeleton and jointed appendages suitable for attachment of muscles.
• The arthropod integument consists of a single layered epidermis (hypodermis) which secretes a complex cuticle of two zones
• Procuticle - the thicker inner zone, is composed of protein and a chitin (a polysaccharide) laid down in layers.
• Epicuticle - the thinner outer zone of the cuticle, lying on the external surface above the procuticle. it is nonchitinous complex of proteins and lipids that provides a protective moisture-proofing barrier to the integument.
• An arthropod cuticle may be tough but soft and flexible layer, or it may be hardened, like those from crabs and lobster shells
• Crabs and lobster's cuticle is stiffened by the calcification, the deposition of calcium carbonate in the outer layers of the procuticle
• Insects hardening occurs via sclerotization
• sclerotization is the formation of a highly resistant protein, sclerotin.
• Epidermis is a thin, outer stratified squamous layer, simple in structure but it gives rise to most derivatives of the integument, such as hair, feathers, claws and hooves.
• cells of the basal part in epidermis undergo frequent mitosis (stratum germinativum) to renew layers that lie above.
• In epidermis, as outer layers of cells are displaced upward by new generations of cells beneath, an exceedingly tough, fibrous protein called keratin accumulates in the interior of the cells,
• in the epidermis, there is a process called KERATINIZATION wherein cells become cornified, resistant to abrasion and water diffusion, forms stratum corneum (dandruff, calluses, scales of reptiles, foot pads of mammals)
• dermis is a dense connective tissue layer containing blood vessels, collagenous fibers, nerves, pigment cells, fat cells, and connective tissue cells called fibroblasts.
• Dermis support, cushion, and nourish the epidermis, which is devoid of blood vessels. Other cells present in this layer are macrophages, mast cells, and lymphocytes, which provides a first line of defense if the outer epidermal layer is broken
• Epidermal derivatives are formed by the epidermis and comprise of epidermal glands, hard horny structures like scales, scutes, beaks, horns, claws, nails, and hoofs, feathers, hairs and structures that form the exoskeleton of an animal
• inside the epidermal gland is a mucous gland, they secrete slimy of sticky mucus on coming in contact with water.
• inside the epidermal gland is a poison gland, it is multicellular cutaneous glands that secretes bitter, irritating, and dangerous substance. many fishes and amphibians have this.
• Under the epidermal gland, a luminescent glands or photophores - a multicellular epidermal glands that serve as light-emitting organs. Light emitted is not intense, may be of many hues, and serves to attract prey.
• in the epidermal gland is also a femoral gland, these are found in male on the ventral surface of each thigh, in a single row 12-18 femoral pores from knee to cloacal aperture. Their sticky secretion hardens in air to form temporary tiny spines that serve to hod the female during copulation.
• under the epidermal gland is the Uropygial gland, found in birds. It forms a prominent swelling just above the tail or uropygium. it is branched and alveolar and exudes an oily secretion used for lubricating beak, preening feathers and attracting the opposite sex during breeding season due to odoriferous nature.
• the oil secreted in the uropygial gland contains pomatum which is picked up by beak and used for preening and water proofing.
• in the epidermal gland, Sweat glands or sudoriferous glands are abundant in the skin of most mammals. they are slender coiled tubes embedded deep in the dermis, with their long ducts opening on skin surface. A little urea and some salts are eliminated.
• The sweat glands focuses on different parts of the body

  human - palm and armpits

  cats and mice- lips

  ruminant -muzzle and skin between toes

  bats - sides of head

  hippopotamus - ears
• in the epidermal gland, sebaceous glands, are branched alveolar glands opening into hair follicles of mammals. They may open directly onto skin surface such as around the genital organs, tip of the nose, or edges of lips. The oily secretion is called sebum.
• ceruminous glands of external ear canals are modified sebaceous glands. their wavy or greasy secretion, called cerumen.
• Meibomian glands of eyelids, which spread their oily secretion over the exposed surface of the eyeball, are modified sebaceous glands.
• in the epidermal gland, scent glands are modifications od either sebaceous or sudoriferous glands of mammals. Their odorous secretions serve to repel foes or attract members of the opposite sex.
• in the epidermal gland, mammary glands is a characteristics of mammals, these are compound tubular glands that produce milk during lactation period of feeding the young ones.
• Epidermal scales is a continuous layer of repetitious thickenings of stratum corneum. These may be shed entirely by molting or in small flakes.
• Claws or talons are curved, laterally compressed keratinized projections from the tips of digit.
• Hooves are enlarges keratinized plates found on the edge of ungulate digits.
• nails are keratinized epithelial cells produced at the base and push it forward. they provide protection from mechanical injury and stabilize skin for better grasping. Found only on primates.
• Horns are tough, cornified layer of the integument. Their core is bone, which is of dermal origin. It is found in bovines, antelope, sheep, goats, bison, wildebeest. They are retained year-round and grow throughout the animal's lifetime.
• baleen found in some whales. It is a series of keratinized plates that arise from oral epithelium. These sheets hang from the palate along its length and acts as a sieve.
• Beaks is an epidermal structure; jaws are covered by keratinized sheaths in birds and turtules