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 The integument consists of the skin and its derivatives:
and
.
 The skin of two animals or different parts of the same animal can look quite dissimilar depending on its color, thickness, or types of derivatives that it produces.
 Despite these different appearances, the basic structure of all skin is nearly the same. It consists of two major layers: epidermis , an outer layer that is subdivided into several other layers and the dermis , a connective tissue layer
 Underneath the skin is the hypodermis (or subcutis ) which may consist of adipose cells, glands or bone.

 Skin derivatives may be waterproof, abrasionresistant covering that can be used for insulation, protection, weapons, locomotion
 The skin or the derivatives may be colored for camouflage, thermoregulation, or communication.
 The skin contains receptors for cutaneous sensation.
 Maintains water balance, Vitamin D synthesis

 Superficial layer that may be divided into several regions
 Contains numerous types of glands that may secrete mucus, slime, poisons, enamels, pheromones, photophores, etc.
 Various kinds of derivatives arise from cornified layer of tetrapod epidermis

FISHES and AQUATIC AMPHIBIANS:
 Mostly unicellular goblet and granular cells that secrete mucus and other substances, e.g. alkaloids, toxins or nutritious mucus (eaten by hatchlings)
 Teleosts have PHOTOPHORES or light-emitting multicellular glands (luciferase
)

Morphologically varied (simple or compound, saccular, tubular, or both)

Secretions could be merocrine (intact cells, e.g. sweat glands), holocrine
(cellular, e.g. oil glands), or apocrine (intermediate, e.g. mammary glands)

MUCOUS GLANDS - loss maybe due to thick stratum corneum; retained only in lubricated surfaces of mammals
GRANULAR GLANDSsecrete toxic or irritating alkaloids; chiefly located on back and feet (e.g., femoral glands of male lizards form temporary spines to hold female); absent in birds and mammals
OIL GLANDS -water-repellant secretion of avian uropygial glands is transferred to feathers during preening
SEBACEOUS GLANDSalveolar glands that secrete the oily sebum, usually exuded into hair follicles; ceruminous glands of ear canal secrete cerumin; Meibomian glands moisten eye conjunctiva
SUDORIFEROUS GLANDScoiled tubular glands that extend deep into the dermis; thermoregulators
SCENT GLANDSpheromones secreted by sebaceous and sudoriferous glands

MAMMARY GLANDScompound alveolar glands arising from milk lines that spread beneath the dermis, with supernumerary nipples forming above patches
Milk letdown is under neurohormonal control
Marsupials secrete milk from modified sweat glands on surface of hair tufts in the absence of nipples.

Keratinized outer layer
, rare in aquatic forms, except for cornified spines and teeth in buccal cavity of cyclostomes and anuran tadpoles; mostly found in skin derivatives of tetrapods that help prevent dessication

Found only in amniotes; overlapping folds in squamates; large polygonal scales called scutes are found on snake belly and turtle’s plastron.
Horny scales of birds are overlapping plates of keratinized epidermis.

 Claws first appeared in basal amniotes and persisted in birds and in most mammals.
 Claws evolved into nails in primates, and into hoofs in ungulates; usually worn down by abrasion, except squamates which shed them.
 Claws and nails are local modifications of skin, as can be seen in their retention of epidermal, dermal and subcutis layers.
 Claws serve primarily to protect underlying tissues, but are also used for scratching, digging or as a weapon.

 Basic structure consists of a horny dorsal plate
( unguis ), and a softer ventral plate ( subunguis or sole )
 Partially surrounded by the unguis in ungulates is a softer pad, the cuneus .

 Are highly specialized epidermal structures that have evolved from the scales of reptiles.
 The color of feathers serve as camouflage and to protect birds from predators.
 The color of feathers serve to communicate sex type. This is called sexual dimorphism when the male and female of a species display different plumages.
 Feathers repel water with the aid of the uropygial glands' oily secretions rubbed over the body during preening.
 This is particularly important in waterfowl, where oil spills saturate the feathers and destroy the bird's delicate protective covering.

CONTOUR FEATHERSgive a bird its general shape
Each vane consists of barbs, barbules, flanges and hooklets that interlock with the flanges on the next barb.

 FLIGHT FEATHERScontour feathers specialized for flight.
 DOWN FEATHERSsmall, fluffy feathers lying underneath and between contour feathers; short calamus, barbs lack hooklets

hairlike feathers, few barbs and barbules at the tip; follicles are richly supplied with nerve endings.
resemble filoplumes but lack terminal barbs; screen eyes, ear and nasal openings of foreign matter

DERMAL PAPILLAmound of dermal mesodermal cells that indents the undersurface of the epidermis and induces mitotic activity in the basal layer.
FEATHER PRIMORDIUMpimple-like elevation on epidermis resulting from growth of dermal papilla, which soon becomes vascularized
FEATHER FOLLICLEa pit lined with epidermis that develops around base of feather primordium; at the base of a feather follicle is a growth zone that pushes the distal tip of the growing feather, now a feather sheath .

PIN FEATHERgrowing feather in its sheath, which eventually splits open to stretch out barbs and enable shaft to elongate.
Dermal papilla dies and becomes pulp, leaving an opening, the inferior umbilicus . New feathers may arise from reactivated dermal papillae.

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HAIR consists of dense keratin from cornified cells, trapped air vacuoles, and varying quantities of melanin. Cells are produced by the germinal epidermis at the bulb of the hair follicle.

 The bulb encloses the dermal papilla ; at its root, hair cells cornify; remainder of hair is known as shaft . A membranous cuticle covers each hair, composed of thin, transparent cornified squamous cells arranged like shingles
 Coarse hairs contain a medulla , composed of irregular, shrunken cornified cells.

When the
, a smooth muscle that is inserted on the wall of the hair follicle contracts, gooseflesh results, or gives the carnivore its ferocious appearance.

Guard hairs are associated with sebaceous glands that help them waterproof the skin. Wool hairs or underfur are good insulators. Vibrissae are primarily tactile.
Guard hairs
Underfur
Vibrissae

BOVINE HORNS (cows) and PRONGHORNS
(antelopes)- consist of a core of dermal bone and sheath of horn; antelopes annually shed their branched and horny covering

GIRAFFE HORNSstunted antlers that remain in velvet throughout life; also paired and protrude from the frontals, but they are permanent, unbranched
HAIR HORNSrhinoceros; composed of agglutinated keratinized hair-like epidermal fibers resting roughened area of nasal bone; not shed

 ANTLERS are dermal bone attached to the frontal bone.
 Deer antlers develop in males, starting growth covered in velvety hair, which are rubbed off at maturity, exposing naked bone
 Males shed them off after rutting season.

BALEEN - whales; whalebone plates in oral epithelium, with fringes that strain food out of the water passing through them
RATTLES rattlesnake; rings of horny stratum corneum attached to tail after each molt.
COMBS - roosters; covered with thick, waxy stratum corneum

BEAKS the bird beak is the functional counterpart of the lips and teeth of mammals.
It is covered with horny sheath, covering both the upper and lower jaws. It grows continuously throughout the lifetime of a bird.
The shape, strength and organization of the beak varies depending on whether it is on a bird of prey, a seed-eater, or a fish-eater.

ISCHIAL CALLOSITIESmonkeys and apes; for sitting
KNEE PADScamels; for kneeling
TORI or APICAL PADScats; epidermal pads for “pussyfoot” walking
CORNS and
CALLUSES - temporary thickenings where stratum corneum is subjected to unusual friction

Consists of collagenous connective tissue, blood vessels, small nerves, pigment cells, lymphatics, naked and encapsulated exteroreceptors, bases of multicellular glands, hairs or feathers and their erector muscles, chromatophores

 Has an ancient and persistent potential to form bone, e.g. armored fishes
 Generalized pattern consist spongy bone, dentine (with spiny elevations called denticles ), and an enamel-like substance on surface.
 Dermal armor was protective, but is also a reservoir of calcium and phosphates
 Large plates gave rise to thinner fish scales, or parts of the skull and pectoral girdle skeleton

Scales are overlapping dermal plates of bone covered with epidermal tissue. 4 types are found:

1. PLACOID - same as paleoniscoid scales, but arising from the bony plate is a specialized denticle ; may have given rise to gnathostome teeth; found in elasmobranchs
2. RHOMBOID - retain primitive
4 layers of dermal bone;
Osteichthyans a. COSMOIDcosmine is not a tissue but a complex canal system associated with dentine and enamel layers; found in Sarcopterygians, absent in modern fishes

b. GANOID - ganoin is a form of enamel. The paleoniscoid type is found in Actinopterygians
(Polypterus), while some Neopterygians (Amia and gars) lost the spongy and dentine layers.
3. ELASMOIDformed from thin lamellar bone with a fibrous plate; flexible and transparent; most teleosts c. CTENOID - comblike free border d. CYCLOID - Amia, Latimeria and Dipnoi

ARMADILLOS - small polygonal bones united and extending to midventral line.
CROCODILIANS - oval osteoderms at the back, with cornified crests
TURTLES - scales compose the carapace and plastron

 CHROMATOPHORESpermanently branched dermal pigment cells; all are derived from neural crest. o Melanophores - melanin (brown) granules in cytoplasmic organelles called melanosomes ; melanocytes contain melanin granules in striated muscle and meninges o Lipophores - lipid-soluble; consist of: xanthopores
(yellow) and erythropores (red) o Iridophores - contains guanine , a prismatic substance
 Physiologic color changes are reflexive and result from movement of pigment granules into or out of the processes.
 Dispersal of pigment granules is under control of neurotransmitters or hormones (intermedin and melatonin ).
 Morphologic color changes are slow and depend chiefly on seasonal pigment synthesis.

Lack scales.
Hagfishes are also called “slime eels” due to abundant unicellular mucous glands in mutilayered epidermis.
Horny denticles in buccal funnel and cornified teeth are periodically shed and replaced.
Dermis is thin, but tough due to interwoven collagenous CT.
Contains many melanophores which adheres to underlying body musculature.

 Ancient placoid scales have bony basal plate in the dermis, and projects with a spine on epidermis, giving it a sandpaper texture.
 Epidermis has thicker layers than agnathan skin; dermis is composed of 2 well-defined layers.

 Unicellular cells are less abundant; some goblet cells are modified to secrete toxins.
 Few multicellular glands, limited to base of male claspers
 Photophores invade dermis, and lose connections with epidermis.
 A denser continuous sheet of melanophores on the back epidermis and less denser sheet on belly makes a shark less visible from above and below the water.
 Chimaeras have slippery skins, having lost their scales, and more mucous glands.

Unicellular epidermal mucous glands; a few multicellular glands, such as granular glands that secrete poisonous alkaloids
Deep sea forms have photophores that permit species recognition, warnings or lures
Dermis of Polypterus and gars contain ancient ganoid scales; modern teleosts have cycloid or ctenoid scales, or both.
Scaleless teleosts develop abortive embryonic scales.

Scales are absent.
Abundant epidermal multicellular mucous glands make the skin moist and slimy; granular glands abundant in toads.
Epidermis has incipient stratum corneum, except in toads where a layer of cornified cells impede dessication; cornified appendages rare, except in horny teeth of tadpoles.
Dermis is attached to underlying musculature, but anurans have abundant subcutaneous lymph sinuses.
Caecilians and a few tropical toads have tiny bone scales in the back.

Thick stratum corneum with variety of specialized cornified structures: scales, scutes, beaks, rattles, claws, plaques, and spiny crests, which maybe periodically shed by ecdysis .
Dry skin, with few integumentary glands: granular glands have protective or pheromonal secretions.
Dermis has bony deposits ranging from osteoderms to large bony plates with prominent cornified crests
(absent in snakes).

Epidermis and dermis are delicate membranes loosely attached to underlying muscles, making skin mobile, except on feet and head where scales, spurs, claws and horny beaks are found.
Integumentary glands are absent except for the uropygial gland at base of tail.
No osteoderms present, except the spur of dermal bone in male game fowls on each ankle, fused to the metatarsus.

Thickened epidermis consists of 3 strata: stratum corneum , stratum granulosum and mitotic stratum germinativum . The stratum lucidum is a 4 th layer present in epidermal soles and palms.

Epidermal glands have greater functional variety: sebaceous (secretions such as mammary glands), or sudoriferous (sweat glands).
Cornified structures include hair (modified into bristles, vibrissae, quills), scales, claws, horns.
Dermis is thicker than epidermis due to presence of many hair follicles, erector muscles, glands, supportive CT, encapsulated sensory nerve endings and greater vascularity.
Skin is separated from underlying muscle by loose CT called superficial fascia, with adipose

Care for the mammalian integument: a multibillion-$ industry !