Integumentary System

Integumentary System

The integument, commonly called the skin with all its derivatives, is the outer covering of the body. Inserted betweenthe internal and external environment of the animal, performs a great variety of functions and gives rise to such diversestructures as shell, arthropod cuticle, scutes, hair, feathers, and horn.

•covering and protection from mechanical injury and entrance of foreign materials; protective coloration; protection against ultraviolet radiation

•secretion (cutaneous glands); release of repelling or attracting secretions

•excretion of metabolic wastes (cutaneous glands)

•sensation (due to the presence of nerve endings and tactile cells)

•respiration – frogs use the skin, which is highly impregnated with blood vessels, as an accessory organ or respiration

•absorption – in the frog, the stratum corneum is thin and thus easily allow entrance of water

•regulation of body temperature – applicable only to homoiothermic animalshomoiothermous animals – warm-blooded animals or those with a regulated body temperature because of their heat-

conserving body (Aves and Mammalia)Poikilothermous animals – cold-blooded animals whose body temperature closely follows that of their environment

•pigments function in concealment, warming and recognition

Functions of the integument:

Invertebrate Integument

•with firm elastic pellicle(Paramecium)

Protozoans

•covered by delicate cell membrane(Amoeba)

•Soft-bodied aquatic invertebrate/ those of moist environments on land ex. cnidarians, flatworms and slugs epidermis is made up of a single layer of cells.

multicellular invertebrate animals are provided with a tissue, the single layer epidermis.



Annelida (earthworm) – epidermis contains a delicate non-cellularcuticle secreted by the epidermis as an additional covering

•Platyhelminthes (flukes and tapeworm) and Nemahelminthes (Ascaris) – epidermis contains a resistant cuticle


•Characterized by a jointed chitinous exoskeleton and jointed legs•Examples are crabs, scorpions, crustaceans and insects

Arthropods


Arthropod Integument

-For protection and support-The exoskeleton, which is secreted by the epidermis, functions both as a point of attachment for muscles and as a protective armor, but it imposes limitations on growth and must be periodically molted if the animal is to undergo much increase in size.

Consists of single-layered epidermis

Secretes a complex cuticle of two zones.

procuticle

-Thicker inner zone-Composed of chitin

(polysaccharide)

epicuticle

-Thin outer zone-External surface above

procuticle-Nonchitinous complex of proteins & lipids



Decapod crustaceans:

Cuticle is stiffened by calcification Deposition of calcium carbonate in the outer layers of procuticle



Insect hardening occurs, When protein molecules bond together w/ stabilizing cross-linkages w/in & between adjacent lamellae of the procuticle.

sclerotization Formation of a highly resistant & insoluble protein sclerotin

When arthropods molts,

-epidermal cells first divide by mitosis-digested materials are then absorbed & consequentlynot lost to the body-in space beneath old cuticle, a new epicuticle &procuticle are formed-After old cuticle sheds, new cuticle thickened &calcified or sclerotized


The vertebrate integument consists of two principal parts, the epidermis and dermis

Vertebrate Integument

•Dermis (true skin)1.the inner, thicker layer of the skin2.made up mostly of connective tissue fibers, smooth muscles, blood vessels and sensory nerve endings, especiallytactile corpuscles (specialized nerve endings that respond to tactile, thermal and pain stimuli)3.mesodermal in origin (dermatome, epimere)4.dermal derivatives of the skin – scales of fishes, antlers (horns of deer).

•Epidermis1.the outer, thinner but stratified layer of the skin2.consists primarily of cells3.ectodermal in origin4.epidermal derivatives – hair, nails, claws, scutes, hoofs, beaks and bills, horny scales (reptiles and birds), feathers,spines, enamel of the teeth, glands, horns (hollow and true horns of ruminants)


This epidermal layer becomes especially thick in areas exposed to persistent pressure or wear such as calluses,foot pads of mammals, and the scales of reptiles and birds.


The epidermis is a stratified squamous epithelium, consisting usually of several layers of cells.

The basal part is made up of cells that undergo frequent mitosis to renew layers that lie above.

As outer layers of cells are displaced upward by new generations of cells beneath, an exceedingly tough, fibrousprotein called keratin accumulates in the interior of the cells.

Gradually, keratin replaces all metabolically active cytoplasm. The cell dies and is eventually shed.

This process is called keratinization, and the cell, thus transformed, is said to be cornified.

Cornified cells, highly resistant to abrasion and water diffusion, comprise the outermost stratum corneum.



The dermis mainly serves a supportive role for the epidermis.

Most amphibians lack dermal bones in theirskin, whereas in reptiles dermal bonesprovide the armor of crocodilians, the beadedskin appearance of many lizards, and alsocontribute to the shell of turtles.

Bony (teleost) fishes have bony scales fromdermis, and lizards have horny scales fromepidermis. Dermal scales of fishes are retainedthroughout life. Epidermal scales of reptilesare shed periodically.


Their basic structure is the same, with a central bonycore covered by a vascularized nutritive layer of thedermis, and an outer epithelial layer.

Dermal bone also gives rise to antlers, as well as thebony core of horns. Structures such as claws, beaks,nails, and horns are made up of combinations ofepidermal (keratinized) and dermal components.

This epithelial layer has a germinative componentresponsible for the continual growth of horns, hooves,claws, and beaks.

The outer epithelial layer is keratinized.


•photophores – connective tissue cells which make the animal luminous (deep sea sharks)

Other structures present in the skin

chromatophores and pigments glands

Chromatophores

–specialized connective tissue cells which contain pigments

Types of chromatophores depending upon the pigments present

•melanophores – connective tissue cell which contain black or brown pigments (melanin)

•lipophores – connective tissue cells which contain red and yellow pigments

•erythrophores – contain red pigments (erythrocin)

•xanthophores – contain yellow pigments (xanthin)

•guanophores – connective tissue cells which contain a colorless, white crystalline material (guanin) which makesanimal iridescent (fishes)

Types of glands according to the type of secretion•serous gland – watery, thin film of secretion; protein rich product (sweat gland)•oily gland – oily, thick secretion; lipid secretion (oil gland)•mucous gland – slippery secretion due to mucin; carbohydrate rich (mucous gland)

Types of glands according to structure•unicellular glands – one-celled glands (lingual glands)•multicellular glands – many-celled glands (mucous glands)

Types of glands according to the method of secretion•merocrine gland (true gland) – the glandular cells merely produce the secretion and no part of the cell goes togetherwith the secretion; the cell then remains intact or is not destroyed in the process of secretion (sudoriferous or sweatgland)•apocrine gland – the secretion gathers at the tip of the gland, then a portion of the cytoplasm of the cell producingthe secretion is chipped off and goes together with the secretion (mammary gland)• holocrine gland – the entire cell which produces the secretion goes together with the secretion so that new cells areconstantly produced to replace the lost cells (sebaceous glands; sebum- lubricate skin & hair)

Glands

merocrine gland

apocrine gland holocrine gland

•epidermis is thin and glandular and closely applied to scales embedded in the dermis

•glands secrete a mucus that coats the body and protects against disease and injury

•on sharks and rays the scales are covered with enamel and project through the skin

•such scales in the mouth region probably gave rise to the first vertebrate teeth

Brief description of vertebrate skin

Fishes

Amphibians•its skin is glandular and moist; thin and naked•for respiration and absorption

Land vertebrates (amphibians, reptiles birds and mammals)

have a stratified epidermis of several cell layers with the outermost portion cornified.


Reptiles• skin is very much thicker (especially the epidermis) and is provided with exoskeletal structures like scales,scutes and plates (for protection and preservation of the loss of body fluids)• it is thickened into scales, sometimes underlaid with bony scutes• reptile-like scales are also found on the legs of birds and tails of rodents

Reptiles, birds and mammals• the cornified part is dry and tougher, more resistant to abrasion and water loss


Birds• skin is thin, loose and covered withexoskeletal structures like feathers, scales,claws and beak or bill (serve as bodycovering, insulation, protection and forflight)

• covered with feathers (nonliving cornifiedproducts of the epidermis that conservebody heat, protect against abrasion, smoothcontours, and provide streamlining)

• feathers form the broad surfaces of wingsand tail in flight


•The human skin resembles that of other mammals but isscantily haired and thin in most parts.

•skin of mammals contain sweat glands, important in coolingthe body, and sebaceous glands, which secrete a fatty, oilysubstance that keeps the skin and hair pliable and reduces therate of evaporation of water

Mammals

•in many mammals fat deposits in the dermis furthercontribute to insulation.

•Pigment scattered throughout the skin, being concentrated inthe epidermis in mammals.


THE HUMAN SKIN Considered as the largest organ

Functions

Skin is a tough, elastic material that prevents rapid evaporation of water from our bodies. Itprevents our inner tissues from completely drying up.

Summary of functions•covers the body and protects deeper tissues from drying and injury•protects from invasion of infectious microorganisms•temperature regulation•acts as an accessory mechanism for tactile and pressure corpuscles•excretory function, eliminating water with the various salts that compose perspiration, and the deadcells themselves become an important way of eliminating salts•important light screen for the underlying living cells absorbing powers:; absorb oily materials placedin contact with

The skin consists of two distinct layers•epidermis, cuticle•dermis, corium or cutis vera

PARTS OF THE SKIN

•five regions of the epidermis:1.Stratum corneum – horny or outer layer2.Stratum lucidum – clear or translucent layer3.Stratum granulosum – granular layer4.Stratum spinosum – prickle cell layer5.Stratum germinativum – germinal or basal layer

Epidermis (Epi = upon + dermis = skin)

•The epidermis (cuticle) is stratified squamous epithelium. It varies in thickness in different parts of the body,being thickest in the palms of the hands and soles of the feet and thinnest on the ventral surface of the trunk andinner surfaces of the limbs.

•It forms a protective covering on every part of the true skin and is closely molded on the papillary layer of thecorium

•Devoid of blood vessels

•The three outer layers consists of cells that are constantlybeing shed and renewed from the cells of the stratumgerminativum

•cells then pass various phases ofdegeneration and eventually becomescales and are rubbed off

Stratum germinativum

•a layer of columnar cells that formsthe deepest part of the epidermis

•cells contain a pigment thatdetermines the darkness of the skin

•growth of the epidermis is bymultiplication of the cells of thegerminative layer

•cells divide to form daughter cellscontinually and newly-formed cellspush the more mature cells towardsthe surface


•variable thickness and composedof irregularly (many-sided) shapedcells

Stratum spinosum

•live cells and represent maturegerminal cells

•called prickle-cell layer becausethe surface of the cells is coveredwith short cytoplasmic spines orprojections


•cells are in transition between s.germinativum and the horny cellsto the superficial layers

Stratum granulosum

•cells with granules whichrepresents an early stage ofdegeneration


• cells have lost their nuclei andcellular outlines due to thedegenerative process

Stratum lucidum


•the reaction is acid and manykinds of organisms, whenplaced upon the skin aredestroyed, presumably by theeffect of the acidity

Stratum corneum

•protoplasm of the cell hasbecome changed into a proteincalled keratin, which acts as awaterproof covering


•Highly sensitive and containsnumerous blood vessels, nervesglands, hair follicles and papillae

Dermis

•Corium or true skin which liesunderneath the epidermis andcomposed of loose connectivetissues with fibrous and elastic tissuefiber in between. Due to the fibersdermis is flexible and elastic.

•Fat cells may be present, blood andlymph capillaries pass freely throughthe dermis but very few nerveendings penetrate into the epidermis

Two layers of the dermis

1. Papillary or superficial layer

•lies next to the epidermis

•layer is increased by small conicalelevations called papillae.

•the cells of the germinal layer of theepidermis fit into these papillae andhollows in between them. Thisresults in ridges on the skin surface-utilized in fingerprinting procedures.

Dermis

Two layers of the dermis

2. Reticular or deeper layer

•attached to the parts beneath by asubcutaneous loose connectivetissue

•consists of strong bands of fibroustissue and some fibers of elastictissue. These bands interlace, andthe tiny spaces formed by theirinterlacement are occupied byadipose tissue and sweat glands.

Dermis

APPENDAGES OF THE SKINNails/Ungues

•are composed of clear, horny cells of the epidermis, joined so as to form a solidcontinuous plate upon the dorsal surface of the phalanges.

•each nail is closely adherent to the underlying corium, which is modified to form what iscalled bed or matrix

•the body of the nail is the part that is visible (shown)•the hidden part is the nail groove also called as the nail root•the lunule/lunula is the crescent shaped white area that can be seen on the part nearest the root.

•the nails appear pink except the lunulebecause the blood in the capillary bedshows through it

•the eponychium is the outer horny layerof epidermis at the base of the nail thattends to grow out over the nail body

Hairs

•the hairs or pili are growths of the epidermis,developed in the hair follicles.

•hair follicle or hair shaft is a small canalopening upon the skin surface and extendingdown into the dermis.

•the part that lies within the follicle is knownas the root, and that portion which projectsbeyond the surface of the skin is called theshaft.

•root of hair is enlarged at the bottom of the follicle into a bulb.

•hair has no blood vessels but receives nourishment from the blood vessels.

APPENDAGES OF THE SKIN

Arrector (Arrectores Pilorum) Muscles

•connected with each follicle are smallbundles of involuntary muscles called arrectormuscles

•they arise from the papillary layer of thecorium and are inserted into the hair folliclebelow the entrance of the duct of a sebaceousgland

•these muscles are situated on the side towardwhich the hairs slope and when they contractunder the influence of cold and fright, theystraighten the follicles and elevate the hairs,producing the roughened condition of the skinknown as “gooseflesh”


Glands of the Skin

Sebaceous glands

•small secreting glands that lie beside andopen into hair follicles.

•each gland consists of a secreting part, analveolus, that leads into a central canal (orduct). This duct leads into a follicle.

•these occur everywhere over the skin surfacewith the exception of the palms of the handsand soles of the feet

•abundant in the scalp and face and arenumerous around the apertures of the nose,mouth, external ears and anus


•sebum serves to protect the hairs frombecoming too dry and brittle, as well as frombecoming too easily saturated with moisture

Glands of the Skin

Sebaceous glands


•sebum is the secretion of the sebaceousglands. It contains fats, cholesterol,albuminous material, remnants of epithelialcells and inorganic salts

•largest sebaceous glands are found on thenose and other parts of the face. giving risk tothe condition commonly known as blackheads,pimples.

Glands of the Skin

Sudoriferous glands

•abundant over the whole skin but are largest and mostnumerous in the axillae, the palms of the hands the solesof the feet and the forehead

•simple tubelike glands consisting of asingle canal or duct, and a coiledsecreting part. The duct opens upon theskin surface and has a layer of epithelialcells surrounding its canal

•each gland consists of a single tube, with ablind, coiled end that is lodged in thesubcutaneous tissue. The coiled end, thetube is continued as the excretory duct ofthe gland up through the corium andepidermis and finally opens on the surfaceby a pore


•perspiration or sweat contains the sameinorganic constituents as the blood but inlower concentration with the chief salt ofsodium chloride

Glands of the Skin

Sudoriferous glands

•under ordinary circumstances, theperspiration that the body is continuallythrowing off evaporates from the surface ofthe body without one’s becoming aware of itand is called insensible perspiration

•when more sweat is poured upon the surfaceof the body that can be removed at once byevaporation, it appears on the skin in the formof drops and is then spoken of a sensibleperspiration


Ceruminous glands

•skin lining the auditory canal containsmodified sweat glands which secrete a yellow,pasty substance resembling wax which is calledcerumen

•an accumulation of cerumen deep in theauditory canal may interfere with hearing


Integumentary System

Science

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