Integument

Integument presentation

1. Comparative Anatomy of Vertebrates Integument and its derivatives 1 By- Sanju Sah St. Xavier’s college, Maitighar , Kathmandu Department of Microbiology

2. 2 Integument  Integument : The skin and its derivatives  S k i n : Ex t e r n al b o d y c o v eri n g , c o n t i n u o u s w i t h t h e m u c u s e y e - membrane lining of buccal cavity, rectum, eyelids, conjunctiva and urinogenital duct.  Barrier between external and internal environment .  T h e t ype o f e x t e r n al e n vi r o n me n t w h e t h e r a q u a t ic or terrestrial, influences the characters of skin.  Evolution of vertebrate integument is correlated with the transition of vertebrates from aquatic to terrestrial environment.

3. General structure of Integument Vertebrate skin bears 2 layers: Epidermis and Dermis . Relative abundance of two layers depends on environment. Epidermis and dermis are closely united but differ greatly in their nature and origin. 3 VS of skin of a Mammal

4. Epidermis: It is the outer layer; derived from embryonic ectoderm. It is stratified squamous epithelium (multilayered). Lowermost layer resting on basement membrane is a layer of columnar living cells called Stratum germinativum or stratum Malpighi. Cells of stratum germinativum divide mitotically forming upper layers. O u t e r region o f m a n y l a y e r s of f l a t tened ( s qu amo us ) k e r a t ini z e d cells is stratum corneum. Keratin: a kind of tough, insoluble and waterproof protein. Keratinization: r e p l a c em e n t of cellular cytoplasm by keratin. 4

5. 5 Epidermis (Contd.) Stratum corneum provides protection against mechanical and chemical injuries, fungal/bacterial infection and loss of body moisture. Cells of stratum corneum are periodically moulted. It is thin, bearing mucous glands in aquatic vertebrates. It is thicker in terrestrial vertebrates with scales, feathers, hairs, nails, claws, horns etc. Epidermis is separated from dermis by a thin and noncellular bilayered basement membrane made of glycoproteinous substance (2 layers- basal lamina + reticular lamina).

6. 6 Dermis/Corium: It is thicker. It bears fibrous connective tissue, blood vessels, lymph vessels, nerve fibres, sensory corpuscles, white collagen fibres and yellow elastic fibres. I t al s o b e a r s s o m e b r a n c h e d / s t e l l a t e c ells c alled Chromatophores. Chromatophores are of three types: : contain brown to black melanin. Lipophores / Xanthophores : contain yellow-red fatty pigment. I r i d oc y t e s / Gua n o p h o r e s : c o n t ain c r y s t als o f gua n i n e w h i c h refract light.

7. Skin is attached with underlying muscles by areolar tissue (hypodermis). Evolutionary trend of skin : in anamnia : decrease in thickness allowing greater mobility and in amphibians permit cutaneous respiration also. in amniotes : progressively thicker (the largest organ in mammalian body) to prevent loss of water and to retain the body heat. 7

8. 8 Major Functions of Integument 1. Protection Against mechanical and chemical injuries Against loss of moisture Against bacterial/fungal infection Spine, claws, nails, hooves, horns etc. serve for offence and defense. Protective colouration serves to escape from enemies. Against solar radiation. 2. Secretion Mucous glands, poison glands, uropygial glands in birds, sebaceous glands, sweat glands, scent glands, mammary glands, lacrymal glands, ceruminous glands etc.

9. 9 Major Functions of Integument 3. Thermal regulation Fur, feathers, scales etc insulate and conserve body heat in cold climate. Sweat glands provide cooling by evaporation. For loss of heat- dermal blood vessels dilate, increase blood flow. Skin becomes radiator of heat and rate of perspiration also increases. For the conservation of heat- dermal blood vessels constrict. 4. Locomotion Fin rays of fishes; webs of frogs, turtles, aquatic birds etc. Adhesive pads, claws, digits etc on climbing and feathers of wings, patagia on flying.

10. 10 Major Functions of Integument 5 . Excretion Excess of water, salts and urea- eliminated in sweat. Gills of marines fishes bear chloride secreting cells. During ec d y si s, s h e dd i n g o f s k in al s o g e t s rid o f f s o me metabolic wastes. 6. Storage Stores fat in blubber of whales and seals Fat is stored in subcutaneous fatty layer of the animals prior to hibernation and aestivation. Fat deposit on the hypodermis also helps in insulation and acts as cushion.

11. 11 Major Functions of Integument Sensation : skin bears sensory corpuscles sensitive to touch, pain, pressure, temperature, moisture, chemicals etc. Sexual selection : brilliantly coloured feathers, skin, antlers etc lead to sexual dimorphism and serve to attract opposite sex for mating. Synthesis : of Vitamin D in mammals. Cutaneous respiration in amphibians. P a r e n t al c a r e : b r o o d p o u c h es u n d er th e s k in o f some f ishes and amphibians protect unhatched eggs.

12. 12 Derivatives of Integument Epidermal glands, Epidermal scales and scutes, dermal scales and scutes, digital cornifications, horns, feathers and hairs. A. Epidermal glands: Formed from Malpighian layer of epidermis often invade the dermis. They may be unicellular or multicellular; tubular or alveolar in shape and simple or compound (branched). Bear cuboidal or columnar secreting cells. 9 ma j o r t y p es- m u c o u s , p ois on , l u mi n esc e n t , f e m o r al, uropygial, sweat, sebaceous, scent and mammary glands.

13. Derivatives of Integument Mucous glands : unicellular (fishes) or multicellular, secrete mucin, forms slimy and sticky mucus when mixed in water. Mucus keeps the skin moist, slippery and protects against the bacteria and fungi. Abundant in fishes and amphibian skin. Poison glands : in many fishes and amphibians, secreting bitter and irritating secretions. Parotoid glands of toad are aggregations of poison glands. Mucus gland 13

14. Derivatives of Integument iii) Luminescent glands/photophores : in deep sea luminous bony fishes, m u c o u s some multicellular glands emitting light. Superficial c ells f o rm mag n i f y i n g le n s , b as a l p a rt b e a r s luminescent cells surrounded below by reflecting pigment cells. It serves to attract preys. iv) Femoral glands : Only the skin glands present in some male lizards. Present on ventral surface of thigh secreting sticky substance that serves to hold the female during copulation. 14

15. Derivatives of Integument v ) U r o p y gial integumentary glands : gl a nd s O n ly t h e f o un d in b i r d s , p r es e n t as a p r o m i n e n t s w elli n g j u s t a b o v e th e t ai l / u r o p y g i u m . I t is t h e b r a n c h ed gla n d for secreting lubricating o ily beak, alveolar s ub s t a n c e preening f e a th e r s and attracting opposite sex. 15

16. Derivatives of Integument vi) Sweat glands/ Sudoriferous glands: simple coiled tubular glands on skin of mammals only. Little urea and some salts dissolved in water are eliminated as sweat. It also helps in thermal regulation. Absent in scaly and spiny anteaters and marine mammals. Distribution restricted in some: only on soles of feet ( cats and mice), lips (rabbit), muzzle and between toes (Ruminants), sides of head (bats), ears (hippopotamus). vii) Sebaceous glands: are branched alveolar glands opening into hair follicles of mammals. They secrete oily substance sebum for lubrication of hair and skin. C e ru mi n o u s glands of external ear canals are modified sebaceous glands secreting cerumen/ear wax. Meibomian gla n d s o f e y eli d s sec r e t i n g oil y s ub s t a n c e a r e modified sebaceous glands. 16

17. Derivatives of Integument viii) Scent glands: modified sweat or sebaceous glands of mammals. They are used to repel or attract members of opposite sex, maintain territory, signal for other members etc. May occur between the digits /interdigital glands (goat, rhino etc), near eyes on head / preorbital glands (deer family), navel on abdomen (musk deer), around anus / perianal glands (many carnivores and rodents). 17

18. Derivatives of Integument ix) Mammary glands : are compound tubular glands that produce milk during lactation period. In monotremes (egg laying mammals), mammary glands lack nipples or teats and are modified sweat glands. In other mammals, they possess nipples and are modified sebaceous glands. Distribution and number of mammary glands and nipples vary with species (2 in many mammals to 25 in Opossum). 18

19. Derivatives of Integument B. Dermal Scales and Scutes Develop from dermis and hence mesodermal in origin. The bony dermal scales are not shed but increase in size during life. Present in fishes and some reptiles and mammals. i. Dermal scales of fishes The overlying epidermis wears off, so dermal scales are exposed forming exoskeleton. Cosmoid scales occurred in extinct lobe-finned fishes (crossopterygii), Placoid scales in Chondrichthyes; Ganoid scales in ganoid fishes (chondrostei and holostei); Cycloid and Ctenoid scales in modern teleosts. ii. Dermal scales a n d s c u t es of tetrapods : d e r m a l s c al e s or o s t e o d e r ms a r e p r ese n t i n s o m e A p o d a (Amphibia), li z a r d s , c r o c o d iles a n d alligators (Reptiles); s o me arma d o l lis a n d whales (mammals). 19

20. Types of Scales in fishes Development of Dermal Scales Labeo rohita (Rohu) 20

21. 21 Derivatives of Integument C. Epidermal Scales and Scutes After evolutionary loss of dermal scales of fishes, amniotes develop scales formed from epidermis. Epidermal scales appear for the first time in Reptiles. They are cornified derivatives of the Malpighian layer and are generally shed and replaced. Reptiles have continuous outer covering of horny epidermal scales. Snakes and lizards (squamatans) have thin, small and overlapping scales which are periodically moulted. Crocodilians and turtles have large and thick scutes, not overlapping but touching each other and supported by underlying dermal bones.

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23. Derivatives of Integument In birds, small epidermal scales are present on the shank, foot and base of beak. The sheath of beak is also modification of stratum corneum. Some mammals like rat and beavers bear scales on tail and foot. Scaly anteaters bear large scales which undergo ecdysis. 23

24. Derivatives of Integument D. Digital cornifications: Claws, nails and hoofs are modifications of stratum corneum at the tips of digits and all are made in the same plan. i. Claws : made their appearance first in reptiles. A claw bears hard, pointed curved, horny dorsal plate called Unguis and relatively soft ventral plate called subunguis; both enclosing the tip of the digit covering the last phalanx. 24

25. Derivatives of Integument ii. Nail In P r im a t es (m a mm a l s), claws are modified into nails. U n g u i s is b r oa d an d fl a t , subunguis is softer and much reduced. T he tip of the d i git f o r ms h i ghly sensiti v e an d v asc u l a r pad. Growth of the unguis takes place from the nail root lying below the skin in nail groove. 25

26. Derivatives of Integument iii. Hoofs H o o f s a r e mo d i f ied c la w s a n d are characteristics of ungulates. Ung u is is U o r V - s h a p e d , t h i c k a n d curved around the end of the digit. S ub u n guis is g r e a t l y th i c k e n e d touching the ground. S u b u n g u is s u r r o u nd s a s o f t e r h o r n y substance, the cuneus. 26

27. E. Horns Present only in hoofed mammals (even hoofed- artiodactyla and uneven hoofed –perissodactyla). They are the product of stratum corneum and present on head forming organ of offense and defense. i. True Horns : In Bovidae (goat, sheep, cattles), true or hollow horns are present. They are unbranched, cylindrical and tapering. Bears hollow dermal bony core arising from frontal bone of skull and covered by epidermal horny hollow cap. Permanent structures, grow throughout the life and are never shed. ii. Prong horns : True horns, horny epidermal sheath bears 1 to 3 branches (prongs) which are shed annually. Present in Russian antelope ( Antilocapra ). 27

28. Derivatives of Integument iii. Antlers: Characteristics of Family- Cervidae (deer family). Present only in male, except in reindeer and caribou. They are shed annually. Bears solid outgrowth of dense connective tissue with Calcium deposition connected to the frontal bone. During growth, it is covered with hairy and vascular skin- the velvet. When growth is complete, the velvet wears off. After the breeding season, the antlers are also shed and new antlers develop the following year. Its formation is controlled by the hormones of testes and anterior lobe of pituitary gland. 28

29. Derivatives of Integument iv. Giraffe horns: They are short, unbranched and permanent antlers present in both sexes. E ach c o n si s t s o f d e r m al c o r e c o v e re d by sim p le h airy s k in o r v el v e t w h i c h is n e v er shed. v. Hair /Rhino /keratin fibre horns: Present on both the sexes of Rhinoceros, perched upon roughened area of nasal bone. They are made of thick hairy and keratinized epidermal fibres fused together. Th e y a r e p er m a n e n t s t r u c tu r es, if b r o k en grow again. Asian Rhino has single horn, while African species has two horns; one behind the other. 29

30. It is in threat for its skin derivative – the horn 30

31. Derivatives of Integument F. Feathers / Plumage: Present only in birds. They are dry, nonliving and cornified light weight, elastic and waterproof products of stratum corneum of epidermis. They show different colours due to presence of pigments of various shades and structural arrangement. Development is similar to that of scales and are moulted and replaced seasonally. 31 Types of Feathers: major 3 types iii. i. Contour feathers: Quills are larger present on wings (remiges) and tail (retrices). Coverts are smaller and cover the body. ii. Down feather: very small having barbs with barbules. Filoplumes: delicate, hairlike feathers with long slender stalk and terminal barbs.

32. Derivatives of Integument G. Hairs/ Pelage: Characteristics of mammals. C o v er th e en t ir e a n imals), reduced b o d y ( f u r r e d t o p a t c h es (human) and scattered (whales). T h e y are also the cornified epidermal products of integument. Each hair originates from a tubular i n v agi n a t i o n o f s t r a tu m germinativum of epidermis (hair follicle) into dermis. Hair papilla contains blood vessels and nerves, nourishes the root and adds new cells forming the shaft. 32

33. Derivatives of Integument 33 • The hair shaft consists of three layers: Cuticle made of overlapping scales, cortex containing pigment cells and medulla containing air spaces. • The involuntary pilli ” muscle is “ Arrector associated with each hair follicle. Hairs serve for insulation and as sensitive tactile organs (vibrissae).

34. Integument in Vertebrates 1. Cyclostomata Skin consists of epidermis and dermis. Epidermis is multilayered and non-keratinized. Epidermis consists of three types of secretory cells or unicellular glands: mucous cells secrete slime, elongated club cells are probably neural or scab forming and granular cells are of unknown function. 34 Dermis consists of cutis with white collagen fibres and yellow elastic fibres and it also bears melanocytes or pigment cells which can migrate and change the colour dark or pale. Scales are absent. A layer of subcutaneous tissue contains blood vessels, fat and connective tissue. V.S. of Skin of Cyclostome

35. Integument in Vertebrates (Contd.) 2. Fishes : Epidermis has several layers of cells; typical stratum corneum (with keratinized cells) is absent. It bears unicellular goblet cells / mucus gland cells secreting mucus. Mucus makes skin slimy reducing friction, protects skin from bacterial and fungal infection and assists in control of osmosis. Some multicellular glands are present, mostly in Dipnoi. D e r mis c o n t a i n s c o nn ec t i v e t issue, b l o o d v esse l s , l y m p h vessels, nerves, muscles and collagen fibres. Collagen fibres run parallel to the surface. Dermis bears dermal scales. 35

36. Elasmobranchs have placoid scales, Chondrostei and Holostei have ganoid scales and Teleostei have Leptoid (cycloid and ctenoid)scales. Many bony fishes show brilliant colours due to chromatophores and iridocytes with guanin in dermis; which causes iridescence. The uses of colours are : Cryptic for concealing Sematic for warning Epigamic or sex colour mostly found in males, more brilliant during breeding season. 36 V.S. of Skin of Elasmobranch V.S. of skin of Teleost

37. 3. Amphibia: Integument is thin and less intimately attached to underlying muscles due to large number of subcutaneous lymph spaces. No exoskeleton. Epidermis is many layered. Outermost layer is Stratum corneum, protects and prevents loss of moisture. It is constantly moulted under the control of pituitary and thyroid glands. Large number of multicellular glands are present. Mucus glands secrete mucus that keeps the skin moist for cutaneous respiration. Cutaneous poison glands secrete toxic secretion that serves to ward off enemies. 37

38. Dermis bears two layers: outer loose stratum spongiosum and inner compact and dense stratum compactum. Chromatophores occur in stratum spongiosum of dermis. Collagen fibres run both vertically and horizontally. Extinct Labyrinthodontia beared dermal scales. Living Amphibians have no exoskeleton. Apoda/Gymnophiona like Ichthyophis bear dermal plates on dermis. V.S. of Skin of Ichthyophis 38

39. 4. Reptiles: Integument is thick and dry with almost no skin glands to prevent evaporation of water. Stratum corneum is well developed, thicker that makes skin dry. It is variously modified into overlapping scales, spines, scutes, shields, plates, claws, rattles etc. forming exoskeleton. Exoskeleton is periodically shed – ecdysis or moulting. Squamatans have overlapping epidermal scales while Crocodolians and Chelonians have non- overlapping scales and their dermis also bears b o n y d ermal p l a t es c alled osteoderms. 39 V.S. of Skin of Lizards

40. Reptiles have relatively few or almost no skin glands except scent glands for sexual attarction near cloaca of some snakes, femoral glands on thigh of some lizards and musk glands of musk turtles and alligators. Dermis bears chromatophores on upper layer by which some lizards and snakes exhibit elaborate colour patterns. Lower layer of dermis has collagen fibres which lie at right angles. 40

41. 41 5. Birds: Integument is thin and loosely attached to achieve maximum freedom of movement for flight. It is dry and devoid of skin glands except Uropygial or preen gland on tail which is well developed in aquatic birds. Oily or waxy secretion of preen gland is used for preening feathers and prevents beak from being brittle. Epidermis is stratified and delicate except on shank and feet. Stratum corneum is modified into feathers, scales, claws, spurs and sheaths of beak. Claws are restricted to toes, may also occur on one or two fingers in flightless birds.

42. Epidermal feathers form protective body coverings. They are of three major types: Contour, down and filoplumes. D e r mis is th i n w i t h i nt e r lac i n g c o nn e c t i v e t issue f i b r es, abundant muscle fibres for moving the feathers, blood vessels and nerves. Dermis bears upper spongy vascular layer and lower compact layer. Skin of birds has no chromatophores. Melanocytes with pigment occur only in feathers and scales. Body colours are mainly due to reflection and refraction of light from feathers. V.S. of skin of bird 42

43. 6. Mammals: Mammalian skin is elastic, water proof and thickest of all vertebrates, especially the dermis is very thick and tough. Epidermis and dermis have reached the highest degree of specialization in mammals. Epidermis is thick and differentiated into 5 layers, from outside: Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum germinativum / Malpighi 43 Section of Epidermis in mammals

44. Modifications of stratum corneum include epidermal scales, hairs, bristles, claws, nails, hoofs, horns etc. Based on functions, 5 major types of multicellular glands are present: sweat, sebaceous, mammary, lacrimal and scent glands. Mucous glands are absent in epidermis. Melanocytes are the branched stellate cells with pigments present in between the cells of stratum germinativum. Albinism results from the lack of pigments and melanism results from the presence of excess of black pigments. V.S. of skin of mammals 44

45. Dermis consists of connective tissue, blood vessels, nerve fibres, sensory corpuscles, glands, fat cells and unstriated muscles. Hairs are present. Hair shaft is projected above, hair root is embedded in hair follicle of dermis. Blood vessles and nerves project into the hair at hair papilla. Hair follicle is connected to the dermis by arrector pilli muscles regulating the movement of hairs. Hair colour is due to the varying intensities of brown or black pigment 45 granules between and within the hair cells of hair cortex. L.S. of a hair