Integumentary System


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Bio 102: Fundamentals in Animal Biology. The Integumentary system: skin, horns, nails, etc.

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Integumentary System

  1. 1. Integumentary System
  2. 2. Integumentary System The integument, commonly called the skin with all its derivatives, is the outer covering of the body. Inserted between the internal and external environment of the animal, performs a great variety of functions and gives rise to such diverse structures as shell, arthropod cuticle, scutes, hair, feathers, and horn.
  3. 3. •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 animals homoiothermous 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:
  4. 4. Invertebrate Integument •with firm elastic pellicle (Paramecium) Protozoans •covered by delicate cell membrane (Amoeba)
  5. 5. •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. Invertebrate Integument
  6. 6. Invertebrate Integument Annelida (earthworm) – epidermis contains a delicate non-cellular cuticle secreted by the epidermis as an additional covering •Platyhelminthes (flukes and tapeworm) and Nemahelminthes (Ascaris) – epidermis contains a resistant cuticle Invertebrate Integument
  7. 7. •Characterized by a jointed chitinous exoskeleton and jointed legs •Examples are crabs, scorpions, crustaceans and insects Arthropods Invertebrate Integument
  8. 8. 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 Invertebrate Integument
  9. 9. Arthropod Integument Decapod crustaceans: Cuticle is stiffened by calcification Deposition of calcium carbonate in the outer layers of procuticle Invertebrate Integument
  10. 10. Arthropod Integument 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 & consequently not 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 Invertebrate Integument
  11. 11. The vertebrate integument consists of two principal parts, the epidermis and dermis Vertebrate Integument
  12. 12. •Dermis (true skin) 1.the inner, thicker layer of the skin 2.made up mostly of connective tissue fibers, smooth muscles, blood vessels and sensory nerve endings, especially tactile 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). •Epidermis 1.the outer, thinner but stratified layer of the skin 2.consists primarily of cells 3.ectodermal in origin 4.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) Vertebrate Integument
  13. 13. 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. Vertebrate Integument 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, fibrous protein 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. Vertebrate Integument
  14. 14. Vertebrate Integument The dermis mainly serves a supportive role for the epidermis. Most amphibians lack dermal bones in their skin, whereas in reptiles dermal bones provide the armor of crocodilians, the beaded skin appearance of many lizards, and also contribute to the shell of turtles. Bony (teleost) fishes have bony scales from dermis, and lizards have horny scales from epidermis. Dermal scales of fishes are retained throughout life. Epidermal scales of reptiles are shed periodically. Vertebrate Integument
  15. 15. Their basic structure is the same, with a central bony core covered by a vascularized nutritive layer of the dermis, and an outer epithelial layer. Dermal bone also gives rise to antlers, as well as the bony core of horns. Structures such as claws, beaks, nails, and horns are made up of combinations of epidermal (keratinized) and dermal components. This epithelial layer has a germinative component responsible for the continual growth of horns, hooves, claws, and beaks. The outer epithelial layer is keratinized. Vertebrate Integument
  16. 16. •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 makes animal iridescent (fishes)
  17. 17. 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 together with the secretion; the cell then remains intact or is not destroyed in the process of secretion (sudoriferous or sweat gland) •apocrine gland – the secretion gathers at the tip of the gland, then a portion of the cytoplasm of the cell producing the 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 are constantly produced to replace the lost cells (sebaceous glands; sebum- lubricate skin & hair) Glands
  18. 18. merocrine gland apocrine gland holocrine gland
  19. 19. •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
  20. 20. 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. Brief description of vertebrate skin
  21. 21. 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 Brief description of vertebrate skin
  22. 22. Birds • skin is thin, loose and covered with exoskeletal structures like feathers, scales, claws and beak or bill (serve as body covering, insulation, protection and for flight) • covered with feathers (nonliving cornified products of the epidermis that conserve body heat, protect against abrasion, smooth contours, and provide streamlining) • feathers form the broad surfaces of wings and tail in flight Brief description of vertebrate skin
  23. 23. •The human skin resembles that of other mammals but is scantily haired and thin in most parts. •skin of mammals contain sweat glands, important in cooling the body, and sebaceous glands, which secrete a fatty, oily substance that keeps the skin and hair pliable and reduces the rate of evaporation of water Mammals •in many mammals fat deposits in the dermis further contribute to insulation. •Pigment scattered throughout the skin, being concentrated in the epidermis in mammals. Brief description of vertebrate skin
  24. 24. THE HUMAN SKIN Considered as the largest organ Functions Skin is a tough, elastic material that prevents rapid evaporation of water from our bodies. It prevents 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 dead cells themselves become an important way of eliminating salts •important light screen for the underlying living cells absorbing powers:; absorb oily materials placed in contact with
  25. 25. The skin consists of two distinct layers •epidermis, cuticle •dermis, corium or cutis vera PARTS OF THE SKIN
  26. 26. •five regions of the epidermis: 1.Stratum corneum – horny or outer layer 2.Stratum lucidum – clear or translucent layer 3.Stratum granulosum – granular layer 4.Stratum spinosum – prickle cell layer 5.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 and inner 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 the corium •Devoid of blood vessels •The three outer layers consists of cells that are constantly being shed and renewed from the cells of the stratum germinativum
  27. 27. •cells then pass various phases of degeneration and eventually become scales and are rubbed off Stratum germinativum •a layer of columnar cells that forms the deepest part of the epidermis •cells contain a pigment that determines the darkness of the skin •growth of the epidermis is by multiplication of the cells of the germinative layer •cells divide to form daughter cells continually and newly-formed cells push the more mature cells towards the surface Epidermis (Epi = upon + dermis = skin)
  28. 28. •variable thickness and composed of irregularly (many-sided) shaped cells Stratum spinosum •live cells and represent mature germinal cells •called prickle-cell layer because the surface of the cells is covered with short cytoplasmic spines or projections Epidermis (Epi = upon + dermis = skin)
  29. 29. •cells are in transition between s. germinativum and the horny cells to the superficial layers Stratum granulosum •cells with granules which represents an early stage of degeneration Epidermis (Epi = upon + dermis = skin)
  30. 30. • cells have lost their nuclei and cellular outlines due to the degenerative process Stratum lucidum Epidermis (Epi = upon + dermis = skin)
  31. 31. •the reaction is acid and many kinds of organisms, when placed upon the skin are destroyed, presumably by the effect of the acidity Stratum corneum •protoplasm of the cell has become changed into a protein called keratin, which acts as a waterproof covering Epidermis (Epi = upon + dermis = skin)
  32. 32. •Highly sensitive and contains numerous blood vessels, nerves glands, hair follicles and papillae Dermis •Corium or true skin which lies underneath the epidermis and composed of loose connective tissues with fibrous and elastic tissue fiber in between. Due to the fibers dermis is flexible and elastic. •Fat cells may be present, blood and lymph capillaries pass freely through the dermis but very few nerve endings penetrate into the epidermis
  33. 33. Two layers of the dermis 1. Papillary or superficial layer •lies next to the epidermis •layer is increased by small conical elevations called papillae. •the cells of the germinal layer of the epidermis fit into these papillae and hollows in between them. This results in ridges on the skin surface- utilized in fingerprinting procedures. Dermis
  34. 34. Two layers of the dermis 2. Reticular or deeper layer •attached to the parts beneath by a subcutaneous loose connective tissue •consists of strong bands of fibrous tissue and some fibers of elastic tissue. These bands interlace, and the tiny spaces formed by their interlacement are occupied by adipose tissue and sweat glands. Dermis
  35. 35. APPENDAGES OF THE SKIN Nails/Ungues •are composed of clear, horny cells of the epidermis, joined so as to form a solid continuous plate upon the dorsal surface of the phalanges. •each nail is closely adherent to the underlying corium, which is modified to form what is called 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 lunule because the blood in the capillary bed shows through it •the eponychium is the outer horny layer of epidermis at the base of the nail that tends to grow out over the nail body
  36. 36. Hairs •the hairs or pili are growths of the epidermis, developed in the hair follicles. •hair follicle or hair shaft is a small canal opening upon the skin surface and extending down into the dermis. •the part that lies within the follicle is known as the root, and that portion which projects beyond the surface of the skin is called the shaft. •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
  37. 37. Arrector (Arrectores Pilorum) Muscles •connected with each follicle are small bundles of involuntary muscles called arrector muscles •they arise from the papillary layer of the corium and are inserted into the hair follicle below the entrance of the duct of a sebaceous gland •these muscles are situated on the side toward which the hairs slope and when they contract under the influence of cold and fright, they straighten the follicles and elevate the hairs, producing the roughened condition of the skin known as “gooseflesh” APPENDAGES OF THE SKIN
  38. 38. Glands of the Skin Sebaceous glands •small secreting glands that lie beside and open into hair follicles. •each gland consists of a secreting part, an alveolus, that leads into a central canal (or duct). This duct leads into a follicle. •these occur everywhere over the skin surface with the exception of the palms of the hands and soles of the feet •abundant in the scalp and face and are numerous around the apertures of the nose, mouth, external ears and anus APPENDAGES OF THE SKIN
  39. 39. •sebum serves to protect the hairs from becoming too dry and brittle, as well as from becoming too easily saturated with moisture Glands of the Skin Sebaceous glands APPENDAGES OF THE SKIN •sebum is the secretion of the sebaceous glands. It contains fats, cholesterol, albuminous material, remnants of epithelial cells and inorganic salts •largest sebaceous glands are found on the nose and other parts of the face. giving risk to the condition commonly known as blackheads, pimples.
  40. 40. Glands of the Skin Sudoriferous glands •abundant over the whole skin but are largest and most numerous in the axillae, the palms of the hands the soles of the feet and the forehead •simple tubelike glands consisting of a single canal or duct, and a coiled secreting part. The duct opens upon the skin surface and has a layer of epithelial cells surrounding its canal •each gland consists of a single tube, with a blind, coiled end that is lodged in the subcutaneous tissue. The coiled end, the tube is continued as the excretory duct of the gland up through the corium and epidermis and finally opens on the surface by a pore APPENDAGES OF THE SKIN
  41. 41. •perspiration or sweat contains the same inorganic constituents as the blood but in lower concentration with the chief salt of sodium chloride Glands of the Skin Sudoriferous glands •under ordinary circumstances, the perspiration that the body is continually throwing off evaporates from the surface of the body without one’s becoming aware of it and is called insensible perspiration •when more sweat is poured upon the surface of the body that can be removed at once by evaporation, it appears on the skin in the form of drops and is then spoken of a sensible perspiration APPENDAGES OF THE SKIN
  42. 42. Ceruminous glands •skin lining the auditory canal contains modified sweat glands which secrete a yellow, pasty substance resembling wax which is called cerumen •an accumulation of cerumen deep in the auditory canal may interfere with hearing APPENDAGES OF THE SKIN