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Comparative Vertebrate Anatomy > Integument > Flashcards

Flashcards in Integument Deck (72):
1

What are the functions of the integument?

  1. Mechanical protection against injury, attacks, chemicals 
  2. Protection from invasion of microorganisms
  3. Regulates body temperature
  4. Houses sensory organs
  5. Elimination of wastes, excretion and secretion
  6. Adaptive coloration
  7. Vitamin D synthesis
  8. Facilitates locomotion
  9. Storage of fat and glycogen
  10. Respiration in some vertebrates

2

What do all vertebrates have in skin?

Dermis and Epidermis

3

What is the structure of the epidermis in vertebrates?

In all vertebrates, generally a stratified squamous epithelium lying on a basement membrane.

4

What is the stratum germantivum?

  • Deepest layer of the epidermis
  • The layer that undergoes mitosis with its daughter cells pushing upward.

5

Describe the function of moist epidermis?

  • Permeable to some degree facilitating respiration.
  • In lower vertebrates such as amphibians

6

What is the stratum corneum?

the surface layer of sloughing dead cells

7

How did the epidermis become impervious?

With the invasion on land it became impervious by means of invasion of keratin, which kills the cells.

8

What lies between the stratum corneum and the stratum germantivum?

a variety of different layers depending on the vertebrate.

Varied and may produce mucus, poisons, photophores, enamel, or protein keratin that waterproofs skin, or produces feathers, hair, claws, scales.

9

What is the structure of the dermis?

In general (especially fishes and amphibians)

  • looser outer stratum spongiosum (s. laxum)
  • deeper stratum compactum

10

What are the fibers that make up the dermis?

  • Strong collagen fibers (mostly)
  • elastic fibers (few)

both are embedded in the matrix.

11

What penetrates the dermis?

  • fibers (strong collagen, elastic fibers)
  • blood vessels
  • nerves
  • many glands of the epidermis

12

What is the structure of the S. compactum? Why is it important?

Has dense bands of collagen fibers usually oriented in a preferred direction.

Important for mechanical protection (except where other structures take over function [bony armor/scales])

13

What is the importance of the dermis?

Dermis is important in temperature regulation because it is richly vascularized, especially true in mammals and birds.

14

What causes skin color?

Due to chromatophores or pigment cells of the dermis, which tend to congregate near the epidermal-dermal border.

15

What are common types of chromatophores?

Melanophores (melanocytes)

Contain black, brown or red melanin

16

What are melanophores (Melanocytes)

Common types of chromatophores. They contain black, brown or red melanin.

17

What is the hypodermis?

Deep to the dermis and superficial to the muscle

composed of loose connective tissue and adipose tissue.

Also referred to as the superficial fascia

18

What are the three principle types of hard tissue? compare softness

Enamel (hardest)

Dentine (softer than enamel)

Bone (softest)

19

Enamel Structure

  • (epidermal origin) hardest
  • elongate crystals of hydroxyapatite
  • has no internal cells and tubules
  • 3% organic.  
  • Lies superficially on teeth, denticles, scales or armor plates.

20

Where does enamel lie?

It lies superficially on teeth, denticles, scales or armor plates.

21

What is enameloid?

Similar to enamel but slightly different in development.

22

What is ganoine?

A form of enamel

23

What is dentine?

  • (dermal origin) softer than enamel
  • same salts as enamel
  • about 25% content of organic fibers
  • has tubules running through it.

24

What are the different forms of dentine?

osteodentine

orthodentine

cosmine

25

What is the tubule arrangement of cosmine?

Cosmine has tubules arranged in radiating tufts.

26

What is the organic content of bone?

30% organic content

27

Phylogeny of skin

Earliest vertebrates had soft skin like lampreys and hagfishes; the latter have no scales. Ancestral vertebrates then may have developed small scales called lepidomoria. These were also found on young "ostracoderms" and placoderms. Eventually the scales became fused plates of dermal armor such as seen in adult "ostracoderms" and placoderms. The "ostracoderms" had bony plates of dermal armor over most of their bodies, even within the “ostracoderms" there was a steady regression in dermal armor. The descendants of the ancient armored fishes, the lampreys and hagfishes, have no hard parts in their skin. In placoderms also find hard dermal plating, although trend is towards smaller units of it. The elasmoid scale of teleosts is a remnant of this ancient armor. Elasmoid scales have acellular lamellar bone with collagen fibers making it soft. They are either cycloid (rings) or ctenoid (cteni = tooth). Elasmoid scales have rings called circuli grouped into annuli, and radiating lines called radii. The placoderms had dermal denticles on top of their bony armor. Over the jaw margins, these denticles were enlarged and served as teeth; In the Chondrichthyes they form dermal denticles/placoid scales. The denticles overlying the mouth form teeth. These denticles have lamellar bone, a pulp cavity, dentine and enameloid layer, the same layers we see in teeth and placoid scales.

28

From primitive dermal armor evolved:

1. Dermal bones of skull. 2. Dermal components of shoulder girdle 3. Bony teeth 4. Body scales; bony ossicles of caecilians; perhaps osteoderms of crocodilians, perhaps shell bones of turtle, gastralia or bones that lie in ventral abdominal muscles of various reptiles, fin rays of fishes, scales of fishes. The general trend in tetrapods and fishes has been towards a steady reduction and loss of the dermal armor.

29

Dermal Teeth

As mentioned, teeth evolved from the odontodes (denticles) on the surface of the ancient armor. These had lamellar bone, and dentine capped with enamel. The denticles that lay near the edge of the mouth formed teeth.

30

Shark teeth

are attached to the jaw by collagenous Sharpey's fibers. One or two functional rows lie at the jaw margin and numerous replacement rows lie lingual to it. Waves of replacement occur; i.e. the rows move together such that a particular tooth is in the functional position for about one or two weeks. They fall out afterwards. Therefore they are polyphyodont and generally homodont.

31

The teeth of other vertebrates

can be attached to the bone on its outer surface (pleurodont) e.g. anurans and many lizards, or directly to the jaw by hard tissue at its base (acrodont) e.g. most bony fishes, or in sockets (thecodont) e.g. mammals, crocodilians. Most vertebrates are polyphyodont, replacing their teeth continuously. Emerged teeth cannot grow in size so this lets them change size with age. Some have only two tooth generations (man) and are called diphyodont.

32

Bony fish teeth

are usually conical or blade-like and usually all the same in shape; i.e. homodont. Some sharks and bony fishes have heterodont dentitions, for example, incisor-like teeth anteriorly and crushing teeth posteriorly. In addition to jaw teeth, bony fishes can have teeth on the roof and floor of the mouth, i the tongue and in the pharynx (pharyngeal teeth).

33

Modern amphibians

have simple, conical teeth (most toads have no teeth). Extant birds lack teeth. Many reptiles also have a homodont dentition of simple conical teeth. These are used for grasping and piercing prey. Most reptiles are polyphyodont and continuously replace their teeth. Turtles lack teeth. Some reptiles are heterodont, e.g. snakes with anterior or posterior fangs. Many snakes can move the right and left pterygoid and palatine bones and their attached teeth separately, walking the prey into the mouth without opening it.

34

Mammals

are usually heterodont. Teeth pierce, shear, crush or grind. Plant food has to be ground up as there are no enzymes to break down the cellulose cell walls. Most mammals are diphyodont with a first set of milk or deciduous teeth, then a second permanent set. Some marsupials only replace one tooth in each jaw.

35

Tooth Structure

Vertebrate teeth typically have a crown that is exposed, and a root or base which is below the gum. The pulp cavity inside has blood vessels and nerves. The bulk of the tooth is dentine, and the unworn crown is covered with enamel. The enamel might contain iron oxides, hardening it and making it appear brownish-yellow e.g. beaver. Teeth held in sockets have a form of avascular bone called cementum, anchoring them to the jawbone as well as collagenous Sharpey's fiber that form a periodontal membrane/ligament. Typically, mammals have incisors, canines, premolars (bicuspids) and molars (tricuspids). The formula for man is 2/2, 1/1. 2/2. 3/3. The check teeth (molars and premolars) are often multicuspid. The tusk of an elephant is an elongated incisor tooth made of pure dentine. Walrus and wild boar have enlarged canines. In mammals, the teeth may continue to grow from open roots throughout life (incisors in rodents), but this is rare.

36

Some trends in mammalian dentition include

gradual switch from homodont to heterodont dentition to process different food types; reduction or loss of teeth in insect eaters, e.g. armadillo and anteater; very enlarged canines for piercing and killing prey, e.g., saber-tooth tiger; enlarged canines for killing and modified premolars and molars (carnassials) for shearing bone, e.g. dog; loss of canines plus a large diastema, and grinding cheek teeth for herbivory e.g. deer, horse; loss of upper incisors for shearing plant material e.g. cow (0/3, 0/1, 3/3, 3/3), and deer; or a generalized dentition for omnivory, e.g. bear.

37

Fish Skin

Epidermis shows little or no regional cellular specialization. Unicellular mucous glands (club cells, granular cells, goblet cells) lie in epidermis. Club cells can release an "alarm substance". The dermis is composed of an outer stratum laxum and an inner more dense stratum compactum. The collagen fibers of the compactum form helices around the body. The scales, which are dermal derivatives, follow this helical arrangement around the fishes body. Pigment cells are mostly in the dermis and they can have black, yellow, red, orange, silvery, or blue pigment, e.g., coral reef fishes. Photophores in skin can produce bacterial or chemical light.

38

Amphibian Skin

Epidermis lacks distinct layers and is only a few cell layers thick. Some have a thin layer of keratinized stratum corneum cells on outside, which is shed every few days. Epidermally derived mucous glands are abundant; as are granular or poison glands that secrete toxins16. Because derived mucous glands are abundant; as are granular or poison glands that secrete toxins16. Because stratum corneum is so thin, they must live in moist habitats. Aquatic species and amphibian larvae in general lack keratinized skin. Skin in many amphibians is a major respiratory organ. Keratinized or horny teeth are found on tadpoles, and claws of African clawed toad Xenopus are keratin the dermis is composed of a more superficial spongy layer (s. laxum) and a deeper, compact layer (s. compactum). Fossil amphibians had dermal (bony) ossicles, and only legless caecilians have dermal scales embedded in the skin now.

39

Reptile skin

With adaptation to terrestrial life, epidermis of reptiles forms complete body covering of keratinized scales. This affords protection against desiccation, gives mechanical protection, and is used for locomotion. Epidermis is now generally thicker, with a stratum germinativum and thick stratum corneum. There are few epidermally derived glands. In the squamate lizards and snakes there an inner and outer epidermal generation of the epidermis. Molting and shedding of the skin in lizards and snakes occurs between the latter two regions. Reptiles have two general types of epidermal scales: snakes and lizards - scales arranged in longitudinal rows, each scale overlapping the other. The hinge between scales is thinner keratin. Rattles of rattlesnakes are specialized scales left behind after shedding. Turtles and crocodiles - these scales do not overlap; in turtles, the scales arise on top of bony armor. Stratum germinativum produces scales and they "pile up" if they are not worn away. Because each successive scale is larger, it gives appearance of growth rings. These scales are not shed on crocodilians and some turtles (but irregularly shed on some turtles such as the Florida slider). These large, plate-like epidermal scales, such as on crocodilians, turtles, and snakes (ventral scales on snakes) are called scutes. Dermis is thin, being composed of two layers (not called s. laxum and s. compactum). Mucous glands are absent. There are some glands (epidermal origin) that are involved in reproductive behavior, e.g., along the lower jaw of the crocodilians, under the thigh in some lizards.

40

Birds

The skin of birds is thin, loosely attached and weakly keratinized, adapting to the movement of the underlying muscles. Epidermal scales are found on the feet, and they have heavily keratinized beak17 and feathers. The epidermis is generally only a few cells thick. Skin is essentially free of glands, except a single uropygial or preening gland, which secretes oil to waterproof feathers, and salt gland in marine Pigment is present in feathers, scales and beak, but skin may be weakly pigmented18. Coloration of skin and feathers can also be structural, i.e. interference of light. Dermis is thin, well vascularized, composed mostly of irregular fibers.

41

Beaks

are made of thickened, keratinized and compact epidermal cells. (Teeth are not present in adults with beaks, but may make an appearance in development, e.g. parrot.)

42

Feathers

probably evolved to provide insulation, no doubt evolved from epidermal scales of reptilian ancestor as the early development of feathers and scales are quite similar. Feathers are molted and shed once or twice a year. Not all feathers are shed at once.

43

Different types of feathers

Contour feathers

Down feathers

Bristles of filoplumes (hair feathers)

44

Contour Feathers

cover the body and on the wing are used as air foils.

On the wing they are called flight feathers.

Feathers have a quill (or calamus), shaft (or rachis), and the vane made of barbs, barbules, and hooklets on the barbules to keep feather together.

Contour feathers in birds lie in feather tracts called pterylae.

45

Down Feathers

have little or no shaft, no hooklets.

These are short feathers that lie all over the body for insulation.

46

Bristles or Filoplumes (hair feathers)

are modified contour feathers that lie around mouth, over eye or around nostrils.

47

Feather color

Yellow, orange, red, brown and black feather color are result of pigments;

white is due to microstructure and light passing through it;

blue and green iridescent colors are structural colors.

48

Mammal Skin

Skin of mammals is relatively thick. Typically - deepest layer is stratum germinativum where mitosis occurs19; above this there is a variety of layers, the outermost layer is the stratum corneum. It is cornified because of keratin which replaces the cytoplasm. The dermis contains elastic, reticular, and collagen fibers, and is well supplied with blood vessels, nerves, glands and sense organs. It has two layers: the papillary layer is superficial and has dermal papillae and larger dermal ridges that protrude into epidermis, the latter gives us fingerprints and footprints; deeper reticular layer has bundles of thicker collagen fibers running in preferred directions, Langer's lines.

49

Epidermal Derivatives

Various glands develop as down growths from the epidermis. Sweat glands are either, eccrine sweat glands secrete sweat and cool body, or apocrine sweat glands (located in axilla, around anus, scrotum, labia majora usually empty into a hair follicle), important in sex smells. Sweat glands are confined to mammals, although some animals, such as whales, don't have them. Sebaceous glands are also limited to mammals and drain into hair follicles. Their oily secretion sebum waterproofs the hairs. Scent glands are modified apocrine glands found in many mammals, e.g. anal glands of dogs and cats. Ceruminous wax glands in ear canal produce cerumen.

50

Hair

is characteristic of mammals and its evolutionary origin is unclear. Some feel it came from reptilian scales, but dermis does not play such an important role in its development. Others feel it came from reptilean mechanoreceptors. Typical hair has shaft, and root set in a hair follicle. At its base, the root is expanded into a small bulb into which projects a dermal papilla carrying nerves and blood vessels. Only here are there living cells. As cells become keratinized and die, they push upward forming the hair. Forms 2-3 layers. In coarser hair, there is a central medulla of shrunken cells and large air spaces; next, the pigmented cortex makes bulk of hair. The outer cuticle is composed of scaly cells. Sebaceous gland pours sebum onto hair to waterproof it i Arrector r pili smooth muscle controls erection of hair for added insulation. Straight hairs are circular in cross section; curly or wavy hairs are oval in cross section. Hairs are constantly shed, but some mammals produce winter coat and shed most of it in summer. Most furred animals have long guard hairs over a denser coat of underhair (underfur). Hairs take on a variety of shapes and functions: vibrissae or whiskers, quills of porcupines (modified guard hairs), eyelashes, eyebrows.

51

Mammary Glands

Confined to mammals.

They are modified sweat glands or sebaceous glands that secrete milk.

Usually there is a nipple, but monotremes have ancestral condition of no nipple but tufts of hair on which milk accumulates. Mammary glands develop along a milk line in which two or many mammary glands might develop.

The artiodactyl (even toed mammals- pigs, camel, cattle, deer etc.) teat has an enlarged cistern for copious milk storage and quick release.

52

Cornified structures

May be excessive deposition of keratin in skin such as in elephant, hippopotamus, rhinoceros or discrete structures may be formed. Baleen is made of hairlike keratin fibers.

53

Nails, Claws, Hoofs

tough keratinized structures of epidermal origin.

Claws are found on few amphibians

common on reptiles, birds and mammals.

Outer plate or unguis of true claw is hardened by keratin and calcification, possibly formed from a modified scale; beneath that is softer subunguis.

Ungulates have a modified claw, the hoof, the unguis is the hoof proper, the subunguis is the softer underlying part.

In primates, the nail replaces the claw. The unguis is the conspicuous part. Most felids can protract the claws with muscles, and have "hyper-retractility" by means of an elastic ligament. The cheetah has an autapomorphic state of reduced retractility. The claws of digits 2-5 are straighter, thicker and more elongated than other felids, resembling canid claws. The hind limbs have even less retractility. This is associated with its predatory behavior of chasing down prey and it presumably gives it better traction, but results in somewhat worn and less sharp claws. Consequently it cannot hook its prey with its claws as other felids do, its uses its dew claw (claw 1) to hook the hide of its prey as it chases it and throws it off balance. It then suffocates its prey.

54

Horns, Antlers

used in reproduction, protection and offense.

Horns first found in dinosaurs.

  • Rhinoceros horn - epidermal keratin fibers glued by horny cells, not shed, continuous growth sits on small bony prominence.
  • Giraffe horns - are bony projections covered by skin.
  • True horns of cattle, sheep, gazelles, goat, antelope, bison, wildebeest is composed of hollow bony core with keratin fibers over it. They are permanent.
  • Pronghorn antelope have bony projections from skull covered by horny skin; core is permanent and cap is shed annually.
  • Antlers of deer, elk, moose, and caribou have a projection of bone covered by skin during development (velvet), skin dries and sheds when mature before mating season, and later antler shed. New antler is formed each breeding season.

55

Describe the skin of early vertebrates

Earliest vertebrates had soft skin like lampreys and hagfishes; the latter have no scales.

56

what are lepidomaria?

Ancestral vertebrates then may have developed small scales called lepidomoria. These were also found on young "ostracoderms" and placoderms.

57

Describe the integument of ostracoderms and placoderms

lepidomoria. These were also found on young "ostracoderms" and placoderms. Eventually the scales became fused plates of dermal armor such as seen in adult "ostracoderms" and placoderms. The "ostracoderms" had bony plates of dermal armor over most of their bodies, even within the “ostracoderms" there was a steady regression in dermal armor. In placoderms also find hard dermal plating, although trend is towards smaller units of it.

58

Describe the skin of the lamprey and hagfish

The descendants of the ancient armored fishes, the lampreys and hagfishes, have no hard parts in their skin.

59

What are elasmoid scales?

The elasmoid scale of teleosts is a remant of this ancient. Elasmoid scales have acellular lamellar bone with collagen fibers making it soft. They are either cycloid (rings) or ctenoid (cteni = tooth). Elasmoid scales have rings called circuli grouped into annuli, and radiating lines called radii.

60

Dermal denticles in the placoderms

The placoderms had dermal denticles on top of their bony armor. Over the jaw margins, these denticles were enlarged and served as teeth

61

Dermal denticles in the Chondrichthyes?

Over the jaw margins, these denticles were enlarged and served as teeth; In the Chondrichthyes they form dermal denticles/placoid scales. The denticles overlying the mouth form teeth. These denticles have lamellar bone, a pulp cavity, dentine and enameloid layer, the same layers we see in teeth and placoid scales.

62

What did teeth evolve from?

teeth evolved from the odontodes (denticles) on the surface of the ancient armor. These had lamellar bone, and dentine capped with enamel. The denticles that lay near the edge of the mouth formed teeth.

63

Describe Shark teeth

are attached to the jaw by collagenous Sharpey's fibers. One or two functional rows lie at the jaw margin and numerous replacement rows lie lingual to it. Waves of replacement occur; i.e. the rows move together such that a particular tooth is in the functional position for about one or two weeks. They fall out afterwards. Therefore they are polyphyodont and generally homodont.

64

Epidermal Scales and structures

  • keratinized scales are found on tails of rat, beaver, mouse and opossum.
  • Scaly anteater (pangolin) of Asia and Africa has complete covering of scales;
  • armadillo has scales over dermal plates.
  • Baleen in toothless whales is made of keratin - used for filter feeding. 

65

Which derivatives are emphasized in fish?

Dermal Derivatives

66

Which derivatives are emphsized in tetrapods?

Epidermal Derivatives

67

Describe the skin of a bird

  • Thin
  • Loosely attached
  • weakley keratinized
  • Epidermis generally only a few cells thick
  • Skin essentially free of glands (except uropygial/preening gland, salt gland)
  • Pigment present in feathers, scales, beak, but skin may be weakly pigmented
  • Coloration of skin/feathers can also be structural (i.e. interference of light)
  • Dermis =Thin, well vascularized, composed mostly of irregular fibers)

68

What are beaks made of?

thickened, keratinized and compact epidermal cells

teeth no present in adult beaks, but my make an appearance in development (parrot)

69

What is the uropygial/ preening gland

secretes oil to waterproof feathers. only gland in aves skin.

70

What is salt gland?

gland in the skin of marine birds

71

What do extant birds use feathers for?

display

insulation

camouflage

flight

72

How are feathers shed?

They are molted and shed once/ twice a year

Not all feathes are shed at once.