The document discusses the integumentary system across different chordate groups. It describes the key features of skin in protochordates, cyclostomes, fish, amphibians, reptiles, birds, and mammals. The integumentary system generally consists of an outer epidermis layer and inner dermis layer, with variations in features like keratinization, glands, scales/feathers/hair, and pigment cells across groups. The skin serves protective, sensory, and excretory functions for chordates.

1. Dr. P.B.Reddy
M.Sc,M.Phil,Ph.D, FIMRF,FICER,FSLSc,FISZS,FISQEM
PG DEPARTMENT OF ZOOLOGY
GOVERTNAMENT PG COLLEGE, RATLAM.M.P
reddysirr@gmail.com
Comparative anatomy integumentary system

4.  The integumentary system comprises the skin and its
appendages. Skin + derivatives= Integument.
 It aims to protect the body from various kinds of
damage, such as loss of water or damages from outside.
 The integumentary system in chordates includes hair,
scales, feathers, hooves, and nails.
 It may serve to water proof, and protect the deeper
tissues.
 Excrete wastes, and regulate body temperature.
It is the attachment site for sensory receptors to detect
pain, sensation, pressure, and temperature.
Integumentary system

5. Functions (Jack of all trades and Master of none)
 Maintains the body's equilibrium.
 The acts as the body's first line of defense.
 Regulates the body temperature change, and homeostasis.
 Protect the body's internal living tissues and organs.
 Protect against invasion by infectious organisms.
 Protect the body from dehydration.
 Help excrete waste materials through perspiration.
 Act as a receptor for touch, pressure, pain, heat, and cold (Tactile
receptors)
 Protect the body against sunburns by secreting melanin.
 Generate vitamin D through exposure to ultraviolet light.
 Store water, fat, glucose, vitamin D.
 Maintenance of the body shape and outline.
 Formation of new cells from stratum germinativum to repair minor injuries
Protect from UV rays.
 It distinguishes, separates, and protects the organism from its
surroundings.
 Some invertebrates and frogs respire (cutaneous) using the outer layer

6. Skin
 The skin is the largest organ of the body.
 In humans, it accounts for about 12 to 15 percent of total body weight
and covers 1.5-2m2 of surface area.
 The is composed of two major layers of tissue: the epidermis and dermis.
(The hypodermis or subcutaneous layer is not part of the skin)
 The epidermis is the outermost layer, providing the initial barrier to the
external environment.
 It is separated from the dermis by the basement membrane.
 The epidermis contains melanocytes and gives color to the skin.
 The deepest layer of epidermis also contains nerve endings.
 Beneath this, the dermis comprises two sections, the papillary and
reticular layers, and contains connective tissues, vessels, glands, follicles,
hair roots, sensory nerve endings, and muscular tissue.
 The deepest layer, the hypodermis, is primarily made up of adipose
tissue. Substantial collagen bundles anchor the dermis to the hypodermis in
a way that permits most areas of the skin to move freely over the deeper
tissue layers.

7.  The epidermis, derived from somatic ectoderm,
The epidermis is the top layer of skin and made up of
epithelial cells.
 It does not contain blood vessels.
 Its main functions are protection, absorption of
nutrients, and homeostasis.
 It provides a barrier to infection from
environmental pathogens and regulates the amount
of water.
 In structure, it consists of a keratinized stratified
squamous epithelium; four types of cells:
keratinocytes, melanocytes, Merkel cells, and
Langerhans cells.
Keratin is a waterproofing protein. Millions of dead
keratinocytes rub off daily (ecdysis or moulting).
 The layers of the epidermis include the stratum
basale (the deepest portion of the epidermis),
stratum spinosum, stratum granulosum, stratum
lucidum, and stratum corneum (the most superficial
portion of the epidermis).
 Fishes and amphibians have a mucus layer for
bacterial and mechanical
Epidermis
The epidermis of fish and of most
amphibians consists entirely of live
cells, with only minimal quantities of
keratin in the cells of the superficial
layer. It is generally permeable, and
in the case of many amphibians, may
actually be a major respiratory
organ.

8. Dermis
 The dermis is the middle layer of skin, composed of dense irregular
connective tissue and areolar connective tissue .
Collagen with elastin are arranged in a diffusely bundled and woven
pattern.
 The dermis has two layers.
 One is the papillary layer which is the superficial layer and consists
of the areolar connective tissue. The other is the reticular layer which
is the deep layer of the dermis and consists of the dense irregular
connective tissue.
 These layers serve to give elasticity to the integument, allowing
stretching and conferring flexibility, while also resisting distortions,
wrinkling, and sagging.
 The dermal layer provides a site for the endings of blood vessels
and nerves.
 Many chromatophores are also stored in this layer, as are the bases
of integumental structures such as hair, feathers, and glands.

9. Epidermal Derivatives of the Integument
A) Keratin Structures
New epidermal cells are formed continuously in the lower layers of the epidermis. In terrestrial vertebrates, new
epidermal cells push more superficial ones to the stratum corneum, the outer-most epithelial layer. In the
process of self-destruction, these exterior epidermal cells accumulate protein products called keratin. Keratinized
or cornified skin serves to prevent water escape and to protect against friction and direct mechanical stimulation
(e.g. calluses in humans). The production of all of the following structures involves keratinization:
Epidermal Scales: a continuous layer of repetitious thickenings of the stratum corneum; These scales
may be shed entirely or in small flakes. Examine preserved specimen of snake and dried specimens of
bird legs and feet.
Claws and Talons: curved, laterally compressed keratinized projections from the tips of digits. See dried
specimen of cat claws and bird talons.
The possible functions of these structures
Hooves: enlarged keratinized plates found on the ends of ungulate digits. Examine the hooves of pig and
horse.
Nails: keratinized epithelial cells produced at the name base by pushing the existing nail forward. Protect
from mechanical injury and stabilize skin for better grasping. Found only in primates.
Horns: a tough, cornified layer of the integument covers horns. Their core, however, is bone, of dermal
origin. Horns are found in bovines (cattle, antelope, sheep, goats, bison, wildebeest). They are retained
year-round and grow throughout the animal’s lifetime.
Baleen: found in some whales, is a series of keratinized plates that arise from oral epithelium. These
sheets hang from the palate along its length. use would the sieve-like action of these plates be.
Beaks: epidermal structures, jaws are covered by keratinized sheaths in birds.
Feathers: are believed to have evolved from reptilian scales. Columns of epidermal cells project into the
skin initially to form an invagination called the feather follicle.
Hair: just as in feathers, there is an initial in growth of epidermal cells to form the hair follicle, followed by
an outward growth of keratinized cells to form the hair shaft. Both feather and hair possess dermal
papillae, shafts, an inner pulp and columns of specialized keratinized cells. Hair is characteristic of
mammals.

10. B) Glands (unicellular and multicellular)
 Epidermal glands are formed from the Malpighian layer of the
epidermis. They arise from the epidermis and often penetrate the
dermis. These are lined by cuboidal or columnar cells.
Specialized to secrete specific products (oil, sweat, milk, etc.).
 These cells are derived by an infolding of the epidermis.
 In many cases they retain a connection to the stratum
corneum whereby their secretions can be released at the skin
surface.
 Hair follicles, sebaceous glands, sweat glands, apocrine glands, and
mammary glands are considered epidermal glands or epidermal
appendages, because they develop as down growths or diverticula of
the epidermis into the dermis.

11. COMPARISION
The fundamental structure of skin in all the vertebrates is the same but
there are certain variations in different classes.
1. Protochordata:
In Branchiostoma the skin is simple without keratin. The epidermis is
single layered made of tall or columnar cells. These are ciliated in
Balanoglossus. Epidermis has numerous unicellular gland cells which
secrete a thin cuticle in Branchiostoma. Dermis (corium) is gelatinous in
Amphioxus.

12. 2. Cyclostomata:
 Epidermis is multilayered (stratified) but has no
keratin.
 It has three types of unicellular gland cells- mucous
glands secrete mucous, club cells probably scab-forming
cells, and granular cells are of unknown function.
 Below the epidermis is the cutis formed of collagen
and elastic fibers. Star-shaped pigment cells are also
present in the cutis.
3. Pisces: The epidermis has several layers of simple and thin
cells, but there is no dead stratum corneum.
 The outermost cells are nucleated and living.
 The stratum Malpighi fills the outer layers of cells
which have some keratin.
 Unicellular goblet or mucous gland cells are found in
the epidermis, as in all aquatic animals.
 The mucus makes the skin slimy reducing friction
between body surface and water, protects the skin from
bacteria and fungi, and assists in the control of osmosis.
 Multicellular epidermal glands like poison glands and
light producing organs (photophores) may also be
found. The epidermis rests on a delicate basement
membrane.

13.  The mucus makes the skin slimy reducing friction between body surface and water, protects
the skin from bacteria and fungi, and assists in the control of osmosis.
 Multicellular epidermal glands like poison glands and light producing organs (photophores)
may also be found. The epidermis rests on a delicate basement membrane.
 The dermis contains connective tissue, smooth muscles, blood vessels, nerves, lymph
vessels, and collagen fibers. The connective tissue fibers are generally not arranged at right
angles, but run parallel to the surface. Scales are embedded in the dermis and projected above
the epidermal surface.
These are of five types. The elasmobranches have placoid scales, Chondrostei and Holostei
have ganoid scales, while most Teleostei have cycloid and ctenoid scales lodged in pouches of
the dermis. Extinct Crossopterygii had cosmoid scales.
Many bony fishes show more brilliant colours than any other group of animals. The colours of
fishes are due to chromatophores and iridocytes.
(a) Chromatophores in the dermis are derived from neural crest cells. They contain pigments
which not only produce colours but also cause variations of colours. Chromatophores
containing brown or black pigment are known as melanophores and those containing red,
yellow, or orange pigment are collectively called lipophores.
(b) Iridocytes or guanophores are reflecting cells. They have no pigment but contain crystals
of guanin. They lie in the dermis and cause iridescence. Iridocytes reflect light from guanin
crystals to produce white or silvery colours if the iridocytes are below the scales, if the
iridocytes are above the scales they cause iridescent hues. By combinations of
chromatophores and iridocytes various colours are produced, e.g., blue is produced by
reflection from iridocytes, the blue combines with yellow pigment to produce green.

14. 4. Amphibia:
 The epidermis is multilayered.
 The stratum corneum made of flattened, highly keratinized cells. Such a
dead layer appears first in amphibians. The stratum corneum is an
adaptation to terrestrial life. It not only protects the body but prevents any
excessive loss of moisture.
In ecdysis, the stratum corneum is cast off in fragments or as a whole in
some.
 The dermis is relatively thin, it is made of two layers, an upper loose
stratum spongiosum and a lower dense and compact stratum compactum.
Connective tissue fibers run both vertically and horizontally.
 There are two kinds of glands, they are multicellular mucous glands and
poison glands in the dermis, but they are derivatives of the epidermis.
 The mucous glands produce mucus which not only forms a slimy
protective covering but also helps in respiration.
 The poison glands found in toads as parotid glands produce a mild but
unpleasant poison which is protective, keep the enemies away.
 In the upper part of the dermis are chromatophores which have black
melanophores and yellow lipophores, these produce the colour of the skin.


15.  The ability of the skin for changing colour to blend with the environment is well
developed.
 Skin of labyrinthodontia, the stem Amphibia had a armour of dermal scales.
 Bony dermal scales are found embedded in the skin of some Gymnophiona (Apoda)
and a few tropical toads. These scales are absent in modern Amphibia.
The skin is sensitive to light in amphibians, especially in cave-dwelling forms.
 It is an important organ of respiration, and also enables the frog to respire under
water for long periods, during hibernation or aestivation it is the only organ of
respiration.
 The skin is loose being attached to muscles only at certain places by connective
tissue septa which mark the boundaries of subcutaneous lymph spaces.

16. Reptilia:
The integument is thick and dry.
 It prevents any loss of water.
 It has almost no glands, this is an
adaptation to prevent evaporation of
water.
 The epidermis has a well-developed
stratum corneum and well adapted to
a terrestrial life.
 The epidermis produces horny
scales. Scales are shed periodically in
fragments or cast in a single slough,
as in snakes and some lizards.
 The scales often form spines or
crests.
 Below the epidermal scales are
dermal bony plates. These are
retained for life and are not shed off.


17. The dermis is thick and has an upper loose connective tissue layer and
a lower layer tella subjunctiva and separating the two is a horizontal
layer of fibrous connective tissue.
 The upper layer has an abundance of chromatophores in snakes and
lizards like fishes and amphibians.
 Many lizards and snakes have elaborate colour patterns, for
concealment or as warning colours. In Calotes, the chromatophores have
no nerve fibers, they are controlled by hormones of the posterior lobe of
the pituitary. In Chameleon, chromatophores are controlled by the
autonomic nervous system.
 Reptiles essentially lack skin glands.
 Many lizards have glands near the cloaca.
 Musk glands in the throat and cloacal opening of crocodilians function
during courtship.
 Generation glands found recently are associated with periodic
shedding of the skin.


18. 6. Aves:
 The integument is thin, loose, dry and devoid of glands except a
uropygial gland at the base of the tail whose secreted oil is used for
preening the feathers, especially in aquatic birds.
 The stratified epidermis is delicate, except on shanks and feet where
it is thick and forms epidermal scales.
 The claws, spurs and horny sheaths of beaks are also the
modifications of stratum corneum of epidermis.
 Claws and beaks are variously modified in birds according to habitat.
 The rest of the body has a protective covering of epidermal feathers
which are evolved from epidermal scales.
 Feathers protect and insulate the body, i.e, keep the body warm.


19. The dermis is thin and has
interlacing connective tissue fibres,
abundant muscle fibres for moving
feathers, blood vessels and nerves.
 The dermis forms an upper
vascular and spongy layer and a
lower compact layer.
 The dermis also contains fat cells.
The skin has no chromatophores.
 Pigment found in melanocytes
migrates into feathers and scales.
 Colour patterns of birds are vivid;
 They are for concealment,
recognition, and sexual stimulation.
 The colours are mainly produced
by reflection and refraction of light
from surface of feathers.

20. 7. Mammalia:
The skin (Fig. 41.19) is elastic and waterproof and is much thicker than
in other vertebrates, especially the dermis is very thick and tough and
is used for making leather. The epidermis is thickest in mammals and is
differentiated into five layers- stratum corneum, stratum lucidum,
stratum granulosum, stratum spinosum and stratum germinativum or
Malpighian layer.

21.  The outer layer of stratum corneum containing keratin, its cells lose their nuclei, but
the cells are not dead as believed before.
 They secrete several hormones, one of which represses the mitotic activities of the
Malpighian layer. In places of friction, such as soles and palms, the stratum corneum is
very thick.
 Stratum corneum is variously modified in various mammals to form epidermal scales,
bristles, hairs, claws, nails, hoofs and horns etc.,
 Below the stratum corneum is a refractive stratum lucidum in certain regions only.
 The stratum lucidum is now known as a barrier layer. It prevents passage of
substances into or out of the body.
 Stratum lucidum contains a chemical known as eleidin.
 Keratohyalin and eleidin are intermediate products in the formation of keratin.
 Below this is a stratum granulosum which is having darkly-staining granules of
keratohyalin.
 Below the stratum granulosum is a stratum spinosum whose cells are held together by
spiny intercellular bridges, each bridge has two arms in close contact, one arm arising
from each cell.
 Lastly there is a stratum germinativum or Malpighian layer which rests on a thin
basement membrane.
 The Malpighian layer forms new cells continuously which move towards the surface
and become flat and keratinised till the stratum corneum has flat, cornified cells made
only of keratin.
 This layer is sloughed off continuously and replaced by new cells. There are no mucous glands
in the epidermis of mammals. The keratin from the epidermis at ends of digits forms claws, nails

22.  The dermis is best developed in mammals.
 The upper part of the dermis in contact with the epidermis is the papillary
layer which is made of elastic and collagen fibers with capillaries in between
and lower part of the dermis is a reticular layer having elastic and collagen
fibers.
 In both layers there are blood vessels, nerves, smooth muscles, certain
glands, tactile corpuscles, and connective tissue fibers extending in all
directions.
 Below the dermis the subcutaneous tissue has a layer of fat cells forming
adipose tissue which helps to maintain body heat.
 no pigment-bearing chromatophores in mammals.
 In man some branching dendritic cells or melanoblasts lie between the
epidermis and dermis, they contain pigment.
 The epidermis forms hairs, sudorific glands, sebaceous glands and
mammary glands.


23. Sebaceous glands are out
pushings of the wall of hair
follicle and produce an oily
substance which keeps the hair
supple and prevents its wetting in
water.
 It also lubricates the skin.
 In the dermis are present
coiled sudorific or sweat glands,
which occur all over except lips
and glans penis.
 Mammary glands are modified
sebaceous glands, but in
monotremes they are modified
sudorific glands.
 They are functional only in
females for producing milk for the
young. Mucous glands are not
found in mammals.