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

1. Integumentary
System

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. •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. Invertebrate Integument
•with firm elastic pellicle
(Paramecium)
Protozoans
•covered by delicate cell membrane
(Amoeba)

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

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. Arthropod Integument
Decapod crustaceans:
Cuticle is stiffened by calcification Deposition of calcium carbonate in the outer layers of
procuticle
Invertebrate Integument

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

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. 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. 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. 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. •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. 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. merocrine gland
apocrine gland holocrine gland

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. 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. 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. 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. •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. 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. The skin consists of two distinct layers
•epidermis, cuticle
•dermis, corium or cutis vera
PARTS OF THE SKIN

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. •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. •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. •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. • cells have lost their nuclei and
cellular outlines due to the
degenerative process
Stratum lucidum
Epidermis (Epi = upon + dermis = skin)

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)

33. •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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. •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.

41. 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

42. •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

43. 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