Saturday, July 25, 2009

Vertebrate Integumentary System

THE INTEGUMENTARY SYSTEM
The Vertebrate’s outer covering….i.e. the skin
FUNCTIONS:
1. Support and protection (primary function)
2. Reception/transduction of ext. stimuli
3. Material transport (excretion, resorption, dehydration, rehydration)
4. Thermoregulation
5. Gas exchange
6. Nutrient storage
7. Locomotion
8. Behavior (sexual selection, aggression, identification)
9. Sound production

SKIN IS FUNCTIONALLY A UNIT WITH 3 PARTS:
1. Epidermis
2. Dermis
3. Basement Membrane Complex
The Epidermis:
Outermost layer
An Ectodermal derivative
Often glandular

The Dermis (=corium)

Innermost layer
A mesodermal derivative
Neural Crest gives rise to chromatophores or dermal
armor if present
Contains a neural and vascular supply

The Basement Membrane Complex

In between epidermis and dermis
Outer single layer = Basal Lamina
Inner layers = Basal Lamella

SURVEY OF VERTBRATE SKIN

Amphioxus

Epidermis limited to columnar cells and mucous cuticle

Agnatha

Epidermis is more complex with club and granule cells

The Fishes

General characteristics:

Epidermis is very thin, with 2 cell types….epidermal
cells and unicellular glands (mucous)
Mucous cuticle on surface
Microridges to hold mucous in place
Dermis contains chromatophores

Three types of chromatophores:
Melanophores (brown or black pigment)
Lipophores (xanthophores with yellow pigment and
erythrophores with red pigment)
Iridophores (reflective)

Dermis produces a dermal scale in many

Chondrichthyes:

Placoid scales or dermal denticles
Outer enamel; inner dentin
Epidermis does not cover scales

Osteichthyes:

Bony fish scales are covered by a thin layer of epidermis



Osteichthyes-Sarcopterygii:

Cosmoid Scales
Dermally derived
Outer enamel, intermediate dentin, bony core

Osteichthyes-Actinopterygii:

Dermal scales of three basic types….

Ganoid (Gars, Bichirs)

Dermally derived
Outer enamel (=ganoin), inner bone

Cycloid and Ctenoid (Teleosts that bear scales)

Dermally derived
Scales entirely of lamellar bone
Annuli and Circuli

Amphibia

Epidermis with thin stratum corneum and very little
keratin; Leydig cells
Dermis with chromatophores, poison glands and mucous
glands
Scales are rare


Reptilia

Epidermal scales, with thick outer layer of keratin
Thinner “hinge” region
Inner layer of epidermis regenerative….sloughing

Outer scale surface (Oberhäutchen) often sculpted
…microepidermatoglyphics
Dermis with chromatophores in many
Dermis may possess Osteoderms

Birds

Epidermis thin and bilayered…stratum corneum and
stratum basale
Dermis well-vascularized and innervated
Very few glands

Unique epidermal feathers (of keratin) with basic
structure:
Calamus (quill)
Rachis (shaft)
Barbs, barbules and hooklets

Basic feather types:
Flight, Down, Filoplume and Contour

Feathers probably arose as epidermal scale modifications


Epidermal chromatophores produce pigments which are
carried into feather during development, but
feather surface provides structural color

Feather development
Epidermal feather primordium, dermal papilla,
“collar” and eruption
Feathers grow in tracts, and are connected together in the
dermis by tiny feather muscles

Mammals

Epidermis with 5 layers:
Stratum corneum – outer, keratinized
Stratum lucidum – no organelles
Stratum granulosum – keratin development
Stratum spinosum – developing cells
Stratum basale – germination layer

Epidermal glands present in dermis:
Sebaceous (oil) - Holocrine
Sudoriferous (sweat) – Merocrine

Gland types based on fate of product:
Exocrine – ducted; product into ducts
Endocrine – ductless; product into blood

Gland types based on cellular mode of secretion:
Cytogenic – whole cells; testes and ovaries
Holocrine – product is entire cell contents
Sebaceous
Merocrine – product moves through cell membrane
often by exocytosis; salivary, pancreas
Apocrine – product is cytoplasm at tip of cell;
Mammary

Dermis well-vascularized and innervated
Hair produced in epidermis, and unlike scales and feathers
is an ingrowth of epidermis into the dermis
Root and Shaft
Cuticle, Cortex and Medulla
Fur (pelage) is a thick covering of hair
Guard hairs – longer, coarser
Underfur – shorter, finer
Hairs moved by arector pili muscles

Integumental Derivatives

Integumental derivatives result from on of three processes:

I. Functional Epithelial Extinction (FEE) which leads to “Structured Ectodermal Derivatives”

II. Ectodermal-Mesodermal Interaction (EMI)
which leads to “Structured Ectodermal-
Mesodermal Derivatives”


III. Delamination (DEL) which leads to “Structured
Mesodermal Derivatives”

I. Structured Ectodermal Derivatives

A. Integumental glands

Mucous – Fishes (unicellular)
Amphibians (multicellular)
Poison – Fishes (unicellular/multicellular)
Amphibian, one bird (multicellular)
Venom – Reptiles (modified salivary)
Platypus (modified sweat?)
Salivary – Primarily tetrapods
Musk (scent) – Reptiles, Mammals
Preen (uropygial) – Birds
Sebaceous(oil) - Mammals
Ceruminous (wax) – Mammals, Turkey
Sudorifereous (sweat) – Mammals
Mammary – Mammals (modified sebaceous?)
Photophore Glands – Deep sea fishes

B. Keratinized integument

A manifestation of FEE….several processes:

1. Shedding: Continuous loss of small flakes or cell groups. Probably in all vertebrates…even in areas of specialized thickenings (callouses, palmar and plantar surfaces).

2. Sloughing: Periodic loss of large complete sheets of skin.

Many fishes (mucous cuticle)
Most amphibians (with autophagy)
Reptiles (may be accompanied by autophagy)
Birds (feet)
Some seals, whales, elephants, cervid velvet


3. Molting: Periodic loss of specialized keratinized
ectodermal derivatives

Hair…..including baleen, quills
Feathers
Shell-breaker (=egg caruncle)…epidermal
structure of birds, turtles, crocodilians, tuatara
(Egg Tooth of lizards and snakes is a true tooth)
Turtle scutes
Lamprey “teeth”
Nuptial Pads

4. Retention: Rather permanent specialized
keratinized ectodermal derivatives.

Rattlesnake rattle
Beaks



Horn
True horn: bony spike from skull sheathed
in keratinized epidermis…never “shed”,
never branched (except for Pronghorn)

Not to be confused with:
Antlers (Usually branched,
no keratinization; often shed)
Giraffe “horns” (Bony core covered by
permanent epidermis..no
keratinization…never sloughed or “shed”)
Rhinoceros “horn” (fused mass of epidermal
hair-like papillae…no bone involved

Claws, Nails, Hoofs
All containing Unguis and Subunguis

Digital caps (amphibian “claws”)
Local thickenings – Tori, friction ridges


II. Structured Ectodermal-Mesodermal Derivatives

Composite structures derived from an interaction between Ectoderm and Mesoderm, such as

Dermal Scales
Teeth



III. Structured Mesodermal Derivatives

Structures derived primarily from Mesoderm, such as

Dermal Plates, or “Armor”
Armadillo
Crocodilian osteoderms
Turtle bony plates
Fat storage structure
Panniculus adiposus
Integumentary muscle
Panniculus carnosus
Bone


Reference:http://www.cst.cmich.edu/users/gilli1jc/Part%202%20Integument.htm

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