INTEGUMENTARY SYSTEM

Variations among vertebrates depend on:- number and complexity of glands- epidermal specialized structures- extent of bone formation

Functions:1. protection and support2. locomotion3. thermoregulation and osmoregulation4. gas exchange and secretion5. storage of nutrients6. reproductive7. sensation of stimuli

Major Parts of the Integument

I. The EpidermisFeatures:

A. GlandularTypes based on shape/appearance:

1. Unicellular = typically mucus-containinga. club cells = binucleate and elongatedb. granular cells = found in lampreys and many other fishesc. goblet cells = with narrow base and wide apical endd. sacciform = contain membrane-bound toxic secretions

2. Multicellulara. Tubular

i) simple tubular – Ex. mental, ceruminousii) simple coiled – Ex. Mammalian sweat gland.iii) branched tubular - Ex. axillary sweat glandiv) compound – Ex. monotreme mammary glands

b. Saccular (alveolar)i) Simple -- Ex. frog poison gl.ii) Branched -- Ex. sebaceous gl.iii) Compound -- Ex. therian mammary gland

Types based on secretions:1. mucous 2. sudoriferous (watery)3. sebaceous4. mammary

Types based on mode of secretion:1. merocrine – secretion via the cell membrane2. holocrine - cells are discharged with their secretions3. apocrine - accumulated secretions at outer end of the cell are pinched off along

with some cytoplasm

Figure 1. Different forms of multicellular glands.

B. KeratinizationKeratinocytes are prominent in the epidermal layer

Sublayers:1. Str. Germinativum/basale = innermost, highly mitotic2. Str. Spinosum = prickle cell layer3. Str. Granulosom = contains keratohyaline granules4. Str. Lucidum = cells lack organelles5. Str. Corneum = composed of dead skin cells

EPIDERMAL DERIVATIVES

1. Epidermal scales= derived from the stratum germinativum= include SCUTES= typical of amniotes= thinning at scale joints allow for movement

Examples: Belly of snakesExposed sides of turtle plastron and carapaceFacial, area, legs and feeet of birdsArmadillo scalesBeaver and rat tails

2. Claws, hoofs and nails= at the end of the digits= basic structure : UNGUIS (horny dorsal plate) and SUBUNGUIS (soft ventral plate)

3. Feathers = found among birds= kinds: contour, down, filoplume= Feather development involves two components:

Mesodermal Component Epidermal Component

DERMAL PAPILLA is formed FEATHER PRIMORDIUM is inducedThe DP is vascularized

The DP dies and becomes pulp as the INFERIOR UMBILICUS is formed.

The FP elongates as FEATHER FOLLICLE developsGROWTH ZONE from germinative layer gives rise to the FEATHER SHEATH.CORNIFICATION leads to the formation of barbs.The sheath splits open as the shaft elongates to full growth.

4. Hair = composed mainly of α-keratin= Basic parts: Root and Shaft= Development of hair involves:

a. Epidermal ingrowth (hair primordium)b. Dermal papilla organizes and vascularizesc. Hair shaft rises out of hair follicled. Melanophore granules contribute to hair color

= Other related structures:- ARRECTOR PILI = attached to hair follicle- PELAGE = thick covering of hair or fur (includes guard hairs

and underfur)- VIBRISSAE = whiskers- QUILLS and SPINES

6. Horns = special keratinized structures on the heads of ungulatesExamples: a. Bovine horn

b. Pronghornc. Hair horn = composed of agglutinated hairlike fibers

7. Other Cornified structures:- Baleen (“whalebone”)- Snake rattles- Avian beaks- Ischial callosities- Knee pads (e.g. camels) and tori (epidermal pads)- Apical pads (at ends of digits)- Corns and calluses- Egg tooth (in hatchlings) = an example of keratinized teeth

II. The Dermis= Basic component: Collagenous connective tissue= has the potential to form BONE= Functions of dermal bone: - protective

- storage site

DERMAL DERIVATIVES:A. Dermal scales or plates

Generalized Pattern:4 = Enamel or enamellike substance3 = Dentin (surface elevations are called denticles)2 = Spongy bone (vascularized or with blood channels)1 = Lamellar bone

Classification of Dermal scales:1. PLACOID = 4, 3, 1

= basal plate + spine (specialized denticle)

2. RHOMBOID (4, 3, 2, 1)Subtypes:a. Ganoid = characteristic of basal actinoptergyians

= 4: GANOINE

b. Cosmoid = characteristic of extinct sarcopteryigians = 4+3: COSMINE

3. ELASMOID = 1 + connective tissue = Subtypes: CTENOID and CYCLOID

Scale Anlagen = transitory in embryos of fishes without scalesOsteoderm = bony plates in tetrapods (Ex. crocodiles)Other dermal plates in tetrapods:

- Inner plastron and carapace of turtles- Armadillo armor

B. Chromatophores: 1. Melanophores

2. Xanthophores LIPOPHORES

3. Erythropores

4. Iridiophores

C. Dermal bone structures 1. ANTLERS = dermal bone attached to frontal bone in deer

= with VELVET when newly growing= can be shed off

2. Giraffe horns= short projections from frontal bone= remain in velvet throughout life