Skin.

Functions:

Border, protection, osmotic regulation, shape, diffusion of gases, gather/radiate heat.

Epidermis (outter)

Dermis (inner)

Outter layer.

Forms from single layer ectoderm to multilayered epidermis.

Initially forms the stratum base.

Covered by mucus coat.

Outter keratinized coat/cornified layer.

Deepest layer of epidermis.

Directly adjacent to basement membrane.

Proliferating layer (constantly dividing)

First cells formed become the periderm.

Keratin=Dead cells.

Cells that make/produce keratin.

Composed of collagen fiber connective tissue that can be woven into plies.

Forms from the dermatome (mesoderm) and mesynchyme (individual cells of the layer).

Location of dermal bone formation.

Contains chromatophores, nerves, and blood vessels.

Derived from the mesoderm.

Migrates inward.

Individual cells of the layer.

Loose association of mesodermal cells.

Nonkeratinized

Mucus Coat: Hydrophobic Layer

Two cell types: Epidermal (mucus coat), Unicellular (4 types of glands)

1. Club Cells: release chemicals that warn others of  danger.

2. Grandular Cells: produce mucus

3. Goblet Cells: produce mucus

4. Sacciform Cells: Releases repellant/toxin.

No dermal bone.

Placoid Scales: 3 parts

1. enamel: from epidermis
2. dentin: from dermis
3. pulp cavity

Scales formed in dermis, but don't pierce epidermis (dermal scales)

Multilayered epidermis.

keratinized (**)

Multicellular glands in the dermis that reaches the surface through ducts.

Fish Difference: Glands are epidermal and unicellular.

Cutaneous respiration because s. correum is thin.

No scales.

Mucus glands, poison glands.

Keratinized extesively (comp to amphibians)

No dermal or bony support of scales

Fewer glands than amphibs.

Dermal bone (gastralia)

Molting

Epidermal Scales on legs and feet.

Glands: Uropygial and Salt glands

Feathers.

Typically found on marine birds.

Helps to excrete excess salt ingested.

Found on the head.

Nonvascular, nonnervous, products of the skin.

Formed from epidermis.

Laid our in tracts along the body.

Replaced yearly.

Develop follicles.

Flight, Insulation, Aerodynamics, courtship.

Specialized epidermis: keratinized and multilayered.

Keratinized system forms hair, nails, claws, hooves.

Double-layered dermis (outter/deeper layers).

Outter: Fingerlike projections that push up into the epidermis (dermal papillae)

Deeper (Inner): Anchors the dermis to the underlying fascia.

-dermis is location of blood vessels/nerves.

-connective tissue contains collagen and elastic fibers.

Unique Structures:

Hair: slender karotinized rods produced in the hair follicle.

Glands: Mammary, Sebaceous, Sweat (eccrine, apocrin)

Epidermis within the dermis that insulates.

Produce an oily secretion released into hair follicles.

Conditions/water proofs hair.

Produce a thin watery fluid not associated with hair follicles.

Active throughout life, respond to increase body temp.

Active before puberty.