Let's examine generalized skin tissue before we think about all the ways that it has diversified in form and function.

Two layers:

Epidermis

Derived from ectoderm on surface of embryo

Above Dermis: Stratum germinativum-these cells grow toward the surface as they mature and are ultimately sloughed off.

Above Stratum germinativum: a highly variable layer that constitutes the source of much of the integument variation. Most are or will become secretory cells.

Dermis-mesoderm and ectodermal tissue

Enhanced with friction, abrasion or pressure

Stratum germinativum

Reticular lamina (from dermis)

Fibrous connective tissue

Fish Integument

No or very little keratinized stratum corneum

Mucous is the primary surface protector-little rough friction to generate cornified tissue.

Exceptions to the rule: teeth lining oral disk of lampreys

Jaw coverings of herbivorous minnows

Belly skin of mudskippers, walking catfishes and other semi-terrestrial fishes.

Of course, the human mouth is not normally keratinized, but if you eat froot loops twice a day for a month straight..you can induce cornified tissue on the roof of your mouth.

Microridges hold the mucous to the fish.

Epidermal cells-contribute to mucous production

Unicellular glands

Club cells-alarm signals--released by observant individuals

Goblet cells found in bony fishes

Beetles and predators are attracted to the odors..conspecifics are repulsed as well as other species and even insects. Agitated groupers have odors that attract sharks.

1. How does a fish epidermis differ from that of other vertebrates?

Generally lacks a stratum corneum layer in epidermis, outer most layer of epidermis is composed of live cells, outermost epidermal cells contain microridges for holding mucous, or collagen fibers run parallel in multiple laminated layers.

2. If alarm pheromones found in fish skin attract predators, how could they evolve?

Alarm pheromones save close relatives and predators interfere with prey capture and feeding-i.e. interference competition for food. Increases escape potential. SHOW OVERHEAD ALARM PHE.

Ganoid scales have lamellar bone, vascular bone, and enamel (ganoin) whereas teleost scales have lamellar bone only.

So that is what the fish epidermis is composed of-mucous producing cells, alarm pheromone producing cells, living epidermal cells without a stratum corneum and microridges.

Dermis is more laminated in its collagen orientation than most other vertebrate integuments----to provide a smooth surface.

-thus answering the age old mystery of why fish don't get wrinkles.

Dermal bone is often produced by the fish dermis

This is known as dermal bone-any bone derived from dermal mesenchyme is known as dermal bone.

Fish dermal bone gives rise to dermal scales

Scales may have

Dermal bone

Enamel-surface, very hard

Dentin-deep

Now chondrichthyan fish lack dermal bone but have denticles on the surface that produces the placoid scales. These have dentin and enamel but usually no ossification.

The placoderms, cephalospidomorphs and pteryospidomorphs -lamprey and hagfish lack these cranial dermal bones-mucous

If this is starting to sound like words that your dentist might know, that is because scales are histologically and phylogenetically speaking homologous with dermal teeth.

Fish scales

Enamel

Dentin (cosmine)

Vascular bone

Lamellar bone

Enamel (ganoin)

Dentin

Vascular bone

Lamellar bone

Lamellar bone only

Ctenoid-combs or teeth on one end

Cycloid-circuli that are laid down annually

Show overhead of features of tetrapod integument

Tetrapod integuments are different from that of fish, as you might suspect.

The stratum corneum is much thicker and lipid secretions often take the place of mucous for their role in reducing dessication.

Multicellular glands are more common.

Little mucous production (except in amphibians)

Stratum corneum much more developed

Lipid secreted onto epidermis

Multicellular secretory glands rather than individual cells

Glands usually are in dermis rather than epidermis

Amphibian skin provides a nice comparison of integuments for aquatic versus terrestrial environments.

For most amphibians, the integument is a major respiratory organ. In fact, there are some species of lungless salamanders that obtain ALL of their oxygen through the skin.

Because of this, scales are lacking on the surface of the integument (although primitive amphibians had them) and some species of caecilians possess vestigial scales.

Larval amphibians and aquatic adults have Leydig cells within their epidermis. Since amphibians lack heavy mucous layer or a thick stratum corneum, they need some other means of fending off attacks by viruses and bacteria. These cells probably offer this function.

Reptilian integument

Extensive stratum corneum

Epidermal scales present

Modified along the body as feathers

Dermis has many blood vessels and nerve endings

Brood patch.

Uropygial gland-base of tail secretes lipids

Salt gland-located on the head of marine birds

Feather Morphology

Specialized scale

Feathers replaced at least once a year usually asynchronously so that the bird can always fly.

SHOW OVERHEAD OF PARTS OF FEATHERS

Feather types:

Contour feathers: maintain smooth aerodynamic shape

Down feathers: insulation

Filoplume: display

Flight feather: provides lift

Kardong points out that at least one bird species has poisonous feathers and/or glands-the pitohui…in fact he thinks it is so amazing that he repeats it in the text about 3 paragraphs away from each other.

The really interesting point is why do so few birds have poisonous secretions. It is common in fish and amphibians and many reptiles have venom glands in or associated with their mouth. So why are birds so "lame" in their poison secretions?

I don't know, but I thought I'd pose the question.

Since feathers are uniquely avian..how did they evolve?

Three theories: write on board

Possibly an insulation material first. What does this mean about reptilian ancestors? That endothermy evolved first if this is true.

Could they function in thermoregulation prior to that? Maybe. Many desert species have scales that they can angle so that they can shade the body from increased solar radiation.

Regardless of the initial function of bird wings, many of them have a role in flight.

Asymmetrical offset rachis

Produces a twist on downstroke and upstroke.

The epidermis is composed of distinct layers

Epidermis

Stratum corneum

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum basale

Common cells

Keratinocytes

Langerhans cells-immune function?

Merkel cells-mechanoreceptors

Two layers to the dermis

Papillary layer

Reticular layer is deeper and provides an anchor to the underlying hypodermis.

Blood vessels and nerves lie within the dermis but do not extend into the epidermis, which is why you can scrape off the top layer of skin and feel no pain and see no blood.

The dermis does produce some dermal bones which contribute to the pectoral girdle and cranium, except in armadillos which it produces actual dermal bone directly under the epidermis.

Hair is a uniquity (is that a word) of mammals

Filaments of keratin

Root-shaft

Outer portion is the cuticle, inner portion is the cortex, and the center is the medulla.

A dermal papilla feeds the matrix cells of the epidermis and stimulates hair growth.

Epidermal keratinization is continuous

Follicular keratinization is intermittent and localized.

The arrector pili are individual muscles attached to hair shafts and give you the proverbial goose bumps.

Fur (pelage) defined as guard hairs and underfur.

Vibrissae

Quills

Hair decomposes readily and so does not fossilize well.

Because of this, we don't know the evolutionary history of hair. It is suspected to originate as a sensory structure and take on a secondary insulative capacity.

Pterodons—the flying animals that seem to be quite distinct from most other dinosaurs may have had hair. There is some fossil remains of impressions that strongly resemble hair. We also have good evidence of dinosaurs with feathers suggesting an insulation function—and endothermy in dinosaurs.

Mammal integumentary glands

Sebaceous-produce oily secretions (sebum) waterproofs hair

Not present in hand palms or feet soles because it isn't conducive to keeping a good grip on things.

Wax glands-cerumen are derived from sebaceous glands

Meibomian glands of the eyes are derived from sebaceous glands

Sweat glands

Thin sweat glands-not associated with hair follicles-pre-

Puberty function for thermoregulation

Viscous sweat glands-associated with hair follicles-produce

body odor

-Not present in all mammals-most prevalent in primates but may occur on the pads of the feet, mouth area, tail area or back of other mammals.

It is from the sweat glands that urea and salt are excreted…contributing to the odor.

Scent glands are derived from sweat glands

Meibomian glands-eyes

Scent glands-widely

distributed

Mammary glands-females

only