hair, wool, feathers and scales Flashcards
what does it mean that hair, feathers and scales are homologous structures
they share a common ancestry
why are hair, scales and feathers homologous
they all develop from epidermis interacting with underlying mesenchymal tissue
formation of teeth and mammary glands as they are epidermal-mesenchymal
-2 layers come together
-fold
-secrete proteins
hair development steps
-ectodermal bud growing into mesenchyme
-differentiation of the bud and indications of glands
-developed hair follicle with accessory structures
structure of hair
-long thin chain of keratin protein
-central medulla
-thick cortex
-outer cuticle
does wool hair have a medulla
no
3 forms of hair
-wool
-guard
-tactile
wool and guard hair interaction
- usually one primary guard hair and several secondary wool hairs
guard hairs
-lie against the skin
-run in tracts of the same direction
species specific guard hairs
- Mane, tail and fetlock tufts of horses
- Stiff, sparse bristles of pigs
- Long tail hairs of cattle
- Beards of goats
- Spines of hedgehogs
-sheep have hardly any guard hairs (called kemp hairs)
tactile hairs
-mostly on face/head
-reach deep into subcutis or even muscle
-dermal sheath surrounding follicle contains nerve endings
-surrounded by venous sinus (blood waves amplifies the stimulation)
which gland regulates hair shedding in different seasons
pineal gland
hair growth cycle
1) ANAGEN
-growing phase
-most follicles
2) CATAGEN
-transition phase
-growth slows
-atrophy of follicle
3) TELOGEN
-resting phase
-growth stopped
-hair can eventually break free and be shed
4) ANAGEN again
5 functions of hair
-protection
-water resistance
-thermoregulation/ insulation
-communication/ camouflage
-sensory functions
hair protection
-tough keratin hairs covering sensitive strucutres eg- eyes
-guard hairs running in the same direction protecting from predation
hair- water resistance
-oily sebaceous glands opening into the follicle
-same direction tracts of guard hairs
thermoregulation hair function
-wool hairs trap air
-arrector pili and guard hairs
-some sweat glands open into follicle
communication and camouflage hair function
- colours
- arrector pili
-glands opening into follicle
sensory function hair
-tactile hairs
functions of feathers
-insulation
-communication/ display
-flight
bird epidermal layers
-very thin skin that tears easily
1) stratum germinativum (basale)
2) stratum corneum
3 glands in birds
-preen gland
-vent gland
-aural gland
what should you note about developing feathers
- they contain a core of vascular dermis
- a feather may bleed a lot when plucked out or broken (blood feathers)
feather structure
feather structure
-main shaft (middle bit) called RACHIS
-either side of main shaft called VANES
-vanes are made up of BARBS (made of interlocking barbules)
-base of the quill is called CALAMUS
types of feathers
-contour feathers (inc. flight feathers) they are asymmetrical and have a smooth waterproof surface
-down feathers (non-interlocking barbules to trap air)
-semi-plumes (fluffy insulators)
-bristles (few barbs, sensory and protective)
-filoplumes (sensory, helps with flight adjustment)
powder down feathers
produce a fine waxy keratin powder (similar function to preen gland which is cleaning and waterproofing)
functions of feather
» Protection
* Especially important because of thin skin
» Water resistance
* Oily secretion from preen gland, barbules
» Thermoregulation
* Down feathers and semiplumes
* Feather muscles (like mammal arrector pili)
» Communication/ camouflage
* Colours
* Elaborate feathers
* Feather muscles
» Sensory function
* Bristle and filoplumes
» Flight / locomotion
3 layers of reptile epidermis
-stratum germinativum ( basale)
-stratum intermedium
-stratum corneum
osteoderms
-reptiles have these bony plates in the dermis
-in tortoises the shell is formed fro osteoderm fusion with the ribs
why are reptiles at risk of thermal burns
thick keratinised skin reduces skin sensation
specialised cutaneous appendages with different functions in reptiles
- Clear spectacle scales over eyes
- Light-sensitiveparietaleye
- Associated with pineal gland
- Scales and structures that aid locomotion
(snake belly scales, adhesive toe pads) - Cloacal spurs aid reproduction
- Heat sensitive pits for prey detection
- Crests, frills, horns, pouches, spines for display and defence
ecdysis
skin shedding controlled by the thyroid gland
what are the risks of reptiles having permeable skin
more succeptible to infection, parasites, medication overdose
where are fish scales derived from
dermally from the mesodom
what makes fish skin more permeable than other species
little keratinisation/ corneocytes
fish lateral line system
- Sense movement, vibration, pressure in surrounding water
- Orientation, schooling, defence, predation
