hair, wool, feathers and scales

Question 1

what does it mean that hair, feathers and scales are homologous structures

Answer 1

they share a common ancestry

Question 2

why are hair, scales and feathers homologous

Answer 2

they all develop from epidermis interacting with underlying mesenchymal tissue

Question 3

formation of teeth and mammary glands as they are epidermal-mesenchymal

Answer 3

-2 layers come together
-fold
-secrete proteins

Question 4

hair development steps

Answer 4

-ectodermal bud growing into mesenchyme
-differentiation of the bud and indications of glands
-developed hair follicle with accessory structures

Question 5

structure of hair

Answer 5

-long thin chain of keratin protein
-central medulla
-thick cortex
-outer cuticle

Question 6

does wool hair have a medulla

Answer 6

no

Question 7

3 forms of hair

Answer 7

-wool
-guard
-tactile

Question 8

wool and guard hair interaction

Answer 8

• usually one primary guard hair and several secondary wool hairs

Question 9

guard hairs

Answer 9

-lie against the skin
-run in tracts of the same direction

Question 10

species specific guard hairs

Answer 10

• 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)

Question 11

tactile hairs

Answer 11

-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)

Question 12

which gland regulates hair shedding in different seasons

Answer 12

pineal gland

Question 13

hair growth cycle

Answer 13

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

Question 14

5 functions of hair

Answer 14

-protection
-water resistance
-thermoregulation/ insulation
-communication/ camouflage
-sensory functions

Question 15

hair protection

Answer 15

-tough keratin hairs covering sensitive strucutres eg- eyes
-guard hairs running in the same direction protecting from predation

Question 16

hair- water resistance

Answer 16

-oily sebaceous glands opening into the follicle
-same direction tracts of guard hairs

Question 17

thermoregulation hair function

Answer 17

-wool hairs trap air
-arrector pili and guard hairs
-some sweat glands open into follicle

Question 18

communication and camouflage hair function

Answer 18

• colours
• arrector pili
  -glands opening into follicle

Question 19

sensory function hair

Answer 19

-tactile hairs

Question 20

functions of feathers

Answer 20

-insulation
-communication/ display
-flight

Question 21

bird epidermal layers

Answer 21

-very thin skin that tears easily
1) stratum germinativum (basale)
2) stratum corneum

Question 22

3 glands in birds

Answer 22

-preen gland
-vent gland
-aural gland

Question 23

what should you note about developing feathers

Answer 23

• they contain a core of vascular dermis
• a feather may bleed a lot when plucked out or broken (blood feathers)

Question 24

feather structure

Question 25

feather structure

Answer 25

-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

Question 26

types of feathers

Answer 26

-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)

Question 27

powder down feathers

Answer 27

produce a fine waxy keratin powder (similar function to preen gland which is cleaning and waterproofing)

Question 28

functions of feather

Answer 28

» 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

Question 29

3 layers of reptile epidermis

Answer 29

-stratum germinativum ( basale) -stratum intermedium -stratum corneum

Question 30

osteoderms

Answer 30

-reptiles have these bony plates in the dermis -in tortoises the shell is formed fro osteoderm fusion with the ribs

Question 31

why are reptiles at risk of thermal burns

Answer 31

thick keratinised skin reduces skin sensation

Question 32

specialised cutaneous appendages with different functions in reptiles

Answer 32

* 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

Question 33

ecdysis

Answer 33

skin shedding controlled by the thyroid gland

Question 34

what are the risks of reptiles having permeable skin

Answer 34

more succeptible to infection, parasites, medication overdose

Question 35

where are fish scales derived from

Answer 35

dermally from the mesodom

Question 36

what makes fish skin more permeable than other species

Answer 36

little keratinisation/ corneocytes

Question 37

fish lateral line system

Answer 37

* Sense movement, vibration, pressure in surrounding water * Orientation, schooling, defence, predation