Hair, Wool, Feathers and Scales

Question 1

How do hair feathers and scales develop?

Answer 1

From the epidermis interacting with underlying mesenchymal tissue (loose cells in the dermis)

Question 2

Epidermal-mesenchymal interactions

Answer 2

Forms hair, feathers, scales, teeth and mammary glands.
In each case two layers come together, fold, secrete proteins.

Question 3

Hair structure

Answer 3

Long thin chain of keratin
Composed of central medulla, thick cortex and outer cuticle.

Question 4

Types of hair

Answer 4

Straight stiff guard hairs
Fine wavy wool hairs
Thick long tactile hairs (sensory)

Question 5

Tactile hairs

Answer 5

Mostly on face and head
Reach deep into subcutis or even muscle
Dermal sheath contains nerve endings
Surrounded by venous sinus amplifies stimulation

Question 6

Function of the pineal gland

Answer 6

Sensory gland that detects light changes, causes seasonal changes in hair growth

Question 7

Hair growth cycle

Answer 7

1) Anagen- Growing phase most follicles; producing new keratin
2) Catagen- transition phase, slower growth and atrophy of follicle
3) Telogen- Resting phase, growth stops; hair breaks free and is shed.

Question 7

Hair growth cycle

Answer 7

1) Anagen- Growing phase most follicles; producing new keratin
2) Catagen- transition phase, slower growth and atrophy of follicle
3) Telogen- Resting phase, growth stops; hair breaks free and is shed.

Question 8

Functions of hair

Answer 8

• PROTECTION: tough keratin hairs covers sensitive structures (eyelashes)
  -WATERPROOF: sebaceous glands
• THERMOREGULATION: wool hairs trap air, arrector pili, sweat glands
• COMMUNICATION & CAMOUFLAGE: colour, arrector pili
  -SENSORY: tactile hairs

Question 9

Evolution of flight’s consequences

Answer 9

Reduced weight of everything:
Thin skin (cant be stitched) - 2 epidermal layers
Essentially gland-less

Question 10

Feather development

Answer 10

Developing feathers have a core of vascular dermis

Question 11

Feather structure

Answer 11

Main shaft- Rachis
Vanes either side
Made up of barbs with interlocking, microscopic barbules
Base of quil is called calamus

Question 12

Types of feathers

Answer 12

-Contour feathers: includes flight feathers- smooth streamlined
-Hyopenna: afterfeathers associated with contour feathers
-Down feathers: non-interlocking barbules trap air
-Semi-plumes: fluffy insulators
-Bristles: few barbs, sensory and protective
-Filoplumes: sensory and help with flight adjustment

Question 13

Powder down feathers

Answer 13

Produce fine, waxy keratin powder for cleaning and waterproofing
Causes human allergies
Absence is first sign of disease

Question 14

Scales

Answer 14

Reptile epidermis has 3 layers:
-Stratum basale
-Stratum intermedium
-Stratum corneum
Few glands
Homologous to hair and feathers- ectodermal origin
Can have osteoderms- bony plates in dermis

Question 15

Ecdysis

Answer 15

Skin shedding; controlled by thyroid gland
Replaces worn skin; can be sign of underlying problem (dysecdysis) abnormal process
Skin is more permeable- susceptible to infection and overdose
Clear spectacle turns opaque- causes aggression
May need high humidity and rough objects