HAIR Flashcards
What is a hair follicle?
an extension of the epidermis
describe the simple hair follicle:
one, primary hair (known as guard hair)
describe the compound hair follicle:
one primary hair, plus multiple secondary (usually wool) hairs
what animals have simple hair follicles?
horses, cattle pigs humans
what animals have compound hair follicles?
dog, cat, sheep, goats
What are the three basic hair forms?
Guard hairs
Wool hairs
Tactile hairs
What are guard hairs?
stiff straight (topcoat)
What are wool hairs?
Fine wavy (undercoat)
What are tactile hairs?
sensory function (whiskers)
What can guard hair tracts help with?
promote water runoff
differences between guard hairs and wool hairs?
shorter, thinner, wavy
what is the advantage of wool hairs?
traps air between the wool fibres
blood sinus?
spaces around the hair follicle that contains blood - around tactile hair follicle
why blood sinus?
amplify vibrations - increase efficiency of sensory system
why do hairs shed?
they have come to the end of their lifecycle
when does shedding peak?
spring and autumn
what is shedding regulated by?
pineal gland
4 stages of hair lifecycle:
anagen, catagen, telogen, anagen (again)
Describe the anagen stage of the hair cycle:
growth phase - most follicles are in anagen
Describe the catagen stage of the hair cycle:
transition phase, growth slows, atrophy of follicle
Describe the telogen stage of the hair cycle:
resting phase, growth stopped, hair eventually breaks free and can be shed
Describe the anagen (again) stage of the hair cycle:
hair pushed out
5 functions of hair?
protection, water resistance, thermoregulation/insulation, commmunication/camouflage, sensory function
How can hair be useful for protection?
tough keratin hairs covering sensitive structures
how can hairs help with thermoregulation?
wool hairs trap air, arrector pili + guard hairs, some sweat glands open into the follicle
how can hairs help with communication/camouflage?
colours, arrector pili, glands opening into follicle
How many epidermal layers do birds have?
2
what are the two epidermal layers of the birds?
stratum germinativum (basale)
stratum corneum
how many glands do birds have?
only 3 - essentially glandless
name the three glands a bird has:
uropygial (preen) gland
aural gland
vent gland
what do developing feathers contain?
a core of vascular dermis (a blood feather) - therefore it may bleed if plucked or broken
difference between contour and down feathers:
contour feathers have interlocking barbules whereas down feathers don’t but this makes them good at trapping air
how many types of feathers are there?
6
what is the rachis?
main shaft of the feather
what is the calamus?
the base of the quill
tactile hairs equivalent in birds are called?
bristle hairs - on faces of some birds
if birds don’t have a preen gland, what do they have in more abundance?
powder down feathers
describe the powder found in powder down feathers?
fine, waxy keratin powder
what causes allergy to birds?
the powder found in powder down feathers
how many layers does the reptile epidermis have? name them
3
stratum germinativum (=basale)
stratum intermedium
stratum corneum
what are scales homologous to?
to hairs and feathers
hairs, feathers, scales are all homologous meaning?
shared ancestry - all keratin structures from epidermis
Why can reptiles risk thermal burns?
thick keratinised scales which reduce skin sensation
what is ecdysis?
skin shedding
what is skin shedding controlled by?
the thyroid gland
what is dysecdysis?
in reptiles skin is more permeable (when shedding), meaning?
more susceptible to parasites, infection and medication overdose
what happens to snakes when they are shedding?
they go blind - so have a behavioural change
why do snakes go blind during shedding?
the clear spectacle scale over the eye goes opaque as it separates
what is the additional organ that fish have which other organisms do not?
lateral line system
where are the tactile hairs found on a horse?
around the nares (nostrils), eyes and mouth
What type of hair is the mane on a horse?
Guard hair
Which cells determine skin and hair colouration?
melanocytes - in the basal layer of the epidermis. These melanocytes produce melanin granules that travel to the tips of the melanocyte cell, are pinched off and then phagocytosed by surrounding cells
Where are the guard hairs mainly found on a sheep?
Face and legs
Explain the difference between the coat of a horse and the coat of a domestic sheep?
Sheep barely have any guard (kemp) hairs, the coat of a sheep is generally less pigmented (fewer melanin granules from melanocytes)
They have lost the ability to shed their spring coat
Explain how we have to look after sheep differently to horses because of their coats?
Due to barely any guard hairs, sheep can get waterlogged in the rain
They have to be shorn
What forms the undercoat?
wool
What forms the topcoat?
guard hairs
What is the fleece in a sheep?
the guard hairs and the wool hairs together
What are the guard hairs called in sheep?
kemp
