2 - hair, wool, feathers, scales Flashcards
What does homologous mean?
That they are different structures in different animals that share a common ancestor (so have evolved from the same thing).
What layers do feathers and scales develop from?
Epidermis interacting with underlying mesenchymal tissue.
Are hair, wool, feathers and scales homologous?
Yes
What layers do teeth and mammary glands develop?
Through an epidermal mesenchymal interaction
Describe the steps involved in teeth, mammary gland and hair, wool, feather, scale formation.
- The two layers (epidermis and mesenchymal tissue) come together they fold around eachother and then secrete proteins.
Give the 3 steps of hair development
- The epidermal layer of skin forms an ectodermal bud which grows into the mesenchyme/mesoderm.
- The bud differentiates into a primitive hair follicle and then there becomes indications of glands forming.
- There is a developed hair follicle with accessory structures.
What is important about hair and mammals?
Hair is unique to mammals.
Give the structure of hair
Hair is a long thin chain of keratin protein
It is composed of a central medulla, thick cortex and an outer cuticle.
But the structure can vary in proportions depending on hair type.
What are the 3 basic hair forms?
- Stiff straight guard hairs (topcoat)
- Fine wavy wool hairs (undercoat)
- Thick long tactile hairs e.g. whiskers
What is the function of tactile hairs
They have a sensory function
Describe the hair and accessory structures of dog and cat hair.
In dogs and cats:
- Several hairs share one single follicle opening.
- There is usually one primary guard hair attached to the arrector pili and several secondary wool hairs
- Below the sebaceous gland, each individual hair has its own follicle and bulb - they just all share an opening.
How do guard hairs generally sit on the skin?
They lie against the skin and run in the same direction.
Give 4 examples of species specific modifications of guard hairs.
- Mane, tail and fetlock tufts of horses
- stiff, sparse bristles of pigs
- Long tail hairs of cattle
- Beards of goats
What type of hairs make up the sheeps fleece (give proportions of each)
They have hardly any guard hairs (which are called kemp hairs in sheep) and the fleece is almost all wool hairs
What is different about the fleece of wild sheep and domesticated sheep?
Wild sheep have more guard hairs.
Why do healthy animals never lose all their hair?
Because the hairs have offset growing cycles so all the hairs arent shed at once, most are growing.
When does most shedding happen?
Shedding is seasonal - there are peaks in spring and autumn and may also vary geographically.
What is shedding moderated by?
The pineal gland
What regulates shedding?
Day length, temperature, nutrition
Give the stages of the hair growth cycle in order
- Anagen
- Catagen
- Telogen
- Anagen again
Describe anagen
It is the growing phase
Most follicles are in this stage - otherwise youd lose hairs faster than they can be replaced
Describe catagen
The transition phase
The growth of hair slows
You get atrophy of the follicle where it shortens and pushes the hair out
Describe telogen
Resting phase
Growth of the hair is stopped
The follicle shortens to the point where the hair eventually breaks free and can be shed
Describe the second anagen
A new bud starts to form and a new hair grows which helps to push out the old one.
Where are most tactile hairs located?
The face/head
What special tactile hairs do cats have?
Carpus tactile hairs on the carpus
Describe the tactile hairs (and how they work)
They reach deep into the subcutis or even muscle
The hair follicle is surrounded by a venous sinus which is a pocket filled with blood, the blood waves amplify sensory stimulation to the animal.
The dermal sheath that surrounds the follicle contains nerve endings which transmit stimulation to the animal so it can sense what’s nearby.
Name the 5 functions of hair
- Protection
- Water resistance
- Thermoregulation/insulation
- Communication/camouflage
- Sensory function
How does hair function in protection?
There are tough keratin hairs covering sensitive structures like the eyes.
How does hair function in water resistance?
There are oily sebaceous glands that open into the follicle - the oily secretions coat the hair and make it waterproof.
The guard hairs run in tracts in the same direction so water runs along the tracts off the animal
How does hair function in thermoregulation/insulation?
Wool hairs trap air
Arrector pili muscles attach to guard hairs and raise the hairs to elevate them.
Some sweat glands open into the follicle so sweat coats the hair which helps with evaporative heat loss
How does hair function in communication/camouflage
There are different coloured hairs
The arrector pili elevate hairs which can be used in displays
Some glands open into the hair follicle - this spreads smelly substances like pheromones further because it increases surface area so the pheromones can diffuse further into the environment.
How are hairs involved in sensory function?
There are tactile hairs - they sense things nearby.
Other hairs have sensory function but tactile hairs have taken it to the extreme especially with the blood sinus.
What group of animals are feathers unique to?
Birds
How are hairs and feathers homologous?
They are both a keratin structure from the epidermis.
They have a shared ancestry so have similar functions
What animals did feathers first evolve in?
Non avian dinosaurs
What are feathers homologous to in mammals?
Hair
What makes feathers and hairs homologous?
They are both a keratin structure from the epidermis
They have shared ancestry and similar function
What were the 3 functions of feathers in non avian dinosaurs?
Insulation
Communication and display
Later they were used for flight which isnt universal
Comment on the thickness of bird skin
Its very thin and tears easily.
Name the epidermal layers of bird skin
Stratum germinativum (basale) Stratum corneum
Name the 3 glands that birds have - and say where they are
- Uropygial (preen) gland - base of the tail
- Aural gland - near ear
- Vent gland - near back end
Describe the features of developing feathers and considerations you should have for them.
Developing feathers contain a core of vascular dermis (a blood vessel supplying the feather).
This is an important difference from mammal hair.
So, feathers may bleed lots when plucked out or broken.
Blood feathers shouldnt be cut when wing clipping.
What happens to the feathers vascular dermis when the feather has finished growing?
It regresses and becomes a normal feather.
Describe the structure of a feather
Main shaft = rachis
Theres vanes either side which can be asymmetrical t to promote lift
The vanes are made of barbs which have microscopic interlocking barbules hence they stick together.
The base of the quill = calamus.
Name the 6 types of feather and describe them
- Contour feathers - includes flight feathers, they often have asymmetric vanes for an aerofoil shape to promote lift and interlocking barbules for a smooth streamlined waterproof surface
- Hyopenna (afterfeathers) - associated with contour feathers
- Down feathers - have non interlocking barbules to trap air to insulate
- Semi-plumes - like down feathers, are fluffy insulators
- Bristles - have a few barbs, they are sensory and protective in function
- Filoplumes - they are sensory and help with flight adjustment
Do all birds have powder down feathers?
No only some species
What type of birds have powder down feathers?
Species that dont have a preen gland
What do powder down feathers produce and why?
They produce a fine waxy keratin powder which is similar in function to the preen gland - it cleans and waterproofs feathers.
Powder down feathers are often a cause of human allergies - what is the condition called that humans get?
Pigeon fanciers lung
What does absence of powder down feathers indicate in a bird that should have them?
It can be the first sign of disease - psittacine beak and feather disease
Name the 6 functions of feathers
- Protection
- Water resistance
- Thermoregulation
- Communication/camouflage
- Sensory function
- Flight and locomotion
Why is the protective function of feathers so important?
Because bird skin is so thin
How do feathers waterproof birds?
There are oily secretions from the preen gland (or powder down) and interlocking barbules.
Which feathers mainly function in thermoregulation?
Down feathers and semiplumes
How do feathers function in communication and camouflage?
They can be different colours
There can be elaborate feathers which are used in courtship like peacocks
Feather muscles can fluff up feathers for displays
Which feather types mainly have a sensory function?
Bristles and filoplumes
Name the layers of reptile epidermis
- stratum germinativum
- stratum intermedium
- stratum corneum
Are scales homologous to hairs and feathers?
Yes - they are all keratin structures derived from the epidermis
What are osteoderms and which animals have them?
They are bony plates in the dermis, reptiles and amphibians can have them
How is tortoise shell formed?
From osteoderm fusion with the ribs
What is an important consideration of reptile scales in terms of husbandry and why?
They have a risk of thermal burns because their thick keratinised scales reduce skin sensation.
What is reptile skin shedding called?
Ecdysis
Which gland controls ecdysis?
Thyroid gland
In what pattern are scales shed?
Can be all at once or bit by bit
Which species of reptile eats the shed skin?
Geckoes
What is dysecdysis?
Improper shedding
What are 3 considerations needed when reptiles are shedding.
- The skin is more permeable so the animals are more susceptible to infection, parasites and medication overdose if medicating through skin
- The clear spectacle over the eye goes opaque as it separates so the animal may be more agressive because it cannot see.
- The reptiles may need higher humidity and rough objects to shed properly
Which germ layer are fish scales derived from?
They are dermally derived from mesoderm.
Is fish skin or reptile skin more permeable?
Fish
What is the lateral line system composed of?
Modified epithelial cells.
What does the lateral line in fish do?
It senses movement, vibration, pressure in surrounding water so can help the fish with orientation, schooling, defence and predation.
