Integument 2 Flashcards
Hair, feathers, scales and glands
What does hair, feathers and scales all develop from?
- all develop from epidermis interacting with underlying mesenchymal tissue
Hair, feathers, scales are homologous structures what does this mean?
- they share a common ancestry
How can hairs, feathers and scales come to be?
- two layers will come together
- then will then fold
- then secrete proteins which can interact and make individual structures
How do teeth and mammary glands develop?
- through an epidermal-mesenchymal interaction
- a single evolution origin, modified to make all these different ectodermal organs
What are the stages of hair follicle development?
- ectodermal bud growing into mesenchyme
- differentiation of the bud and indications of glands = primitive hair follicle, sweat gland bud, sebaceous gland bud
- developed hair follicle with accessory structure = arrector pili muscle, sweat and sebaceous gland
What is the structure of hair?
- long thin chain of keratin protein
- unique to mammals
What is the hair typically composed of?
- a central medulla
- a thick cortex
- an outer cuticle
The structure of hair can vary and can be used to identify different species.
what is different about wool hair for example?
- it has no medulla
What are the 3 basic hair forms?
- stiff straight guard hairs (topcoat)
- fine wavey wool hairs (undercoat)
- thick long tactile hairs (stiff and straight and project deeply into dermis) = sensory function
What Animals can have a compound follicle be found in?
- dogs
- cats
- sheep
- goats
What is a compound follicle?
- several hairs share a single follicle opening
- usually one primary (guard hair) and several secondary (wool) hairs
- below sebaceous gland, each hair has its own follicle and bulb
What animals have a single follicle?
- horses
- cattle
- pigs
- humans
What is a single follicle?
- one primary (guard) hair
How do you describe the orientation of guard hairs?
- generally lie against the skin and run in tracts of the same direction
Why do guard hairs run in the same direction?
- encourages water to run off skin in one direction
Name some species specific modifications of guard hairs:
- mane, tail and fetlock tufts of horses
- stiff, sparse bristles of pigs
- long tail hairs of cattle
- beard of goats
Domestic sheep have fewer what hairs?
- fewer guard (kemp) hairs
- so fleece is almost exclusively wool hairs
Where are tactile hairs mostly found?
and where can cats also have these hairs?
- mostly on face/head
- cats can have tactile carpus hairs too
How deep do tactile hairs reach?
- reach deep into subcutis or even muscle
What are tactile hairs surrounded by?
- surrounded by a venous sinus
Why are tactile hairs surrounded by a venous sinus?
- blood wave amplifies the stimulation
Tactile hairs also have a dermal sheath surrounding the follicle what does this contain?
- contains nerve endings
Guard and wool hairs have a limited lifespan and are gradually shed - why do are hair cycles offset?
- so healthy animals never totally loose their hair
Lots of shedding is seasonal - when are the peaks?
- spring and autumn
What can shedding be regulated by?
- regulated by pineal gland
- day length, temperature and nutrition
Why are domestic animals starting to shed all year round?
- we have changed their environment so it is at a constant temperature and nutrition is less variable meaning indicators for shedding are less obvious
What makes up the hair growth cycle and what can modify it?
- 3 phases with intrinsic rhythmicity
- can be modified by hormones
In normal-haired animals what phase are most hairs in?
- anagen
Name the 3 phases of hair growth:
- anagen
- catagen
- telogen
What is the anagen phase?
- growing phase
- most follicles
- duration is genetically determined
- hair is tightly anchored in follicle by root sheaths
What is the catagen phase?
- short transition phase
- growth slows
- atrophy of follicle
- involution (by apoptosis - programmed cell death) of inferior portion
What is the telogen phase?
- resting phase
- growth stopped
- hair eventually break free and can be shed due to shortening of follicle
- duration varies between breeds
- cycle starts over
Describe the process of active hair growth in anagen:
- there is a dermal papilla comprised of mesenchymal cells
- epidermal stem cells divide to produce hair shaft and sheath
- hair shaft is dead keratinocytes packed together
What can some atrophic diseases cause?
- miniaturisation of the follicle or arrest the cycle
- such as endocrine diseases
- endocrine alopecia
State the function of hair:
- protection
- water resistance
- thermoregulation/insulation
- communication/camouflage
- sensory function
How does hair protect?
- tough keratin hairs covering sensitive structures such as a tail covering genitalia
How does hair aid in water resistance?
- oily sebaceous glands opening into follicle
- same direction tracts of guard hairs encourages water run off in one direction
How is hair involved in thermoregulation and insulation?
- wool hairs trap air
- arrector pili and guard hairs
- some sweat glands open into follicle
How is hair involved in communication or camouflage?
- melanin (colours) = derived from epidermis
- arrector pili
- glands opening into follicle
How are hairs involved in sensory function?
- tactile hairs
Feathers are unique to birds (dinosaurs) - What are they homologous to?
- homologous to hairs in mammals
= keratin structure from epidermis
= shared ancestor (and similar function)
Feathers first evolved in non-avian dinosaurs for what purposes?
- insulation
- communication/display
- later used for flight
What are the consequences of evolution for flight?
- reduced weight of everything such as bone and skin
- skin is very thin and tears easily
Birds only have 2 epidermal layers what are they?
- stratum gerinativum (basale)
- stratum corneum
Birds skin is essentially glandless, it only has three glands what are these?
- uropygial (preen) gland
- aural gland
- vent gland
Developing feathers contain a core - what is it?
- a core of vascular dermis
= important difference from mammal hair
What may happen if a feather is plucked or broken out?
and
What should you never do to blood feathers?
- may bleed a lot
- should not cut blood feathers when clipping
What is the name for the main shaft of a feather?
- rachis
Feathers have vanes either side which can be asymmetrical - what are they made up of?
- made up of barbs
- with microscopic interlocking barbules
What is the base of the quill called?
- calamus
What is the structure of a contour feather?
- incudes flight feathers
- asymmetric vanes for an aerofoil shape
- interlocking barbules for a smooth streamlined, water proof surface
What are hyopenna (afterfeathers) associated with?
- contour feathers
What is the structure of down feathers?
- non-interlocking barbules trap air
What are semi-plumes?
- like down feathers, fluffy insulators
What is the structure and function of bristles?
- few barbs
- sensory and protective
What are filoplumes?
- sensory
- help with flight adjustment
Some birds have special powder down feathers what do these do?
- produce fine, waxy keratin powder
- similar function to preen gland (cleaning and waterproofing)
- often cause human allergies = pigeon fanciers lung
What birds have more abundant powder down feathers?
- bird species without a preen gland
What can be the fist sign of disease in birds?
- absence of feathers
- e.g. psittacine beak and feather disease
The reptiles epidermis had 3 layers what are these?
- stratum germinativum (basale)
- stratum intermedium
- stratum corneum
What are glands like in reptiles?
- few glands, restricted to certain areas of the body
Reptiles scales are homologous to what?
- hairs and feathers
- shared ancestry = all are keratin structures from epidermis
Reptiles and amphibians can sometimes also have osteoderms - what are these?
- bony plates in the dermis
- in tortoise, shell is formed from osteoderm fusion with ribs
Thick keratinised scales reduce what and what can this lead to?
- reduce skin sensations leading to a risk of thermal burns
Reptiles can have cutaneous appendages with special functions name some:
- clear spectacle scales over eyes
- light-sensitive parietal eye
- associated with pineal gland
- scales and structures that ais in locomotion (snake belly scales, adhesive toe pads)
- cloacal spurs aid in reproduction
- heat sensitive pits for prey detection
- crests, frills, horns, pouches, spines for display and defence
What is the scientific name for shedding?
- ecdysis
What is the role of shedding?
- replaces worn skin
- either whole or bit-by-bit
What controls shedding?
- thyroid gland
What reptile eats shed skin?
- geckoes
What is the name for improper shedding?
- dysecdysis
What issues can dysecdysis cause?
- constriction of body parts
What can cause dysecdysis?
- inappropriate humidity/ not enough rough objects
Inappropriate shedding can be a sign of what?
- underlying disease or husbandry problems
Reptile skin is more permeable what does this lead to?
- more susceptible to infection, parasites and medication overdose
What happens if the clear spectacle over the eye goes opaque as it separates?
- can cause animal to he more aggressive
There are two basic skin glands and further sub-types what are these called?
- sebaceous glands
- sweat glands
- eccrine
- apocrine (can sometimes open into hair follicle)
What are skin glands a modification of?
- the epidermis
- even though they penetrate into the dermis
What are sebaceous glands associated with?
- hair follicles
What structure do sebaceous glands have?
- many lobed (acinar) structure
What do sebaceous glands produce?
- fatty/oily sebum (lanolin in sheep)
What does sebum aid in?
- moistures and waterproofs hair and skin
- allows sweat to spread (thermoregulation)
- antimicrobial function
- pheromones or other scented compounds for communication
Some groups of sebaceous glands are enlarged and visible to the naked eye - what are these?
- horn glands
- glands of infraorbital pouch
What are the two types of sweat glands?
- apocrine
- eccrine
Describe apocrine sweat glands?
- discharge albuminous (protein-rich) sweat
- into hair follicles
- over most of body in domestic animals
- react with bacteria to produce an individuals odour
Describe eccrine sweat glands:
- discharge more watery sweat
- directly onto skin surface
- generally found in certain areas (naked skin)
- footpads of dogs
- nasolabial plate of cattle
What do sweat glands look like?
- coiled and tubular
