Integument 2; Hair, feathers, scales Flashcards
What do hairs, feathers and scales all develop from?
-Develop from the epidermis interacting with the underlying mesenchymal tissue
These are all homologous structures, what does this mean?
They share a common ancestry
What else develops through an epidermal-mesenchymal transition?
Teeth and mammary glands
How does a hair follicle develop?
1) Ectodermal bud grows into the mesenchymal beneath
2) There is then differentiation of the bud and sweat and sebaceous glands start form
3) The developed hair follicle is then formed with all the accessory structures
What are the 3 layers of a hair?
1) Cuticle
2) Cortex
3) Medulla
What is hair made of?
A long thin chain of keratin proteins
What is different about the structure of wool hairs?
They have no medulla
What are the 3 different types of hair?
1) Guard hairs (stiff and straight)
2) Wool hairs (fine and wavy)
3) Tactile hairs (sensory function)
What is the difference between a compound follicle and a single follicle?
Compound follicle - several hairs share a single follicle opening
Single follicle - one, primary guard hair
Describe a compound follicle
- One primary guard hair, several secondary wool hairs.
- Below the sebaceous gland, each hair has its own follicle and bulb
Which species have compound follicles?
Compound = dogs, cats, sheep, goats
Which have single follicles?
Single = horses, cattle, pigs, humans
What is the orientation of guard hairs?
They lie against the skin and run in tracts in the same direction
What features on horses are made of guard cells?
Mane, tail, fetlock tufts
What about on cattle and goats?
- Long tail hairs on cattle
- Beards on goats
What is unique about the structure of tactile hairs?
- Reach deep into the subcutis
- Surrounded by a venous sinus
- There is a dermal sheath surrounding the follicle which contains nerve endings
What is the importance of this venous sinus?
When the hair vibrates, the liquid in the sinus moves and vibrations are amplified in the dermis.
What gland regulates the hair growth cycle?
Pineal gland
What factors affect shedding and hair growth?
- Seasonal (shedding peaks in spring and autumn)
- Affected by day length, temp and nutrition
What phase of the growth cycle are most hairs in?
Anagen phase
What happens in each of the 3 phases of hair growth?
1) Anagan = growing phase
2) Catagen = transition phase, growth slows
3) Telogen = resting phase, growing stops
What type of diseases can cause hair loss?
Endocrine diseases
In the anagen phase, which cells produce the hair and what cells make up the hair shaft?
- Epidermal stem cells divide to produce the hair
- Hair shaft made of dead keratinocytes
How is the hair anchored to the follicle in the anagen phase?
Tightly anchored by root sheaths
How is apoptosis used in the catagen phase?
Programmed cell death at the base of the follicle to make the follicle shorten - follicle is shortest in telogen phase.
How does the hair provide a protective function?
- Tough keratin hairs cover sensitive surfaces
- Can cover sensory organs such as the eye
How do hairs aid with water resistance?
- Oily sebaceous glands open into follicles
- Guard hairs run unidirectional to encourage water flow off
How do hairs aid with thermoregulation?
- Wool hairs trap air
- Arrector pili and guard hairs
- Some sweat glands open into follicle
How do hairs aid with communication and camouflage?
- Melanin (colour)
- Glands open into follicle
What 2 layers are present in the epidermis in birds?
- Stratum germinativum
- Stratum corneum
What 3 glands are present in bird skin?
1) Uropygial gland (preen gland)
2) Aural gland
3) Vent gland
What feathers should be avoided when wing clipping?
Blood feathers
Describe the structure of a feather
- Rachis runs down the middle
- Vane on either edge
- Barbs either side of the rachis
- Calamus at the base of the quill
What are the 6 different types of feather?
1) Contour feathers
2) Hyopenna
3) Down feathers
4) Semi-plumers
5) Filoplumes
What type of feather helps with water waterproofing and flight?
Contour feathers
What type of feather is good for insulation?
Down feathers
What are powder down feathers?
Down feathers that produces fine, waxy keratin powder (helps to keep feathers clean) + waterproofing
Absence of powder can indicate disease
What are the 3 layers of the epidermis in reptiles?
- Stratum germinatium
- Stratum intermedium
- Stratum corneum
What do reptiles (and some amphibians) have that other animals do not?
Osteoderms (bony plates in the dermis)
What leads to reduced skin sensation in reptiles?
Thick keratinised cells
Which gland controls ecdysis (skin shedding)?
Thyroid gland
What are some specialized cutaneous features of reptiles?
- Clear spectacle scale over eyes
- Belly scales aid locomotion in snakes
- Heat sensitive pits aid prey detection
What is dysecdysis?
Improper shedding = old skin can dehydrate and shrink to cut off circulation
What happens to the spectacle scale during shedding?
- Goes opaque
What are the 2 types of skin glands?
1) Sebaceous glands
2) Sweat glands
Describe the structure and location of sweat glands
They are coiled, tubular glands
They sit within the dermis but are derived from the epidermis
What are the 2 different types of sweat glands?
- Eccrine
- Apocrine
What do sebaceous glands look like?
Lobed, acinar structure
What do sebaceous glands produce?
Produces fatty, oily sebum
- Moisturises and waterproofs hair and skin
- Antimicrobial function
- Pheromones released
What do apocrine sweat glands produce?
Discharge albuminous sweat (protein rich)
- Reacts with bacteria to produce odour
Where are apocrine sweat glands found?
Found in haired skin
What do eccrine sweat glands produce?
Discharge watery sweat onto the skin surface
Where are eccrine sweat glands found?
Found in particular areas of naked skin (e.g., foot pads/ nasolabial plate of cattle)
