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
