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