Hair and hair follicles Flashcards
What is hair made of?
It consists of very strong proteins held together by sulphur bonds to form a very un-dissolvable structure (and subsequently undigestable)
What are the two types of hair?
Primary (guard hairs)- accessory glands associated
Secondary (downy hairs)
Can hair grow back after damage?
Hair stem cells live deep in the dermis so hair can grow back even after a severe graze
What is the difference between primary and secondary hair follicles?
Primary hair follicles: have a bulb deep in the dermis and associated sebaceous glands, sweat glands and arrector pilli mm.
Secondary hair follicles: are smaller and not as deep in the dermis the may have an associated sebaceous gland but no sweat glands or arrector pilli muscles
What are the names given to the portions of hair above, at and below the sebaceous gland?
Below is the inferior portion, at the sebaceous gland it is called the isthmus and above it is called the infundibulum
What is the difference between a single and compound hair follicle?
Single hair follicle: a single hair protrudes from the follicular orifice
Compound hair follicle: multiple hairs use the same follicular orifice and converge at the level of the sebaceous gland
Name the three stages of the hair cycle?
Anagen: the growth phase
New hair is produced under the existing hair in the deep dermis
Distinctive bulb containing follicular dermal papilla
Catagen: transitional phase
Rarely seen in normal skin but is a common feature in skin diseases such as alopecia
Telogen: Resting phase
Name some animals that mostly have telogenic growth
Most dogs and cats
Horses
Hedgehogs
Name some animals that mostly have anogenic growth
Angora rabbit
Mohair goat
Poodle
What determines hair growth?
The duration of anagen determines hair length and as an animal ages the amount of time spent in telogen increases
Name the three types of shedding
Seasonal shedding- most follicles exhibit a burst of growth at specific times of the year (due to climatic demands) e.g. Cows, sheep, goats and deer
Wave shedding- shedding and regrowth at specific areas of the body and a gradual spread of new growth from there. 5 main wave patterns are: Caudal, Vetrad (eg autumn moult of rabbit), dorsal, cephalad and diffuse.
E.g. Mice and rabbits
Mosaic shedding – hair enters a cycle while adjacent hairs may remain in anagen so hairs are grown and shed over an entire year. Cats show short period of relative inactivity in winter and a surge of growth in late summer although this is not seasonal change as not all hairs are in the same stage of the cycle.
e.g. cats and dogs
What regulates the hair cycle?
Photoperiod
Temperature
Hormones
Nutritional status & general health
Growth factors e.g. Fibroblast growth factor
Drugs: TGF- beta is a cytokine that will induce hair growth (found in cyclosporine)
What effect do the following hormones have on hair growth: Thyroid hormone Growth hormone Oestrogen Corticosteroids
Thyroid hormone (+ve effect on growth)
Growth hormone (+ve effect)
Oestrogen (-ve effect)
Corticosteroids (-ve effect)
During anagen the hair bulb epithelium undergoes…..
mitosis and the melanocytes provide pigment
What are the characteristics of a hair in catagen?
Occurs in the mid dermis and consists of the involution of the hair bulb and dermal papilla, upward migration of the follicle and papilla and loss of the internal root sheath.
The hair develops a thick glassy membrane (analogous to the basement membrane of the epidermis above the bulb of the follicle)
What are the characteristics of a hair in telogen?
In mid to upper dermis and is recognised by:
A bulb at the level of the attachment of the arrector pilli muscle (1/3 of original length) and much longer
The hair becomes surrounded by the external root sheath which terminates at the sebaceous gland level
The bulb becomes separated from the dermal papilla by a thick basement membrane
The original bulb becomes dormant and the new bulb and papilla form beneath the old follicle
What are vibrissae hairs?
Sinus hairs
Simple follicles with blood filled sinus between the inner and outer layers of the dermal sheath
Found in the nose, above eyes and around lips
Associated with mechanoreceptors
What are tylotrich hairs?
Simple follicles in amongst body hairs associated with mechanoreceptors
What effect does a lack of protein have on the hair and skin?
Poor hair growth
Increased infection rates due to a poorly differentiated epidermis
What effect does a lack of fatty acids have on the hair and skin?
Stark hair growth due to lack of sebum
Greasy or dry skin and hair
What effect does a lack of vitamins and minerals have on the hair and skin?
Copper deficiency in cattle (spectacles)
Vitamin A and zinc are essential for normal skin (zinc rids the squames of their nuclei)
Toxicosis also possible (e.g. Selenium and mercury)
What is Atrophic dermatosis and what can cause it?
Non-itchy bald animals
Common in systemic endocrine disease
Comedones formation occurs and we see Thinning of the dermis and epidermis, Reduction on hair follicles and adnexal structures (sebaceous and sweat glands), All of the hair follicles in telogen and Little inflammation
What is Hirsutism? What can cause it?
Is an increased length of coat and can be caused by:
Addison’s disease - little to no glucocorticoids in the body
Ciclosporin administration which causes anagen and thus length increased
