ENI - Hair Flashcards
Describe the strucure of hair
- Specialised keratinised tubular structure
- Bound by sulfur bonds to be very tough (indigestible)
- 2 types of hair (primay and secondary)
- Cortex, medulla nad cuticle containing variable pigment
Describe the 2 hair types
- Primary: guard hairs, large
- Secondary: downy hairs
Which type of hair are sebaceous and sweat glands mostly associateed with?
Primary (but can be secondary as well)
Outline some species differences in hair structure
- Omnivores and herbivores have simple follicles
- Compound follicles in most sheep
- Density of follicles varies by species, breed, individual and body region
- Dog and cat have compound follicles
What is meant by a simple follicle?
Each follicle contains single hair shaft of approx same size
What is meant by a compound follicle?
Mutliple hairs per follicular ostium
Describe the relationship of the epidermis with the hair follicle
Is continuous with the hair follicle wall
Where are the sebaceous glands located and what is their function in relation to hair?
Adjacent to the follicles at the isthmus, push hair up from beneath via secretions
Describe the regions of hair (moving bottom to top)
- At base have distinct bulb
- Then inferior portion
- Then isthmus
- Then infundibulum
Where is the arrector pili muscle located?
Around the isthmus (by the sebaceous gland)
Describe primary hair follicles
- Bulb deep in dermis
- Associated sebaceous glands, sweat glands and arrector pili muscles
Describe secondary hair follicles
- Smaller, not as deep in dermis
- May have associated sebaceous gland, no sweat glands or arrector pili muscle
- Often compound, but not necessarily
Describe the structure of compound hair follicles
- Bulbs i groups, one large primary and many smaller secondary around it
- Keratin wall, tehn follicular wall
- Commonly grouped together and held in groups by fibrous sheath
What are the different stages of the hair cycle?
- Anagen
- Catagen
- telogen
Briefly outline the anagen phase of the hair cycle
- Growth phase
- New hair produced under previous hair, deep in dermis
- Distinctive hair bulb containing follicular dermal papilla
- Starts deep
- Actively growing so use up energy
- Relatively short period of time in anagen phase
Briefly outline the catagen phase of the hair cycle
- Transitional phase
- Rarely seen in nroaml skin
- Rapid cell death of cells at bottom, changes in keratin structure
Briefly outline the telogen phase of the hair cycle
- Resting phase
- Final stage
- Bulb not as bulbus
Which species have anagenic hair growth?
- Man
- Angora rabbit
- Mohair goat
- Poodle
Which species have telogenic hair growth?
- Most dogs and cats
- Horse
- Hedgehogs
What is meant by anagenic hair growth?
- More anagenic hairs and shorter period between moults
- i.e. hair spends most time growing
What is meant by telogenic hair growth?
- Long periods between moults
- i.e. most time in telogen (resting) phase
- Become increasingly telogenic with age
What determines hair length?
The duration of anagen
What are the different pattens of shedding?
- Seasonal
- Wave
- Mosaic
Describe seasonal shedding
- Follicles exhibit burst of growth at specific times of year to meet climatic demands
- E.g. cow shrorter thicker hair for summer, longer thinner hair (better insulation) for winter
- e.g. cow, sheep, goat, deer
Describe wave shedding
- Shedding and regrowth at specific areas of the body with gradual spread of new growth from there
- e.g. mice
- 5 wave moult patterns: caudal, ventrad, dorsal, cephalad, diffuse
Describe mosaic shedding
- e.g. cats, dogs
- Hair enters cycle while adjacent hairs may remain in anagen with hairs grown and shed over almost entire year in some species
- in cat, short period of relative inactivity in winter, surge of growrth in late summer
- Similar to seasonal change, but not all follicles within hair groups are at same stage of cycle at any one time
What is the hair cycle regulated by?
- Photoperiod
- Temperature
- Hormones
- Nutritional status and general health
- Growth factors
- Drugs
How does alopecia occur?
- Heavy insult on animal
- Hair growh intruncated
- Falls out in one go
What is the blood supply to the anagen bulb?
Via dermal papilla
What are the 6 layers of the anagen hair bulb?
- Medulla
- cortex
- Cuticle
- Huxley layer, Henle layer (inner root sheath)
- Outer root sheath (continuous with epidermis)
- Glassy membrane (basement membrane)
- All surrounded by dermal (fibrous) sheath
Describe the transition from anagen to catagen hair bulb
- In mid dermis
- Involution of hair bulb and dermal papilla
- Upward migration of follicle and papilla
- Loss of internal root sheath
- Thick glassy membrane develops
- Short: 2-3 weeks in man, 2-3 days in mous
Describe the development of the anagen hair
- Deep dermis
- Mesenchymal origin
- New hair pushed out old telogen hair
- Dermal papilla develops into hair and inner root sheath
- Canalisation (apoptosis) allows separation of hair into separate structure
- Exchange of melanin to give hair colour
How is hair shaft moved up the follicle?
Rachet-like mechanism
Descirbe the structure of the telogen hair
- In mid to upper dermis
- Bulb at level of attachment of arrector pili
- Surrounded by external root sheath, terminates sebaceous gland level
- Bulb separated from dermal papillae by thick basement membrane
- Original bulb dormant, elongated shape
- New bulb and papilla form beneath old follicle
- Pushed out by new hair
What is the role of hair?
- Insulation
- Signalling
- Physical protection
Explain the role of hair in epidermal regrowth
- Epidermis continuous with follicular wall
- If epidermis removed, some still present in follicle
- Should be enough stem cells to growth back
- i.e. hair acts as an epidermal stem cell reserve
Describe the structure of vibrissae
- Simple follicles
- Blood-filled sinus between inner and outer layers of dermal sheath i.e. blood filled sinus either side of hair shaft
Describe the function of vibrissae
- Mechanoreceptors
- Wobble in follicle when touched due o fluid environment
- Sense around the face (nose, above eyes, lips etc)
Describe the function of tylotrich hairs
- Simple follicles in amongst body hairs
- Mechanoreceptors
- Not as advanced as vibrissae
Give examples of primary nutritional disease that can lead to impaired cutaneous function
- Protein deficiency
- Fatty acid deficiency
- Vitamin and mineral deficiency or toxicosis
Describe the effect of protein deficiency on cutaneous function
- Poor hair growth (protein intensive process)
- Increased infection rates as epidermis weakened by low protein
Describe the effects of fatty acid deficiency on cutaneous function
- Stark hair growth
- Greasy or dry skin and hair
- Is essential for sebum production
Describe the effects of vitamins and minerals on cutaneous function
- Copper deficiency: pale, thin coat, lack of melanosome transport into hair and skin
- Vit A: hyper or hypo gives scaly skin
- Zinc: parakeratosis, is involved in keratinocyte differentiation
- Toxicosis of selenium and mercury
Give secondary nutritional diseases that can cause cutaneous dysfunction
- Hepatic dysfunction
- Pancreatic dysfunction
- Bowel disease
- Genetic inability to absorb minerals
Explain how hepatic dysfunction can lead to cutaneous dysfunction
- Reduced amino acid supply
- Necrosis of skin - hepatocytaneous cutaneous syndrome
- Loss of ability to make skin cells
Explain how pancreatic dysfunction can lead to cutaneous dysfunction
- Poor fat absorption - dry scurfy skin and pruritus
- If skin disrupted in this way, tends to become itchy
Explain how bowel disease can lead to cutaneous dysfunction
Poor absorption of various nutrients
Explain how genetic inability to absorb minerals can lead to cutaneous dysfunction
- e.g. Zn in Siberia husky - Zn-responsive dermatosis
- Clinically see crusted hyperparakeratosis and bacterial infection
- Histologically see parakeratosis
- Zn neede for normal keratinisation
Which hormones affect hair growth and what is their action?
- MSH creates colour differences
- Thyroid hormone stimulates hair growth
- Growth hormone stimulates hair groth
- Adrenal cortical hormones decrease hair groeth
- Oestrogen decreases hair growth
- Melatonin influences moulting and hair growth cycle
Describe atrophic dermatosis (what and cause)
- Common histological pattern in systemic endocrine disease
- Can be caused by hyperadrenocorticism, hypothyroidism, Sertoli cell tumour
- Reduced hair growth (telogenisation and later alopecia)
- Comedone formation
How do endocrine disorders lead to atrophic dermatosis?
- Hyperadrenocorticism: cortisol increased
- Hypothyroidism: thyroid hormone decreased
- Sertoli cell tumour: increaed oestrogen
describe the histological appearance of atrophic dermatosis
- Thinning of epidermis
- Thin dermis
- Reduction in hair follicles and adnexal structures (sebaceous and sweat glands)
- All hair follicles in telogen
- Little inflammation
What is the effect of steroids on skin?
- Thin epithelium
- Few glands
- Empty epidermis
- Collagen strands weaker
- Infection
- No hair/all hairs in telogen with no new anagen
