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Endo > Hair > Flashcards

Hair Flashcards

1
Q

Describe the strucure of hair

A
  • 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
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2
Q

Describe the 2 hair types

A
  • Primary: guard hairs, large

- Secondary: downy hairs

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3
Q

Which type of hair are sebaceous and sweat glands mostly associateed with?

A

Primary (but can be secondary as well)

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4
Q

Outline some species differences in hair structure

A
  • 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
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5
Q

What is meant by a simple follicle?

A

Each follicle contains single hair shaft of approx same size

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6
Q

What is meant by a compound follicle?

A

Mutliple hairs per follicular ostium

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7
Q

Describe the relationship of the epidermis with the hair follicle

A

Is continuous with the hair follicle wall

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8
Q

Where are the sebaceous glands located and what is their function in relation to hair?

A

Adjacent to the follicles at the isthmus, push hair up from beneath via secretions

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9
Q

Describe the regions of hair (moving bottom to top)

A
  • At base have distinct bulb
  • Then inferior portion
  • Then isthmus
  • Then infundibulum
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10
Q

Where is the arrector pili muscle located?

A

Around the isthmus (by the sebaceous gland)

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11
Q

Describe primary hair follicles

A
  • Bulb deep in dermis

- Associated sebaceous glands, sweat glands and arrector pili muscles

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12
Q

Describe secondary hair follicles

A
  • Smaller, not as deep in dermis
  • May have associated sebaceous gland, no sweat glands or arrector pili muscle
  • Often compound, but not necessarily
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13
Q

Describe the structure of compound hair follicles

A
  • 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
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14
Q

What are the different stages of the hair cycle?

A
  • Anagen
  • Catagen
  • telogen
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15
Q

Briefly outline the anagen phase of the hair cycle

A
  • 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
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16
Q

Briefly outline the catagen phase of the hair cycle

A
  • Transitional phase
  • Rarely seen in nroaml skin
  • Rapid cell death of cells at bottom, changes in keratin structure
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17
Q

Briefly outline the telogen phase of the hair cycle

A
  • Resting phase
  • Final stage
  • Bulb not as bulbus
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18
Q

Which species have anagenic hair growth?

A
  • Man
  • Angora rabbit
  • Mohair goat
  • Poodle
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19
Q

Which species have telogenic hair growth?

A
  • Most dogs and cats
  • Horse
  • Hedgehogs
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20
Q

What is meant by anagenic hair growth?

A
  • More anagenic hairs and shorter period between moults

- i.e. hair spends most time growing

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21
Q

What is meant by telogenic hair growth?

A
  • Long periods between moults
  • i.e. most time in telogen (resting) phase
  • Become increasingly telogenic with age
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22
Q

What determines hair length?

A

The duration of anagen

23
Q

What are the different pattens of shedding?

A
  • Seasonal
  • Wave
  • Mosaic
24
Q

Describe seasonal shedding

A
  • 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
25
Q

Describe wave shedding

A
  • 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
26
Q

Describe mosaic shedding

A
  • 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
27
Q

What is the hair cycle regulated by?

A
  • Photoperiod
  • Temperature
  • Hormones
  • Nutritional status and general health
  • Growth factors
  • Drugs
28
Q

How does alopecia occur?

A
  • Heavy insult on animal
  • Hair growh intruncated
  • Falls out in one go
29
Q

What is the blood supply to the anagen bulb?

A

Via dermal papilla

30
Q

What are the 6 layers of the anagen hair bulb?

A
  • 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
31
Q

Describe the transition from anagen to catagen hair bulb

A
  • 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
32
Q

Describe the development of the anagen hair

A
  • 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
33
Q

How is hair shaft moved up the follicle?

A

Rachet-like mechanism

34
Q

Descirbe the structure of the telogen hair

A
  • 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
35
Q

What is the role of hair?

A
  • Insulation
  • Signalling
  • Physical protection
36
Q

Explain the role of hair in epidermal regrowth

A
  • 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
37
Q

Describe the structure of vibrissae

A
  • Simple follicles

- Blood-filled sinus between inner and outer layers of dermal sheath i.e. blood filled sinus either side of hair shaft

38
Q

Describe the function of vibrissae

A
  • Mechanoreceptors
  • Wobble in follicle when touched due o fluid environment
  • Sense around the face (nose, above eyes, lips etc)
39
Q

Describe the function of tylotrich hairs

A
  • Simple follicles in amongst body hairs
  • Mechanoreceptors
  • Not as advanced as vibrissae
40
Q

Give examples of primary nutritional disease that can lead to impaired cutaneous function

A
  • Protein deficiency
  • Fatty acid deficiency
  • Vitamin and mineral deficiency or toxicosis
41
Q

Describe the effect of protein deficiency on cutaneous function

A
  • Poor hair growth (protein intensive process)

- Increased infection rates as epidermis weakened by low protein

42
Q

Describe the effects of fatty acid deficiency on cutaneous function

A
  • Stark hair growth
  • Greasy or dry skin and hair
  • Is essential for sebum production
43
Q

Describe the effects of vitamins and minerals on cutaneous function

A
  • 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
44
Q

Give secondary nutritional diseases that can cause cutaneous dysfunction

A
  • Hepatic dysfunction
  • Pancreatic dysfunction
  • Bowel disease
  • Genetic inability to absorb minerals
45
Q

Explain how hepatic dysfunction can lead to cutaneous dysfunction

A
  • Reduced amino acid supply
  • Necrosis of skin - hepatocytaneous cutaneous syndrome
  • Loss of ability to make skin cells
46
Q

Explain how pancreatic dysfunction can lead to cutaneous dysfunction

A
  • Poor fat absorption - dry scurfy skin and pruritus

- If skin disrupted in this way, tends to become itchy

47
Q

Explain how bowel disease can lead to cutaneous dysfunction

A

Poor absorption of various nutrients

48
Q

Explain how genetic inability to absorb minerals can lead to cutaneous dysfunction

A
  • e.g. Zn in Siberia husky - Zn-responsive dermatosis
  • Clinically see crusted hyperparakeratosis and bacterial infection
  • Histologically see parakeratosis
  • Zn neede for normal keratinisation
49
Q

Which hormones affect hair growth and what is their action?

A
  • 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
50
Q

Describe atrophic dermatosis (what and cause)

A
  • 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
51
Q

How do endocrine disorders lead to atrophic dermatosis?

A
  • Hyperadrenocorticism: cortisol increased
  • Hypothyroidism: thyroid hormone decreased
  • Sertoli cell tumour: increaed oestrogen
52
Q

describe the histological appearance of atrophic dermatosis

A
  • Thinning of epidermis
  • Thin dermis
  • Reduction in hair follicles and adnexal structures (sebaceous and sweat glands)
  • All hair follicles in telogen
  • Little inflammation
53
Q

What is the effect of steroids on skin?

A
  • Thin epithelium
  • Few glands
  • Empty epidermis
  • Collagen strands weaker
  • Infection
  • No hair/all hairs in telogen with no new anagen

Endo (30 decks)

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