Structure Of The Skin - Appendages Flashcards
What are the three skin appendages
Hair, nails, glands
What are the three main skin glands
•Sebaceous
•Apocrine
•Eccrine
Where are sebaceous glands found in the body
Widely distributed:
largest glands in face and chest
=> most common areas of acne!!
Where are sebaceous glands in the skin and where do their secretions leave the skin
Wrapped around the hair follicle (pilosebaceous unit)
Holocrine secretion opening into pilary canal
Are sebaceous glands always active
No, they are hormone sensitive & so are quiescent pre-puberty. This explains the relationship between puberty & acne
What liquid do sebaceous glands secrete & what is this composed of
Sebum
- a mixture of lipids
- e.g. squalene, wax esters, TG and FFA
What is the role of sebaceous glands
Control moisture loss & protect against fungal infection
Where are eccrine sweat glands located in the skin and where do they open into
Located in the dermis
Secrete onto skin surface
Where are eccrine sweat glands most prominent
palms, soles, forehead and axillae
How are eccrine sweat glands regulated
Sympathetic cholinergic nerve supply –
mental, thermal and gustatory stimulation
What is the function of eccrine glands
cooling by evaporation
moisten palms / soles to aid grip
Describe the secretions produced by the eccrine sweat glands
Sweat
- Hypotonic fluid
- Mainly water (~98%)
- Some electrolytes e.g. NaCl, but most electrolytes reabsorbed
Where are apocrine sweat glands located in the skin
The dermis
They develop as part of the pilosebaceous unit
Where are apocrine sweat glands most prominent
Axillae, groin, eyelids, ears, mammary and perineal regions
How are apocrine sweat glands regulated
Androgen dependent
Describe the fluid secreted by apocrine glands & explain its odour
Produce an oily fluid which produces an odour after hitting the skin and being decomposed by bacteria
Name the phases of hair follicle growth & state what happens in them
Anagen = growing
Catagen = involuting
Telogen = resting
Exogen = shedding
Where in the body does skin not have hair follicles
(& so no pilosebaceous units & so no sebaceous/ apocrine glands)
Hands, soles of the feet & lips
How is hair follicle growth regulated
It is influenced by hormonal levels e.g. thyroxine, androgens
Is hair loss permanent in alopcia areata (autoimmune hair loss) Why or why not?
No - autoimmune reaction doesn’t permanently damage the follicle
What are pilosebaceous units composed of
Hair follicle
Hair shaft
Arrector pili muscle
Sebaceous glands
What is the role of arrector pili muscles
When it contracts it causes the hair to stand erect, and a “goosebump” forms on the skin
This serves as a thermoregulator to help maintain body temp in cold conditions
What are the three segments of a hair follicle
- Infundibulum - between the sebaceous gland duct & the epidermal surface
- Isthmus - between the insertion of the arrector pili muscle & the sebaceous gland duct
- Hair bulb - contains the hair matrix & hair papilla, is the deepest part of the hair follicle
What determines/ produces hair pigmentation
Melanocytes, that are located just above the dermal papilla
What is the papilla of the hair follicle (dermal papilla) & what is its role
Specialised connective tissue at the base of a hair follicle
Have androgen receptors & control hair growth
Provides oxygen/blood supply to hair bulb
What changes in the dermal papilla are associated with hair thinning
Reduced size & cellular activity
Describe the 3 layers of the hair shaft
Outer layer - Cuticle made up of keratin
Middle layer - Cortex made up of specialised keratinocytes
Inner layer - Medulla (only found in thick, coarse hair)
Name the two layers that cover the hair follicle cortex
External & internal root sheath
Does the hair shaft grow?
No - the hair follicle is the part that grows
Compare the hair structure of an Asian vs Black vs Caucasian individual
Asian hair
- straight hair
- strong hair
- round, large cross-sectional hair follicle
- fastest growing hair
- high/low hair density
Caucasian hair
- straight/ curly hair
- strong hair
- round/oval cross-sectional hair follicle
- fast/slow growing hair
- highest hair density, most moisture content
Black hair
- curly hair
- fragile hair
- ellipsoidal cross-sectional hair follicle
- slowest growing hair
- lowest hair density
Where is nail produced
Nail matrix
What is nail composed of
Specialised keratins
Name a drug that increases nail growth
Anti fungals
Name the main components of nail
Nail matrix - where growth occurs, under skin
Cuticle - protects nail matrix
Nail bed - underneath the nail plate
Nail plate - the nail itself
Name the three layers of the nail plate
Dorsal (outermost)
Intermediate
Ventral (innermost)
Summarise the three glands
Distribution
- sebaceous glands - largest in face & chest
- apocrine gland - axilla, mammary, ear, groin/perineal, eyelid
- eccrine (sweat) glands - most in palm/soles, forehead, axilla
Location
- sebaceous glands - wrapped around hair follicle
- apocrine glands - dermis, develop into pilosebaceous unit
- eccrine (sweat) glands - dermis
Opening
- sebaceous glands - pilary canal
- apocrine glands - pilary canal
- eccrine (sweat) glands - skin surface
Regulation/ stimulation
- sebaceous glands - hormone sensitive, activated by puberty
- apocrine glands - androgen dependant
- eccrine (sweat) glands - sympathetic cholinergic NS
Secretions
- sebaceous glands - sebum (mixture of lipids)
- apocrine glands - oily fluid
- eccrine (sweat) glands - hypotonic fluid (~98% water)
Role
- sebaceous glands - controls moisture, prevents fungal inf.
- eccrine (sweat) glands - cool by evaporation, moisten palms
Associated clinical disorder
- sebaceous glands - acne
- apocrine glands - HS
- eccrine (sweat) glands - Miliaria
