11. Hair and Nails Flashcards
Function of hair
Protection (against UV damage)
Sensation (sensory innervation within follicles which can amplify sensation)
Thermoregulation (minimal in humans)
Communication
What are hair and nails comprised of?
Keratin
Products of hair follicle and nail matrix (respectively)
Where is hair?
Everywhere except mucous membranes, palms and soles
Only 5% of hair is on scalp
When does hair start growing?
3rd Trimester in utero
What is the pilo sebaceous unit comprised of?
Hair follicle
Hair shaft
Arrector pili muscle
Sebaceous gland
What is a hair follicle?
Invagination of epidermis containing a hair
What is the hair shaft comprised of?
Outer cuticle that encloses a cortex of packed keratinocytes
+ An inner medulla (in terminal hairs)
Where are germinative cells and melanocytes found?
In hair bulb
Arrector pilli muscle (autonomic control) is vestigal in humans
Contracts with cold, fear and emotion
To erect hair, produces goose pimples
Where are sebaceous glands found?
Associated with follicles, especially those of the scalp, face, chest and back
What are sebaceous glands formed of and what do they produce?
Formed of epidermis derived cells
Produce an oily sebum
When do sebaceous glands become large and active?
At puberty
As sensitive to Androgens
How is Sebum produced?
By holocrine secretion
In which cells disintegrate to release their lipid cytoplasm
Name the 3 types of hair
Lanugo
Vellus
Terminal
Describe Lanugo hair
Fine and long
Formed in fetus at 20 weeks.
Normally shed before birth but may be seen in premature babies
Occur in anorexia.
Describe Vellus hair
Short, fine and light coloured
Cover most of body
Describe Terminal hair
Longer, thicker and darker.
Found on scalp, eyebrows, eyelashes, and pubic, axillary and beard areas.
Originate as a vellus hair, differentiation is stimulated at puberty by androgens.
Pubic Louse
Adapted to grip terminal hair
Related to gorilla louse
Eyelashes – site for pubic louse attachment
Head lice and body lice are genetically different
Head lice only target hair on head - do not carry disease
Body lice can carry disease and do not target hair on head
Demodex mite
lives inside hair follicle of everyone,
not harmful
What is the only type of hair that a medulla is found in?
Terminal
How are hair fibres composed?
Keratin protein forms filaments which are supercoiled to form larger filaments, grouped/ linked together to form strong strands
Genetic defects in keratin
causes genetic syndromes with effects on hair, skin and nails
The Hair cycle
Anagen- Growing phase
Catagen- Resting phase, stops growing
Telogen- Sheds
Different hairs in different locations have different
Anagen length
determines maximum length of hair
Synchronicity of hair
Hair in synchronicity at birth
All hairs synchronise,
Leading to complete hair loss at 3 months
What is the normal synchronicity of hair?
normal for all hairs to asynchronous
Occurs after birth
Telogen effluvium
A cause of hair loss All hairs become synchronous again Premature termination of Anagen -->Telogen Diffuse Hair Loss Many causes e.g. stress Regrowth over 3-6 months
Testosterone Paradox
Hairs become thicker & pigmented
Androgens cause vellus follicle to become terminal follicle
Occurs on scalp of men (androgen sensitive area- Androgenic alopecia)
Causes hair to undergo miniaturisation
Miniturisation of hair
Each cycle hair becomes slightly smaller until it is wispy
and no follicle is left
Female pattern alopecia
hair thinning on top of head, but side preserved
androgens have a smaller role as more complex
Hirsutism
Hairy, in male patterned distribution (when it should not be) e.g. beard
e.g. In females / children caused by excessive androgen drive e.g. By PCOS, Drugs, Excess androgens
Alopecia Areata
autoimmune condition
Immune privileged state of anagen stops, leading to patchy hair loss
Folliculitis
Inflammation of follicles e.g. acne
Function of nails
Protection (weapon) – Chemical, physical Touch – Manual dexterity Communication – socially
Structure of nails
Mostly hard “hair” keratin
Strong:
– Longitudinal Ridging
– Curvature
What does nail matrix contain?
Dividing cells which mature, keratinize and move forward to form nail plate
Thickness and growth rate of nail plate
Thickness: 0.3-0.5mm
Growth rate: 0.1mm /day (finger nail)
What produces the small amount of pink colour of nails?
Adjacent dermal capillaries
What is the visible part of the nail matrix?
White lunula
What is the Hyponychium of a nail?
Thickened epidermis that underlies the free margin of the nail.
What is the nail surface produced by?
Proximal nail bed
Clubbing
Tip of fingers swollen
Nail is distorted >180 degrees
Many disorders cause clubbing e.g. Lung cancer
Beau’s Lines
Systemic illness or severe trauma causes ridge in nail
Koilonychia
spoon shaped nails
inherited, can indicate iron deficiency anaemia, hyperthyroid, drugs
Psoriasis
Pitting in nail
Salmon spots- psoriatic plaques visible under nail
Onycholysis- nail plate splits away from nail bed
Yellow nail syndrome
Rare
Onset 40-50 with lung/sinus disease
Nail Pigmentation
Melanonychia Striata or Melanoma
Streaks indicates something in nail matrix is making pigment
Systemic sclerosis
Giant capillaries
Microhaemorrhages
Dermoscopy finding disrupted/ irregular/ thrombosed hairpin vessels on nail cuticle
sign of Systemic Sclerosis
