9 - Hair and Nails Flashcards
Where are hairs found on the human body?
over the entire surface of the skin, with the exception of the glaborous skin of the palms, soles, glans penis and vulval introitus
Where is the follicle density greatest?
on the face
What are the functions of the hair?
- protection
e.g. against UV damage, minor injury and eyelashes protect the eyes - sensation
hairs have sensory innervation within the follicles which can amplify sensation.” - thermoregulation (minimal in humans)
- communication / sexual attraction
Recall and describe the different types of hair
LANUGO - fine and formed in fetes 20 weeks - shed before birth TERMINAL - long, thick, dark - scalp, eyebrows, eyelashes, pubic, axillary and beard region - starts off as villus, differentiation in puberty triggered by androgens VELLUS - short, fine, light hair - covers the body
State the sections/layers of the hair follicle (the pilo-sebaceous unit)
The hair follicle is an invagination of the epidermis containing a hair.
INFUNDIBULUM - the portion above the site of entry of the sebaceous duct
ISTHMUS - (section of the follicle) contains the sebaceous gland units and the arrector pili muscle.
(SUPRABULBAR layer)
HAIR BULB
What are the layers of the hair shaft?
- outer cuticle
- cortex - consists of packed keratinocytes
- inner medulla (in terminal hairs).
What are the sebaceous glands/gland units?
Where are they found?
What cells are they made up of?
What is their function?
- are found associated with follicles (especially those of the scalp, face, chest and back)
- they are formed of epidermis derived cells
- they produce an oily sebum
NOTE: the glands are small in children but become large and active at puberty, being sensitive to androgens. Sebum is produced by holocrine secretion in which the cells disintegrate to release their lipid cytoplasm.
What is the arrestor pili muscle and what function does it have?
it is smooth muscle (under autonomic control)
it is vestigial (useless) in humans, it contracts with cold, fear and emotion to erect the hair, producing ‘goose pimples’
What does the hair bulb contain?
germinative cells and melanocytes (which synthesise pigment)
it is fed by blood from the dermal papilla.
What are the phases of hair growth?
- anagen
- catagen
- telogen
What happens in the anagen phase of hair growth?
Growing phase.
Lasts 3-7 years for scalp hair, only 4 months for eyebrows.
At any one time 80-90% of scalp hair are in anagen
highly vascularised and energy intensive
What happens in the catagen phase of hair growth?
Resting phase and lasts 3-4 weeks.
Hair protein synthesis stops, the follicle retreats towards the surface.
At any one time, 10-20% of scalp hairs are in catagen.
What happens in the telogen phase of hair growth?
Shedding phase, distinguished by the presence of hairs with a short club root.
Each day 50-100 scalp hairs are shed, with less than 1% of hairs being in telogen at any one time.
What is the dermal papilla?
They are a part of the papillary dermis
(the uppermost layer of the dermis. It intertwines with the rete ridges of the epidermis)
The dermal papilla are the superficial projections of the dermis (corium) that interdigitate/interlock with recesses in the overlying epidermis; they contain vascular loops and specialised nerve endings and are arranged in ridgelike lines best developed in the hand and foot (fingerprints). Their primary purpose to hook up the epidermis to a blood supply.
The ridges they form greatly increase the surface area between the dermis and epidermis. The main function of the dermis is to support the epidermis, so this greatly increases the exchange of oxygen, nutrients, and waste products between these two layers. Additionally, the increase in surface area prevents the dermal and epidermal layers from separating from each other by strengthening the junction between them. With age, the papillae tend to flatten and sometimes increase in number.
Dermal papillae also play a pivotal role in hair formation, growth and cycling.
How do the length of the stages of hair growth change with age?
anagen phase decreases in length - the rate of hair growth slows
telogen phase increases - hair loss
What is telogen effluvium?
What can the causes stem from?
occurs when there is a marked increase in hairs shed each day/thinning of hair.
This is a result of an increased proportion of hairs shifting from the growing phase (anagen) to the shedding phase (telogen)
(normally only 10% of the scalp hair is in the telogen phase, but in telogen effluvium this increases to 30+%)
this can have emotional, as well as physiological causes (hypothyroidism, sepsis and anaemia)
What are the effects of sex hormones (i.e. testosterone) on hair?
the testosterone surge in the beginning of puberty causes villus hair to change into terminal hair - pubic and axillary hair grows first
In the elderly, nose and ear hair
In the scalp, there is androgen sensitive hair - this determines the balding pattern
What is androgenic alopecia?
the most common type of progressive hair loss.
it is caused by a combination of genetic and hormonal factors. Dihydrotestosterone (DHT) is the main hormone responsible in genetically susceptible individuals.
DHT causes scalp hair loss by inducing a change in the hair follicles on the scalp. The hairs produced by the affected follicles become progressively smaller in diameter, shorter in length and lighter in colour until eventually the follicles shrink completely and stop producing hair.
What are the functions of nails?
protection of the tip
facilities grasping
touch - sensitivity of the finer/toe
communication
What is the structure of nails?
consists of a plate of hardened and densely packed keratin
alpha keratin
little Ca2+
longitudinal ridging
proximal to distal curvature
draw a diagram of a bail with the following labelled:
nail matrix nail root cuticle (eponychium) nail plate (distal edge of the nail plate) hyponychium nail bed
What is the thickness of the nail plate?
0.3 - 0.5 mm
What rate to finger nails and toenails grow at?
0.1 mm/day
toenails grow more slowly
What produces the pink colour of the nail?
the adjacent deal capillaries
What does the nail bed produce?
a small amount of keratin
the nail bed adheres to the nail plate
What happens in the nail/geminal matrix?
it contains dividing cells which mature, keratinise and move forward to form the nail plate
the nail grows from the germinal matrix
What is the lunula?
the crescent-shaped whitish area of the nail bed
it is the visible part of the root of the nail/the matrix
What is the hyponchium?
the thickened epidermis that underlies the free margin of the nail
What and where is the onychodermal band?
It is situated towards the distal end of the nail.
This is the seal between the nail plate and the hyponychium.
