9 - Hair and Nails

Question 1

Where are hairs found on the human body?

Answer 1

over the entire surface of the skin, with the exception of the glaborous skin of the palms, soles, glans penis and vulval introitus

Question 2

Where is the follicle density greatest?

Answer 2

on the face

Question 3

What are the functions of the hair?

Answer 3

• 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

Question 4

Recall and describe the different types of hair

Answer 4

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

Question 5

State the sections/layers of the hair follicle (the pilo-sebaceous unit)

Answer 5

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

Question 6

What are the layers of the hair shaft?

Answer 6

• outer cuticle
• cortex - consists of packed keratinocytes
• inner medulla (in terminal hairs).

Question 7

What are the sebaceous glands/gland units?
Where are they found?
What cells are they made up of?
What is their function?

Answer 7

• 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.

Question 8

What is the arrestor pili muscle and what function does it have?

Answer 8

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’

Question 9

What does the hair bulb contain?

Answer 9

germinative cells and melanocytes (which synthesise pigment)

it is fed by blood from the dermal papilla.

Question 10

What are the phases of hair growth?

Answer 10

• anagen
• catagen
• telogen

Question 11

What happens in the anagen phase of hair growth?

Answer 11

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

Question 12

What happens in the catagen phase of hair growth?

Answer 12

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.

Question 13

What happens in the telogen phase of hair growth?

Answer 13

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.

Question 14

What is the dermal papilla?

Answer 14

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.

Question 15

How do the length of the stages of hair growth change with age?

Answer 15

anagen phase decreases in length - the rate of hair growth slows
telogen phase increases - hair loss

Question 16

What is telogen effluvium?

What can the causes stem from?

Answer 16

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)

Question 17

What are the effects of sex hormones (i.e. testosterone) on hair?

Answer 17

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

Question 18

What is androgenic alopecia?

Answer 18

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.

Question 19

What are the functions of nails?

Answer 19

protection of the tip
facilities grasping
touch - sensitivity of the finer/toe
communication

Question 20

What is the structure of nails?

Answer 20

consists of a plate of hardened and densely packed keratin

alpha keratin
little Ca2+
longitudinal ridging
proximal to distal curvature

Question 21

draw a diagram of a bail with the following labelled:

Answer 21

nail matrix
nail root
cuticle (eponychium)
nail plate
(distal edge of the nail plate)
hyponychium
nail bed

Question 22

What is the thickness of the nail plate?

Answer 22

0.3 - 0.5 mm

Question 23

What rate to finger nails and toenails grow at?

Answer 23

0.1 mm/day

toenails grow more slowly

Question 24

What produces the pink colour of the nail?

Answer 24

the adjacent deal capillaries

Question 25

What does the nail bed produce?

Answer 25

a small amount of keratin

the nail bed adheres to the nail plate

Question 26

What happens in the nail/geminal matrix?

Answer 26

it contains dividing cells which mature, keratinise and move forward to form the nail plate

the nail grows from the germinal matrix

Question 27

What is the lunula?

Answer 27

the crescent-shaped whitish area of the nail bed

it is the visible part of the root of the nail/the matrix

Question 28

What is the hyponchium?

Answer 28

the thickened epidermis that underlies the free margin of the nail

Question 29

What and where is the onychodermal band?

Answer 29

It is situated towards the distal end of the nail.

This is the seal between the nail plate and the hyponychium.