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Biology of Hair and Nails
Trichinosis Molecular and Cellular Pathology
Dr Tim Scott-Taylor Health and Human Sciences
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Topics
Topics covered; the nature of hair follicles structure of keratin normal patterns of hair growth causes of hair lost
Tutorial; review of skin structure and function light microscopy
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Learning Objectives
to know the nature of skin follicles and hair
growth
to know the function of hair in animals and
humans
to know the structure of hair fibres
to understand the causes and treatment of
hair loss
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Hair
Longitudinal filamentous growth from the skin Composed of keratin Found mainly in mammals; definition of phylum Wool, fur, pelage
Function: insulation protection protective coloration ornamentation / communication sensory (vibrissae)
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Skin and Keratin
Keratinized stratified squamous epithelium is found only in the skin
Keratin accumulation within maturing cells effectively waterproofs the cells, blocking diffusion of nutrients and wastes. The cells subsequently die.
Hair is specialised adaptation of epithelial production of keratin
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Keratocytes
• keratocytes are cells that make
keratins
• >40 highly insoluble proteins
forming a network in the cytoplasm
of keratocytes.
• transform from undifferentiated
basal cells to cornified skin cells.• four continuous layers basal
spinous granular cornified
recognizablehistologically
In the course of approximately 13 days columnar basal cells mature through a polygonal spinous cell, a diamond-shaped granular cell to a flat cornified cell that covers 25 basal cells.
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Parts of Hair
Hair follicle; involution of epidermis
Root; implanted in skin
Shaft or scapus; projecting from
surface
hair Bulb; root enlargment, soft, white
Papilla; dermal, blood and nerves
Sebaceous glands; open into follicle
Arrector muscle; attached to
epidermis
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Nails
Longitudinal section through nail and its nail
groove
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Claws, Nails, Hooves and Spurs
Keratin structures found in all mammals except cetaceans (whales). Derived from reptile claws. Consist of dorsal unguis = nail plate
ventral subunguis = sole plate a) claws - unguis is curved and encloses the subunguis
retractable in some carnivores. b) hooves - Unguis completely surrounds subunguis.
cloven hooves in even-toed ungulates (Artiodactyls) c) spurs - in male monotremes a hollow keratin spur on hind legs
poison gland associated with it. d) nails - only in primates. Flat unguis + subunguis
greater precise manipulation of food or tools.
Some Horns and antlers rhino horn - mass of keratin threads produced by epidermis bovid horn - bony core, horny sheath, no shedding pronghorn - bony core, horny sheath shed annually
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Hair is a Defining Feature
Comparison Reptiles - Mammals
Reptiles Mammals
scales
few epidermal glands
no mammary glands
3-chambered heart
ectothermy
little cerebral
development
indeterminate growth
egg laying
hair
many epidermal glands
mammary glands
4-chambered heart
endothermy
much cerebral
development
determinate growth
live birth
Hair is characteristic of the phylla
Temperature regulation was a fundamental development in mammalian evolution
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Animal Hair
Fur, coat, pelage, wool: furry insulating covering Special adaptations; Spines; porcupine
Bristles; lion’s maneUV transporter; polar
bear dolphins, whales; aquatic adaptation
(otters and seals)
Size and hair; mass 1/ follicle per cm2
eg elephant, rhinoceros heat loss
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Types of Animal Hair
Vibrissae; elongated + stiffenedassociaed with many nerve
fibers mainly tactile receptors
facial and carpalespecially in
carnivores
primatesrodentia
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Underhair; main function is insulation.
a) wool long soft and curly angora
b) fur fine relatively short hairdefinitive growth
c) velli down or fuzz with velvety appearance
Types of Animal Hair
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Types of Animal Hair
Guard hair; long, straight and pointed overhairs present on most mammals
a) awns stiff intermediate sized hair, protects downb) spines enlarged, stiff guard hairs with finite growth
evolved parallel hedgehogs ~6 times in mammals spiny anteaters
tenrecs barbs porcupines
poisonous montremes
c) bristles long firm hair eg. horse and lion manes#
hair serves to insulate, to conceal, to signal, to protect, and to sense the immediate surroundings. Insulation serves to conserve heat, but can protect against excessive heat eg camel
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Tenrec
•Tenrec ecaudatus(tailless tenrec)
•The common tenrec occurs on Madagascar and on the Comoro Islands, between Madagascar and Africa.
• Pelage is not dense and is a combination of hairs and blunt spines.
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Spiny Anteaters
Echidnas, genus Tachyglossus, subclass Holotheria.
monotreme found only in Australia
and New Guinea. lays a single egg that is
kept in her pouch for seven to ten days until spines begin to harden
• Pelage a mixture of spines and quills
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Hair on Humans Filamentous growth from the skin Mainly in mammals; genus definition Function head: protective,
ornamentaleyelashes: protect eyes from dusteyebrows: shield eyesaxillae; wicking of sweat
scalp palmsaxillae solespubes penischest labiabeard fingers
mucus membranes Naked ape
terminal hair
bareeverywhere else covered in vellus hair
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Naked Ape
Great apes have sparse and bare areas but none extensiveWhy is man different????1). Adaptation; cool forest to hot savana bipedal
locomotion upright stancebut other cursorial apes, eg gorilla, chimpanzee, no lossape pelage shields from UV, wind, radiant heat
2). Eco-parasites; fitness cost high cohabitation, communal living but other gregarious apes, eg chimpanzee, no loss
3). Aquatic ape; 5-7 e6 yr BC, Danakil region Ethiopiaextended period wading lifestyle
hair loss and subcut. fat more efficient theory not account for eccrine gland, density same as gorilla an chimp but developed for sweat production
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Neoteny
paedomorphism slowing of certain aspects of physiological development retention by adults of juvenile physical characteristics dogs share many physical features of immature wolves Louis Bolk 1926: "man is a primate fetus that has become
sexually mature" advocated by; Desmond Morris: The Naked Ape
Stephen Jay Gould: chimp bone brain 4 fold increase in hominid brain size over past 3e6 years loss of body hair a side effect
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Types of Hair
Languno: fine hair covers nearly entire embryo
Vellus: poorly pigmented, short, peach fuzz growing most areas
Terminal: fully developed, longer, coarser thicker and darker
Middle ear hair
Although vellus hair continues to develop and accounts for 6% to 25% of scalp hair, it is less noticeable because of its light pigmentation
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Depth
vellus follicles situated high in the dermis
large terminal follicles rooted deep in the subcutaneous fat
Dermis
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Variable Skin
The density of hair and the numbers of associated eccrine glands varies with different situations in the body
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Hair Growth
Hair elongates from the dermal papilla
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Length And Growth Rate
Length of hair and growth rate per day vary for each site on the body
hairs on the head 70cm / 0.35mm Eyebrows 3cm / 0.15mm beards and whiskers 28cm / 0.4mm armpit hairs 8cm / 0.3mm pubic hairs 10cm / 0.2mm
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Normal Hair Growth
Cyclical pattern
Anagen = growth phase2.5 – 3
yearsCatgen = shortTelogen = resting 100
days
asynchronous
anagen1000 days
catgen
Telogen100 days
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Growth Cycle
• 100 to 150,000 follicles on the scalp
• ~95% of them are in an active growth phase called Anagen
• ~5% completed their growth phase
• Telogen hairs typically remain in the scalp for about three months before they are shed.• shampooing, combing or brushing typically releases hair at a rate of about 50 to 80 per day.
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Functions of Human Hair
head hair for insulation and protection; trauma UV
eyelashes blink to prevent entry into eye eyebrows, like awnings, protect the eyes from
sunlight and sweat that might be hazardous body hair for insulation; goose bumps
traps air residual?
axilla; wicking of sweat long hair; marker of health?
secondary selection
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Inner Ear Hair
Hairs in the ampullae of the semi-circular canals are responsible for balance
Otoliths, crystals of calcium carbonate, floating in gelatinous medium of the saccule brush against the stereocilia of the inner ear. This movement generates stereotypic awareness
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Hair Colour
Two types of melanin account for all possible hair colors:Eumelanin: colors hair brown to black Pheomelanin: an iron-rich pigment
colours hair yellow-blonde to red
Both made from amino acid tyrosine, by tyrosinase. Increased tyrosinase activity results in darker hair color
Melanocytes in the hair bulb contain subcellular organelles melanosomes; synthesize and store melanin.
Melanocytes deliver the melanosomes to keratinocytes, where they are incorporated into the growing hair shaft
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Long Hair
anthropologists speculate functional significance of long head hair may be adornment
byproduct of secondary natural selection once other somatic hair had been lost
or Fisherian runaway sexual selection;lustrous hair is a visible marker for a health waist length hair = ~1 m or 39 inches long
~80 months, 7 years, to grow long period of nutrition stability hygiene
explain why long hair attractive both sexes
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straight hair is round
Shape Affects Curls
curly hair is flattened
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Hair Structure
medulla = central core of cuboidal cells
cortex = highly packed cells
cuticular scale = outer layer
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Follicle The hair follicle consists of two coats—an outer or dermic,
and an inner or epidermic. The outer or dermic coat is formed mainly of fibrous tissue;
it is continuous with the dermis, is highly vascular, and supplied by numerous minute nervous filaments.
Dermal coat consists of three layers The most internal is a hyaline basement membrane, well-marked only in the larger hair follicles, it is limited to the deeper part of the follicle
Outside this is a compact layer of fibers and spindle-shaped cells arranged circularly around the follicle; this layer extends from the bottom of the follicle as high as the entrance of the ducts of the sebaceous glands.
Externally is a thick layer of connective tissue, arranged in longitudinal bundles, forming a more open texture and corresponding to the reticular part of the dermis; in this are contained the blood vessels and nerves.
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Keratins
A long-chain protein of >300 residues contain a high proportion glycine H
smallest amino acids alanine methyl sterically-unhindered hydrogen bonding between the amino and carboxyl groups peptide bonds on adjacent protein chains closely aligned and tightly bound fibres tertiary structure: fibres twisted in helical filaments second in stength to chitin in organic molecules
side chains
tight-helices
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Keratin Secondary Structure
keratin molecules > 300 residues high proportion of smallest of
amino acids; glycine H side group alanine, methyl side group.
sterically-unhindered hydrogen bonding between the amino and carboxyl groups of peptide bonds on adjacent protein chains
close alignment and strong binding between chains
keratin molecules twist around each other to form helical intermediate filaments.
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Keratin Tertiary Structure
keratin molecules twine around each other in a left-hand helix coil structure
two helices in turn form another left rotating helical fibre, called a protofibril
eight protofibrils form a circular or square structure, called a microfibril, that is the basis of the structure of hair.
This structure is stretchy and flexible and can be compared to a rope containing various threads that are twined together.
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The Arrangement of Fibres
• The a-helix coiled keratin molecules are wound together in protofibrils.• protofibrils are bound
together into microfibrils
• Bundles of microfibrils are stitched together to make macrofibrils
• Each hair is wrapped in a cuticle made up of protein scales and contains macrofibrils embedded in matrix proteins
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Interchain Bonding
In addition to intra- and intermolecular hydrogen bonds, keratins have large amounts of the sulfur-containing amino acid cysteine ~14%
disulfide bridges confer additional strength rigid, permanent, thermally-stable crosslinking
similar to sulfur bridges in vulcanized rubber
disulfide bonding contributes to insolubility of keratins
pungent smells of burning hair and rubber due to the sulfur compounds formed
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Strength
Intra- and intermolecular hydrogen bonds disulfide bridges that confer additional strength and
rigidity by permanent, thermally-stable crosslinking It can be made to curl ’permanently’ or set
temporarily. The breakage and reseting of the interchain bonds allow hair to regain its shape. Hair can stretched about 70%.
Cross-linking creates strength. Hair is equivalent in strenght to iron wire. A wound strand of 5 mm can withstand a weight of 60kg
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Static
The close connections of chains is associated with the hair's ability to become charged with static electricity.
keratin is a good insulator of heat and electricity
The capacity to hold an electric charge is refered to as triboelectric
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Styling
hair heated with steam and pulled breaks the relatively weak hydrogen bonds the a-helices
The a-helices can elongate without breaking the molecules
• matrix proteins form a tangled supporting mechwork linked by many disulphide bridges. These bridges are also disrupted with moist heat• new interchain hydrogen bonds and disulphide bridges are formed after styling to keep the hair in its new style
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Nails Growth
Nail
Growth occurs from a nail bed over a keratin matrix layer
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Nail Keratin
Nailbed The nailbed is an essentially parallel epidermal structure located directly beneath the fingernail formed with parallel lines spaced at intervals. During normal growth, the fingernail travels over the nailbed.
The nail is also composed of keratin microfibrils but the molecules are arranged in flat B-pleated sheets
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Nails Arranged in Stacks
The molecules of b-keratin in finger and toe nails are organised in sheets stacked in layers. The proteins still fall into two groups; the helical and matrix, but in nail there is less sulphur in the matrix than in the hair matrix.
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Hair Length
Sexual selection; visible marker of health
1.25 cm / 0.5 inch per month: good hygiene39 cm = 7 years nutrition
healthstabilty
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Dimorphism
• male androgens at puberty
• testosterone
• vellus - terminal hair
• affects growth rate
weightlength
androgen sensitivity
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Hair and Culture
Much variation in style and length in different times and places
Egypt head hair shaved, especially children long single lock of hair growing
Middle ages: shaved head + wig 17 to 18th C: long hair
eg Cromwell Napoleon
Washington
WWI: lice and fleas brought typhus, short hair adopted
Maasai warrior
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Body Hair
attitudes towards hair on the human body also vary between different cultures and times
some cultures excessive chest hair on men is a symbol of virility and masculinity, other societies display a hairless body as a sign of youthfulness
ancient Egypt, people regarded a completely smooth, hairless body as the standard of beauty
adopted Greeks; hairless body = youth and beauty (strigyl)
Islam; many hair tenets, five traits of fitrah Western societies; removal, bikini fashion,
‘manscaping’
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Hirsutism
Hormonal changes alter hair presence and thickness
Vellus hairs on face of women,
invisible/inconspicuous
Oestrogen, antagonist of DTH
Menopause; thicker and darker
Diseases;
Polycystic ovary syndrome
Cushing's disease
ovarian or adrenal gland tumors
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Hair Loss
Whales & porpoises, and walrus use blubber for insulation.
Elephants, rhinos, hippos - warm climate, favorable mass/surface ratio -> retention of heat no problem.
molt = continuous or seasonal (1 or 2x /year) hair replacement
seasonal fur color change: arctic fox, hares, some weasels
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Hair Loss
caused by range of factors; genetic agingskin conditionsdiseases medications, eg anti-cancer drugs.mechanical damageskin infections.
The followings are the most common Alopecia areata Telogen effluvium Alopecia androgenica = Male Pattern Hair Loss
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Alopecia androgenica
characterized by "receding hairline" from lateral sides of the forehead
follicular miniaturization, shaft width decreases becoming fragile
30% males by 50 yrs 50% by 65 years66% of adult males
largely genetically determined caused by male hormones or
androgens esp DHT
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Male Pattern Baldness
occur in varying forms in about 66% of adult males at some point
characteristic (i) receding hair from lateral forehead stages; (ii) bald patch develops on vertex (iii) coalescence of patches
pattern baldness is classified on the Hamilton-Norwood scale I-VIII
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Process of Balding
In presence of DTH in genetically prone men, hair undergoes progressive thining;
- the anagen growth phase is shortened so the hair is shorter when it stops growing- overseveral life cycles progressive follicular miniaturization decreases shaft width and hair becomes thinner and shorter
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Treatments
Finasteride (marketed in the U.S. as Propecia) Minoxidil (marketed in the U.S. as Rogaine) Saw Palmetto (Serenoa repens) is an herbal DHT
inhibitor
easier to prevent the aging and falling out of healthy hairs than to regrow hair
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Alopecia Areata
characterized by patchy scalp hair loss
many as 1 in 1,000 people some time
most common causes are medications, pregnancy, birth control pills, thyroid malfunctions, anemia, syphilis, and arthritis
autoimmune response, immunological rejection, anti-follicular
Often resolves spontaneously 50% of people will have recurrence
Cyclosporins may have dramatic effects but are usually temporary
careful review of your medical history
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Alopecia Universalis
• complete loss of hair from all site of body
• some are born with some hair but begin losing it quickly
• can be inherited as an autosomal recessive trait. • traced to mutation in a gene dubbed HR in chromosome band 8p21.2. human homologue of mouse "hairless" gene
• Several families known where hairlessness passed through 3 generations
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Telogen Effluvium
characterized by sudden diffuse hair loss
general thinning of the hair over a period of months
most commonly experienced by those who have just given birth, or are undergoing chemotherapy
Also caused infection, severe chronic illness, severe psychological stress, majorsurgery, hyperthyroidism, Crash Diets resulting in poor health or inadequate protein, and medications
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Trichotillomania characterized by incessant
pulling or plucking of one's own hair
tillein Greek for "to pluck, pull out children, males most commonly
in adulthood and adolescence, most patients are females
hair manipulations usually occur sedentary activities, reading, writing, or watching television
impulse control disorder mental state characterized by
tension with gratification or relief from the hair pulling
once the behavior is established, it becomes habitual, regardless of the initial causative emotional problem
Resolution requires psychological intervention
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Tinea Capitis
infection characterized by bare patches of skin on the scalp
fungal infection of the skin of the scalp, eyebrows and eyelashes
most commonly found in children ages 10 and under,
scaly non-inflamed area of skin seborrheic dermatitis
person-to-person transmission. The organism remains viable on combs, brushes, couches, and sheets
Since effective treatment of Tinea Capitis by griseofulvin in the 1950s incidence dropped from 14% to 1.2%
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Aging
pigment in the hair is lost, hair becomes colourless time varies from person to person men tend to become grey at younger ages than
women pale blond hair becomes white instead of grey
red hair becomes a sandy color and later white gray or white appearance due to air bubbles in
medula scattering light scalp hair loss or thinning with aging in both sexes half of all men are affected by male pattern
baldness by the time they are 50
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Death
It is commonly claimed that hair and nails will continue growing for several days after death.
This is a myth; the appearance of growth is actually caused by the retraction of skin
as the surrounding tissue dehydrates, nails and hair become more prominent
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Histological Prep
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Crossectional View
medullacortex
cuticle
dermal sheath
epidermal sheath