Hair Flashcards
What does the human hair consist of?
follicle and shaft
Shaft
can see
mitochondrial DNA
contains keratin
Follicle
can not see
mitochondrial and nuclear DNA
cells and blood vessels
When is hair individual evidence?
DNA - except identical twins
Hair is a type of
trace evidence
If hair is left behind it is…
Locard’s principle of exchange
Why do we have hair?
regulates temperature
decreases friction
protects skin against UV light
acts as a sense organ
The hair shaft
made of keratin, a protein that make hair strong and flexible
Three layers of the hair shaft
medulla (inner)
cortex
cuticle (outer)
The cuticle
a transparent outer layer of the hair shaft
scales point toward end of hair, revealing younger and older ends of hair
in human hair, overlapping scales are flat and narrow = imbricate
The cortex
largest part of hair shaft
contains most of melanin in hair
distribution and size of pigment granules vary from person to person
The medulla
center of hair
can be pigmented or unpigmented
Six types of hair
head hair eyebrows and eyelashes beard and mustache hair underarm hair body hair pubic hair
Hair varies from region to region on the..
body of the same person
Four phrases of the hair growth cycle
Catagen
Telogen
Exogen
Anagen
Anagen
the state in which hair grows
.5 inches per month on average
short phrase: stress, poor diet, and aging
Catagen
the period of time in which the hair detaches from the blood vessels and dermal papilla
lack of oxygen and nutrients
lasts for two weeks
Telogen
hair detached and resting in skin
last three months
Exogen
an extension of the telogen characterized by the shedding of telogen hair
Bleaching
lightens hair by oxidizing pigment makes it brittle can disturb scales on cuticle artificial = sharp line natural (bleaching from the sun) including the cuticle and cortex
Dyeing
dye stains entire hair including the cuticle and cortex
can use growth rate of hair (.44 mm per day on average) to calculate time since death
Pattern of pigmentation
Human: pigmentation is denser toward the cuticle
Animal: pigmentation is denser toward the medulla
Medulla
Animal: is thicker in animals to provide insulation
Greater than or equal to .5 = animal
Less than or equal to .5 = human
Cuticle patterns
Imbricate = like overlapping roof tiles; humans Coronal = like stacked crowns; mice Spinous = like spines or petals; cats
Collecting hair in an investigation
plucking shaking scraping using tape vacuum
Macroscopically
look at length, color, and curliness
Mircoscopically
medulla pigmentation pattern, cortex pigmentation, and types of cuticle scales
measure meduallary index
Because hair grows out of the skin anything ingested or absorbed through your skin
food, water, drugs, toxic substances
Analysis can reveal
a person’s travels, their diet their drug intake, and toxin
The more melanin present in the hair
the more binding of drugs such as cocaine and morphine
Washing of hair does not eliminate the drugs through
anything that destroys the pigment will decrease binding of the drugs
