Chapter 3: The Study of Hair Flashcards
Hair is considered as what kind of two evidences?
- Trace Evidence
- Class Evidence
Characteristics of Hair
- can be easily left behind
- secondary transfer (common w/ animal hair)
- does not easily compose
- offers clues to racial background
- chemical tests (drugs, heavy metals, nutritional deficiencies)
- DNA (if follicle is present)
What is the function of hair?
- regulates body temperature
- decreases friction
- protects against sunlight
- acts as a sense organ
Structure of Hair
- Hair shaft
- Sebaceous Gland
- Follicle
- Papilla
Follicle
structure in the skin
Hair Shaft
made of (Keratin) > a protein produced in the skin
Papilla
contain the blood vessels that supply the nutrients to feed the hair & help it grow
Sebaceous Gland
secretes oil & helps to keep the hair conditioned
Keratin
made up of amino acids in a spiral shape
Hair Shaft
- Cuticles
- Cortex
- Medulla
- Pigment granules made of melanin
3 Layers of the Hair Shaft
- Cuticle
- Cortex
- Medulla
Cuticle
- the transparent outer layer of the hair shaft
- made up of scales that overlap each other and protect the inner layers of the hair
- human hair has a cuticle scales that are flattened & narrow which are called imbricated (animal hair is diff.)
Cortex
- the largest part of the hair shaft
- part of the hair that contains the pigment or melanin that gives the hair its color
- amount of pigment varies from person to person
Medulla
- center of the hair
- can be hollow or filled w/ cells
- 5 diff. medulla patterns
Medulla Patterns
- Continuous
- Interrupted (Intermittent)
- Fragmented or Segmented
- Solid
- None
Continuous
one unbroken line of color
Interrupted (Intermittent)
pigmented line broken at regular intervals
Fragmented or Segmented
pigmented line unevenly spaced
None
no separate pigmentation in the medulla
How can hair vary?
- Shape
- Length
- Diameter
- Texture
- Color
Head Hair
circular or elliptical cross section
Eyebrows & Eyelashes
circular w/ tapered ends
Beard Hair
thick & triangular/coarse/double medulla
- underarm
- body hair
What happens w/ treated hair?
- bleaching hair removes pigment & gives hair a yellow color (hair is brittle/disturbs the scales on cuticle)
- changes the color of the hair shaft
- cuticle & cortex take on the color of the dye
Racial Differences
- beard racial categorization can be made by identifying certain characteristics of hair
- characteristics may not be applicable to all individuals in these groups
- individual hair cannot be assigned to any of these groups
Animal Hair
- pigment is denser toward the medulla
- bonded color patterns
- medulla: thicker
Human Hair
- pigment is denser toward the cuticle
- no bonded color patterns
- usually one color
Medulla Index
- diameter of medulla/diameter of the entire hair
- index < .5 human hair
How are hair samples collected during an investigation?
- plucked
- shaving
- scrapping
- placing tape over the surface so that hair sticks to it
- vacuum large surfaces
Life Cycle of Hair
- Anagen
- Catagen
- Telogen
Anagen
- lasts 1,000 days
- 80-90% of human hair is in this stage
- active growth
Catagen
- 2%
- hair grows & changes/turns grey
Telogen
- 10-18%
- hair follicle is dormant. hair is easily lost
How do you analyze a hair sample?
- Macroscopically
- Microscopically
- Fluorescence Microscope
Macroscopically
hair length, color & curliness (naked eye)
Microscopically
pattern of the medulla, pigment of the cortex & types of scales on the cuticles
Fluorescence Microscope
can detect dyes & hair treatments
Neuron Activation Analysis
- used to identify 14 different elements in a 2cm long strand of hair
- high energy neutrons bombard the hair
- Cu, Au, Mn, Na, Ag, Sb, Ar, Br
- Probably of 2 ppl having the same concentration of 9 diff. elements is 1 in a million
Why is hair follicle important?
- blood & tissue attached to the follicle can be analyzed
- DNA analysis
Another name for a hair follicle is the….
called follicular tag
The hair shaft is considered what kind of evidence?
Class evidence
How can you test for substances in the hair shaft?
- hair grows out of the skin & the chemicals that the skin absorbs can become Incorporated in the hair
- chemicals, toxins and drugs and be detected
