form & structure of hair. hair is frequently found at a crime scene hair is frequently found at...
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Form & Structure of HairForm & Structure of Hair
Hair is frequently found at a crime sceneHair is frequently found at a crime sceneLocard Exchange PrincipleLocard Exchange Principle
Hair is considered class evidenceHair is considered class evidenceCould possibly be individualized if root tissue Could possibly be individualized if root tissue
is still attached to the hairis still attached to the hairVery useful in supporting Very useful in supporting
circumstantial evidence circumstantial evidenceCan be used to place someone Can be used to place someone
at the crime scene at the crime sceneCan link a criminal with the crimeCan link a criminal with the crime
From hair, one can determine:From hair, one can determine:
If the source is human or animalIf the source is human or animal
RaceRaceo SometimesSometimes
Based on shape of hairBased on shape of hair
Origin of the location on the source’s bodyOrigin of the location on the source’s body
Whether the hair was forcibly removedWhether the hair was forcibly removed
o By whether or not root attachedBy whether or not root attached
Whether the hair has been treated with Whether the hair has been treated with chemicalschemicals
If drugs have been ingestedIf drugs have been ingested
Human body has about 5 million hairsHuman body has about 5 million hairso Most are downy hair covering bodyMost are downy hair covering body
Hair is continuously shed & renewed Hair is continuously shed & renewed throughout lifetimethroughout lifetimeo About 100/24 hour period on head aloneAbout 100/24 hour period on head alone
Much higher rate of loss for body hairMuch higher rate of loss for body hair
Hair on the headHair on the heado Blonds have most – about 120,000 strandsBlonds have most – about 120,000 strandso Redheads have least – about 80,000 strandsRedheads have least – about 80,000 strandso Black/Brown in the middle – about 100,000 Black/Brown in the middle – about 100,000
strandsstrands
Must understand structure of hair to Must understand structure of hair to analyze itanalyze it
Made up of cross-linked protein polymersMade up of cross-linked protein polymerso Very resistant to breaking downVery resistant to breaking down
Grows from a tube-like organ called a Grows from a tube-like organ called a folliclefollicleo Located in the dermisLocated in the dermis
Follicle is linked to the body’s blood Follicle is linked to the body’s blood supplysupplyo Whatever is taken into body is distributed Whatever is taken into body is distributed
to part of hair growing at that timeto part of hair growing at that timeo Important in analyzing hair for drugs & Important in analyzing hair for drugs &
poisonspoisonsHair shaft extends through Hair shaft extends through
epidermis & ends at tip epidermis & ends at tipo Shaft composed of Shaft composed of
dead cells dead cells
Composed of three parts:Composed of three parts:oCuticleCuticle
Clear, outer covering of shaftClear, outer covering of shaftMade of tough, overlapping scalesMade of tough, overlapping scales
Scales finer in humans compared to animalsScales finer in humans compared to animalsoCortexCortex
Made of protein called keratinMade of protein called keratinEmbedded with pigment that gives hair colorEmbedded with pigment that gives hair colorContains air sacs called cortical fusiContains air sacs called cortical fusi
Different shapes & sizesDifferent shapes & sizesPossible class characteristicPossible class characteristic
oMedullaMedullaCanal running down center of cortexCanal running down center of cortexMay be dark or translucent depending on May be dark or translucent depending on contentscontents
Outer most layer of hair covered with scalesOuter most layer of hair covered with scalesScales point toward tip of the hairScales point toward tip of the hairScales differ among species of animalsScales differ among species of animals
o Named based on their appearanceNamed based on their appearanceThree basic scale patterns include:Three basic scale patterns include:
o CoronalCoronal Mouse Mouse
o SpinousSpinous Cat Cat
o ImbricateImbricate Human Human
To visualize scalesTo visualize scales::
Paint clear fingernail Paint clear fingernail
polish on a glass slide.polish on a glass slide.
When the polish begins When the polish begins
to dry, place a hair on to dry, place a hair on
the polish.the polish.
When it is almost dry, When it is almost dry,
lift off the hair and lift off the hair and
observe the scale observe the scale
imprints.imprints.
What pattern is seen in What pattern is seen in
this slide?this slide?
Gives hair its shapeGives hair its shape Has two major characteristics:Has two major characteristics:
oMelanin is pigment that gives hair its colorMelanin is pigment that gives hair its colorProduced by melanocytes located in the follicleProduced by melanocytes located in the follicle
oCortical fusi are air spaces usually found near Cortical fusi are air spaces usually found near
the rootthe rootSometimes found throughout the cortexSometimes found throughout the cortex
May be dark or translucentMay be dark or translucento Depends on whether it contains air, liquid, or Depends on whether it contains air, liquid, or
pigmentpigmentMay be continuous, interrupted, or May be continuous, interrupted, or
fragmentedfragmentedHuman hair usually lack a medulla or has Human hair usually lack a medulla or has
one that is fragmented one that is fragmented o Except for Native Americans & Asians whose Except for Native Americans & Asians whose
hair have a continuous medullahair have a continuous medullaAnimal hairs have wide variety of medullar Animal hairs have wide variety of medullar
patternspatternso Patterns can identify some speciesPatterns can identify some species
Hair’s core that is not always visibleHair’s core that is not always visible Comes in different types and patternComes in different types and pattern Patterns Include:Patterns Include:
oInterruptedInterruptedoFragmentedFragmentedoContinuousContinuousoStackedStackedoAbsentAbsent
Human medulla may be continuous, Human medulla may be continuous, fragmented, or absentfragmented, or absent
Determined by measuring the Determined by measuring the diameter of the medulla then diameter of the medulla then dividing it by the diameter of the dividing it by the diameter of the hairhairo MI = MI = medulla diametermedulla diameter x 100 x 100 hair diameterhair diametero Medullary index for human hair is Medullary index for human hair is
generally <33 generally <33o Medullary index for animal hair is Medullary index for animal hair is
generally >50 generally >50
Deer MI = 100 Raccoon MI = 80 Human MI = 25
May be straight, curly, or kinkyMay be straight, curly, or kinkyoDepends on the cross-sectionDepends on the cross-section
Cross-section may be:Cross-section may be:o RoundRoundo OvalOvalo Crescent-shaped:Crescent-shaped:
RoundRound(Straigh(Straigh
t)t)
OvalOval(Curly(Curly
))
Crescent moonCrescent moon (Kinky)(Kinky)
Asians & Native AmericansAsians & Native Americanso Round cross section & no twistingRound cross section & no twisting
Caucasians, Mexicans, & Middle Eastern Caucasians, Mexicans, & Middle Eastern heritageheritageo Oval cross section & rarely twist Oval cross section & rarely twist o Evenly distributed pigmentationEvenly distributed pigmentation
African heritageAfrican heritageo Crescent-shaped cross section with a twistCrescent-shaped cross section with a twisto Dense, clumped pigmentation Dense, clumped pigmentation
UndulatedUndulated
TwistedTwisted
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