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Hair evidence & criminal investigation
Small hairs can not escape the prying eyes of an expert.
Grows almost everywhere
Naturally shed.
Be left on clothing or scen
e unintentionally / force
OutlineBiology features of hair Introduction
Hair structure
Hair growth
Color & shape
Distribution
Forensic identification Whether the hair-like evidence in question is hair?
Whether the hair originated from an animal or a human?
Individualize a human hair.
body area? damage? Poison?
Biology features of hair
• produced from hair follicle( 毛囊 )
• develop hair follicles during fetal
development (胎儿发育)
• composed of keratin( 角蛋白 )
Introduction
Medulla 毛髓质
Filled with air
Appears opaque 不透明
Filled with liquid
Appears translucent 半透明
Hair structure
Medulla 毛髓质
Not present in all human hairs
Presence of medulla varies quite a bit: even hair to hair
continuous Interrupted Fragmented
Hair structure
Five regions of a single head hair (from proximal to distal)
Same hair,
different medulla
Hair structure
Human hair
Be continuous or discontinuous.
Not large,<1/3 the width of the hair shaft
Medulla: important for species identification
cattle
deer
deer
Animal hair
Be continuous.
>1/3 the width of the hair shaft
Specific pattern
Medulla
Hair structure
• spindle-shaped cells
• parallel to the length of the hair
• Embedded with pigment granules
Hair cortex 毛皮质
梭形细胞
Hair structure
Uniform distribution Peripheral distribution
One-side distribution Central distribution
Pigment distributionHair structure
Human hairGreater than medulla, >1/3
Distribution of pigment: even, slightly
more towards cuticle
Animal hairLess than width of medulla,<1/2
Distribution of pigment: Central or denser towards medulla
Cortex
Hair structure
Hair cortex 毛皮质
The cortex varies in:
• Thickness
• Texture
• Color
Important for matching.
纹理
Hair structure
Hair cuticle 毛小皮
•outer layer of the shaft•overlapping scales
•Characteristic:–How many are there per centimeter –How do they overlap–Its overall shape –Its thickness– Whether or not it contains pigment.
Important in species distinguishing
Hair structure
Coronal Scales冠状鳞片
Bat/some other rodent 啮齿类
Spinous Scales
棘状鳞片 Cats, seals and mink
Bat 蝙蝠 Mink 水貂
Scales are triangular in shape and tend to lift away from the hair at their tips
Hair structure
Anagen Phase 生长初期
High metabolic and mitotic activity; 2-6 years
Follicle re-forms.
Need a strong pull to detach them from the papilla.
Roots : appear fleshy, sometimes with pigmentation.
Sheath tissue may be attached.
Sheath 毛根鞘
Catagen Phase 生长中期
The inner root sheath begins to disintegrate 蜕变 .
Melanin 黑色素 production stops.
The hair gradually stops growing ; 2 to 3 weeks.
Hairs stay attached to the remains of the follicle
Appears brush-like but with no sheath adhering
No sheath
Telogen phase 生长终期
Follicle is very short , the papilla is separated.
Mitotically inert and contain less DNA.
Lasts for 3-4 months.
No sheath attached, little or no pigment.
Telogen finishes when a new anagen phase commences.
Hair color & hair shape
Influenced heavily by genes.Intentional alteration (perming 烫 /dyeing) can affect the physical appearance
The distribution of hair 毛发分布
Except for the lip, palm, footplate, finger and toes.
The body area determined by
the length, shape, color, stiffness, curliness, microscopic
appearance.
continuous double medulla trace medulla,soft
Beard 胡须Limb 腿毛
Pubic 阴毛
Stiff , curl
Naturally shed hairs, Undamaged, club-shaped roots.
Forcibly removed hairs
Tissue attached
Forcibly removed hairs
Exhibit stretching and damage to the root area
Anagen Phase Catagen Phase Telogen Phase
Which phase? Naturally shed or Forcibly removed?
A B C
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