HAIR ANALYSIS - PowerPoint PPT Presentation

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HAIR ANALYSIS

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  1. HAIR ANALYSIS

  2. Hair • Hair grows from a hair follicle • The parts of a hair include the bulb, root, and shaft • The bulb is an expansion at the end of the hair from which the rest of the hair grows • The root of the hair is the part of the hair that is embedded in the skin • The shaft of the hair is the part that can be seen

  3. Hair (cont.) • The shaft of the hair is made up of keratin and has 3 layers: • Cuticle • Cortex • Medulla

  4. The Cuticle • Transparent, outermost layer that helps hold the medulla and cortex together • Scale-like in appearance, the scales point away from the scalp

  5. The Cortex • Surrounds the medulla and consists of flattened cells • It is the largest part of the hair shaft • This layer contains the pigment (melanin) that gives hair its color

  6. The Medulla • The medulla is the central part of the hair and is made up of large cells separated by air spaces; it can be:

  7. Medullary Index • A ratio of the size of the medulla compared with the size of the entire hair • MI = x/y where x is the medullary diameter and y is the total diameter

  8. MedullaryIndex (cont.) • In humans, the MI is less than 1/3 • In animals, the MI is greater than ½

  9. Pigmentation: Human vs. Animal • Human hair tends to have more pigment toward the cuticle while animals have more pigment towards the medulla • Animal pigments are often found in solid masses called ovoid bodies while human hairs are usually one color along the length • Animal hairs can change color abruptly creating a banded pattern; humans do not have banded hair

  10. Cuticle: Human vs. Animal • Some mammals (i.e. rodents and bats), have scales that give the appearance of a stack of crowns; these are called coronal • Some mammals (i.e. cats, seals, and minks), have scales that resemble petals; these are called spinous • Humans have scales that are flattened and narrow; these are called imbricate

  11. Types of Hair • Scalp: has a uniform diameter in cross-section • Beard: coarse, curved, and when viewed in cross-section has a distinctive triangular shape • Eyebrow, nose, ear, and eyelid: shorter and stubbier than scalp hair and have wide medullas • Axillary: have unevenly distributed pigments; end in a fine point when uncut • Auxiliary: oval or triangular, depending on whether the body region has been regularly shaved • Pubic:oval or triangular

  12. Hair Growth Hair proceeds through 3 stages as it develops: • Anagenstage: • hair actively grows • cells around the follicle rapidly divide and deposit materials in the hair • 80-90% of hairs are in this stage • Catagenstage: • hair grows and changes • 2% of hairs are in this stage

  13. Hair Growth (cont.) • Telogenstage: • follicle becomes dormant • hair easily lost during this stage • 8-18% of hairs are in this stage

  14. Hair Dyes • Cause hair to have less pigment granules • Hair dyes will color both the cortex and the cuticle so the cuticle’s inner margin is obscured or dark • Because hair grows at a rate of 1.3 cm per month, it is possible to determine the amount of time that has passed since the hair was dyed

  15. Forensic Hair Analysis • When hair is found at a crime scene, forensic scientists use the medullary index to determine if the hair is human or animal • If the hair is human, the part of the body from which it originated can be determined • Because hair from one part of the body are not always the same (brown hair with some gray), 50 hairs are usually collected from the suspect’s head

  16. Race Determination • African: hairs are curly with densely packed, unevenly distributed pigment granules; medulla is discontinuous or absent • European: often straight or wavy with pigment that is more evenly distributed; medulla is discontinuous or absent • Asian: straight with continuous medulla and thick cuticle