Morphology and Structure of Hair

Transcription

1 Hairs & Fibers

2 Morphology and Structure of Hair

3 Morphology of Hair An appendage of the skin that grows out of an organ known as the hair follicle. Extends from its root or bulb embedded in the follicle, continues into a shaft, and terminates at a tip end.

4 The Shaft of Hair Composed of three layers: cuticle, cortex, and medulla.

5 Morphology: Cuticle Protective coating made of overlapping scales, produce a characteristic pattern Scales always point toward tip of hair Not useful in individualizing human hair Can be used for species identification

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7 Preserving scale pattern Since examination of internal structure of hair requires loss of scale pattern, a scale case is made. Clear nail polish on microscope slide Hair embedded and allowed to dry before removed.

8 Differences between animal hairs and human hairs There are three basic scale structures that make up the cuticle coronal (crown-like), spinous (petal-like), and imbricate (flattened). Combinations and variations of these types are possible.

9 Differences between animal hairs and human hairs The coronal, or crown-like scale pattern is found in hairs of very fine diameter and resemble a stack of paper cups. Coronal scales are commonly found in the hairs of small rodents and bats but rarely in human hairs.

10 Differences between animal hairs and human hairs Spinous or petal-like scales are triangular in shape and protrude from the hair shaft. They are found at the proximal region of mink hairs and on the fur hairs of seals, cats, and some other animals. They are never found in human hairs.

11 Differences between animal hairs and human hairs The imbricate or flattened scales type consists of overlapping scales with narrow margins. They are commonly found in human hairs and many animal hairs.

12 Differences between animal hairs and human hairs Human hairs are generally consistent in color and pigmentation throughout the length of the hair shaft, whereas animal hairs may exhibit radical color changes in a short distance, called banding. The distribution and density of pigment in animal hairs can also be identifiable features. The pigmentation of human hairs is evenly distributed, or slightly more dense toward the cuticle, whereas the pigmentation of animal hairs is more centrally distributed, although more dense toward the medulla. The medulla, when present in human hairs, is amorphous in appearance, and the width is generally less than one-third the overall diameter of the hair shaft. The medulla in animal hairs is normally continuous and structured and generally occupies an area of greater than one-third the overall diameter of the hair shaft.

13 Morphology: Cortex Made of spindle-shaped cells aligned in a regular array, parallel to the length of the hair Embedded with pigment granules that give hair its color The color, shape and distribution of the granules provide points for forensic comparison

14 Your natural Hair color is determined by three factors 1. The type of natural color pigment melanin present in your hair's cortex. Eumelanin (black pigment) Phenomelanin (red/yellow pigment) 2. How many melanin granules exist 3. Whether those granules are close together or far apart

15 How Melanin pigments determine your natural haircolor: Black hair contains densely packed melanin granules full of eumelanin. Brown hair has a loose pattern of eumelanin-filled granules or granules blended with eumelanin and phenomelanin, depending upon its cool or warm tones and its darkness or lightness. Blonde hair contains few granules with minimal bits of eumelanin. In fact, the eumelanin is so sparse that the color of blonde hair is the color of the hair fiber itself. Red hair has loosely packed granules containing phenomelanin.

16 What causes gray hair? As you age, your natural production of pigment slows down and your natural color loses its color strength. This doesn't happen to every hair at the same time, so the contrast between the hair with no color and the hair that still has some color causes it to look gray. So how gray your hair actually looks is determined by the percentage of strands with no color vs. the pigmented strands.

17 Morphology: Medulla canal like structure of cells that runs through the center of the cortex

18 Medullary Index Measure of the diameter of the medulla relative to the diameter of the hair shaft Usually expressed as a fraction Humans: medullary index < 1/3 Animals: medullary index > 1/2

19 Medullae of Different Species

20 Medulla Shape Medulla shape is another characteristic that varies from species to species UNISERIAL (rabbit) MULTISERIAL (rabbit) VACUOLATED (dog, fox, common) LATTICE (deer) AMORPHOUS (human, common) 20

21 Medulla of Different Species

22 Forensic Analysis of Medulla Presence of medulla varies quite a bit: even hair to hair Human head hairs generally have no medulla or may be fragmented ones; except Mongoloid (Asian) race whose medulla is usually continuous Most animals have medulla that is continuous or interrupted The shape of the medulla can help identify a species Examples: Most animals and humans: cylindrical Cats: pearl shape Deer: spherical occupying whole hair shaft

23 Comparison of Animal and Human Hair Medullary Index 1/2 Medulla is present for all animals Medulla is continuous for most animals Medulla is patterned for most animals Medulla is fragmented only some animals and humans Medulla is cylindrical in shape (most animals) Medullary Index <1/3 Medulla is absent for most humans Medulla is continuous for Mongoloid race

24 Identification and Comparison of Hair Morphological Characteristics do not allow individualization of a human hair to any single head or body Hair when collected with an adequate number of standards/references can provide strong circumstantial evidence Scale structure, medullary index, and medullary shape are most often used for hair comparison Evidential value lies with degree of probability associated with a questioned hair and an particular individual 11 percent of all morphological hair matches are generally found to be non-matches meaning microscopic hair comparisons are presumptive in nature must be confirmed by DNA comparisons

25 Human Hairs Racial Determination Body Area Age and Sex? Forcibly Removed?

26 Can the racial origin of hair be determined? Forensic terms: Caucasoid, Negroid, Mongoloid Mongoloid has continuous medullae Caucasian has even distribution of pigment in cortex Negroid has unevenly distributed pigment.

27 Racial Determination Usually kinky, containing dense, unevenly distributed pigments. Mongoloid Negroid Cross section is flat to oval in shape. Usually straight or wavy with very fine to coarse pigments that are more evenly distributed. Cross section are oval to round in shape. Caucasoid Usually coarse containing pigment granules larger in size than Caucasians. Cross sections are round in shape.

28 Head Hairs Long with moderate shaft diameter and diameter variation Medulla absent to continuous and relatively narrow when compared to the structure of hairs from other body areas Often with cut or split tips Can show artificial treatment, solar bleaching, or mechanical damage Soft texture, pliable

29 Pubic Hairs Medulla relatively broad and usually continuous when present Shaft diameter coarse with wide variations and buckling Root frequently with tag Tip usually tapered, rounded, or abraded Stiff texture, wiry

30 Limb Hairs Diameter fine with little variation Gross appearance of hair is arc-like in shape Medulla is discontinuous to trace with a granular appearance Soft texture Tips usually tapered, often blunt and abraded, rounded scale ends due to wear

31 Facial Hairs (Beard/Mustache) Diameter very coarse with irregular or triangular cross-sectional shape Medulla very broad and continuous, may be doubled

32 Chest Hairs Shaft diameter moderate and variable Tip often darker in color, long and fine, arc-like Medulla may be granular Stiff texture

33 Axillary or Underarm Hairs Resemble pubic hairs in general appearance, but less wiry Medullary appearance similar to limb hairs Diameter moderate and variable with less buckling than pubic hairs Tips long and fine, frequently with bleached appearance

34 Other Body Hairs Eyebrow: Stubby, some diameter fluctuation, saber-like in appearance Eyelash: Short, stubby with little shaft diameter fluctuation, saber-like in appearance Trunk: A combination of features of limb and pubic hairs, a transitional hair

35 Tip of the Shaft Burned Cut Razored Split

36 Root of Hair Provide the tools to produce hair and continue its growth 3 Stages of Growth (different looking roots) Anagen -initial phase may last up to 6 years, root is flame shaped Catagen transition phase (2-3 weeks), root is elongated Telogen phase where hair naturally falls out of the skin, root is club-shaped

37 Hair Growth Cycle

38 Forcibly Removed? Pulled Forcibly Removed Shed

39 Brushed-out hairs all have this kind of root. A normal telogen hair with a hard 'club' end, seen under (left) a light microscope and (right) an electron microscope This is an anagen hair, one which was pulled out and not ready to be shed. An anagen hair that has been plucked out: notice the soft, sticky tail

40 Collection of Hair Evidence

41 Collection of Hair Evidence Questioned and Reference hair must come from same area of the body; one cannot, for instance compare head hair to pubic hair. The collection of 50 full length hairs from all areas of the scalp will normally ensure a representative sampling of head hair.

42 Collection of Hair Evidence A minimum collection of 24 full length pubic hairs should cover the range of characteristics present in this type of hair. All collected hairs must be full-length so that the investigator can see if the color and morphological features vary throughout the length of the hair.

43 Packaging of Hair Evidence Recover all hair present. If possible, use fingers or tweezers to pick up hair, place in paper bindles or coin envelopes which should then be folded and sealed in larger envelopes. Label the outer sealed envelope. If hair is attached, such as in dry blood, or caught in metal or a crack of glass, do not attempt to remove it but rather leave hair intact on the object. If the object is small, mark it, wrap it, and seal it in an envelope. If the object is large, wrap the area containing the hair in paper to prevent loss of hairs during shipment

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45 Fibers: Natural Derived entirely from animal or plant sources Most prevalent plant fiber is cotton. Its widespread use has made its evidential value almost meaningless Cotton has a ribbon-like shape with twists at regular intervals Animal sources include sheep (wool), goats (mohair, cashmere) and many other sources Cotton Wool

46 Man-Made Fibers Fibers derived from either natural or synthetic polymers The fibers are made by forcing polymeric material through the holes of a spinneret Rayon and then nylon were the first two man-made fibers (year 1911)

47 Regenerated Fibers Man-Made Fibers Con t Made from regenerated cellulose (wood or cotton pulp) Include such fibers as rayon, acetate, and triacetate Synthetic Fibers Currently manufactured Made from synthetic chemicals called polymers Include such fibers as nylons, polyesters, and acrylics

48 ID and Comparison of Man-Made Fibers Fabrics that can be fitted together at their torn edge are easy to match Microscopic comparison of color and diameter Comparison of lengthwise striations and pitting on the surface of a fiber The shape of the fiber ex. Wayne Williams case Cross sections are generally helpful Note: Combined factors of color, size, shape, microscopic appearance, chemical composition, and dye content make it very unlikely to find two different people wearing identical fabrics

49 ID and Comparison of Man-Made Fibers con t. The chemical makeup of the fiber itself can be examined through the following: Infrared microspectrophotometry Refractive Index The chemical makeup of the dyes in the fiber can be examined through the following: Liquid chromatography Visible light microspectrophotometry