HAIR AND FIBERS 2014 Abridged Version. Forensic Science: Fundamentals & Investigations, Chapter 3 2 The Function of Hair Regulates body temperature Decreases

HAIR AND FIBERS 2014Abridged Version

Forensic Science: Fundamentals & Investigations, Chapter 3

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The Function of Hair•Regulates body temperature •Decreases friction•Protects against sunlight


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The Structure of Hair

• A follicle embedded in the skin produces the hair shaft• Three layers (illustrated above): • the inner medulla• the cortex • the outer cuticle


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The Structure of Hair

Hair Morphology

• The most basic components of hair are keratin, a very strong protein that is resistant to decomposition, and melanin, a pigment.• The keratins form groups that interact

and interconnect to form very stable fibrils. It is this property of hair that makes it such a prime example of physical evidence.


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Cuticles, Cortex, and Medulla


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Types of Cuticle and Cortex

• Cuticle: • the outermost layer • over-lapping scales that protect the inner layers

• Cortex: • Thickest layer • Contains most of the pigment • Distribution of pigment varies • Usually denser nearer the cuticle

CUTICLE TYPES

• The cuticle of a hair is the thin, translucent layer surrounding the shaft. It consists of scales of hardened, keratinized tissue that vary from species to species, and includes such patterns as:• Coronal, or “crown – like.” Rare in

humans; typical of rodents. Found in hairs of very fine diameter.• Spinous, or “petal – like.” Never

found in humans. Common in cats, seals, and minks.• Imbricate, or “flattened.” Common

in humans.

Coronal

Spinous

Imbricate

Cuticle

Photomicrograph of a mink hair possessing a Spinous cuticle.

Photomicrograph of a bat hair possessing a Coronal cuticle.

Photomicrograph of a human hair possessing an Imbricate cuticle.


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Types of Medulla

Medulla

Photomicrograph of a human hair with no medulla.

Photomicrograph of a hair with trace medulla.

Photomicrograph of a hair with a clear, continuous medulla.


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Animal Medulla Patterns (all continuous)


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The Life Cycle of Hair Hair proceeds through 3 stages as it develops: • Anagen stage: • hair actively grows• cells around the follicle rapidly divide and deposit materials in the hair

• Catagen stage: • hair grows and changes

• Telogen stage: • follicle becomes dormant

Hair Growth• Growth of mammal hair goes through

three distinct phases:• Anagenic phase can last for up to

6 years. Follicle is attached to the root by the papilla. The hair must be pulled to be lost. If pulled, a follicular tag is left, which can be used later to test the mitochondrial DNA.• Catagenic phase lasts only 2-3

weeks. Hair keeps growing, but the bulb shrinks.• Telogenic phase lasts for 2-6

months. Hair becomes naturally loose and sheds.

Hair in Anagenic Phase

Hair in Catagenic Phase

Hair in Telogenic Phase


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Life Cycle of Hair

2-6 years 1-3 weeks 2-6 months


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Treated Hair • Bleaching • disturbs the scales on the cuticle and • removes pigment • leaves hair brittle and yellowish

• Dyeing colors the cuticle and the cortex


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Animal Hair and Human Hair• Pigmentation:

• animal hair is denser toward the medulla• human hair tends to be denser toward the

cuticle

• Banded Color Patterns: • possible in animals• not in humans

• Medulla: much thicker in animals • Has a medullary index (MI) of 0.5 or

greater• Humans’ MI is 0.33 or lower


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Animal Hair Micrographs

Medulla patterns fromdifferent types of hair.(a) Human head hair(b) Dog fur(c) Deer hair(d) Rabbit fur(e) Cat fur(f) Mouse hair


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Using Hair in an Investigation

• Macroscopic investigations indicate • length • color • curliness

• Phase contrast microscopy shows• presence of dye or other treatments

• Electron microscopes yield yet more detail


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Testing for Substances in the Hair Shaft • Chemical or Drug tests: presence of various substances• Hair grows about 1cm/monthEX) If a test located the presence of heroin 2 cm from the hair follicle, how long ago was the person exposed to that drug? • Neutron Activation Analysis (NAA)• Gives specific concentrations of substances


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Testing the Hair Follicle • Microscopic assessment• Cost effective and quick

• Blood test• Determine blood type (small capillaries that nourish follicle

• DNA analysis • Identification with a high degree of confidence


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Microscopic Assessment

• Preparation of hair slide• Obtain or cut transparency slide and roll of clear tape• Place your sample on the slide, then use clear tape to secure

it. Try to remove air bubbles around it. • Label by writing your name, then slide type

J. Arnold

Hair w/follicle


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HAIR EXEMPLAR LAB

• Be sure to keep all your labeled slides for this lab. You may store them in a bag or attach

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HAIR AND FIBERS 2014 Abridged Version. Forensic Science: Fundamentals & Investigations, Chapter 3 2 The Function of Hair Regulates body temperature Decreases