hair and fibers. hair morphology the most basic components of hair are keratin, a very strong...
Post on 29-Dec-2015
Embed Size (px)
Hair and Fibers
Hair MorphologyThe 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.
Hair is produced from a structure called the hair follicle. Humans develop hair follicles during fetal development, and no new follicles are produced after birth.
The Function and Structure of Hair Hair on mammals helps to regulate body temperature, decrease friction, and protect against sunlight. Hair consists of (a) a hair shaft produced by (b) a follicle embedded in the skin. A hair has three layers (illustrated above): the inner medulla, the cortex, and the outer cuticle.
Types of Cuticle and Cortex The Outer 2 Layers The Cuticle is the outermost layer made of over-lapping scales that protect the inner layers of the hair. The Cortex is the thickest layer containing most of the pigment giving hair its color. The distribution of pigment in the cortex varies from person to person. Pigment, commonly, is denser nearer the cuticle.
Hair Cuticle The cuticle is a translucent outer layer of the hair shaft consisting of scales that cover the shaft. Cuticular scales always point from the proximal or root end of the hair to the distal or tip end of the hair.
Types of Medulla The medulla (the inner section) can be hollow or filled, absent, fragmented, continuous, doubled, pigmented, or un- pigmented.
Medulla The medulla is a central core of cells that may be present in the hair. HumanAnimalDeer
Types of Hair Buckled Blunt Double MedullaThe cross section of a hair can be circular, triangular, irregular, or flattened influencing the curl of the hair. The texture of a hair can be coarse or fine. Different regions of the body on which hair can vary are (1) head, (2) eyebrows and lashes, (3) mustache and beard, (4) underarms, (5) overall body (auxiliary hair), and (6) pubic.
The Life Cycle of Hair Hair proceeds through 3 stages as it develops: During the long anagen stage, hair actively grows. The cells around the follicle rapidly divide and deposit materials in the hair. In the catagen stage, the hair grows and changes. Hair is in the telogen stage when the follicle becomes dormant. During this stage, hairs easily can be lost.
Growth Cycles of HairAnagen Growing phaseAverage growth about 2 per month90% of hair is growing at one timeGrows for a period of 2-6 yearsDuration of hair life affected by gender, age, type of hair, heredity, nutrition, & health
Growth Cycles of HairScalp hairs grows faster on women than men.Grows faster between 15-30 and slows sharply after age 50Catagen Transition phaseEnds the growth phase and lasts only one to two weeksFollicle canal shrinks & detaches from the dermal papillaHair bulb disappears and the shrunken root end forms a rounded bulbLess than 1% of the scalp hair is in the catagen phase at any one time
Growth Cycles of HairTelogen Resting phaseAfter catagen, the follicle begins a three to six month phase of restingAbout 10% of hair is in telogen phase at one timeAfter telogen, the cycle begins againEntire growth cycle repeats itself every four to five years
Electronmicrograph showing new hairs emerging from the hair follicles of the scalp
Treated Hair Forensic investigators sometimes can link hair from a location with an individual. Bleaching disturbs the scales on the cuticle and removes pigment leaving hair brittle and a yellowish color.Dyeing colors the cuticle and the cortex of the hair shaft. Because of this and because hair grows daily, a persons treated hairs will have specific char- acteristics in common with her or his lost hairs.
Slight Lifting Normal cuticle
Racial Differences Hair examiners have identified some physical characteristics that generally can be associated with broad, racial groups. These characteristics, however, will not apply to all individuals in these groups. In addition, at times, it will be impossible to assign specific hairs to any of these groups be-cause their characteristics are poorly defined or hard to measure.
Animal Hair and Human HairCore: the medulla -- Thickest layer: the cortex -- Outermost: the cuticle Pigmentation in animal hair is denser toward the medulla. In Humans it tends to be denser toward the cuticle. Unlike human hair, animal hair abruptly can change colors in banded patterns. The medullary index is different. In animals the medulla is much thicker than it is in humans.
Animal Hair and Human Hair Spinous Coronal ImbricateThe outermost layer of the hair shaft (the cuticle), is typically different in animals and humans. The cuticle scales in animals tend to resemble petals (spinous) or they give the appearance of a stack of crowns (coronal). The cuticle scales in humans commonly are flattened and narrow (imbricate).
Bat Hair and Mink Hair
Human HairThe imbricate or flattened scales type consists of overlapping scales with narrow margins. They are commonly found in human hairs
Using Hair in an Investigation Macroscopic investigation can indicate length, color, and curliness. Microscopic investigation can indicate fine detail in hair structure. Phase contrast microscopy, for example, can show the presence of dye or other treatments. Electron microscopes can provide more detail of the surface or interior of the sample. In the sample above, note the overlapping scales and the pigment granules in the cortex.
Hair Forensics: CollectionHairs can be recovered from items using a number of different techniques. Some of the methods used to collect hairs from clothing and bedding items are scraping, shaking, taping, and picking. Debris from large carpeted surfaces might be vacuumed into a filtered canister. If the specific location of a hair on a clothing item is important, it might be necessary to pick off the hair or tape the item and record where the hair was removed.
Hair Forensics: Which Hairs?Head hairs and pubic hairs exhibit a greater range of microscopic characteristics than other human hairs; therefore, head and pubic hairs are routinely forensically compared. Twenty-five randomly selected head hairs are generally considered adequate to represent the range of hair characteristics of that individual. It is recommended that the same number of hairs be collected from the pubic region.
Things to consider when viewing hairLength: Length is considered, although hairs may have been cut between the time of deposition of the questioned specimen and the collection of a known sample. In addition, there may be a significant difference in the lengths of the shortest and longest hairs on an individual's head. Tip: The tip can be cut, broken, split, abraded (rounded), or finely pointed as illustrated by An individual's grooming, hygiene, health, and nutrition can affect these features.
Glass-Cut or Broken Hair Tip
Cut Hair Tip
Worn Razor-Cut Tip
Testing for Substances in the Hair Shaft Chemicals that the skin absorbs often can be detected by analysis of the hair shaft. A forensic scientist can perform chemical tests for the presence of various substances. The hair shaft can be examined in sections to establish a timeline for exposure to toxins. Neutron Activation Analysis (NAA) can determine concentrations of substances in the sample.
Testing the Hair Follicle Microscopic assessment of the follicle is performed first because it is cost effective and quick. If a microscopic match is found, the follicle can be blood tested and perhaps show the blood type. If a microscopic match is found, the follicle can be DNA analyzed to provide identification with a high degree of confidence.
What is this?LICE
Introduction and How Forensic Scientists Use FibersFibers often fall off and are picked up during normal activities. Very small fibers easily shed from most textiles and can become trace evidence. In an investigation, collection of fibers within 24 hours is critical. Fiber evaluation can show such things as the type of fiber, its color, the possibility of violence, location of suspects, and point of origin.
Sampling and Testing Weaving spun fibers (yarns) together produces clothing and many textiles. Shedding from an article of clothing or a textile is the most common form of fiber transfer.Natural fibers require only an ordinary microscope to find characteristic shapes and markings. Infrared spectroscopy can reveal something of the chemical structure of other fibers that, otherwise, may look very much alike.
Sampling and TestingIf a large quantity of fibers is found, some can be subjected to destructive tests such as burning them in a flame (see analysis key above) or dissolving them in various liquids. Crimes can be solved in this way by comparing fibers found on different suspects with those found at the crime scene.
Fiber Classification Natural Fibers woven wool textile Animal fibers (made of proteins): Wool from sheep, cashmere and mohair from goats, angora from rabbits, and hair from alpacas, llamas, and camels are commonly used in textiles. Shimmering silk from caterpillar cocoons is longer and not as easily shed.
Fiber Classification Natural FibersPlant fibers (made of t