Medical Forensics Notes
The Biology of Hair Hair is composed of the protein keratin, which is also the primary component of finger and toe nails.
The Biology of Hair Hair is produced from a structure called the hair follicle. Humans develop hair follicles during fetal development, and no more new follicles are ever produced after birth. Hair color is mostly the result of pigments, which are chemical compounds that reflect certain wavelengths of visible light.
Follicle Hair is an appendage of the skin that grows out of a hair follicle.
The follicle contains more than enough cells for simple DNA Analysis.
Root A hair grows as it extends from the root embedded in the follicle.
Root: Shape and size of the hair root is determined by the current phase of growth.
Anagen phase (initial growth phase) may last up to 6 years. The root is attached to the follicle. Gives a flame-shaped appearance. Catagen phase (transition stage) may last 2 to 3 weeks. Bulb becomes elongated as it shrinks and is pushed out of the follicle. Telogen phase (falls out) lasts 2 to 6 months. The hair is pushed out and the bulb looks club-shaped.
Hair that has DNA: Hair that has all or a portion of the follicle attached to it is said to have a Follicular Tag. Be low is the difference between a hair with and a hair without one.
The Biology of Hair Hair shape (round or oval in cross-section) and texture (curly or straight) is influenced heavily by genes. The physical appearance of hair can be affected by nutritional status and intentional alteration (heat curling, perms, straightening, etc.).
The Biology of Hair The body area (head, arm, leg, back, etc.) from which a hair originated can be determined by the sample s length, shape, size, color, and other physical characteristics. In order to test hair evidence for DNA, the root must be present.
Hair Structure: Hair is composed of three principal parts: 1. Cuticle 2. Cortex 3. Medulla
Hair Structure: The structure of hair has been compared to that of a pencil with the medulla being the lead, the cortex being the wood and the cuticle being the paint on the outside.
Cuticle The cuticle is the outside covering of the hair. It is formed by overlapping scales that always point toward the tip of the hair.
These scales are formed from special cells that are hardened and flattened while progressing from the follicle.
The Cuticle Varies in: Its thickness, Whether it contains pigment. Scale Characteristics: Number per centimeter, How much they overlap, Their overall shape, How much they protrude from the surface. The cuticle is important in distinguishing between different species but not useful between different people.
Types of Cuticle Scales There are three basic scale structures that make up the cuticle coronal (crown-like), spinous (petal-like), imbricate (flattened). Combinations and variations of these types are possible.
Coronal, or Crown-like scales 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. Longitudinal view of coronal scales. Photomicrograph of one type of coronal scales.
Spinous or Petal-like scales 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. Scale pattern in mink hairs. Diagram of spinous scales.
Imbricate or Flattened-scale Consists of overlapping scales with narrow margins. They are commonly found in human hairs and many animal hairs. Figure 89 is a, and Figure 90 is a photomicrograph of the distalscale pattern in mink hairs. Dog Hair. Diagram of imbricate scales.
Cortex The main body of the hair. Composed of elongated and fusiform, spindleshaped cells called microfibrils that run parallel to the length of the hair. It may contain cortical fusi, pigment granules, and/or large oval-toround-shaped structures called ovoid bodies.
Cortical Fusi Irregular-shaped airspaces of varying sizes. They are commonly found near the root of a mature human hair, although they may be present throughout the length of the hair.
Pigment Granules Small, dark, and solid structures that are granular in appearance and considerably smaller than cortical fusi. They vary in color, size, and distribution in a single hair. In humans, pigment granules are commonly distributed toward the cuticle, except in redhaired individuals. Animal hairs have the pigment granules commonly distributed toward the medulla. Pigment distribution in human hair. Pigment distribution in red human hair. Pigment distribution in animal hair.
Pigment granules are absent in grey hairs
Ovoid Bodies Larger than pigment granules. Solid structures that are spherical to oval in shape, with very regular margins. They are abundant in some cattle and dog hairs as well as in other animal hairs. To varying degrees, they are also found in human hairs. Ovoid Bodies in Dog Hair.
The Cortex Varies in: Thickness Texture Color Distribution of the cortex is perhaps the most important component in determining from which individual a human hair may have come.
Medulla The medulla is a central core of cells that may be present in the hair. If it is filled with air, it appears as a black or opaque structure under transmitted light, or as a white structure under reflected light.
In human hairs: The medulla is generally amorphous in appearance, whereas in animal hairs, its structure is frequently very regular and well defined. The medulla is the most predominant hair feature in many species. Human head hairs tend to be absent or fragmented. Humans and most other animals have medulla that are nearly cylindrical.
The Medulla May vary in: Thickness Continuity - one continuous structure or broken into pieces Opacity - how much light is able to pass through it It may also be absent in some species. Like the cuticle, the medulla can be important for distinguishing between hairs of different species, but usually not between hairs from different people.
4 Basic Patterns of Medulla: Serial medulla is the term used to a describe multiple medulla within a single hair
Medulla Pattern Subcategories: Patterns can also be combined. For example: Serial interrupted.
What Type of Medulla do you see?
Medullary Index The fraction of the hair s width occupied by the medulla [between 0 and 1] Measured by the medullary index, expressed as a fraction. Human medullary index is usually less than 1/3. Most other animals = ½ or greater.
Can the body area from which the hair originated be determined? Yes: Scalp hair show very little difference in diameter along the shaft and has a more uniform distribution of pigment molecules. Pubic hairs are short, curly, and have wide variation in shaft diameter. Beard hairs are usually short and have a triangular cross-section.
Can the race of hair be determined? First, we have to discuss race in forensics: There are three categories that all races are placed in: Mongoloid. Caucasoid. Negroid.
Can the race of hair be determined? Mostly yes. Negroid hair is usually kinky, containing dense and unevenly distributed deposits of pigments. Cross-sections of Caucasian hair are round to oval in shape. Negroid hair is flat to oval in cross-section.
Follicle Shape Determines Hair Form and Texture.
Human Hairs
Horse Hair
Dog Hair
Cat Hair
Mouse Hair
Rabbit Hair
Deer Hair
Cow Hair
Pig Hair
Hair Identification: Animal Vs Human Hairs Human hairs are distinguishable from hairs of other mammals. Animal hairs are classified into three basic types. Guard hairs that form the outer coat of an animal and provide protection. Fur or wool hairs that form the inner coat of an animal and provide insulation. Tactile hairs (whiskers) that are found on the head of animals and provide sensory functions. Other types of hairs found on animals include tail hair and mane hair (horse). Human hair is not so differentiated and might be described as a modified combination of the characteristics of guard hairs and fur hairs.
Hair Identification: Animal Vs 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 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. The root of human hairs is commonly club-shaped, whereas the roots of animal hairs are highly variable between animals.
Conclusions There are three basic conclusions that can be reached from a microscopic examination and comparison of hairs. If the hairs from the questioned (Q) source exhibit the same microscopic characteristics as the hairs in a known (K) hair sample, they can be associated to the source of the known hairs. The hairs from the questioned source are microscopically dissimilar to the hairs in a known hair sample, they cannot be associated with the source of the known hairs. The questioned hairs exhibit both similarities and slight differences to hairs found in a known hair sample, no conclusion can be reached about their origin.