Hair

Extra-Credit ‡Bring in some animal hair (pets) ‡About 20 hairs ‡No roadkill samples!

Today’s Goal ‡Students should be able to correctly describe the biology of hair structure and hair growth. ‡This knowledge will serve as a foundation for investigative activities using microscopes.

At the Crime Scene  Human hair is one of the most frequently found pieces of evidence at the scene of a violent crime. It can provide a link between the criminal and the crime.  Why is it so abundant at a crime scene?

Hair at the Scene ‡A violent struggle can remove a large quantity of hair ‡Hair is shed naturally (about 100 head hairs per day) (about 100 head hairs per day)

What is hair? ‡1) Outgrowth of protein from human or animal skin ‡2) Grows from an organ called a hair follicle ‡3) Dead tissue

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Hair Shaft Composed of: CCuticle— CCortex— MMedulla—

Composed of:  A) Cuticle—  outside covering, made of overlapping scales  B) Cortex—  inner layer made of keratin and imbedded with pigment; also contains air sacs called cortical fusi  C) Medulla—  inside layer running down the center of the cortex

How will I remember this?

‡Cuticle – Cut on the outside of your body ‡Cortex ‡Medulla – Middle!

The Cuticle 1)The cuticle is the outermost layer of hair which is covered with scales. The scales point toward the tip of the hair. Scales differ between species of animals and are named based on their appearance. The three basic patterns are:  Coronal  Spinous  Imbricate

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Cat

Bat

The Cuticle is analogous to… ‡Shingles on a roof ‡Both protect ‡Scales keep out water & bacteria Kendall/Hunt Publishing Company

The Cortex 1)The cortex gives the hair its shape. The main portion of a hair shaft. 2)It has two major characteristics :  Melanin—pigment granules that give hair its color  Cortical fusi—air spaces, usually found near the root but may be found throughout the hair shaft

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The Medulla The Medulla 1) T TT The medulla is the hair core that is not always visible. The medulla comes in different types and patterns. Types:  Intermittent or interrupted--  Fragmented  Continuous  Stacked  Absent—not present

Human Medulla Human medulla may be continuous, fragmented or absent.

Medullary Index 1)Determined by measuring the diameter of the medulla and dividing it by the diameter of the hair.  Medullary Index for human hair is generally less than 1/3.  For animal hair, it is usually greater than 1/2. mouse

Medullary Index ‡A hair was found at a crime scene. ‡Investigators want to know whether it is human or not. The diameter of the hair is 100 micrometers. The diameter of the medulla is 25 micrometers. What is the medullary index?

Hair Growth ‡1) Hair does not grow continuously ‡2) There are 3 phases of growth ‡3) At any given moment, a certain percentage of hairs are ready to fall out

Hair Growth  A) Terminology  Anagen—hair that is actively growing; lasting up to 5 years *85% in this phase *85% in this phase  Catagen—hair is not growing; a resting phase *3-4% in this phase *3-4% in this phase  Telogen—hair that is dying and ready to fall out; lasting two to six months *10-13% in this phase *10-13% in this phase  Length—about 0.5 mm per day or 1 centimeter per month; approximately one half inch per month

The Root Human roots look different based on whether they have been forcibly removed or if they are telogen hairs and have fallen out. Fallen outForcibly removed