HairHair

Extra-CreditExtra-Credit‡ Bring in some animal hair Bring in some animal hair

(pets)(pets)‡ About 20 hairs About 20 hairs ‡ No roadkill samples!No roadkill samples!

Today’s GoalToday’s Goal

‡ Students should be able to Students should be able to correctly describe the correctly describe the biology of hair structure biology of hair structure and hair growth.and hair growth.

‡ This knowledge will serve This knowledge will serve as a foundation for as a foundation for investigative activities investigative activities using microscopes.using microscopes.

At the Crime SceneAt the Crime Scene

Human hair is one of the Human hair is one of the most frequently found most frequently found pieces of evidence at the pieces of evidence at the scene of a violent crime. It scene of a violent crime. It can provide a link between can provide a link between the criminal and the crime.the criminal and the crime.

Why is it so abundant at a Why is it so abundant at a crime scene?crime scene?

Hair at the SceneHair at the Scene‡ A violent struggle can A violent struggle can

remove a large quantity remove a large quantity of hairof hair

‡ Hair is shed naturallyHair is shed naturally

(about 100 head hairs per (about 100 head hairs per day)day)

What is hair?What is hair?‡ 1) Outgrowth of protein 1) Outgrowth of protein

from human or animal skinfrom human or animal skin‡ 2) Grows from an organ 2) Grows from an organ

called a hair folliclecalled a hair follicle‡ 3) Dead tissue3) Dead tissue

Kendall/Hunt Publishing Company 7

Hair ShaftHair Shaft

Composed of: Cuticle— Cortex— Medulla—

Hair ShaftHair Shaft

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 How will I remember this?this?

How will I remember How will I remember this?this?

‡ Cuticle – Cuticle – Cut on the Cut on the outside of outside of your bodyyour body

‡ CortexCortex‡ Medulla – Medulla –

Middle!Middle!

The CuticleThe 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

Kendall/Hunt Publishing Company 13

CatCat

BatBat

The Cuticle is The Cuticle is analogous to…analogous to…

‡ Shingles on a roofShingles on a roof‡ Both protectBoth protect‡ Scales keep out water & Scales keep out water &

bacteriabacteria

Kendall/Hunt Publishing Company

The CortexThe 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 MedullaThe Medulla

1) The medulla is the hair core that is The medulla is the hair core that is not always visible. The medulla not always visible. The medulla comes in different types and patterns.comes in different types and patterns.

Types: Intermittent or interrupted-- Fragmented-------------------- Continuous--------------------- Stacked------------------------- Absent—not present---------

Human MedullaHuman Medulla

Human medulla may be continuous, fragmented or absent.

Medullary IndexMedullary Index

1)Determined by 1)Determined by measuring the diameter measuring the diameter of the medulla and of the medulla and dividing it by the dividing it by the diameter of the hair.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 IndexMedullary Index

‡ A hair was A hair was found at a found at a crime scene. crime scene.

‡ Investigators Investigators want to know want to know whether it is whether it is human or human or not.not.

The diameter of The diameter of the hair is 100 the hair is 100 micrometers. micrometers. The diameter of The diameter of the medulla is the medulla is 25 25 micrometers.micrometers.

What is the What is the medullary medullary index?index?

Hair GrowthHair Growth

‡ 1) Hair does 1) Hair does not grow not grow continuouslcontinuouslyy

‡ 2) There are 2) There are 3 phases of 3 phases of growthgrowth

‡ 3) At any 3) At any given given moment, a moment, a certain certain percentage percentage of hairs are of hairs are ready to fall ready to fall outout

Hair GrowthHair Growth A) TerminologyA) Terminology

AnagenAnagen——hair that is actively growing; lasting up to 5 hair that is actively growing; lasting up to 5 yearsyears

*85% in this phase*85% in this phase

CatagenCatagen——hair is not growing; a resting phasehair is not growing; a resting phase

*3-4% in this phase*3-4% in this phase

TelogenTelogen——hair that is dying and ready to fall out; lasting hair that is dying and ready to fall out; lasting two to six monthstwo to six months

*10-13% in this phase*10-13% in this phase

LengthLength——about 0.5 mm per day or 1 about 0.5 mm per day or 1 centimeter per month; approximately one centimeter per month; approximately one half inch per monthhalf inch per month

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

Fallen out Forcibly removed