Structure - Persistence of Friction Skin and Matrix Composition Flashcards
What is another term for friction skin?
Volar skin
In what groups of animals is friction skin found in?
Primates
List the 5 general descriptions of the skin?
- One of the largest organs in the body
- Performs several functions
- Contains skeleton and organs; sensory input
- Waste elimination
- Largest external organ
List some of the functions of the skin.
3
- Protection
- Sense of touch
- Temperature regulation
Define friction skin.
A raised portion of the epidermis of the palmar or plantar skin consisting of one or more connected ridge units of friction skin.
To what to areas is friction skin localized?
Palmar and plantar
What is the commonly accepted reason for primates having friction skin?
Grip
How does friction skin contribute to our ability to grip?
2
- Easier to pick up small items with hands
- Provides traction while walking barefoot
How much of our total skin surface area is accounted for by friction skin?
~ 5%
What is contained in each friction ridge unit?
2
One sweat gland and one pore
Why is it important to understand friction ridge composition?
If an expert is qualified to present evidence related to fingerprinting, they must have a basic understanding of its properties, how it forms and its composition.
Describe friction ridge development at 6 weeks.
2
Hand is paddle-like
Volar pads can be seen
Describe friction ridge development at 8 weeks.
Fingers separate
Describe friction ridge development at 10 weeks.
Digital pads are distinct
Describe friction ridge development at 12 weeks.
2
Friction ridges start to develop in basal layer
Volar pads regress
Describe friction ridge development at 17 weeks.
Pattern formation complete
What are the only things that friction risges are affected by?
Explainable differences.
Give examples of explainable differences that cant affect friction ridges.
6
- Scarring
- Disease
- Growth
- Weight fluctuations
- Skin grafting
- Occupation-related issues
How are ridges formed from ridge units?
As ridge units grow, they fuse together to form ridges
True or false: All ridge units grow for the same amount of time and at the same rate.
False. They all grow for the same amount of time but at different rates
What are sweat pores?
Opening on surface of skin from sweat glands
What is poroscopy?
The study of the size and shape of pores.
What is edgeoscopy?
Study of edges and ridges.
What are incipient ridges?
Ridges that were not fully formed at differentiation.
What are incipient ridges also known as?
False or nascent ridges
List some characteristics of incipient ridges.
4
- May not always record at crime scenes or on inked impressions
- Not as thick as fully developed ridges
- Frequently fragmented
- May not contain pores
How many layers of skin is friction skin comprised of?
2
What are the two layers that make up the friction skin?
Epidermis and dermis
Describe the epidermis.
15-20 layers of dead cells that are shed off and replaced continuously from the basal layer.
What is the basal layer often referred to?
The generating layer
Describe the process of skin cell migration.
Cells created in the basal layer will migrate upward through the other four layers of the epidermis to the surface where they are sloughed off as dead skin cells.
How long does the process of skin cell migration and shedding take?
~ 1 month
How does scarring occur?
When there is damage/penetration of the basal layer.
List the layers of the epidermis from superficial to deep.
5
- Stratum corneum (horny)
- Stratum lucidum (hyalin)
- Stratum granulosum (granular)
- Stratum Spinosum (spinous)
- Stratum basal(e) (basal)
What is the dermis?
Thick foundation layer
How is the epidermis attached to the dermis?
Double row of dermal papillae (“little skin pegs”)
List some characteristics of friction skin.
6
- No sebaceous glands
- Eccrine glands only
- More sweat glands per square inch than other skin
- No hair
- Lack of pigmentation
- Over-abundance of nerve endings
What are the three overall pattern types of friction skin?
Arch, loop, whorl
Which basic fingerprint pattern does not contain a core?
Arch
List the basic pattern types from most to least common.
- Loop
- Whorl
- Arch
What affects the development of friction ridge patterns?
Tension and pressure on volar pads during fetal development
What volar pad positioning is associated with a whorl pattern?
High volar pad
What volar pad positioning is associated with the loop pattern?
Intermediate pad
What volar pad positioning is associated with an arch pattern?
Low volar pad
Do identical twins have the same fingerprints?
No
List some damaging effects to friction skin.
4
- Injury
- Disease
- Amputation
- Mutilation
What are the five basic characteristics that combine to produce ridge patterns?
- Ridge ending
- Bifurcation
- Ridge dot/unit
- Short ridge/island
- Enclosure/lake
Describe fingerprint composition.
Combination of different sources, including naturally secreted materials like sweat, sebum or lipids, and foreign materials picked up through daily contact with items and surfaces outside the body.
What are the three sources of natural secretion in the human body?
- Eccrine glands
- Sebaceous glands
- Apocrine glands
What two natural sources of secretion are significant for friction ridge identification?
Eccrine and sebaceous glands
Why aren’t apocrine glands considered significant for fingerprint identification?
Primarily found in underarm and genital areas.
Describe the composition of eccrine sweat.
98.5%-99.5% water
0.5%-1.5% solids
What solid materials can be found in eccrine sweat?
Inorganic salts and organic substances
Where on the body are sebaceous glands found?
Areas associated with hair follicles
Describe the composition of sebum.
Comprised mainly of saturated fats, waxes and squalene.
List some foreign materials that are commonly found in a fingerprint deposit.
6
- Blood
- Paint
- Automotive lubricants
- Industrial grease
- Oil
- Cooking/food residue
List the common factors that can affect the composition of fingerprint secretions and the concentration of certain components.
7
- Rate and duration of sweating
- Dietary habits
- Age
- Gender
- Physical health
- Physical exertion
- Stress
How can rate and duration of sweating impact fingerprint composition?
Excessive and prolonged sweating can dilute the concentration of solids within the sweat.
How can dietary habits impact the composition of fingerprints?
Dietary intake influences secretion content, meaning certain food intake or absence can change the composition of secretions.
How can age impact fingerprint composition?
Concentration of solids within sweat tends to decrease as we age.
How can gender affect the composition of fingerprints?
Females generally have lower concentrations of solids than males.
How can physical health impact fingerprint composition?
Can influence sweat quantity, relating back to rate and duration of sweating.
How can physical exertion impact fingerprint composition?
Physical activity will potentially increase or promote sweating.
How can stress impact fingerprint composition?
Elevated stress or anxiety has been shown to cause in increase in rate of sweating and concentration of solids.
Describe a take away impression.
Formed by the removal of material from the surface by fingerprints.
What is the method for capturing take-away impressions?
Oblique lighting to locate and photograph. Generally do not lift well.
Why do take away immpressions generally not lift well?
Tape has static charge to it, which will interact with dust or other material.
Why do we take elimination fingerprints?
3
- Incriminate
- Corroborate
- Eliminate
List some methods for obtaining elimination prints.
4
- Rolled - ink impressions C-216 RCMP form
- Rolled ink - glass and paper method
- Porelon fingerprint ink pad
- Avery adhesive shipping labels with black powder