Ridgeology

Question 1

Definition of Ridgeology

Answer 1

The study of the uniqueness of friction ridge structures and their use for personal identification.

Question 2

What are the layers of the skin?

Answer 2

Epidermis Dermis Hypodermis

Question 3

Two types of skin

Answer 3

Smooth skin - contains hair, sweat glands and sebaceous oils. Does not contain friction ridges.

Volar skin - only contains sweat glands (no sebaceous), completely covered in friction ridges (no voids), and may appear light in colour. Ridges and sweat increase friction between solar surfaces the surfaces they contact.

Question 4

What are the characteristics of the Epidermis?

Answer 4

• stratified squamous epithelium - continually regenerates cells lost at the surface due to exfoliation - comprised primarily of keratinocyoctes (keratin protein that provide structural support)

Question 5

What are the layers of the Epidermis?

Answer 5

(top to bottom) Horny Hyalin Granular Spinous Basal

Question 6

Characteristic of the Basal Layer

Answer 6

• Also referred to as the generating layer ( stratum germinativum) • A single layer of columnar shaped cells attached to the basement membrane • Newly generated cells are pushed upwards to replace exfoliated surface cells • Cells of the basal layer are bound together by desmosomes

Question 7

Characteristic of the Spinous Layer

Answer 7

• Stratum spinosum • 2 to 4 cells thick • The cells change in shape • exhibit the first changes to the cell structure for the synthesis of the keratin process

Question 8

Characteristics of the Granular Layer

Answer 8

• Stratum granulosum • These are the last of the “living” cells • Display the first precursors of keratin, which marks the onset of cellular death

Question 9

Characteristics of the Hyalin Layer

Answer 9

• Stratum lucidum • Keratin fills the inside of the cell

Question 10

Characteristics of the Horny Layer

Answer 10

• Stratum corneum • Can be up to 100 cells thick • Have accumulated keratin and cell death has occurred • Cells are large and flat

Question 11

Structural elements for the persistency of friction skin

Answer 11

• adherence of the epidermal cells to each other (desmosomes) - attachment of the basal cell layer to the basement membrane (hemidesmosomes, bundles of fibrils and microfibrils) - attachment of basement membrane to the dermis (fibrils and microfibrils) - primary and secondary ridges are the blue print for the surface friction ridges - basal layer keratinocytes ensure the constant regeneration of cells of friction skin

Question 12

What are dermal papillae?

Answer 12

• blunt, peg-like formations found on the surface of the dermis - fit into pockets on the underside of the epidermis and fill the voids between primary and secondary ridges - develop after the secondary ridges reach the same level as the primary ridges (approximately week 24) - contain blood capillaries and nerve endings - run in two rows, one on each side of the primary ridges - break down over time into smaller less structured units

Question 13

Two types of damage to friction skin

Answer 13

Permanent - damage to basal layer or beyond - physical cuts or other injury - genetic problems/diseases

Temporary - basal layer not damaged - physical cuts (superficial) - warts (virus), calluses, blisters, skin disease (eczema)

Question 14

Friction Ridge Development (fetal growth)

Answer 14

3 Weeks - epidermis is one cell thick 6 Weeks - volar pads start to appear on the palm and interdigital areas, followed by the fingers - located on 5 finger, 4 interdigital areas, and 2 palm (thenar and hypothenar) 8 Weeks - digits have separated - thumb has rotated resulting in flexion creases 10.5 to 12 Weeks - volar pads begin to regress - contours become progressively less distinct because of the rapid growth of the hand - primary ridges begin to form on the underside of the epidermis - primary ridges continue to grow and develop until the entire surface is covered - early development is rapid and longest ridges and bifurcations are formed first - new primary ridges form from existing ones 15-17 Weeks - secondary ridges begin to appear and form between existing primary ridge - primary ridges cease to develop in areas where secondary ridges are started (Time of Differentiation) 20 Weeks - secondary ridge are established and the final friction ridge configuration is complete. 20-24 Weeks - secondary ridges form until reach the same depth of primary ridges - dermal papillae begin to form when secondary ridge formation is complete

Question 15

Factors Affecting Differential Growth of Friction ridges

Answer 15

Random timing of events - Timing of the onset of primary ridge development in conjunction with the regression of the volar pads - Timing of the onset of secondary ridge development Random growth processes - Number of ridge units forming a ridge is random - The path a friction ridge takes is random - Where a ridge starts and stops is random - Ridge thickness or thinness is random - Ridge alignment, bifurcation or misalignment is random - Pore locations are random - Friction ridges are 3 dimensional, therefore height of the ridge is also a consideration Random pressures - Pressure from the size and shape of volar pads - Pressure from neighboring ridges - Pressures in the womb - Numerous genetic and physical pressures

Question 16

What are incipient ridges?

Answer 16

Immature ridges

Did not have time to fully develop prior the time of differentiation.

Based on the same structure as matrue primary ridges (Okajima)

Question 17

What are the differences between friction ridges and incipient ridges?

Answer 17

Incipient ridges are:

Thinner

Fragmented

Usually do not have fully developed pore formations