Chapter 3 Flashcards
What are there primary skin tissues formed between 3-8 weeks EGA?
The ectoderm that goes on to form the epidermis, the mesoderm which forms the dermis, and the endoderm which forms organs.
During late embryological development the embryo undergoes morphogenesis. What is that?
Morphogenesis refers to the formation of shape.
- -at 4 weeks EGA limbs begin to form….hands are paddle like but grow into adult form…..volar pads appear
- -by end of week 8 the embryo is 25 mm long and weighs 1 gram
- -9-12 weeks: nervous system and organs develop, limbs are moving….primary ridges begin forming at 10.5 weeks…..from this point on embryological development is complete, and further maturation is fetal growth
- -second trimester growth of bones, volar pads regress, and minutiae are set
Discuss hand development in utero.
- hand appears paddle like until 6 weeks
- 7-8 weeks fingers separate and bones harden
Volar pad development order a dad regression.
Volar pads are transient swellings of tissue called mesenchyme under the epidermis
- -interdigital pads form first around 6 weeks EGA, followed by thenar and hypothenar
- -7-8 weeks EGA volar pads develop on digits from thumb to little finger……thenar crease begins to form in Palm, followed by flexion creases in fingers at 9 weeks EGA…..thumb rotates around at 8-10 weeks
- -pads remain well rounded during their rapid growth from 9-10 weeks ……distal transverse crease At 11 weeks and proximal transverse crease at 13 weeks
- -as volar pads growth slow, their contour becomes progressively less distinct on the rapidly growing surface…..this has been called regression…..volar pads not actually shrinking, but are overtaken by faster growth of of the surrounding surface…..by 16 weeks volar pads have completely merged with friction ridge surfaces
Primary ridge formation.
- -at around 10.5 weeks basal cells of epidermis divide rapidly….shallow ledges can be seen on bottom of the epidermis…theses ledges delineate overall pattern that will become permanent on volar surface
- -the theory: the units of rapidly multiplying cells increase in diameter, randomly, growing into one another along lines of relief perpendicular to the direction of compression
- -primary ridges mature and extend deeper into dermis until about 16 weeks EGA
- -the finger is rapidly expanding, and new primary ridges form and existing ones separate because of digit growth…..voids keep getting filled in, and Hale reports that new ridges pull away from existing ones to fill in gaps and form bifurcations
- -regardless if the mechanism of minutiae formation is mechanical or static, fusion or chemical, the exact location of any mrpd is governed by a random series of infinitely interdependent forces acting across that particular area of skin at that moment
Secondary ridge formation
By 15 weeks EGA the primary ridges are experiencing growth in two directions: downward penetration of sweat glands, and upward growth from cell proliferation……generally the entire volar surface is ridged by 15 weeks
- -15-17 weeks is time of differentiation….secondary ridges appear between primary ridges on underside of epidermis
- -as secondary ridges are forming downward and increasing the surface area of attachment to the dermis, the primary ridges are pushing cells to the surface to keep up with growing hand…these two forces cause infolding of epidermis above the attachment site of secondary ridges…..they mature up until 24 weeks EGA, and the process is mirrored on the surface as furrows
Secondary ridge formation
By 15 weeks EGA the primary ridges are experiencing growth in two directions: downward penetration of sweat glands, and upward growth from cell proliferation……generally the entire volar surface is ridged by 15 weeks
- -15-17 weeks is time of differentiation….secondary ridges appear between primary ridges on underside of epidermis
- -as secondary ridges are forming downward and increasing the surface area of attachment to the dermis, the primary ridges are pushing cells to the surface to keep up with growing hand…these two forces cause infolding of epidermis above the attachment site of secondary ridges…..they mature up until 24 weeks EGA, and the process is mirrored on the surface as furrows
Formation of dermal papillae.
Begin to form at 23 weeks…..and continue to become more complex into adulthood
Symmetrical vs asymmetrical volar pads
Size and height of volar pad
If the volar pad and other elements of finger growth are symmetrical during primary ridge formation then a symmetrical pattern will result (whorl or arch)
If the volar pad and growth factors are asymmetrical you get a loop
The height of the pad affects the core-delta ridge count
The timing of the onset of volar pad regression and the timing of onset of primary ridge formation affect the total ridge count
–diet, chemical intake, hormone levels can all affect growth rate
–anything that affects the tension across the surface of finger could affect the ridge alignment and pattern
Formation of friction skin is derived from an interaction of genetics and environmental factors—–the best example is identical twins…..total friction ridge count would be more inheritable than pattern type
Studies have been done to examine patterns within specific ethnicities…..
Which three areas does primary ridge formation occur.
The apex of the volar pad
The tip of the finger
Area below delta
These three fields converge, forming a delta or deltas
What was Whipples phylogenetic theory?
–early mammals were covered with scales, each with a hair…..friction on volar skin made the hairs disappear…….the sebaceous gland that was related to the hair changed to a sweat gland to provide moisture for gripping……scales lined up and fused together in rows to further assist with grip…..through natural selection this mutation became prevalent
Pattern abnormalities. Incipient ridges
Cummins was one of the most prominent researches in this field……aplasia is a condition where the person has no friction ridge….also known as epidermolysis…..another condition is disassociated ridges
Incipient ridges are believed to be hereditary…..Okajima affirmed that they are permanent without sweat glands
The basis of persistence and the basis of uniqueness are found in what.
The basis of persistence is found in morphology and physiology–the epidermis faithfully reproduces the 3D ridges due to physical attachments and constant regulation of cell proliferation and differentiation
The basis of uniqueness lies in embryology and differential growth factors
