2: Intro to MSK Anatomy and Embryology Flashcards
when does limb development begin?
- starts towards end of the 4th week of gestation
- upper limb first then lower limb 1-2 days later
what triggers limb development?
- induced by activation of a group of mesenchymal cells in the somatic lateral plate mesoderm (LPM).
limb buds form deep to a thick band of ectoderm called the?
Apical Ectodermal Ridge (AER)
what induces AER formation?
induced by the paracrine growth factor FGF-10 from the underlying mesoderm.
what is the function of the apical ectodermal ridge (AER)?
- produces FGF-8 (fibroblast growth factor) that interacts with underlying mesoderm to promote limb growth in a proximo-distal axis.
what does the zone of polarising activity (ZPA) refer to?
- mesodermal cells that aggregate at the base (posterior) aspect of each limb bud.
what is the function of the ZPA?
The zone of polarizing activity (ZPA) is an area of mesenchyme that expresses Shh genes which instruct the developing limb bud to form along the anterior/posterior axis and patterns the digits.
which period of gestation do digital rays form in hand plates; outlining the pattern of the digits?
6th week > day 41
in which stage of gestation do digit rays and digits in foot plates develop?
7th week > day 46
at which stage of gestation to separate digits (fingers and toes) occur?
8th week
which limb buds are larger and paddle shaped?
UL buds
which limb buds are smaller and flipper like?
LL buds
describe the stages in development of the upper limb bones
- all bones of UL are formed from lateral-plate mesoderm and undergo endochondrial ossification (+ membranous for the clavicle only).
- 5th week, LPM condenses within the limb bud.
- 6th week, condensed mesoderm chondrifies to form a hylaine cartilage model of UL.
- Weeks 7-9: primary ossification centres in clavicle, humerus, radius and ulna
- weeks 9-birth: primary ossification centres in metacarpals and phalanges.
which is the first bone to ossify in the body?
clavicle
what does the axis artery of the upper limb produce/give rise to?
- common interosseous a. (regresses in adult), radial and ulnar arteries.
- persists as the axillary artery, brachial artery, anterior interosseous artery + deep palmar arch in the adult.
the terminal plexus of the axis artery of the upper limb forms what?
palmar arches (superficial and deep)
what produces the axis artery of the lower limb?
umbilical artery, ends as a terminal plexus
what does the axis artery of the lower limb produce and persist as?
- produces anterior tibial a. (continues as the dorsalis pedis a.) + posterior tibial a. (terminates as medial + lateral plantar a.).
- persists as the inferior gluteal a., sciatic a. (accompanies the sciatic nerve), proximal part of popliteal a. + distal part of peroneal a.
which artery produce the femoral artery?
external iliac artery (separate 2nd arterial channel that connects with the axis a.)
which artery produces the profunda femoris artery?
femoral a.
the terminal plexus of the lower limb axis artery forms what?
deep plantar arch
describe the rotation of the upper limbs
- week 4, limb buds oriented coronally.
- week 6, rotate horizontally into a sagittal orientation.
- week 7 (6-8), rotate laterally 90 degrees so elbows are dorsal with the extensors posterior. Flexion at the wrist joint is analogous to plantar flexion at the ankle joint.
describe the rotation of the lower limbs
- week 4, limb buds oriented coronally.
- week 6, rotate horizontally into a sagittal orientation.
- week 7, rotate medially 90 degrees so knees are ventral with the extensors anterior and the flexors posterior. Dorsiflexion at the ankle joint in analogous to extension at the wrist joint.
