Embryology Flashcards
On what wall of the embryo do limb buds initially develop?
Ventrolateral
Approximately what week do limb buds begin to appear?
4 weeks
Where does the tissue for limb bud development originate from?
Lateral mesoderm, derived from the somatic layer of the lateral plate mesoderm.
What does the remnant of the notochord become in an adult?
What condition is associated with it?
Nucleus pulposus
Slipped disc - herniated
What is the differing function of the lateral plate mesoderm and somites in limb development?
Lateral plate mesoderm - limb skeleton
Somites - muscles
Describe the three degress of asymmetry in limbs
Proximodistal axis - shoulder to fingers
Dorsovental axis - no hairy palms
Anteroposterior axis - left/right hands are mirror images
What is the core of the limb bud made from?
Mesenchyme
What is the function of the apical ectodermal ridge?
Orchestrates limb development from proximal to distal. Stops differentiation of the mesenchyme directly below it, final stage is the appearance of paddles before it regresses.
What is the function of the zone of polarising activity?
Allows the generation of asymmetry in the limbs. (anteroposterior axis determination_
Is a signalling centre located at the posterior base of the limb bud.
Controls patterning and maintains the AER.
Describe how digital rays form.
Mesenchyme condensation within the plates which become cartilagenous models of the digital bones.
What portion of the spine does the upper and lower limb bud appear opposite?
Upper - caudal cervical spine segments
Lower - Lumbar and sacral spinal segments
Describe how development of the brachial plexus determines innervation of specific muscles.
Muscles are compartmentalised and nerves grow into common muscle masses.
Anterior divisions regroup to form medial and lateral cords so flexors are derived from these.
Posterior divisions regroup to form the posterior cord so extensors are supplied by this.
Describe the difference between a dermatome and myotome.
Dermatome - strip of skin supplied by a single spinal nerve
Myotome - muscle or group of muscles supplied by a single spinal nerve
What does the cardiovascular system derive from?
Mesodery
Describe the folding that leads to the final position of the heart.
Lateral folding creates the heart tube. A pair of primitive vessels forms and predominate either side. Early vessels pushed together to make one large tube at the same time as the gut.
Cephalocaudal folding brings it to the thoracic region.
What are blood islands?
A composite of primitive blood cells and capillaries. Found either side of the midline.