1 - Embryology Flashcards
Gastrulation results in what 3 germ layers?
Endoderm, Mesoderm, Ectoderm
When does the process of gastrulation occur? What is it?
Day 16 - The embryo gastrulates from a bilaminar disc to a trilaminar disc, forming the three embryonic tissue layers
What occurs during neurulation?
Process by which the neural plate edges fold to form the neural tube.
During/After neurulation, the mesoderm divides into which layers?
Lateral Plate Mesoderm (parietal/visceral)
Intermediate Mesoderm
Paraxial Mesoderm (Directly adjacent to the neural tube)
What germ precursor is the origin of somitomeres/ somites?
Paraxial Mesoderm
By what day are the somites formed? How many of each vertebral level?
By day 35 - 44-45 somites total 4 Occipital 8 Cervical 12 Thoracic 5 Lumbar 5 Sacral 8-10 Coccygeal The first occipital and the last 7 coccygeal disappear
Somites evenually differentiate? What to?
Dermomyotome - skin/muscles
Sclerotome - gives rise to bones of the trunk and parts of the skull.
Bones in the body develop via two different methods of ossification. Which are those? Describe the differences.
Intramembranous - Undifferentiated mesenchymal cells differentiate into osteoblasts which form bone
Endochodndral - Bone replaces cartilaginous model
Describe the three steps of muscle fiber formation
Myoblasts —> Myotubes —> Muscle Fibers
Which muscle cell precursors form the muscles of the limb? What other structures are formed by these precursors?
Abaxial Precursors aka - ventrolateral (Limbs, Abdominal Wall, Infrahyoid)
Which muscle cell precursors form the muscles of the back? What other muscles do they form?
Primaxial Precursors aka Dorsomedial cells (Back, Shoulder Girdle, Intercostals)
Explain how the development process of somites is the cause for certain muscle groups being innervated by the same nerve/level
Muscle cells for the limbs are derived from somites form specific segmental levels. Start out segmental as “myotomes”. The myotomes which correspond to a certain nerve/level. These myotomes can either fuse or split resulting in a group of musles being innervated by one nerve, or a group of nerves innervating one large muscle.
When do the limb buds for the upper and lower limbs first appear?
Upper - 26d
Lower - 28d
What part of growth/differentiation do the Hox genes regulate?
Axes and Patterning
What is the AER and what does it do?
apical ectodermal ridge - essential for the proximal-distal axis. It signals for proliferation of the underlying mesenchymal cells, while causing adjacent cells to remain undifferentiated. Active mesenchymal cells aggregate at the posterior margin of the limb bud to form a ZPA (responsible for A-P axis)
When the notochord regresses in the vertebral column it leaves a small part behind called?
The nucleus pulposus
What precursor is responsible for the formation of the annulus fibrous of IV discs?
Mesenchyme
Underlying cause of accessory ribs?
Extra vertebral body
Underlying cause of fused ribs?
Missing vertebral body
What is the underlying cause of spina bifida occulta?
incomplete neural arc
What is Klippel-Feil syndrome?
aka brevicollis
congenital absence or fusion of cervical vertebra
What exactly is mesenchyme? What does it contribute to?
Somatic layer of the lateral plate mesoderm - gives rise to bones, tendons, ligaments, joints, vessels, and dermis
Describe what a chordoma is
remnants of the notochord that may give rise to malignant tumors that invade bone; they develope at the base of the skull and in the lumbar region
At which time does the mesenchyme of the hand and foot plates condense to start forming the digital rays?
6th week for hands
7th week for feet
