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
Describe the ZPA and its clinical importance with regard to pregnant women
Zone of polarizing activity - responsible for the patterning of the a/p axis of limbs. Its action is done partially via the release of retinoic acid. Pregnant women who ingest retinoic acid during a cirtical period for limb development could have a child with duplicate limbs or other limb deformities
When does the process of osteogenesis begin?
8th week, primary ossification centers are present in all long bones by the 12th week
What is the primordial version of the brachial artery and what arteries are fromed from its branching patterns?
Primary axial artery - form the radial and ulnar arteries
What is the most critical time for limb development?
Problems during the 4th and 5th weeks are most likely to result in a congenital anomaly
While the cause of most limb defects is of unknown etiology, what substance is famous for causing many limb defects?
Thalidomide
Define amelia
congenital absence of an entire limb
Define meromelia
congenital absence of part of a limb
What is achondroplasia?
the cause of dwarfism (1 in 15,000) the limbs are bowed and short. Results from a disturbance of endochondral ossification at epiphyseal plates
What is thanatophoric dysplasia?
Lethal skeletal dysplasia (1 in 20,0000) Infants die soon after birth due to respiratory failure. Due to a fibroblast growth factor (FGF) receptor deficiency.
Describe congenital clubfoot (Talipes)
general for any defect involving the TALUS. Results from abnormal orientation of the foot that prevents normal weight bearing. Unknown etiology (for certain) could be caused by envrionmental factors
What is genu recurvatum?
congenital hyperextension of that knee that generally returns to normal alignment without intervention
In the case of a limb anomaly, what mesenchymal precursor is to blame?
Lateral plate mesoderm?
What gene is the cause of Marfan’s syndrome?
Fibrillin 1!!!!!
In the case of duplication of digits or limbs, what would be the major causing factor? (2 answers)
Over-active ZPA
Retinoic Acid during pregnancy
Somites are formed from which portion of the mesoderm?
Paraxial mesoderm
3 major things that mesenchyme develops into?
Fibroblasts
Chondroblasts
Osteoblasts
Majority of the bones in the body are formed from the ___________. There are other sources (3) which form ___________.
- Sclerotome
- Lateral Plate somatic layer - sternum, shoulder/pelvic girdles
Neural Crest - bones of skull
Head somitomeres - base and cranial vault of skull
Describe the rotation of the limbs in embryonic development
Upper limbs rotate 90 deg. Laterally
Lower limbs rotate 90 deg. Medially
