1 - Embryology

Question 1

Gastrulation results in what 3 germ layers?

Answer 1

Endoderm, Mesoderm, Ectoderm

Question 2

When does the process of gastrulation occur? What is it?

Answer 2

Day 16 - The embryo gastrulates from a bilaminar disc to a trilaminar disc, forming the three embryonic tissue layers

Question 3

What occurs during neurulation?

Answer 3

Process by which the neural plate edges fold to form the neural tube.

Question 4

During/After neurulation, the mesoderm divides into which layers?

Answer 4

Lateral Plate Mesoderm (parietal/visceral)
Intermediate Mesoderm
Paraxial Mesoderm (Directly adjacent to the neural tube)

Question 5

What germ precursor is the origin of somitomeres/ somites?

Answer 5

Paraxial Mesoderm

Question 6

By what day are the somites formed? How many of each vertebral level?

Answer 6

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

Question 7

Somites evenually differentiate? What to?

Answer 7

Dermomyotome - skin/muscles

Sclerotome - gives rise to bones of the trunk and parts of the skull.

Question 8

Bones in the body develop via two different methods of ossification. Which are those? Describe the differences.

Answer 8

Intramembranous - Undifferentiated mesenchymal cells differentiate into osteoblasts which form bone
Endochodndral - Bone replaces cartilaginous model

Question 9

Describe the three steps of muscle fiber formation

Answer 9

Myoblasts —> Myotubes —> Muscle Fibers

Question 10

Which muscle cell precursors form the muscles of the limb? What other structures are formed by these precursors?

Answer 10

Abaxial Precursors aka - ventrolateral (Limbs, Abdominal Wall, Infrahyoid)

Question 11

Which muscle cell precursors form the muscles of the back? What other muscles do they form?

Answer 11

Primaxial Precursors aka Dorsomedial cells (Back, Shoulder Girdle, Intercostals)

Question 12

Explain how the development process of somites is the cause for certain muscle groups being innervated by the same nerve/level

Answer 12

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.

Question 13

When do the limb buds for the upper and lower limbs first appear?

Answer 13

Upper - 26d

Lower - 28d

Question 14

What part of growth/differentiation do the Hox genes regulate?

Answer 14

Axes and Patterning

Question 15

What is the AER and what does it do?

Answer 15

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)

Question 16

When the notochord regresses in the vertebral column it leaves a small part behind called?

Answer 16

The nucleus pulposus

Question 17

What precursor is responsible for the formation of the annulus fibrous of IV discs?

Answer 17

Mesenchyme

Question 18

Underlying cause of accessory ribs?

Answer 18

Extra vertebral body

Question 19

Underlying cause of fused ribs?

Answer 19

Missing vertebral body

Question 20

What is the underlying cause of spina bifida occulta?

Answer 20

incomplete neural arc

Question 21

What is Klippel-Feil syndrome?

Answer 21

aka brevicollis

congenital absence or fusion of cervical vertebra

Question 22

What exactly is mesenchyme? What does it contribute to?

Answer 22

Somatic layer of the lateral plate mesoderm - gives rise to bones, tendons, ligaments, joints, vessels, and dermis

Question 23

Describe what a chordoma is

Answer 23

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

Question 24

At which time does the mesenchyme of the hand and foot plates condense to start forming the digital rays?

Answer 24

6th week for hands

7th week for feet

Question 25

Describe the ZPA and its clinical importance with regard to pregnant women

Answer 25

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

Question 26

When does the process of osteogenesis begin?

Answer 26

8th week, primary ossification centers are present in all long bones by the 12th week

Question 27

What is the primordial version of the brachial artery and what arteries are fromed from its branching patterns?

Answer 27

Primary axial artery - form the radial and ulnar arteries

Question 28

What is the most critical time for limb development?

Answer 28

Problems during the 4th and 5th weeks are most likely to result in a congenital anomaly

Question 29

While the cause of most limb defects is of unknown etiology, what substance is famous for causing many limb defects?

Answer 29

Thalidomide

Question 30

Define amelia

Answer 30

congenital absence of an entire limb

Question 31

Define meromelia

Answer 31

congenital absence of part of a limb

Question 32

What is achondroplasia?

Answer 32

the cause of dwarfism (1 in 15,000) the limbs are bowed and short. Results from a disturbance of endochondral ossification at epiphyseal plates

Question 33

What is thanatophoric dysplasia?

Answer 33

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.

Question 34

Describe congenital clubfoot (Talipes)

Answer 34

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

Question 35

What is genu recurvatum?

Answer 35

congenital hyperextension of that knee that generally returns to normal alignment without intervention

Question 36

In the case of a limb anomaly, what mesenchymal precursor is to blame?

Answer 36

Lateral plate mesoderm?

Question 37

What gene is the cause of Marfan’s syndrome?

Answer 37

Fibrillin 1!!!!!

Question 38

In the case of duplication of digits or limbs, what would be the major causing factor? (2 answers)

Answer 38

Over-active ZPA

Retinoic Acid during pregnancy

Question 39

Somites are formed from which portion of the mesoderm?

Answer 39

Paraxial mesoderm

Question 40

3 major things that mesenchyme develops into?

Answer 40

Fibroblasts
Chondroblasts
Osteoblasts

Question 41

Majority of the bones in the body are formed from the ___________. There are other sources (3) which form ___________.

Answer 41

1. Sclerotome
2. Lateral Plate somatic layer - sternum, shoulder/pelvic girdles
   Neural Crest - bones of skull
   Head somitomeres - base and cranial vault of skull

Question 42

Describe the rotation of the limbs in embryonic development

Answer 42

Upper limbs rotate 90 deg. Laterally

Lower limbs rotate 90 deg. Medially