Embryology I

Question 1

Gestational/obstetric calendar vs. Ovulatory calendar

Answer 1

Gestational/obstetrical calendar includes 2 weeks prior to fertilization, while Ovulatory does not.

Question 2

Acrosome reaction

Answer 2

Occurs approximately 7 hours post sex. Sperm enters corona radiata via hyaluronidase.

Question 3

Zone reaction

Answer 3

Sperm penetrates the ZP by releasing acrosin, esterases, and neuramidases.

Question 4

Cleavage overview

Answer 4

Occurs about 30 hours post sex.
Increase in cell number, but decrease in cell size,
Results in morula development on day 3.

Question 5

Day 5
Day 6
Day 7

Answer 5

Day 5: Fluid pours in creating a blastocyst cavity. Creates early blastocyst.
Day 6: Implantation on the posterior uterus.
Day 7: Creation of a late blastocyst.
By Day 7, the ZP should be gone.

Question 6

Summary of Week 1

Answer 6

Fertilization
Cleavage 
Formation of the blastocyst
ICM (embryoblast) created
Implantation

Question 7

Trophoblast

Answer 7

Give rise to placenta.
Releases EPF in first 10 days.
Gives rise to cytotrophoblast and syncytiotrophoblast.

Question 8

Cytotrophoblast

Answer 8

Mitotically active stem cell layer. Replaces trophoblast cells.

Question 9

Syncytiotrophoblast

Answer 9

Provides nutrients for the embryo.

Release hCG and alerts the body that it is pregnant.

Question 10

Epiblast gives rise to:

Answer 10

Ectoderm

Amnion and amniotic cavity

Question 11

Hypoblast gives rise to:

Answer 11

EE Endoderm –> EE Mesoderm, prechordal plate and umbilical vesicle.

Question 12

EE Mesoderm

Answer 12

EE coelom
EE somatic mesoderm: lines trophoblast and covers amnion.
EE splanchnic mesoderm: lines umbilical vesicle.

Question 13

Summary of Week 3

Answer 13

Gastrulation occurs.
CNS development
Heart development

Question 14

Saccrococcygeal teratoma

Answer 14

Remnant of primitive streak.

Question 15

Oralpharyngeal teratoma

Answer 15

Abn migration of germ cells.

Question 16

Notochord

Answer 16

Mesoderm.
Provides longitudinal axis for embryo.
Provides the framework for the vertebral column.
Induces the formation of the neural plate and CNS.

Question 17

Chordoma

Answer 17

Believed to be formed from remnants of notochord.

Question 18

Allantois

Answer 18

Diversion from UV and made of endoderm.
Template for umbilical arteries and veins.
Becomes urachus.

Question 19

Paraxial Mesoderm

Answer 19

Somites

• Myotome (muscle)
• Sclerotome (skeleton)
• Dermatome (dermis)

Question 20

Intermediate Mesoderm

Answer 20

Urogenittal

-kidneys, gonads.

Question 21

Lateral Plate Mesoderm

Answer 21

Somatic or Splanchnic.

-CT (blood, lymph, mesenteries, CV.)

Question 22

Induction on the neural plate

Answer 22

Notochord release SHH and causes neural groove to dip into the mesoderm and pinch off the neaural tube. Two small remnants of neural crest cells remain.

Question 23

Neural tube closure

Answer 23

Occurs at rostral and caudal NP.
Primary - brain to lumbar
Secondary - sacrum to coccyx.

Question 24

Spina bifida is a result of:

Answer 24

Failure of the caudal NP to close.

Question 25

Neural crest cells

Answer 25

Only sensory Ns.
ex:
Dorsal root ganglia
Schwann cells
Melanocytes
Chromaffin cells
Bones of the face

Question 26

Spina bifida occulta

Answer 26

Benign (10% of population have it).

-Failure of spinal processes to close.

Question 27

Meningocele

Answer 27

Dura mater creates cyst filled w/ CSF.
Absence of vertebral arches.
May or may not cause defects.

Question 28

Meningomyelocele

Answer 28

SC exists in a cyst outside of the spine.

Patient will have sensory and motor defects.

Question 29

Myelocele

Answer 29

SC is opened and exposed. Opening must be closed or patient is at a high risk for infection.

Question 30

Failure of rostral neural pore to close causes:

Answer 30

Anencephaly: not compatible with life (top of head is open).
Encephalocele: growth on head. Can contain brain tissue.

Question 31

Meninges develop from:

Answer 31

Meninx primitiva and is mesoderm origin (sclerotome)

Question 32

Pachymeninx gives rise to:

Answer 32

Dura mater (mesoderm)

Question 33

Leptomeninges gives rise to:

Answer 33

Arachnoid mater and pia mater (neural crest cells).

Question 34

Mesenchyme

Answer 34

Embryonic CT.

Question 35

Intramembranous ossification

Answer 35

Mesenchyme –> bones

ex: skull and facial bones

Question 36

Endochondrial ossification

Answer 36

Mesenchyme –> cartilage –> bone

ex: everything else

Question 37

Production of the vertebral column

Answer 37

From the scleratome.

Caudal dense and cephalic loose fuse to form a vertebra.

Question 38

Intervertebral disk

Answer 38

Nucleus pulposis: from notochord.

Annulus fibrosis: Fibrous tissue from sclerotome.

Question 39

Sternum

Answer 39

From somatic lateral plate mesoderm.

Question 40

Ribs

Answer 40

From sclerotome.

Question 41

Caudalization

Answer 41

Gain of function. Will look like section below.

Question 42

Cephalization

Answer 42

Loss of function. Will look like section above.

Question 43

Myotome gives rise to:

Answer 43

Epimere and hypomere.
Epimere - epaxial muscles (back)
Hypomere - hypaxial muscles (C, T, L, S myotomes)

Question 44

Poland Syndroma

Answer 44

Hypomere cells do NOT migrate to chest.
Absence of Pect Major and Minor.
Missing 2-4 ribs.
Associated with syndactyly.

Question 45

Prune Belly Syndrome

Answer 45

Partial or complete absence of of abdominal musculature.
Mostly in males.
Problems with testes to descend (crytorchidism)
Poor formation of UT and bladder.