Early Embryology

Question 1

decreased AFP seen with what syndrome

Answer 1

downs syndrome

Question 2

three periods based on fertilization age

Answer 2

0-3 weeks: early embryo

3-8 weeks: embryonic organogenesis

8-38 weeks: fetal period

Question 3

major events week 1

Answer 3

cleavage

morula enters uterus

zona pellucida breaks down

blastulation

Question 4

two layers of blastocyst

Answer 4

embryoblast and trophoblast

Question 5

implantation occurs when

Answer 5

5-6 days after fertilization

Question 6

decidua

Answer 6

endometrium of pregnancy

Question 7

trophoblasts turns into what two layers

Answer 7

cytotrophoblast (mitotically active inner layer)

and syncytiotrophoblast (adjacent to maternal blood supply, produces hCG)

Question 8

hydatidiform moles

Answer 8

2 types

1. complete: fertilization of empty oocyte, fetus is entirely missing
2. partial: oocyte with two sperm (or diploid sperm)

causes high hCG, severe nausea and vomiting, vaginal bleeding, spontaneous abortion

Question 9

major events week 2

Answer 9

embryoblast changes into epiblast and hypoblast

2 cavities form: amniotic cavity and primitive yolk sac

extraembryonic mesoderm forms between yolk sac and cytotrophoblast (which then makes chorionic cavity)

(trophoblast has greater growth than embryoblast)

Question 10

two sections that embryoblast transofrms into

Answer 10

epiblast (inner, columnar cells related to amniotic cavity)

hypoblast (outer cuboidal cells adjacent to yolk sac)

Question 11

two layers of extraembryonic mesoderm

Answer 11

somatic: lines trophoblast and amnion
splanchnic: lines yolk sac

Question 12

3 layers of chorion

Answer 12

1. extraembryonic somatic mesoderm
2. cytotrophoblast layer
3. syncytiotrophoblast layer

Question 13

oligohydramnios

Answer 13

low volume (<500mL) of amniotic fluid

• Causes
  
  • low placental blood flow
  • renal agenesis or obstructive uropathy
• complications (Potter Sequence)
  
  • pulmonary hypoplasia
  • facial defects and limb defects
  • compression of umbilical cord

Question 14

polyhydramnios

Answer 14

high (>2L) amniotic fluid

• Causes:
  
  • fetus does not swallow usual amount of fluid (CNS anomalies)
  • esophageal atresia
• complications:
  
  • premature rupture of membranes/premature birth
  • intrauterine growth restriction

Question 15

major events week 3

Answer 15

• gastrulation
  
  • epiblast cells become motile and converge on the midline of dorsal disc forming primitive streak
  • primitive groove makes opening for cells to migrate ventrally
  • thickening at end forms primitive node and pit
• epiblast layer gives rise to 3 germ layers

Question 16

3 germ layers of epiblast

Answer 16

• Endoderm: epiblast cells that replace entire hypoblast layer
• Mesoderm: from cells that migrate between existing layers
• Ectoderm: cells that remain in epiblast after gastrulation completes

Question 17

sacrococcygeal teratoma

Answer 17

forms from primitive streak persists longer than it should, causing cell proliferation and tumor formation in sacral area

Question 18

notochord develops from

Answer 18

migrating mesoderm cells

Question 19

direction of neural tube closure

Answer 19

cranial to caudal (and cranial end closes ~2 days before caudal end, during week 4)

Question 20

derivatives of surface ectoderm

Answer 20

• epidermis, nails, hair, subcutaneous glands, mammary glands, anterior pituitary, enamel, lens of eye

Question 21

derivatives of neural ectoderm

Answer 21

CNS, retina, posterior pituitary gland, pineal body

Question 22

paraxial mesoderm

Answer 22

• organizes into somitomeres in head region (then into somites, number correlates with age)
  
  • each somite has its own sclerotome, myotome, dermatome
  • gives rise to majority of axial skeleton (vertebal column, base of skull, ribs)

Question 23

intermediate mesoderm

Answer 23

gives rise to urogenital system

Question 24

lateral plate mesoderm

Answer 24

makes body (somatic mesoderm and overlying ectoderm) wall and gut wall (splanchnic mesoderm and underlying endoderm)

forms bones of limbs, sternum, pelvic girdle and shoulder girdle (appendicular skeleton)

Question 25

what makes gut (fore/mid/hind)

Answer 25

endoderm (and yolk sac in hindgut)

Question 26

meckels diverticulum

Answer 26

aka ileal diverticulum * most common congenital defect of GI system * due to persistence of vitelline duct * no symptoms (but can contain ectopic gastric or panceatic mucosa)

Question 27

embryological sources of bone are

Answer 27

paraxial mesoderm lateral plate somatic mesoderm neural crest cells (ectomesenchyme)

Question 28

which skull bones by neural crest cells

Answer 28

frontal, sphenoid, squamous temporal, nasal, lacrimal, zygomatic, maxilla, incicive, mandible

Question 29

which bones arise via intramembranous ossification and when

Answer 29

majority of bones of face and flat bones of skull, clavicle end of week 7 of development

Question 30

what bones arise via endochondral ossification

Answer 30

long bones of extremities, pelvic and shoulder girdle, vertebral column

Question 31

time frame of endochondral bone formation

Answer 31

* 6 weeks: hyaline cartilage bone model forms * 8-12 weeks: primary centers of ossifaction are formed * 38 weeks: some secondary centers of ossification are present * after birth: most secondary centers of ossification are formed