Embryology Weeks 4-8

Question 1

What is neurulation?

Answer 1

Processes involved in the formation of the neural plate and neural folds and closure of the folds to form the neural tube

Completed by the end of the fourth week

Question 2

What is the neural plate?

Answer 2

Neuroectoderm that will fold along it central axis to form the neural groove

Question 3

What signaling pathway is essential for neural crest development?

Answer 3

Wnt/B-catenin signaling

Question 4

What is the role of the neural crest?

Answer 4

Migrate widely and form many components of the PNS

E.g. dorsal root ganglia, autonomic ganglia, meninges of spinal cord

Question 5

Describe completion of neurulation.

Answer 5

Two neural folds fuse and pinch off to become the neural tube

Fusion of the folds begins in the middle of the embryo moves cranially and caudally

Question 6

What is paraxial mesoderm and what does it give rise to?

Answer 6

Thickened column of mesenchymal cells nearest to the neural tube.

Gives rise to somites

Question 7

What does intermediate mesoderm give rise to?

Answer 7

Urogenital system

Question 8

What does the lateral plate mesoderm give rise to?

Answer 8

Bulk of the tissues of the body wall, wall of the digestive tract, and limbs

Question 9

What do somites give rise to?

Answer 9

Most of the axial skeleton and associated musculature, as well as adjacent dermis

Question 10

What is myelomeningocele?

Answer 10

Failure of closure at the caudal end of the neural tube

Severe form of spina bifida

Results in hydrocephalus

Question 11

What is anencephaly?

Answer 11

Failure of closure at the rostral end of the neural tube

Question 12

What is the significance of alpha-fetoprotein?

Answer 12

Major component of fetal serum

Elevated levels indicate neural tube defects

Question 13

What causes folding at the cranial and caudal ends of the embryo?

Answer 13

Growth in the long axis out paces growth at the sides of the embryonic disc

Question 14

When do pharyngeal arches begin to appear?

Answer 14

Day 26

Question 15

What happens during weeks 4-8?

Answer 15

All major external and internal structures are established

Major organ systems have started to develop

Exposure to teratogens during this period may cause severe birth defects

Question 16

What are three main functions of the amniotic fluid?

Answer 16

Physically protect the fetus

Provide room for fetal movements

Help regulate fetal body temperature

Question 17

How is amniotic fluid produced?

Answer 17

Dialysis of maternal and fetal blood through blood vessels in the placenta

Question 18

What is hydramnios?

Answer 18

Excessive amount (>2000 mL) of amniotic fluid

Frequently associated with multiple pregnancies and esophageal atresia or anencephaly

Question 19

What is oligohydramnios?

Answer 19

Too little amniotic fluid (<500 mL)

Associated with bilateral renal agenisis (absence of kidneys)

Question 20

What is amniocentisis?

Answer 20

Wthdrawaly of a small amount of amniotic fluid via needle insertion

Not usually performed until weeks 13 or 14

Used to make prenatal diagnosis (e.g. trisomy 21)

Question 21

What is the lecithin to sphingomyelin ratio used for?

Answer 21

Determination of fetal maturity

Question 22

What is the placenta?

Answer 22

Flat organ mediating exchange between the fetal and maternal circulatory systems

Organized to provide a very large surface area

Question 23

What are the maternal and fetal components of the placenta?

Answer 23

Maternal - decidua basalis, portion of endometrium

Fetal - chorionic villi

Question 24

What is the role of the umbilical vein?

Answer 24

Carry oxygenated blood back to the fetus

Question 25

How does the maternal circulation and fetal circulation interact?

Answer 25

Fetal circulation stays within vessels within the chorionic villi

Maternal circulation is “emptied” into the intervillous space to bath the villi carrying the fetal blood

Question 26

Where does exchange of nutrients between the fetal and maternal circulation happen?

Answer 26

Across the thin fetal capillaries within the villi

Question 27

What is Wharton’s jelly?

Answer 27

Mucoid connective tissue within the umbilical cord that surrounds the umbilical vessels

Question 28

What are functions of the placenta?

Answer 28

Nutrient and waste exchange between fetal and maternal circulation

Transfer of maternal antibodies

Protein and steroid hormone production (hCG, progesterone, estrogens)

Human placental lactogen synthesis

Question 29

What is placenta previa?

Answer 29

Placenta covers the cervical outlet of the uterine cavity and acts as a physical obstacle

Hemorrhage can occur as a common consequence and can be fatal to the fetus and mother

Question 30

What is erythroblastosis fetalis?

Answer 30

Occurs when fetal erythrocytes are Rh+ but mother is Rh-

Mother’s body forms antibodies to the Rh antigen that will cross the placenta and destroy the fetus