Repro - Embryology (FAS, Twinning, & Placental development)

Question 1

What significance/prevalence does fetal alcohol syndrome have in the US?

Answer 1

One of the leading causes of congenital malformations in the United States

Question 2

What causes fetal alcohol syndrome? In general, what can result from it? Give 7 examples of this.

Answer 2

Newborns of mother who consumed significant amounts of alcohol during pregnancy have an increased incidence of congenital abnormalities, including intellectual disability, pre- and postnatal development retardation, microcephaly, holoprosencephaly, facial abnormalities, (smooth philthrum, thin upper lip, small palpebral fissures, hypertelorism), limb dislocation, and heart defects

Question 3

Explain the difference between dizygotic and monozygotic twins.

Answer 3

Dizygotic twins arise from 2 eggs that are separately fertilized by 2 different sperm (always 2 zygotes), and will have 2 separate amniotic sacs and 2 separate placentas (chorions); Monozygotic twins arise from 1 fertilized egg (1 egg & 1 sperm) that splits into 2 zygotes in early pregnancy

Question 4

On what does the degree of separation of monzygotic twins depend? What else does this factor determine?

Answer 4

The degree of separation between monozygotic twins depends on when the fertilized egg splits into 2 zygotes. The timing of this separation determines the number of chorions and the number of amnions.

Question 5

What chorion and amniotic configurations result from the cleavage of monozygotic twins at 0-4 days, and what percentage of monozygotic twins separate during this period?

Answer 5

Dichorionic diamniotic (either fused placenta or separate placenta); 0-4 days (~25%); See p. 555 in First Aid 2014 for visual

Question 6

What chorion and amniotic configurations result from the cleavage of monozygotic twins at 4-8 days, and what percentage of monozygotic twins separate during this period?

Answer 6

Monochorionic diamniotic; 4-8 days (~75%); See p. 555 in First Aid 2014 for visual

Question 7

What chorion and amniotic configurations result from the cleavage of monozygotic twins at 8-12 days, and what percentage of monozygotic twins separate during this period?

Answer 7

Monochorionic monoamniotic; 8-12 days (< 1%); See p. 555 in First Aid 2014 for visual

Question 8

What chorion and amniotic configurations result from the cleavage of monozygotic twins at > 13 days?

Answer 8

Monochorionic monoamniotic conjoined twins; See p. 555 in First Aid 2014 for visual

Question 9

What chorion and amniotic configurations result from the cleavage of dizygotic twins?

Answer 9

Dichorionic diamniotic; See p. 555 in First Aid 2014 for visual

Question 10

What is the function of the placenta?

Answer 10

Primary site of nutrient and gas exchange between mother and fetus

Question 11

What are 2 parts of the fetal component of the placenta?

Answer 11

(1) Cytotrophoblast (2) Synctiotrophoblast

Question 12

What is the cytotrophoblast of the placenta? Is it a fetal or maternal component?

Answer 12

Inner layer of chorionic villi; Think: “Cytotrophoblast makes Cells”; Fetal component

Question 13

What is the synctiotrophoblast of the placenta? Is it a fetal or maternal component?

Answer 13

Outer layer of chorionic villi; Fetal component

Question 14

What does the synctiotrophoblast secrete? To what hormone is this substance structurally similar? What effect does the substance secreted by synctiotrophoblast have?

Answer 14

Secretes hCG (structurally similar to LH; stimulates corpus luteum to secrete progesterone during first trimester)

Question 15

What is the maternal component of the placenta?

Answer 15

Decidua basalis

Question 16

From where is the Decidua basalis derived? What does it contain? Is it a fetal or maternal component of the placenta?

Answer 16

Derived from the endometrium; Maternal blood in lacunae; Maternal component

Question 17

How may umbilical arteries are there? What function do (does) they (it) serve?

Answer 17

Umbilical arteries (2) - Return deoxygenated blood from fetal internal iliac arteries to placenta

Question 18

How may umbilical veins are there? What function do (does) they (it) serve?

Answer 18

Umbilical vein (1) - supplies oxygenated blood from placenta to fetus

Question 19

To where does the umbilical vein drain, and through what structure(s)?

Answer 19

Drains into IVC via liver or via ductus venosus

Question 20

What 2 general conditions are associated with the presence of a single umbilical artery?

Answer 20

Single umbilical artery is associated with congenital and chromosomal anomalies

Question 21

From where are umbilical arteries and veins derived?

Answer 21

Umbilical arteries and veins are derived from allantois

Question 22

Draw a cross section of the umbilical cord, including and labeling the following structures: (1) Allantoic duct (2) Amniotic epithelium (3) Umbilical arteries (4) Umbilical vein (5) Wharton jelly.

Answer 22

See p. 557 in First Aid 2014 for visual

Question 23

What forms the allantois, and when? To where does the allantois extend? What does the allantois become?

Answer 23

In the 3rd week the yolk sac forms the allantois, which extends into the urogenital sinus. Allantois becomes the urachus, a duct between fetal bladder and yolk sac.

Question 24

What 3 anomalies result from failure of the urachus to obliterate?

Answer 24

Failure of urachus to obliterate results in: (1) Patent urachus (2) Urachal cyst (3) Vesicourachal diverticulum

Question 25

What sign/symptom characterizes a Patent urachus?

Answer 25

Patent urachus - Urine discharge from Umbilicus

Question 26

What causes Urachal cyst? What defines it? What are 2 conditions to which it can lead?

Answer 26

Urachal cyst - Partial failure of urachus to obliterate; Fluid-filled cavity with uroepithelium, between umbilicus and bladder. Can lead to infection, adenocarcinoma

Question 27

What defines Vesicourachal diverticulum?

Answer 27

Outpouching of bladder

Question 28

When does the vitelline duct obliterate? What is another name for this duct, and what is its initial purpose?

Answer 28

7th week - obliteration of vitelline duct (omphalo-mesenteric duct), which connects yolk sac to midgut lumen

Question 29

What 2 anomalies result from failure of vitelline duct to close?

Answer 29

(1) Vitelline fistula (2) Meckel diverticulum

Question 30

What sign/symptom characterizes Vitelline fistula?

Answer 30

Vitelline fistula => meconium discharge from umbilicus

Question 31

What causes Meckel diverticulum? What 2 tissues and 3 symptoms may result from it?

Answer 31

Meckel diverticulum - partial closure (of vitelline duct), with patent portion attached to ileum (true diverticulum). May have ectopic gastric mucosa and/or pancreatic tissue => melena, periumbilical pain, and ulcers.