Repro - Embryology (FAS, Twinning, & Placental development) Flashcards
Pg. 555-557 in First Aid 2014 Pg. 507-508 in First Aid 2013 Sections include: -Fetal alcohol syndrome -Twinning -Placental development -Umbilical cord -Urachus -Vitelline duct
What significance/prevalence does fetal alcohol syndrome have in the US?
One of the leading causes of congenital malformations in the United States
What causes fetal alcohol syndrome? In general, what can result from it? Give 7 examples of this.
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
Explain the difference between dizygotic and monozygotic twins.
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
On what does the degree of separation of monzygotic twins depend? What else does this factor determine?
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.
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?
Dichorionic diamniotic (either fused placenta or separate placenta); 0-4 days (~25%); See p. 555 in First Aid 2014 for visual
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?
Monochorionic diamniotic; 4-8 days (~75%); See p. 555 in First Aid 2014 for visual
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?
Monochorionic monoamniotic; 8-12 days (< 1%); See p. 555 in First Aid 2014 for visual
What chorion and amniotic configurations result from the cleavage of monozygotic twins at > 13 days?
Monochorionic monoamniotic conjoined twins; See p. 555 in First Aid 2014 for visual
What chorion and amniotic configurations result from the cleavage of dizygotic twins?
Dichorionic diamniotic; See p. 555 in First Aid 2014 for visual
What is the function of the placenta?
Primary site of nutrient and gas exchange between mother and fetus
What are 2 parts of the fetal component of the placenta?
(1) Cytotrophoblast (2) Synctiotrophoblast
What is the cytotrophoblast of the placenta? Is it a fetal or maternal component?
Inner layer of chorionic villi; Think: “Cytotrophoblast makes Cells”; Fetal component
What is the synctiotrophoblast of the placenta? Is it a fetal or maternal component?
Outer layer of chorionic villi; Fetal component
What does the synctiotrophoblast secrete? To what hormone is this substance structurally similar? What effect does the substance secreted by synctiotrophoblast have?
Secretes hCG (structurally similar to LH; stimulates corpus luteum to secrete progesterone during first trimester)
What is the maternal component of the placenta?
Decidua basalis
From where is the Decidua basalis derived? What does it contain? Is it a fetal or maternal component of the placenta?
Derived from the endometrium; Maternal blood in lacunae; Maternal component
How may umbilical arteries are there? What function do (does) they (it) serve?
Umbilical arteries (2) - Return deoxygenated blood from fetal internal iliac arteries to placenta
How may umbilical veins are there? What function do (does) they (it) serve?
Umbilical vein (1) - supplies oxygenated blood from placenta to fetus
To where does the umbilical vein drain, and through what structure(s)?
Drains into IVC via liver or via ductus venosus
What 2 general conditions are associated with the presence of a single umbilical artery?
Single umbilical artery is associated with congenital and chromosomal anomalies
From where are umbilical arteries and veins derived?
Umbilical arteries and veins are derived from allantois
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.
See p. 557 in First Aid 2014 for visual
What forms the allantois, and when? To where does the allantois extend? What does the allantois become?
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.
What 3 anomalies result from failure of the urachus to obliterate?
Failure of urachus to obliterate results in: (1) Patent urachus (2) Urachal cyst (3) Vesicourachal diverticulum
What sign/symptom characterizes a Patent urachus?
Patent urachus - Urine discharge from Umbilicus
What causes Urachal cyst? What defines it? What are 2 conditions to which it can lead?
Urachal cyst - Partial failure of urachus to obliterate; Fluid-filled cavity with uroepithelium, between umbilicus and bladder. Can lead to infection, adenocarcinoma
What defines Vesicourachal diverticulum?
Outpouching of bladder
When does the vitelline duct obliterate? What is another name for this duct, and what is its initial purpose?
7th week - obliteration of vitelline duct (omphalo-mesenteric duct), which connects yolk sac to midgut lumen
What 2 anomalies result from failure of vitelline duct to close?
(1) Vitelline fistula (2) Meckel diverticulum
What sign/symptom characterizes Vitelline fistula?
Vitelline fistula => meconium discharge from umbilicus
What causes Meckel diverticulum? What 2 tissues and 3 symptoms may result from it?
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.
