twinning and placental development

Question 1

monozygotic twinning (may be best to draw)

Answer 1

days 0-4: dichorionic and diamniotic. may or may not have a fused placenta. about 25% of monozygotic twins
days 4-8: monochorionic, diamniotic. about 75% of monozygotic twins.
days 8-12: monochorionic and monoamniotic.
after day 13, you have conjoined twins. monochorionic and monoamniotic

Question 2

What are the fetal components of placental development?

Answer 2

cytotrophoblast: inner layer of chorionic villi that makes cells
syncytiotrophoblast: outer layer of chorionic villi that secretes hCG. hCG is structurally similar to LH and stimulates the corpus luteum to secrete progesterone during the first trimester

Question 3

what is the maternal component of the placenta?

Answer 3

decidua basalis. derived from the endometrium. has maternal blood in the lacunae.

Question 4

What is structures are located within the umbilical cord? Pathology?

Answer 4

2 umbilical arteries return deoxygenated blood from fetal internal iliac arteries to the placenta
1 umbilical vein supplies oxygenated blood from the placenta to the fetus. it trainds into the the IVC via the ductus venosus in the liver.
a single umbilical artery is associated with congenital and chromosomal anomalies.

Question 5

From what structure are the umbilical arteries and veins derived?

Answer 5

the allantois

Question 6

What is the allantois? urachus? vitelline duct?

Answer 6

allantois is formed from the yolk sac and extends into the urogenital sinus. it becomes the urachus, which is a duct between the fetal baldder and the yolk sac that passes through the umbiligus. in the adult, it becomes the median umbilical ligament.
the vitelline duct is a duct that connects the yolk sac and the midgut lumen

Question 7

describe the development of the urachus? include timing

Answer 7

urachus comes from the allantois (which is seen in week 3 of development) and connects the fetal bladder and the yolk sac. it should obliterate so that the bladder is only connected to the urogenital sinus (which eventually becomes the urethra). in the adult, the obliterated allantois/urachus is the median umbilical ligament.

Question 8

what are three pathololgy problems that can arise from abnormal urachus development?

Answer 8

1. patent urachus: urine discharge from the umbilicus
2. urachal cysts: partial failure of the urachus to obliterate: fluid filled cavity lined with uroepitheliu, btw the umbilicus and bladder. can cause infection or adenocarcinoma
3. vesicourachal diverticulum: outpouching of the bladder

Question 9

vitelline duct: normal development, including timing

Answer 9

7th week: obliteration of the vitelline duct (between the midgut lumen and the yolk sac.
failure to close can cause a vitelline fistula of meconium discharge from teh umbilicus or a meckel diverticulum. can have ectopic gastric mucosa and/or pancreatic tissue and cause melena, periumbilical pain, and ulcers.