AssessmentsDevelopment of the umbilical cord
Development of the umbilical cord
USMLE® Step 1 style questions USMLE
A 7-year-old girl is brought to the emergency department because of worsening abdominal pain that began yesterday below her umbilicus. She begins vomiting during the physical examination, and has abdominal tenderness and guarding. The area has mild, fixed swelling and is erythematous. Her temperature is 38.3°C (101°F), pulse is 95/min, respirations are 18/min, and blood pressure is 100/55 mmHg. A laparotomy is performed to remove an extraperitoneal mass from the patient. Which of the following is the most likely diagnosis?
During development, the fetus is connected to the placenta via the umbilical cord, a long, flexible stalk that has two small arteries and a large vein.
Oxygenated blood then heads back towards the fetus’s heart through the umbilical vein.
When the baby is born the umbilical cord is no longer needed, so it’s cut off, leaving the navel or belly button.
In week 2 of development, the blastocyst has two parts—an inner part called the embryoblast, and an outer part called the trophoblast, which develops into the cytotrophoblast and syncytiotrophoblast.
The embryoblast has two layers called the epiblast, which contains the amniotic fluid, and the hypoblast, which contains the yolk sac filled with vitelline fluid that can nourish the embryo.
Cells from the epiblast layer start to differentiate into extraembryonic mesoderm cells, so-named because they are outside of the developing embryo.
These are some of the earliest mesoderm cells, and they start to form even while the embryoblast itself is a bilaminar disc.
These mesoderm cells line the inside of the cytotrophoblast and syncytiotrophoblast and form the chorion.
As development progresses, a space called the chorionic cavity develops between the embryoblast and the chorion, and these two structures are connected by a short band of extraembryonic mesoderm called the body stalk.
The body stalk contains the umbilical vessels and is the first of three structures that make up the umbilical cord.
In week 3 of development, the embryo folds in two directions.
In the longitudinal plane, there is a cranial and caudal fold, so that the embryo now looks less like a pancake and more like a little shrimp.
The midgut is open to the yolk sac via a connection called the vitelline duct, which is the second structure in the umbilical cord.
The allantois is the third structure in the umbilical cord.
In week 4 of development, the amniotic cavity folds down and around the embryo.