Early Embryogenesis Anna Campbell Flashcards
What is the difference between gestational age and post-fertilization age?
In the clinic, embryonic age is calculated using gestational age - with day 0 as two weeks prior to fertilization (the beginning of the mother’s last menstrual period). In embryology, embryonic age is calculated with fertilization as day 0. So, gestational age is post-fertilization age + 2 weeks.
What three important events occur at fertilization?
- restoration of the diploid number of chromosomes
- determination of the sex of the embryo
- initiation of cleavage
Home pregnancy tests rely on the presence of hCG. What secretes hCG and when is it first detectable in the urine?
hCG (human chorionic gonadotropin) is secreted by the syncytiotrophoblast. The syncytiotrophoblast is formed during the ‘week of twos’, so hCG is detectable by the end of the second week post-fertilization
What is the amniotic cavity?
A cavity that develops within the epiblast and grows to eventually surround the entire fetus.
What is amniocentesis?
Extraction of fluid and floating developing embryonic cells from the amnion. This can be used to diagnose chromosomal abnormalities and fetal infections. However, this is a rather invasive procedure so it isn’t the first choice for diagnosis.
What is the exocoelomic cavity?
AKA the primitive yolk sac, this cavity develops within hypoblast tissue. In other species it provides nourishment but in humans it eventually shrinks and disappears by the end of the third month.
What is the extraembryonic cavity?
AKA the chorionic cavity, it is a space that is created when the extraembryonic mesoderm splits into the somatic and splanchnic layers. It shrinks throughout development and eventually disappears by the end of the third month.
You have a 14 YO patient that just tested + for a pregnancy test you ordered. What is the name of the substance in her plasma (or in her urine if using a home preg. test) that this test detects? What structure produces it?
hCG produced by the syncytiotrophoblast
The 14-year-old patient is shocked and totally confused. She asks you, “Ok, if I’m pregnant, why did I have vaginal bleeding this morning?” Assuming conception occurred about 2.5 weeks ago, what’s one explanation you can give her?
This could be caused by bleeding trophoblastic lacunae. This is called “implantation bleeding”
List the 3 germ layers. Name the process that forms these 3 layers.
• Ectoderm
o Neural system, skin and appendages that relate to external environment (eyes, ears…)
• Mesoderm
o Musculoskeletal tissue, genitourinary system, body wall and membranes that line cavities
• Endoderm
o Foregut, midgut and hindgut – GI tract and appendages (liver, pancreas) respiratory tract, bladder
-Gastrulation.
A man and woman (they are 33 year-old twins) are sitting next to you on an airplane. Both of them SWEAR they are identical twins. Based on this information, why aren’t they.
Identical (or monozygotic) twins are same sex; they share 100% of genetic information
Your 14 year-old pregnant patient decides to keep the baby. She read a little bit about blood typing from wikipedia the other day, and she is really scared that her baby will have a different blood type than her and will die as a result. How will you placate her?
Reassure her by explaining that the placenta takes away waste, exchanges gases and allows nutrient uptake, but the blood supply of the mother and baby NEVER mix. So even if the blood types are different, neither her nor the baby are at risk for blood type rejection.
