Moorman - Human Development I, Embryogenesis

Question 1

Blastocyst formation

Answer 1

For first 5 days, symmetric mitotic divisions form cell mass. Interior cell hypoxia causes them to migrate toward edge, form hollow blastocyst cavity and clump of cells on one side. Day 6, implantation occurs

Question 2

Implantation & Ectopic Implantation

Answer 2

Normally occurs in uterus. Because fertilization takes place in ampulla, ectopic implantation can occur there most frequently. But can also go into peritoneal cavity, most common PERITONEAL ectopic pregnancy is in rectouterine pouch (internal gooch)

Question 3

Blastocyst layers

Answer 3

Trophoblast: exterior layer, becomes placenta, totipotent
Embryoblast: interior cell mass, becomes embryo, pluripotent

Question 4

Trophoblast & Embryoblast differentiation

Answer 4

Syncytiotrophoblast: Develops vasculature in implanted uteral wall, begins producing HcG
Cytotrophoblast: forms amniotic layer

Embryoblast differs into epiblast (interior) and hypoblast (exterior). Epiblast adhesion on two sides becomes Cloacal Membrane (caudal) and Buccopharyngeal membrane (cranial). Can’t yet differentiate L/R

Question 5

Week 4 (Primitive Streak, primitive node formation)

Answer 5

Primitive streak forms from cloacal membrane (GASTRULATION), establishing embryo directionality.
Primitive node: established at cranial end of primitive streak, contains Shh-containing vesicles and motile cilia. Ssh swept to left side of body to cause L/R differentiation. Failure can cause sinus invertus

Question 6

3 germ layer formation and notochord

Answer 6

Primitive streak cells enter between epiblast and hypoblast to form mesoderm. Also invade hypoblast to form endoderm. Epiblast becomes ectoderm. Epiblast invagination (from primitive node) produces notochord, which develops nervous system

Question 7

Describe Fertilization

Answer 7

Sperm all release acrosome contents to degrade zona pellucida, one sperm fuses with oocyte membrane and releases contents to cell. Fusion causes intracellular [ca2+] increase, causing cortical granules to fuse with membrane and release contents to ECM-telling zona pellucida to not let other sperm fuse (preventing polyspermia).