Lecture 15 - Post-implantation + Placenta Development Flashcards
What does the zona pellucida prevent the embryo from doing?
Adhering to anything other than the uterus
What does the embryo do when it reaches the uterus?
It “hatches” from the zone pellucida in order to attach itself to the uterine wall
What does the blastocyst adhere to?
The endometrium
What is the endometrium?
The epithelium lining the inside of the uterine wall
What is an ectopic pregnancy? List 3 types
Implantation of the embryo in an inappropriate/abnormal location
Tubal - uterine tubes
Ovarian - ovaries
Abdominal - abdominal cavity
What is placenta previa?
Implantation occurring near the cervix of the uterus, resulting in a low lying placenta next to (partial/marginal previa) or covering (complete previa) the cervix
How is the extra-embryonic mesoderm formed?
Cells migrate to become placed between the trophoblast and the membrane surrounding the yolk sac as well as the amnion
What is the extra-embryonic coelom and how is it formed?
A series of cavities form within the extra-embryonic mesoderm
The cavities grow in size until they eventually come together to form a single large cavity, which is the extra-embryonic coelom
The extra-embryonic coelom is completely surrounded by embryonic mesoderm
What is the mesodermal stalk? What does it give rise to?
The mesodermal stalk connects the embryo, amnion and yolk sac with the extra-embryonic mesoderm and trophoblast
It eventually becomes the umbilical cord
How does the blastocyst align itself when implanting?
It alligns itself with the inner cell mass facing the wall of the uterus
How does the embryo implant itself into the uterine wall?
Enzymes secreted by the embryonic trophoblast digest epithelium of the uterus and the ECM of the uterine wall
What is the difference between the endometrium and decidua?
Once implanted, the endometrium is referred to as the decidua
What does the trophoblast secrete? What does this do?
The trophoblast secretes human chorionic gonadotrophin (hCG) which prevents further menstruations
What does the trophoblast differentiate to become? (2)
Cytotrophoblast (cellular trophoblast)
Syncytiotrophoblast (syncitial trophoblast)
What is different about the syncytiotrophoblast when compared to the cytotrophoblast?
The syncytiotrophoblast undergoes nuclear division but no cytoplasmic division, resulting in a syncytium (multiple nuclei in a single cytoplasmic mass)
What is a lacunae?
Large openings/cavities formed in the uterine tissue into which maternal blood leaks into
Diffusion of gases, nutrients and wastes to/from embryonic blood occurs in structures associated with _____
Lacunae
What three layers form the chorion?
Syncytiotrophoblast
Cytotrophoblast
Extra-embryonic mesoderm
Where is the chorion found?
The chorion surrounds the embryo/fetus
What two components make up the placenta? Which one is the embryonic component and which one is maternal?
Chorion (embryonic) + decidua basalis (maternal)
What is the function of the placenta?
Allows for exchange of nutrients + waste between the embryo and the mother
What is the difference between a primary and secondary chorionic villus?
The primary and secondary villi both possess syncytiotrophoblast surrounding cytotrophoblast, but in the secondary villus there is also a core of extra-embryonic mesoderm
What does the extra-embryonic mesoderm create in the core of a chorionic villus?
Blood vessels
Capillaries
Blood cells
What structure connects the embryo/foetus to the placenta? What is it formed from?
The umbilical cord - formed from the embryonic stalk
List the 3 extra-embryonic structures
The amniotic sac
The yolk sac
The allantois
What is the structure + function of the amniotic sac
Structure: amniotic cavity roof: amnion (squamous cells of epiblast origin), floor: epiblast proper. Filled with amniotic fluid, wraps around embryo during embryonic folding, forming amniotic sac
Function: prevents embryo from drying out, storage for metabolic residues, protective structure (shock absorption)
What is the function of the yolk sac?
Produces cells that will form the embryo’s primordial germ line that will migrate into the developing reproductive system to form sperm + egg mother cells
Contains precursors for blood cells
Provides nutrition for the first 2/3 weeks of development
What do the vitelline arteries eventually fuse to become?
The arteries that supply the dorsal mesentery of the gut
Describe the formation and function of the allantois
When the cloacal membrane is formed, a small sac evaginates from the yolk sac - allantois
Waste storage + gas exchange (vestigial in humans because waste and gas exchange can occur in the placenta and mother’s blood)
Becomes surrounded by stalk of extra-embryonic mesoderm; contributes to umbilical cord formation
Walls well-vascularised; blood vessels contribute to umbilical arteries + veins - umbilical circuit
Describe the structure and function of the umbilical cord
2 arteries, 1 vein
Umbilical artery: brings oxygen+nutrient poor blood to the placenta
Umbilical vein: brings oxygen + nutrient rich blood to the sinus venosus of the heart
What happens to blood entering the heart from the placenta?
Rich blood from the placenta is mixed with poor blood from the cardinal veins
What does the left umbilical artery eventually do?
Loses connection with heart, carries blood to developing liver instead (which metabolises the rich nutrients)
