Flashcards in Implantation,placentation +early embryonic development Deck (42)
Define gestational age
-time zero=first day of last menstrual period
-expressed in completed weeks plus days
Define embryonic age
-used in embryolohy
-Time zero is fertilisation (day 14=ovulation)
What is implantation?
-Begins day 6/7
Complete by day 10 (4 days prior to expected period)
-Three stages: 1.) Apposition 2.) Attachment 3.)penetration
When is the endometrium receptive?
During the implantation window(3 day period) which is from day 7-10
What are the different phases of the menstrual cycle?
1.) proliferative phase
2.) Secretory phase split into
Describe the primitive trophoblast
-Rapidly differentiates into two layers
1.) Inner layer composed of mono nuclear cells cytotrophoblastic layer
2.)Synctiotrophobolast outer layer composed of multinucleated cells
Lacunae (inter-communicating fluid filled spaces appear in the rapidly enlarging trophoblastic mass from the 8th day after fertilisation
What is haemochorial placentation characterized by?
-This is part of development of the placenta
-differentation of the endometrium into decidua: enlarged stromal cells and uterine natural killer cells
-Transformation and opening of the uterine spiral arteries
Explain the development of the placenta and early embryo as characterized by the end of the second week
-The end of the 2nd week is characterized by the first appearance of chorionic villi
-Primary villous stems have a central core of cells derived by the proliferarion of the cytotrophoblast
-The primary villi gradually develop mesenchymal cores,which convert them into secondary villi
-The mesenchyal cells within the villi differentiate into blood capillaries, thus forming the tertiary villi
-The vessels from the villi soon become connected with the embryonic heart via vessels that differentiate in the mesenchyme of the chorion and in the connecting stalk
Describe the transition from a primary to tertiary villus, the time duration and characteristics of each.
-A primary villus is present at 2 weeks, this has a cytotrophoblast core
-At 3 weeks a secondary villus is present. This has a mesoderm core (has a smaller cytotrophoblast layer)
-At 4 weeks a tertriary villus is present which contains blood vessels (villous capillary)
Note that they all have cytotrophoblast & synctiotrophoblast
What is the significance of haemochorial placentation?
-Hemochorial placentation is the time that the fetus has an independent circulation making it an independent being
-The fetus is still not totally independent, as it is still dependent on the mother for oxygen, sugar, some amino acids, and basic nutrient supply
Explain the development of the placenta and early embryo beyond the 4th week.
-As the growth continues, the villi on the decidua capsularis (abembryonic) pole degenerate to form the chorion leavae.
-Villi adjacent to the decidual plate rapidly grow and expand to form the chorion frondosum
-The chorion frondosum forms the placenta together with the decidual plate
What is visible on an USS of a placenta, 6 weeks post conception?
-Chorion laevae: this will be away from the definitive placenta and this bit of the placenta is thin
-Chorion frondosum: The definitive placenta forms here so this bit of the placenta is thick.
What makes up the outer layer of fetal placenta?
-Chorion leavae & chorion frondosum
Why must the spiral arteries be dilated?
-Early on, the maternal spiral arteries start to be dilated bu they're plugged by synctiotrophoblast cells in the centre
-This protects the embryo from the maternal blood pressure
-We can use Doppler screening to see if the spiral arteries are open, using ultrasound and looking at the wave forms which are upstream from the spiral arteries
What are the characteristics of the uterine arteries of a non-pregnant woman?
-A lot of elastic recoil
-The arteries are narrow
What are the characteristics of the uterine artery blood flow of a non-pregnant woman?
-Continuous flow throughout the cardiac cycle
-There's a systolic peak but continuous flow in diastole
What is the pattern seen in doppler screening in a woman with pre-eclampsia?
-You get notching, therefore it looks like non-pregnant uterine arteries
When must any interventions for pre-eclampsia take place by?
-definitive placenta forms by about 16 weeks and all transformation of the spiral arteries will be completed by then
-Therefore,any interventions for pre-eclampsia must be before this
What happens to the spiral arteries in pre-eclampsia?
Transformation of the spiral arteries is incomplete
What are the 2 components of the definitive placenta?
1.) The maternal portion, formed by the decidual plate, and
2.) A fetal portion, made by the chorion frondosum
-On the maternal side decidual septa extend into the intervillous spaces, dividing placenta into 10-38 cotyledons
-By the end of the 16th week of pregnancy, the placenta has obtained its definitive form and undergoes no further anatomical modification
What different types of multiple pregnancy exist?
1.) Monozygotic: from one egg, identical; may be monochorionic or dichorionic
2.) Dizygotic : from two eggs, non-identical
What are the risk factors for having a multiple pregnancy
-previous multiple birth
-summer and autumn conceptions
What are the different types of mono zygotic multiple pregnancies?
1.) Dichorionic: cleavage before implanation; each twin has its own chorionic sac
2,)Mono chorionic or dichorionic
3.)Monoamniotic if cleavage takes place after day 8
What is a sacricoccygeal teratoma?
-A remnant of primitive streak
-Benign tumor of the primitive streak
-Within this you can get any kind of tissue/cell type
-Occasionally in utero, this has such a big blood supply that it can cause heart failure on the baby
What happens a the 5th week of pregnancy?
Folding at the longitudinal axis
Which week of pregnancy does the brain develop?
What is holopresencephaly?
-A CNS congenital abnormality
-Failure of the forebrain to divide and develop
-Associated with other midline&facial defects, Trisomy 13
-Severity varies from not being compatible with life to more mild mental retardation
What is Cardiogenesis?
-Determination of mesoderm and neural crest cells for heart formation
-Growth and differentiation processes to become cardiomyocytes
-Migration and transformation processes in order to form the heart
-Day 18-22: Canalization of cardiogenic clusters in the mesoderm results in formation of the paired heart tubes; lateral folding fuses tubes in midline
-Day 22: Arterial &Venous ends fixed. Bulbous cordis and ventricles grow faster than other regions so tube bends on itself. Sinus venosus, Trunchus arteriosus, Bulbus cordis, ventricle, atrium and cardinal veins also form
How and when does a physiological hernia resulting from development of the GI system resolve itself
-Loops return into abdominal cavity and physiological hernia resolves by day 56