Embryology - Embryogenesis Flashcards
Introduction to terminology relevant to the curricular blocks Understand the significance of embryology Understand the initial phases of development Understand the 3 germ layers (gastrulation) and significance Introduction to concepts and stages of later embryogenesis
Name the 3 anatomical planes
- Frontal (coronal) : separates anterior & posterior
- Sagittal: Separates right and left sides
- Transverse (horizontal): separations superior and inferior
How much time takes fertilization?
takes 24 hours
What marks the beginning of fertilization?
Beggining of pre-embryonic period
When does fertilization occurs?
When a spermatozoon and an oocyte contact and unite to form the zygote
What initiate the cleavage of the zygote?
metabolic activation
What could cause the death of a zygote
defect in the molecular and physical sequences
What is the cleavage of the zygote exactly?
Consists of repeated mitotic division of the zygote
What is the name of each cell after the mitotic division?
Blastomere
Why do cells are tightly aligned against each other?
Allows better cell interaction
whats the name of the 12-32 cell stage when it enters the uterus?
Morula stage
What is surrounding the blastomere and the morula?
the Zona pellucida
What happens to the size of the embryo during the blastomere and morula stage?
It does not increase in size
Time line of blastomere, morula
2-cell stage = 30hrs
4-cell stage = 40hrs
8-cell stage = 60hrs
12-32-cell stage = 3-4 days (morula)
what happens at day 5
The morula becomes hollowed by a fluid-filled space
What is the name of the fluid filled space in the morula at day 5?
Blastocystic cavity
What does the fluid to the blastocyst?
Separates the blastocyst into 2 parts
What are the 2 parts of the divided blastocyst?
- outer cell layer : trophoblast (embryonic part of placenta)
- inner mass cell : embryoblast : gives rise to the embryo
What forms the Blastocyst
Trophoblast, embryoblast and the blastocystic cavity
what is the implantation and when does it happen?
Day 6-10 : blastocyst attaches to the endometrial epithelium
In what does the trophoblast differentiates ?
2 layers:
- Cytotrophoblast : layer adjacent to embryoblast
- syncytiotrophoblast: invade endometrial epithelium to establish nutrient circulation
From what is derived the nourishment for the nutrient circulation by the syncytotrophoblast ?
Nourishment is derived from the eroded maternal tissues
What happens after the differentiation of the trophoblast, around day 8?
The blastocyst begins to be embedded in the endometrium
What happens at day 9
Lacunae (small space) appears in the syncytiotrophoblast
what happens around day 9-10?
The blastocyt sinks beneath the endometrial epithelium
By what is filled the implantation site?
B y a closing plug - fibrin coagulum
How are the lacunar networks formed and when?
around day 10-11, formed by fusion of adjacent lacunae
When and how is the uteroplacental circulation established?
Syncytiotrophoblast erodes endometrial capillaries - around day 12
Where usually occur the implantation?
In the uterine endometrium, the superior part of the uterus
Where happens extrauterine pregnancies, usually?
uterine tube (95-98%)
symptoms of ectopic/tubal pregnancy
abdo pain, tenderness, abnormal bleeding and peritonitis
Where occur abdominal pregnancies?
on fimbriae, it could be expelled into the peritoneal cavity and will implant in the rectouterine pouch.
is an abdo pregnancy viable?
May continue to full term and baby can be delivered by laparotomy
Rewind to day 6-7, when the trophoblast proliferates and differentiates into 2 layers, something also happens to the embryoblast simultaneously, what happens?
The embryoblast undergoes morphological changes : bilaminar disc (2 layers) formation
What are the 2 layers of the bilaminar disc of the embryoblast?
Epiblast and hypoblast
What is the epiblast
Primary ectoderm: thick layer of columnar cell related to the amniotic cavity
What is the hypoblast
Primary endoderm: cuboidal cell facing the blastocystic cavity
How is the amniotic cavity created around day 7?
The amnioblast separates from epiblast to form the amnion enclosing the amniotic cavity
How is the primary umbilical vesicle (yolk sac) created around day 7-8?
The hypoblast cell migrate and populate the inner surface of the blastocystic cavity forming the exocoelomic membrane with exocoelomic cavity. the hypoblast with exocelomic membrane form the yolk sac
How is created the extraembryonic mesoderm around day 10-116
Hypoblast cells form a layer of connective tissue between the exocoelomic membrane and the cytotrophoblast
How is called the space that appears in the extraembryonic mesoderm around day 12-13?
Extraembryonic ceolom (cavity)
What does the extraembryonic coelom surrounds ?
It surrounds the amnion and the primary umbilical vesicle exept at the connecting stalk
In what does the extraembryonic coelom separates the extraembryonic mesoderm into?
- extraembryonic somatic mesoderm : lining the trophoblast
- Extraembryonic splanchnic mesoderm: lining yolk sac
What is formed as the extraembryonic coelom forms ?
The secondary umbilical vesicle
High yield diapo about implantation and embryoblast in brief (to review only, no question)
When is the first stage of placenta
late second week
What is a placenta
Fetomaternal organ for metabolic exchange between mother-embryo
From what embryonic and trophoblastic structures is derived the palcenta?
Induced by extraembryonic mesoderm, cytotrophoblast column covered by syncytiotrophoblast, grow into the endometrium forming primary chorionic villi
What is the chorionic villi
vascular process of the chorion
Why do we want to maximize the surface area of where the placenta is implanted (the wave shaped chorionic villi)?
To maximize the contact with the maternal blood for nutrient and gaz exchange
What is the chorionic sac
Composed of extraembryoninc somatic mesoderm and trophoblast layers.
What is IN the chorionic sac
the embryo, amniotic sac and umbilical vesicle
So, when is the fetomaternal circulation etablished?
When the primary chorionic villi appears, late 2nd week.
