Embryology Flashcards
When is the Pre-embryonic Phase?
0-3 Weeks
When is the embryonic phase?
4-8 weeks
When is the foetal phase?
9-40 weeks
What do we call the parent cells of meiosis?
- Spermatogonium
- Oogonium
What happens to the cells produced as a result of oogenesis?
3 of them degenerate to polar bodies and only one forms an active gamete
What section of the sperm enters the ovum?
Only the DNA (pronucleus), it leaves the rest of its cell behind.
What 2 processes occur during week 1?
1 - The zygote is formed and eventually divides to form a blastocyst
2 - The pre-embryo moves through the fallopian tube to the uterine cavity
What does a zygote become after dividing?
A solid ball of cells called a Morula
What happens to the morula as the number/size of cells increases?
It has trouble getting nutrition to the central cells.
How does the morula respond to difficulty getting nutrition to its internal cells?
It forms a blastocyst:
1 - Some cells form an outer lining called a trophoblast
2 - others form an Inner Cell Mass in one corner of the blastocyte
3 - This produced a blastocystic cavity inside.
Whats different about each consecutive cell division?
Theyre faster, almost as if the cell is learning how to do them
Where does fertilisation occur?
In the Fallopian Tube
How does the pre-embryo move through the fallopian tube?
Using ciliated epithelium much like the muco-ciliary escalator of the airway
What hapens when the ciliated epithelium of the fallopian tube fails?
Etopic Pregnancy occurs, i.e. the pregnancy occurs somewhere other than the uterus, most often the fallopian tube
What 3 things occur during week 2?
1 - Implantation & placenta develops
2 - Bilaminar disc forms
3 - Sacs, membranes and cord to nourish the conceptus form
What happens to the trophoblast prior to implantation?
The trophoblast divides into 2 layers collectively called the Chorion
What are the 3 functions of the chorian?
- Uses its villi in the implantation process
- Eventually forms part of the placenta
- Secretes HCG
What is the function of Human Chorionic Gonadotropin?
HCG is secreted by the chorian.
It stimulates the ovary to continue producing the hormones that maintain the endometrium (effectively preventing the monthly ritual of vaginal blood letting)
What do clinicians use HCG for?
Detecting pregnancy
When/how does implantation begin?
~7 days the blastocyte begins burrowing into the uterine wall (endometrium) using the Chorion
What do we call the part of the endometrium deep to the implanted conceptus?
The decidua Basalis
How do HCG levels change over time?
Maternal HCG levels increase till ~12 weeks.
What is the muscular wall surroundin the endometrium called?
The Myometrium
What happens to the Inner Cell Mass once implanted?
The inner cell mass forms a bilaminar disc within the conceptus
What are the layers of cavity & cells formed by the inner cell mass?
Inner cell mass forms a bilaminar disc.
Uterus -> endometrium direction:
Yolk Sac -> Hypoblast -> Epiblast -> Amniotic Cavity
What is the function of the allantoic cavity?
It holds the embryos waste. So it grows as the yolk empties.
What are the functions of the placenta?
- Foetal Nutrition
- Waste/gas Transport
- Immunity
Describe the 2 surfaces of the placenta
The inner foetal surface is smooth with foetal blood vessels
The outer maternal surface is the decidua basalis of the endometrium. Its rough with maternal blood vessels.