embryology

Question 1

What is the follicular phase?

Answer 1

Follicles mature surrounded by the zona pellucida.
Follicles are present in various stages of maturity
First meiotic division begins in utero, arrested, and continues in puberty when levels of GnRH: FSH & LH increase.
When it becomes secondary follicle, it produces oestrogen and progesterone
Graffian follicle is at is most mature and bulges from ovary midway
Completion of Meiosis I occurs 36-48 hours before ovulation
Meiosis II is complete when fertilzation occurs. chromosomes are halved from 46 to 23 (22 autosomes + 1 sex chromosome

Question 2

Tell me about ovulation

Answer 2

begins when oestrogen peaks 24 hours before ovulation
triggered by a greater LH surge, which stimulates prostaglandins & primary oocyte to complete 1st meiotic division & become secondary oocyte.
A spike in temperature indicates that ovulation has occured

Question 3

Tell me about the luteal phase

Answer 3

corpus luteum provides/secretes progesterone until the placenta is fully formed and takes over the role at 12 weeks
if fertilisation does not occur the corpus luteum degenerates into corpus albicans and degraded through lysosomal activity.

Question 4

What happens in the uterine cycle

Answer 4

Menstrual phase days 1-5
Proliferative phase days 6-14
Secretory phase day 15-28

Question 5

Tell me about the menstrual phase

Answer 5

Triggered by a drop in progesterone
no zygote so no message sent from trophoblast to corpus luteum to continue to produce progesterone 
endometrium sheds (stratum basalis and stratum functionalis)

Question 6

Proliferative phase

Answer 6

Matches with the follicular phase
variable length
endometrium thickens in response to rising oestrogen and progesterone
hormones change cervical mucous - less thick and stretchy for sperm motility. Thin around ovulation (Billings method) and then becomes more opaque

Question 7

Secretory phase

Answer 7

Matches with the luteal phase
follows ovulation
progesterone is high causing further thickening of stratum functionalis and secretes glycogen.
rise in basal temperature indicates ovulation has occured (rhythm method)

Question 8

What does the hypothalamus produce?

Answer 8

GnRH which stimulates release of LH & FSH from anterior pituitary

Question 9

Tell me about zygote

Answer 9

undergoes repeated mitotic division (aka cleavage- cleavage increases number of cells)
First division in to 2-cell stage takes approx. 30 hours after fertilisation -further division takes another 12-24 hours

Question 10

What is the morula

Answer 10

16-20 cells

enters the uterine cavity around 4-5 days

Question 11

when does implantation occur?

Answer 11

days 6-7 (its now a zygote/blastocyst)

Question 12

What does the blastocyst cavity seperate into?

Answer 12

Trophoblast - fetal part of placenta and chorion

Inner cell mass - Embryo, yolk sac and amnion

Question 13

What are the two layers of the tophoblast?

Answer 13

syncytiotrophoblast - maternal side of placenta - forms lucunae
cytotrophoblast - fetal side of placenta - forms chorionic villi