18 - Early Development Flashcards
What structures and hormones control the ovarian cycle?
Hypothalamus produce GnRH
Pit.gland releases gonadotropins
Releases FSH & LH
What is a follicle?
Immature fluid filled egg - many stimulated to grow
- only one will soon become an oocyte
- @ start of cycle 15-20 are stim to grow
- FSH influences growth
- one reaches maturity (oocyte)
What is ovulation?
Release of egg from the ovary to the follopian tube
Describe process of fertilisation?
- oocyte transported to Fallopian tube
- sperm travel from cervix to Fallopian tube
- sperm and egg fuse
what must occur before the sperm can fertilise?
capacitation
- glycoprotein coat and proteins from sperm are removed
- then can pass corona radiata
Acrosomal Reaction
- sperm binds to zona pellucida
- release enzymes to penetrate it
3 steps of fertilisation?
- corona radiata penertration
- zona pellucida penetration
- acrosomal enzymes released
- sperm in contact with oocyte
- lysosomal enzymes are released from the granules in the oocytes membrane
- prevent further sperm penetrating - fusion
sperm and oocyte fuse
- oocyte has integrins - interacts with sperm disintegrins
what are the 3 ways in which the egg reacts once the sperm has entered the oocyte?
- zona and cortical reactions
- lysosomal enzymes released from cortical granules - impenetrable
- zona pellucida alters structure - prevent polyspermy
2 - resumption of 2nd meitotic division
- oocyte completes 2nd m.division immediately
3 metabolic activation of the egg
what are the results of fertilisation?
- restores diploid number of chromosomes
- zygote has half from dad etc - sex is determined
- an X carrying sperm - XX female
- Y carrying sper, - XY male - cleavage is iniated
what occurs during cleavage?
- zygote is at 2 cell stage
- mitotic divsions - no of cells increases
- blastomeres
- 3rd divison (8 cells) compaction occurs
- seperates inner and outer cells
- compacted embryo divides
- form morula
- morula inner cells become embryoblast
- outer cells will be trophoblast
how is the blastocyst formed?
- cavity forms in morula
- blastocyst
- enters uterus on 4-5th day
- inner cells become embryoblast
- outer cells will be trophoblast
- will implant in endometrium of uterus
layers of the uterus?
- external perimetrium, medial myometrium, internal endometrium
what 3 phases occur to the endometrioum due to the menstrual cycle?
- proliferative phase
- secretory phase
- menstrual phase (no implantation)
- gravid phases (embryo can be implanted
What occurs in the 1st, 2nd and 3rd stage of implantation?
1st
- embryo attach to the endometrial epithelium
- endothelial cells of the endometrium release cell adhesion mols like integrins
- trophoblast cells (on embryoblast side) have cell.ad molds too
2.
- trophoblast differienciates in to 2 layers
- syncytiotrophoblast (outer) and cytotrophoblast (inner)
- STB cells will penetrate the epithelial cells and insert
3.
- STB becomes invasive
- invades the endometrial stroma
- embryo now bedded into uterus wall lining
What occurs during Phase 1, 2, 3 and 4 of formation of placenta?
1st
- embryo is almost implanted fully
- vacuoles begin to form in STB (fuse to form lacunae)
2nd
- embryo fully imbedded
- STB penetrate deeper in stroma
- erode endothelial lining of the maternal capillaries
- capillaries are congested and dilated - Sinusoids
3rd
- lacunae fuse with the sinusoids - maternal blood can enter
- cytoTB cells penetrate synctitoTB cells to form primary villi
4th
- tertiary villi formed with a capillary netwotk
- links embryonic circ system to umbilical artery and vein
Secretion of hCG?
- human chorionic gonadotropin
- secreted by syncytitiotrophoblast
- needed as it maintains progesterone which maintains endometrium in preg
- indicates embryo was planted
