Reproduction 2- Fertilisation, placenta and pregnancy Flashcards
When must sperm be introduced in order for pregnancy to occur? Why is this?
Between 5 days before and 1 day after ovulation- sperm remain capable of fertilisation for up to 4-6 days and ovulated egg viable for 24-48 hours
How does the egg get moved into the fallopian tube? How many days for egg to move into the uterus from tube?
Smooth muscles of fimbriae causes them to pass over ovary while cilia of fimbriae beat waves towards interior of tube
4 days
Why is sperm mortality extremely high during trip rom vagina to fallopian tube?
Vagina is acidic- protection against yeast and bacterial infections, length and energy requirements large, so more released to increase chance of fertilisation
What is capacitation in relation to spermatozoa? What does this cause?
Final maturation in female genital tract before gain ability to fertilise the oocyte
Previous wavelike beats to be replaced by a more whiplike action that will propel sperm forward in stronger surges
Sperms plasma membrane becomes altered so it will be capable of fusing with surface membrane of egg
Where does fusion of the sperm and egg occur in the fallopian tube? What do many sperm bind to on zona pellucida? What protein? This binding triggers what?
At the ampulla
Glycoproteins- receptors for sperm surface proteins
ZP3 protein
The acrosome reaction
How is polyspermy blocked after fertilisation? What reactions is also initiated? This involves what?
Egg membrane potential is changed- prevents additional sperm from binding
The Cortical reaction- exocytosis of secretory vesicles into space between ZP and egg plasma membrane. Contain enzymes to inactive sperm binding receptors and causes hardening of entire zona pellucida
2 sets of haploid chromosomes each surrounded by distinct membrane known as what? What happens to these?
Pronuclei- equal in size and contain nucleoli
Migrate to centre of cell- haploid chromosomes pair up and DNA replication occurs in preparation for 1st mitotic division.
Pronuclei membranes break down and mitotic metaphase spindle forms
When does cleavage occur? Zygote remains in tube for how long? Why is this?
Day 2-3 of fertilisation
3-4 days
Oestrogen maintains contraction of smooth muscle where tube enters uterus- as progesterone increase, this relaxes
What is cleavage? What occurs during this? Each cell has what feature?
Number of mitotic divisions
No cell growth occurs, increase in cell numbers
Totipotent
What happens during compaction? On what day? Why is this essential?
Cells flatten and maximise intracellular contacts resulting in tight junctions forming and outer cells polarise
Day 4
To be able to differentiate quickly
When does cavitation and differentiation occur? What happens during this? Consists of what 3 things? How many cells? Don’t have quality anymore?
Day 5 Fluid filled cavity--> blastocyst Outer cell layer- trophoblast, inner cell mass and central fluid filled cavity More than 80 cells Lost totipotentiality
When does expansion occur? What happens during this?
Day 5-6
Cavity expands further, diameter of blastocyst increases and zona pellucida thins
When does hatching occur? What occurs during this? Needed for what?
Day 6+
Blastocyst expansion and enzymes result in embryo hatching from zona pellucida
Implantation
When does implantation occur? Embryo reaches uterus on day what? What happens during apposition? When does this occur?
21st day of cycle
Day 5/6
Hatched blastocyst orientates via embryonic pole and synchronises with receptive endometrium- 9 days after fertilisation
What happens during attachment of fertilisation?
Endometrial epithelial cells and trophoblastic cells express integrins which connect with one another
What does the trophoblast differentiate into? What occurs during invasion? During decidual reaction?
Cytotrophoblast and syncitiotrophoblast (erodes endometrial blood vessels- using proteolytic enzymes)
Enzymatic degradation of the basal lamina
Stromal cells differentiate adjacent to blastocyst
Secretion of what substance prevents antigenic rejection of the embryo? What cells are able to provide metabolic fuel and raw materials required for the early growth of the embryo?
Interleukin-2
Nutrient-rich endometrial cells
How long can the endometrial cells provide the embryo for? When does the placenta begin to develop? By what day is this implantation complete?
The first few weeks when the embryo is very small
At blastocyst implantation
By the 11th day post ovulation
The outer cell layer of the blastocyst forms from what? The TCM then does what?
Primary trophoblastic cell mass (TCM)
Invades the endometrium which degenerates and the trophoblast contacts stroma
The embryonic portion of the placenta is supplied by what cells? What extend from the chorion into the endometrium? They contain what? The endometrium around the villi is altered by what?
The outermost layers of trophoblast cells- the chorion
Chorionic villi
Rich network of capillaries that are part of the embryo’s circulatory system
Enzymes and other paraffin molecules secreted from the cells of the invading villi- each villus surrounded by placental sinus of maternal blood
