Lecture 7 - Fertilisation and Implantation

Question 1

Semen reaching vagina?

Answer 1

prostatic and seminal vesicle fluid form a coagulation holding ejaculate together and adhering to female reproductive tract

Question 2

Path of sperm?

Answer 2

cervical mucus typically hostile to sperm movement apart from around the time of ovulation, pre-ovulation it is thin and aligns fibres to allow sperm passage, through uterus for fertilisation at fallopian tube

Question 3

Estrogen and cervical mucus?

Answer 3

increases volume, clear and watery with high threadability receptive to sperm - mucous contains channels for sperm entry

Question 4

Progesterone and cervical mucus?

Answer 4

stimulates highly viscous and cross-linked mucous that is a barrier to sperm penetration

Question 5

Filtering poor sperm?

Answer 5

normal sperm tails cause vibration of mucus, failure to do this may retard progress of poor quality sperm

Question 6

Sperm transport numbers?

Answer 6

99% dnt reach into cervix (2.5hour life-span in vagina), 48hr in cervixand fallopian, 24 in uterus, 5 day clinical suggestion

Question 7

Transport time?

Answer 7

up to 7hr to reach ampulla, 30min in uterus, speed related to fertility, speed reduced by ages and freezing, 20scm/hr

Question 8

Waiting for ovulation?

Answer 8

sperm will travel slower in tubes waiting for ovulation, stored sperm may be released from cervical crypts

Question 9

Uterian immune response?

Answer 9

leucocytes infiltrate to phagocytose dead or dying sperm

Question 10

Capacitation?

Answer 10

loss of cholesterol from sperm membrane, hyperactivation involving greater movement of head and tail for better movement through tortous folds of fallopian tube, preparation for acrosome reaction

Question 11

Acrosome reaction?

Answer 11

Ca influx causes fusion of acrosomal and plasma membranes of sperm head fuse, releasing acrosomal contents (hyaluronidase), requires to be near oocyte

Question 12

Fertilisation?

Answer 12

oocyte survives 24hr, sperm penetrate layer of cumulus cells surrounding egg (aided by hyaluronidase), encounters and digests corona radiata, reaching zona pellucida through which is perivitelline space -> sperm membrane fuses with oolemmal membrane to enter ovum

Question 13

Fertilisation proteins?

Answer 13

ZP-1 ZP-2 ZP3 - 3 is primary sperm receptor, binding induces completion of acrosomal reaction

Question 14

Cortical reaction?

Answer 14

entry of sperm into ovum causes intracellular Ca release, resumes meiosis, cortical granules released into perivitelline space, releasing enzymes that cleave ZP2 and digest ZP3

Question 15

Resumption of meiosis?

Answer 15

dependant on Ca rise destabilising protein netwokr that held chromosomes in metaphase, are now free to move to poles, second polar body shed

Question 16

Development prior to implantation?

Answer 16

2 cells in 30hr, blastomeres divide symmetrically, doubling and compacts to become morula at 8-16 cell 72hrs, 60 cell blastocyte at 96hr, 100 cells in 4-5 days when it shouldve reached uterus

Question 17

Blastocyst?

Answer 17

trophectoderm (placenta) and inner cell mass (embryo), free floats in uterus 2-3 days before attaching to endometrial epithelium

Question 18

Nidation?

Answer 18

attachment of blastocytes to endometrial epithelum via specific adhesion molecules