Coitus, Fertilisation & Preimplantation Flashcards
What are the 4 phases of human sexual response? (EPOR)
Excitement
Plateau
Orgasm
Resolution
When must coitus occur in order for fertilisation to occur?
No longer than 3-5 days before ovulation and no longer than 1 day after
How long are sperm viable?
24-72 hours
How long are oocytes viable for?
12-48 hours
When is the 2nd trimester?
13-28 weeks
Why does sperm DNA show high rates of mutation?
Lack DNA repair system
When is the embryonic period?
First 8 weeks
When is the foetal period?
8-40 weeks
Which type of cells aid transport of oocyte from ovary to fallopian tube?
Cumulus cells cling to the ciliated surface of the fimbriae
How do sperm move through uterus and fallopian tubes?
Own propulsions
Uterine contraction
Why is there such a large number of sperm in ejaculate?
Vagina is acidic
Length and energy required for trip
High sperm mortality
What is the consistency of cervical mucus at ovulation?
High oestrogen results in thin, serous and alkaline mucus which is hospitable to sperm
What is the effect of progesterone on cervical mucus?
Makes it thick and acidic “infertile sperm”
Also prevents pathogens entering uterus when pregnancy has occurred
What results from capacitation of sperm?
Change in wavelike beats of sperm tail to whip-like action to propel sperm forward
Acrosome reaction allows the sperm to fuse with the oocyte
What is the point in capacitation of sperm?
Makes sperm capable of fertilisation
Where does fertilisation normally occur?
Ampulla of uterine tube
What triggers the acrosome reaction?
Rise in intracellular Ca2+ inside the sperm cell when it binds to the zona pellucida
Describe the acrosome reaction
Sperm head contacts with zona pellucida and binds to glycoproteins
Acrosome PM fuses and releases contents, resulting in more Ca2+ entry
Sperm then digest a path through the zona pellucida
What happens in the cortical reaction?
Release of cortical granules that lay beneath the PM, causing the zona pellucida to harden, preventing entry of other sperm
What induces the completion of the second meiotic division of the oocyte?
Rise in intracellular calcium
What happens the sperm head when inside the oocyte?
It enlarges and becomes the male pronucleus
What happens when the male and female pronuclei fuse?
Sperm contributes nuclear material and centrioles
All other organelles are present in the oocyte cytoplasm
Mitochondrial DNA inherited via maternal route
What causes conceptus to remain the the fallopian tube until it reaches 32 cells?
Oestrogen maintains smooth muscle contractions near where fallopian tube enters wall of uterus
What is unusual about cell division from zygote to morula?
Cells increase in number but decrease in size, meaning conceptus reaching the uterus is the same size as the original fertilised egg
What type of cells are the cells reaching the uterus?
Totipotent
When does the conceptus pass into the uterus and why?
Progesterone levels rise 3-4 days after fertilisation allowing the smooth muscle relaxes and conceptus passes into uterus
Which cells give rise to the placenta?
Trophoblast
What cells form the embryo?
Inner cell mass
What do the trophoblast cells differentiate into?
Inner cytotrophoblast
Outer syncytiotrophoblast
What does totipotent mean?
Can divide into any cell type in body, plus extra embryonic or placental cells
What does pluripotent mean?
Can give rise to all cells in the body
