Flashcards in Repro 7.1 Coitus and Fertilisation Deck (60)
During coitus, where is sperm deposited?
Fertilization of the ovum by a sperm and the subsequent establishment of pregnancy
What are the phases of coitus?
Resolution phase +/- refractory period
What happens to semen immediately after ejaculation?
Coagulation by clotting factors (fibrinogen and veiculae)
What does coagulation of semen prevent?
Sperm being physically lost from the vagina
Do all sperm enter the uterus?
No. The vast majority are lost by leakage from the vagina
How far do sperm have to travel in the uterus to reach the uterine tubes and how long does this take?
15 - 20cm
A few hours
What causes transport of the sperm through the uterus?
Their own propulsive capacity
Fluid currents caused by the action of ciliated cells in the uterine tract
WHat happens to sperm during their journey through the uterus?
Undergo a further series of maturational changes - capacitation and acrosomal reaction that results in their acquiring a full capacity to fertilise the ovum
When do sperm first begin to mature?
When they leave the testes and journey through the epididymis. It continues during their storage until ejaculation
How long does capacitation take?
6 - 8 hours
What changes occur in sperm during capacitation?
Removal of a glycoprotein coat promotes changes in the sperm cell membrane
Tail movements change from waves to whip like thrashing movements
They become responsive to signals from the oocyte
What happens when capacitated sperm comes in contact with the oocyte?
When it contacts the zone pellucida the membranes fuse (sperm head binds to ZP3 proteins) and this marks the commencement of the acrosomal reaction
What happens during the acrosomal reaction?
The acrosome swells and liberates its contents by exocytosis
Proteolytic (acrosomal) enzymes and further binding facilitate penetration of the zona pellucida by the sperm
How long does it take for sperm to penetrate the zona pellucida?
What induces capacitation and the acrosomal reaction?
An influx of calcium ad rise in cAMP in the spermatozoa
What does the secondary oocyte contain?
Haploid chromosomes and the bulk of cytoplasm
Surrounded by follicular cells (cumulus) embedded in a gelatinous matrix
Where are the remaining chromosomes after the first meiotic division of the oocyte?
Contained within the first polar body
Where is the site of fertilisation?
The ampulla of the oviduct
What is a zygote?
The product of fusion of the sperm and ovum pronuclei
How many sperm are required at the site of fertilisation?
300 - Needed to disperse the zona pellucida. Only 1 will fertilise the oocyte
How is polyspermy prevented?
What is cleavage?
Series of metabolic changes and rapid mitotic division. Increased number of cells (16-32) without growth (needs to be small enough to pass through isthmus to uterus). Forms a morula
How do identical twins arise?
After cleavage, cells are totipotent therefore if separation of cells occurs, 2 individual embryos can form with identical genetic information
What is a blastocyst?
Consists of an outer layer (trophoblast) which will become the placenta and the inner layer which will become the embryo itself
When the blastocyst forms there is a loss of totipotency
There is also a fluid filled cavity present
What does implantation involve?
Interaction between the trophoblast and the lining epithelium of the uterus (trophoblast develops receptors to adhere). Further imbedding into the endometrium is dependent upon the invasive property of the trophoblast
What part of the trophoblast has invasive properties to further embedding of the embryo into the endometrium?
By what day should the blastocyst be fully embedded in the endometrium?
How is the early placenta established?
Cellular interactions between the blastocyst and the endometrium and the establishment of the relationship between embryonic and maternal tissue