Human Reproductive: Fertilisation and Pre-Implantation

These flashcards cover key concepts from the lecture on fertilisation and pre-implantation, focusing on fertilisation processes, stages, roles of the sperm and egg, and prevention of polyspermy.

What is fertilisation in terms of genetic material?

It involves the merging of genetic material from a haploid sperm cell and a haploid secondary oocyte into a single diploid cell.

During ejaculation, how many spermatozoa are usually deposited in the vagina?

Several hundred million spermatozoa are deposited.

What percentage of spermatozoa are typically lost after ejaculation?

99% of the spermatozoa are lost.

Approximately how many spermatozoa manage to reach the ampulla of the Fallopian tube?

About 200 spermatozoa.

How long does it typically take for sperm to reach the ampulla?

4 to 7 hours.

What aids the passage of sperm through the reproductive tract?

Contractions of the walls of the uterus and oviducts may aid the passage.

What is the viability duration of sperm after deposition in the vagina?

Sperm remain viable for approximately 48 hours.

How long is a secondary oocyte viable after ovulation?

About 24 hours.

When is pregnancy most likely to occur in relation to ovulation?

During a 3-day window, from two days before ovulation to one day after.

What is the outer layer that sperm must penetrate to fertilise the egg?

The corona radiata.

What is the zona pellucida?

A glycoprotein layer inside the corona radiata that sperm must penetrate.

What does the perivitelline space contain?

It contains the first polar body.

What is capacitation in the context of spermatozoa?

Capacitation is a process that makes sperm capable of fertilization.

What happens to spermatozoa during capacitation?

A glycoprotein coat is removed from the sperm cell membrane surface.

What enzymatic changes occur during capacitation?

Enzymes lead to changes that make the acrosome reaction possible.

What is the result of the hyperactivity of spermatozoa during capacitation?

Whipping or whiplash movements of the sperm tail.

Where does fertilization typically occur?

In the fallopian tube.

What is the acrosome reaction?

A swelling of the acrosome that leads to the release of enzymes to penetrate the egg.

What two enzymes are released during the acrosome reaction?

Hyaluronidase and acrosin.

What facilitates sperm penetration through the oocyte layers?

Acrosomal enzymes and strong tail movements of the sperm.

How long does the first phase of fertilization take?

10 to 20 minutes.

What occurs immediately after the sperm's head fuses with the oocyte’s membrane?

There is an immediate cessation of movement by the spermatozoon.

What is the newly fertilized oocyte called?

Zygote.

What problem must the zygote address immediately after fertilization?

Preventing further sperm entry to avoid polyspermy.

What causes the cortical reaction following fertilization?

Release of calcium ions from the endoplasmic reticulum of the oocyte.

What does hyperpolarization of the vitelline membrane do?

It prevents fusion with other sperm.

What structure prevents the entry of further sperm after fertilization?

Cortical granules fuse with the oocyte membrane releasing enzymes.

What is syngamy?

The fusion of male and female gametes.

What metabolic changes occur in the egg after syngamy?

Activation of protein synthesis and meiotic reactivation.

How long does it take for the female pronucleus to appear after fertilization?

4 to 7 hours.

What forms the male pronucleus?

The swelling of sperm chromatin after decondensation.

What genetic change occurs post-syngamy?

Chromosomes from male and female gametes fuse to form a diploid nucleus.

What is the composition of the zygote?

It contains 46 chromosomes, being diploid (2N).

At what point does the first mitotic cell division begin for the zygote?

After fusion and formation of the diploid nucleus.

What type of mitochondria does the developing embryo have?

Only maternal mitochondria.

What are the learning outcomes of this lecture?

Explain fertilization, significance of capacitation, stages of fertilization, and cytological stages to zygote formation.

What is the role of microvilli on the egg membrane during fertilization?

They help in enveloping the sperm head.

What does the term 'polyspermy' refer to?

The entry of multiple sperm into an egg.

How does the zygote manage to undergo the second meiotic division?

It must first complete its developmental processes before the division.

What prevents polyspermy during the initial stage of fertilization?

Fast and slow blocks to polyspermy.

What do the cortical granules contain that helps prevent additional sperm from binding?

Enzymes that impact the zona pellucida.

What is an important structure for the incorporation of the sperm nucleus during syngamy?

Actin containing microfilaments.

What triggers the release of the cortical granules?

Fusion of the spermatozoan head with the oocyte membrane.