Fertilisation & Blastocyst Formation

How is fertilization defined in the context of reproductive biology?

It is the process of union between a mature male gamete (sperm) and a mature female gamete (ovum) to produce a zygote.

Occurs in the oviduct

Where does fertilization typically occur in the fallopian tubes of most farm animals?

The ampullary-isthmic junction.

What timing requirement is essential for the deposition of semen to ensure fertilization occurs?

It must be closely synchronized with ovulation.

When does ovulation occur in the cow relative to the estrous phase?

10-12 hours after the end of the estrous phase.

During which part of the estrous phase does ovulation occur in sheep?

The late estrous phase.

In goats, when does ovulation typically take place?

Few hours after end of estrus

When does ovulation occur in swine (pigs) relative to the estrous phase?

The mid-estrous phase.

What is the estimated fertile life of a cow oocyte?

8-12 hours.

How long is the fertile life of an oocyte in sheep?

16-24 hours.

What is the fertile life of a pig oocyte?

8-10 hours.

Where is semen deposited in the cow and sheep during natural mating?

The vagina.

What is the average volume of a cow ejaculate in milliliters?

4 ml.

What is the typical sperm concentration in a cow ejaculate?

1 billion/ml.

What is the typical volume of a sheep ejaculate?

1 ml.

Where is semen deposited in the pig during mating?

The cervix and uterus.

What is the average ejaculate volume for a pig?

125 ml.

Identify the five steps of sperm transport and fertilization in the female tract.

1. Immediate Transport; 2. Cervix; 3. Uterus; 4. Oviduct; 5. Fertilization.

What are the primary causes of sperm loss during the 'Immediate Transport' phase?

Retrograde loss and phagocytosis.

What is the role of the 'privileged' pathways in the cervix?

To facilitate the transport of motile and morphologically normal sperm while removing others.

In which part of the female reproductive tract is sperm capacitation initiated?

The uterus.

Also phagocytosis

Where is sperm capacitation completed?

The oviduct.

Hyperactivation occurs

What percentage of sperm is lost within 12 hours in the cow due to retrograde transport?

60%.

Where is semen deposited in the ewe to help avoid retrograde transport?

The external cervical os.

How do horses and dogs minimize retrograde sperm loss during copulation?

Semen is squirted directly through the cervix.

Identify the three main parts of a spermatozoon.

The sperm head

Midpiece

Tail

Which organelle in the sperm mid-piece provides energy for motility?

Mitochondria.

Term: Azoospermia

Definition: The total absence of sperm in the semen.

Term: Oligospermia

Definition: A low concentration of sperm in the ejaculate.

Term: Asthenospermia

Definition: Reduced sperm motility (poor movement).

Term: Cryptorchism

Definition: The failure of the testes to descend into the scrotum.

List four types of sperm head abnormalities mentioned in the text.

Nuclear vacuoles

Tapered heads

Ruffled Acrosome

Knobbed Acrosome

List four types of sperm tail abnormalities mentioned in the text.

Coiled tail

Double Midpiece

Folded tail

Detached head

Morphological abnormalities in sperm often reflect underlying _____ problems.

Genetic (or chromosomal).

What characterizes the 'Rapid transport phase' of sperm movement?

Sperm reach the oviducts within minutes but are unable to fertilize the oocyte.

Why?

They have not completed:

• capacitation

• hyperactivation

• acrosome reaction

What is the core process of sperm capacitation?

The progressive destabilization of the plasma membrane to prepare the sperm for fertilization.

Progressive plasma membrane destabilisation:

• removal of glycoprotein coating

• exposure of zona pellucida binding proteins

• altered surface charge

• increased membrane fluidity to aid breakdown of acrosome – digest ZP

During capacitation, what substances are removed from the sperm head?

Glycoprotein coating

How does capacitation aid the breakdown of the acrosome?

It increases membrane fluidity.

Which substances are added to the sperm surface in the epididymis?

Proteins and carbohydrates.

What are 'decapacitation factors' in the context of ejaculation?

Seminal plasma proteins that coat the sperm surface surface.

Protects sperm

What visual characteristic defines hyperactivated motility?

• strong tail beats

• wide amplitude movement

• whiplash motion

The increase in intracellular _____ leads to elevated cAMP during sperm hyperactivation.

Calcium

allows sperm to move through viscous oviduct environment

How long can sperm be stored in the female tract of a bat?

1 year.

What is the sperm storage duration in horses and pigs?

6 days

Horses (possibly longer) – up to 3 months

Where specifically is sperm held during 'Cervical storage'?

Cervical crypts.

Under what hormonal condition will the cervix release stored sperm?

• in absence of progesterone

• around appropriate reproductive timing

cervix also selects against morphological abnormalities

Where do sperm bind for storage within the oviduct?

Cells in the oviductal isthmus.

The release of sperm from the oviductal isthmus coincides with which event?

Ovulation.

Identify the main components of the oocyte structure shown in the slides.

• cytoplasm

• nucleus

• zona pellucida

• perivitelline space

• polar body

What specific glycoprotein on the zona pellucida serves as the primary sperm receptor?

ZP3.
Sperm binds to ZP3 →

triggers next step

List the three main functions of the ZP3 glycoprotein.

1. Structural component of the ZP; 2. Sperm receptor; 3. Inducer of the acrosome reaction.

What biological structure is the acrosome derived from?

The Golgi apparatus.

The acrosome reaction involves multiple fusions between the outer acrosomal membrane and the _____.

Plasma membrane.

Which part of the sperm membrane is exposed following the acrosome reaction?

The inner acrosomal membrane.

Which specific part of the sperm head fuses with the oocyte plasma membrane?

The equatorial segment.

What is the function of cortical granules in the oocyte?

They are released into the perivitelline space to create a zona block to polyspermy.

Why is mitochondrial DNA entirely maternal in origin?

Sperm mitochondria enter the egg but are subsequently destroyed.

What molecule is the specific trigger for $Ca^{2+}$ release during oocyte activation?

Inositol tri-phosphate ($IP_3$).

Which enzyme induces the production of $DAG$ and $IP_3$ to trigger calcium release in the oocyte?

$PLC\zeta$ (Phospholipase C zeta).

What does the 'zona block' do to the zona pellucida proteins?

It cross-links them to make the zona impenetrable to other sperm.

Sperm reach the oviducts within minutes during the _____ transport phase.

Rapid.

What happens to the sperm nucleus once it is inside the oocyte cytoplasm?

It decondenses and forms the male pronucleus.

The _____ space is the gap between the oocyte plasma membrane and the zona pellucida.

Perivitelline.

High-speed sperm manufacturing occurs in the _____.

Testis.

Where does fluid absorption and motility acquisition occur in the male tract?

The Epididymis (Head and Body).

The 'Warehouse and Shipping' center for spermatozoa in the male tract is the _____.

Epididymis (Tail).

Which accessory structure provides metabolic substrates and surface coatings during ejaculation?

Accessory sex glands.

What is the 'delivery system' organ for sperm in the male?

The penis.

Spermatozoa are produced at a rate of approximately _____ per second.

$35000$ to $200000$.

The epididymis tail can store enough spermatozoa for _____ to _____ ejaculations.

$5$ to $10$.

"Sperm storage in the horse can last for $6$ days

but potentially up to _____."

Which species is noted for having very few sperm reaching the site of fertilization relative to its large ejaculate volume?

The pig (swine).