Gamete Transport and Fertilization

Comprehensive review flashcards covering gamete transport, barriers to sperm movement, capacitation, fertilization, polyspermy blocks, zygotic genome activation, genomic imprinting, and early preattachment embryogenesis.

Where does fertilization normally take place

the ampulla of the oviduct.

What mechanisms are responsible for transporting sperm through the male reproductive tract?

Cilia, fluid flow, and muscle contractions.

What molecular modifications occur to spermatozoa during the acquisition of fertilizing ability and motility in the male tract?

Sperm have no protein synthetic ability; they acquire fertilizing ability and motility through the addition and loss of plasma membrane proteins and lipids, as well as the redistribution of proteins and lipids within the sperm.

What is Decapacitation Factor (DF), and what is its physiological role?

A protein, glycolipid, and/or lipid secreted by the epididymis and accessory sex glands that stabilizes the sperm plasma membrane.

How does the anatomical site of semen deposition differ between natural mating and artificial insemination (AI) in cattle?

In natural mating, semen is deposited in the vagina; in artificial insemination (AI), semen is deposited directly into the uterus.

Why can artificial insemination (AI) in cattle achieve pregnancy using a volume of only $0.25\text{--}0.5\,\text{mL}$ compared to a bull's natural ejaculate volume of $2\text{--}8\,\text{mL}$?

AI deposits semen directly into the uterus, bypassing the cervix and avoiding the substantial retrograde sperm loss (up to $60\%$) that occurs when semen is deposited in the vagina.

What difference in retrograde sperm loss occurs at $8\,\text{hours}$ when semen is deposited in the cervix versus the uterine body or horns in cows?

Insemination in the cervix results in a $60\%$ loss of sperm numbers, whereas insemination in the uterine body or horns results in $<25\%$ loss.

What anatomical site of ejaculation and semen characteristics are exhibited by horses?

Site of ejaculation: uterus; Semen characteristics: high volume and distention of the cervix.

What anatomical site of ejaculation and semen characteristics are exhibited by dogs and pigs?

Site of ejaculation: cervix/uterus; Semen characteristics: high volume and retention of the penis during copulation.

What strategy do rodents use to prevent retrograde loss of sperm after ejaculation into the uterus?

Formation of a vaginal plug.

What two types of cervical mucus regulate sperm transport, and what are their respective functions?

Sialomucin is a low-viscosity mucus produced in cervical crypts that creates "privileged pathways" allowing motile sperm to swim forward; sulfomucins are high-viscosity mucus produced in the luminal tips that trap and eliminate abnormal or non-motile sperm via retrograde flow.

What three factors are selectively filtered out by the uterotubal junction (UTJ)?

Abnormal spermatozoa, spermatozoa with low motility, and pathogens.

What immune reaction against spermatozoa in the female tract is depicted in this histological slide?

Phagocytosis by neutrophils (leukocytes), in which leukocytes engulf sperm heads ($\text{SH}$) and leave tails ($\text{ST}$) protruding.

What mechanisms and cues guide spermatozoa toward the oocyte within the female reproductive tract?

Fluid movement, oviduct contractions, ciliated cells, rheotaxis, thermotaxis, and chemotactic factors originating from the oviduct, follicular fluid, and oocyte.

What is sperm docking, and what happens to spermatozoa that fail to dock to the oviduct epithelium?

Sperm docking is the physical attachment of spermatozoa to the oviduct epithelium in the reservoir; without docking, sperm die within $6\text{--}10\,\text{hours}$.

How does sperm capacitation affect the binding ability of spermatozoa to the oviduct epithelium?

Capacitated sperm do not bind to the oviduct epithelium.

According to the UTJ transection experiment, what percentage of oocytes are fertilized when the UTJ is transected at $6\,\text{hours}$, $8\,\text{hours}$, and $12\,\text{hours}$ post-mating?

At $6\,\text{hours}$: $0\%$; at $8\,\text{hours}$: $50\%$; at $12\,\text{hours}$: $83\%$.

What is the fertile lifespan of sperm within the female reproductive tract of cows compared to bitches?

Cow: $1.5\text{--}2\,\text{days}$; Bitch: $9\text{--}11\,\text{days}$.

What is sperm capacitation, and what physiological changes does it involve?

The final maturation of sperm occurring in the cervix, uterus, and oviduct that removes seminal plasma proteins and decapacitation factors from the surface, produces hyperactivated motility, and confers fertilizing capacity without altering sperm morphology.

What specific zona pellucida glycoprotein acts as the receptor for sperm binding?

$\text{ZP3}$.

What membrane fusion events take place during the acrosome reaction?

The outer acrosomal membrane fuses with the sperm plasma membrane, creating pores and vesiculations that release hydrolytic enzymes to digest through the zona pellucida.

What process is shown in this schematic preventing multiple sperm from fertilizing the egg?

The zona block to polyspermy, where intracellular $\text{Ca}^{2+}$ release from the endoplasmic reticulum causes cortical granules to fuse with the oocyte plasma membrane and release contents into the perivitelline space, rendering the zona pellucida impenetrable.

What morphological indicator in the perivitelline space confirms that oogenesis (meiosis) was completed and fertilization took place?

The presence of the second polar body.

What is syngamy?

The fusion of the male and female pronuclei to form a single diploid zygote nucleus.

What is Zygotic Genome Activation (ZGA)?

The developmental stage at which the embryo's own genes begin transcription, shifting embryonic regulation from maternal (oocyte-derived) control to zygotic control.

According to the Inside-Outside Theory of asynchronous cleavage, what determines the fate of a blastomere in an 8-cell embryo?

A blastomere located on the interior of the 8-cell embryo becomes part of the Inner Cell Mass (ICM), whereas a blastomere located on the outside becomes part of the trophectoderm.

What are the structural roles of tight junctions and gap junctions during morula compaction?

Tight junctions form between outer cells to seal them together and block fluid leakage; gap junctions form between inner cells to permit intercellular communication.

What factors cause the blastocyst to hatch from the zona pellucida?

Enzymatic digestion of the zona pellucida by uterine enzymes, production of plasminogen and plasminogen activator by the embryo, and an increase in blastocyst size due to fluid pumping into the blastocoel.

On what day post-ovulation does blastocyst hatching occur in cattle, pigs, and mares/ewes?

Cattle: day $9\text{--}11$; Pigs: day $6$; Mares and ewes: day $7\text{--}8$.

What developmental outcome results in an androgenote (embryo produced from two paternal pronuclei)?

The embryo develops a normal placenta but fails to develop an Inner Cell Mass (ICM), resulting in death during early embryonic development.

What developmental outcome results in a gynogenote (embryo produced from two maternal pronuclei)?

The embryo develops a normal fetus but has an underdeveloped, small placenta, resulting in pregnancy failure midpregnancy.

What developmental process in ruminants and pigs is depicted in this diagram showing morphological progression in the uterus?

Embryonic elongation, transitioning from spherical ($170\,\mu\text{m}$ at day $6$) to ovoid ($375\,\mu\text{m}$ at day $10$), tubular ($2\,\text{mm}$ at day $13$), and filamentous ($200\,\text{mm}$ at day $19$).

How do dizygotic twins differ fundamentally from monozygotic twins in their origin?

Dizygotic twins are non-identical and result from double ovulation, whereas monozygotic twins are identical and result from the splitting of a single fertilized conceptus.