Fertilization and Seminal Fluid

The seminal vesicles, while the largest contributor to seminal fluid volume, are responsible for approximately 20-30% of the total ejaculate.

Prostaglandins within the seminal fluid induce uterine contractions, specifically promoting antegrade propulsion to facilitate sperm migration towards the oviduct.

Coagulase, secreted by the prostate gland, is responsible for the initial coagulation of seminal fluid post-ejaculation, facilitating sperm immobilization within the vaginal canal.

Fibrinolysin, originating from the seminal vesicles, functions to maintain the coagulated state of the ejaculate, ensuring prolonged sperm retention within the female reproductive tract.

Prostate-specific antigen (PSA), while clinically relevant as a marker for benign prostatic hyperplasia, possesses no known physiological role in sperm function or fertilization.

The sperm acrosome primarily houses enzymes such as hyaluronidase and collagenase, critical for penetrating the collagen-rich stroma of the ovarian cortex.

Mitochondria, localized within the sperm head, are the primary ATP source powering flagellar movement, ensuring efficient propulsion towards the oocyte.

Dynein motor proteins, associated with the 9+2 microtubule arrangement of the sperm flagellum, utilize GTP hydrolysis to generate the force required for sperm propulsion.

Seminalplasmin, originating from the prostate gland, functions as a potent immunosuppressant within the female reproductive tract, preventing maternal immune rejection of spermatozoa.

Spermatozoa exhibit optimal motility and fertilizing capacity in a mildly acidic vaginal environment, facilitating acrosomal enzyme stability and preventing premature capacitation.

The zona pellucida, characterized by its translucent red hue under standard histological staining, is primarily composed of fibronectin and laminin glycoproteins.

ZP3 binding proteins, located within the corona radiata cells, mediate the initial attachment of spermatozoa to the oocyte complex prior to zona pellucida interaction.

Capacitation, a process exclusive to the female reproductive tract, is initiated by exposure to high concentrations of progesterone secreted by the corpus luteum.

Hyperactivation of spermatozoa, a consequence of capacitation, is characterized by a decrease in flagellar beat frequency and amplitude, optimizing directional movement towards the oocyte.

Estrogen, peaking during the luteal phase of the menstrual cycle, plays a critical role in promoting sperm capacitation within the fallopian tubes.

The acrosomal reaction is primarily triggered by the interaction of sperm surface proteins with ZP1 receptors on the zona pellucida.

Acrosin, a key enzyme released during the acrosomal reaction, is classified as a hyaluronidase, specifically targeting hyaluronic acid in the corona radiata.

Calcium ion influx into the spermatozoon, subsequent to ZP3 receptor binding, inhibits acrosomal fusion and the release of hydrolytic enzymes, preventing premature zona pellucida digestion.

The fast block to polyspermy is mediated by a transient efflux of potassium ions from the oocyte, resulting in rapid hyperpolarization of the oocyte plasma membrane.

The depolarization of the oocyte membrane during the fast block to polyspermy renders the oocyte refractory to further sperm fusion by inducing conformational changes in ZP3 receptors.

Activation of the smooth endoplasmic reticulum in the oocyte, triggered by sperm-oocyte membrane fusion, leads to a transient decrease in intracellular calcium concentration.

Cortical lysosomes, activated by the calcium surge, release proteolytic enzymes that specifically degrade ZP1 and ZP2 binding proteins, preventing further sperm interaction with the zona pellucida.

The 'hardening' of the oocyte membrane, characteristic of the slow block to polyspermy, is primarily due to the cross-linking of zona pellucida glycoproteins by transglutaminase enzymes released from cortical granules.

The secondary oocyte completes meiosis II immediately upon ovulation, prior to fertilization, resulting in a mature ovum and the extrusion of the first polar body.

Completion of meiosis II in the oocyte results in the formation of a definitive ovum, characterized by a diploid (2N) chromosomal complement.

The polar body, generated during meiosis II, retains a functional nucleus and contributes genetically to the developing zygote, albeit to a lesser extent than the ovum.

The male and female pronuclei, each containing a haploid set of chromosomes, undergo immediate fusion upon formation, directly resulting in the diploid zygotic nucleus.

The formation of the diploid zygote, marked by pronuclear fusion, signifies the culmination of fertilization and the initiation of embryogenesis, specifically the cleavage stage.

The secondary oocyte is arrested in metaphase I of meiosis at the time of ovulation, awaiting a signal to progress to metaphase II and subsequent stages of fertilization.

Citrate, produced by the seminal vesicles, serves as the primary energy substrate for spermatozoa following ejaculation, providing immediate fuel for motility.

Relaxin, secreted by the prostate gland and present in seminal fluid, primarily functions to induce smooth muscle relaxation in the female reproductive tract, facilitating sperm ascent.

Vesiculase-mediated coagulation of seminal fluid is a transient process, persisting for several hours post-ejaculation to ensure sustained sperm attachment to vaginal walls.

The corona radiata, composed of modified cumulus cells, is directly penetrated by the sperm acrosome reaction, facilitating access to the underlying zona pellucida.

ZP2, a glycoprotein component of the zona pellucida, primarily functions as the initial binding receptor for spermatozoa, initiating the acrosomal reaction cascade.

The slow block to polyspermy, initiated by calcium release, is solely dependent on the enzymatic degradation of ZP3 proteins and does not involve any physical hardening of the zona pellucida.

Pronuclear fusion in zygote formation results in a synkaryon, characterized by two distinct haploid nuclei persisting within a shared cytoplasm prior to the first mitotic division.

The initial attachment of spermatozoa to the vaginal walls, facilitated by seminal fluid coagulation, is primarily mediated by fibronectin interactions with the vaginal epithelium.

Capacitation is reversed once spermatozoa reach the ampulla of the fallopian tube, ensuring that the acrosomal reaction is precisely timed for zona pellucida penetration.

The positive membrane potential shift during the fast block to polyspermy is primarily due to an influx of chloride ions, transiently hyperpolarizing the oocyte membrane.

Lysosomal enzymes released during the cortical reaction primarily target and degrade the corona radiata, facilitating zona pellucida hardening as a secondary effect.