M3 Fertilization

Fertilization

The process where a sperm cell from the male and an egg cell from the female unite to form a single cell called a zygote.

oviduct

In mammals, fertilization usually occurs in the ampulla of the __

External fertilization

occurs outside the animal’s body, usually in water.

Internal fertilization

happens inside the body of the female.

Semen Deposition

The anatomical site where sperm is deposited within the female reproductive tract varies among species and has important implications for fertilization efficiency.

These differences affect the distance and environment sperm must traverse before reaching the oviduct.

• Bipartite

• Bicornuate’

• Duplex

• Simplex

Types of Uterus

Bipartite

• Poorly to moderately developed uterine horns.

• Mare, cow

Bicornuate

• Long uterine horns.

• Sow, bitch, queen

Duplex

• Two completely separate uteri, each with its own cervix.

• Rabbits, rodents

Simplex

• A single uterine chamber without horns.

• Humans and other primates

Sperm Transport

After mating, sperm moves in two stages

Rapid phase

Associated with muscular contraction of the tract following coitus, with spermatozoa present in the ampulla of the uterine tube within 5 to 15 minutes after mating

Sustained phase

Continues for some hours; Transports spermatozoa slowly in small amounts from the reservoirs in the cervix and the uterotubal junctions.

• Sialomucin

• Sulfomucin

Two kinds of mucus

Sialomucin

Low in viscosity; Produced by cells in the basal areas of the cervical crypts

Sulfomucin

Viscous; Produced in the apical portions of the cervical epithelium

Vagina → Cervix → Uterus → Uterine Horns → Oviduct

Sperm Pathway

Ovary → Ovulated into fimbriae → Enters infundibulum → Ampulla of oviduct

Oocyte Pathway

Capacitation

• Series of physiological transformations that sperm must undergo to acquire the ability to fertilize an egg.

• Occur naturally within the female reproductive tract and include the removal of surface proteins, increased membrane fluidity, and changes in motility patterns.

cervix

In species where sperm is released into the cranial vagina, capacitation typically starts as sperm move through the __

uterus

In others, such as pigs, where sperm are deposited into the cervix or uterus, capacitation is initiated within the __

isthmus portion

Capacitation is completed in the __ of the oviduct. Only capacitated sperm are capable of binding to and penetrating the oocyte.

Zona pellucida

specialized extracellular matrix surrounding the oocyte, composed of three key glycoproteins

ZP1 and ZP2

provide structural support.

ZP3

serves as the primary receptor for sperm binding.

• Primary binding region

• Acrosome reaction–promoting ligand

Two key regions on the sperm that recognize and interact with the zona pellucida

hyaluronidase and acrosin

Binding of the spermatozoon to the zona triggers the progressive breakdown and fusion of the spermatozoan cell membrane with the outer acrosomal membrane resulting in the release of enzymes which include __.

Acrosomal Reaction

Process in which the sperm's plasma membrane fuses with its outer acrosomal membrane, releasing enzymes that allow the sperm to penetrate the zona pellucida.

cortical reaction

Once a sperm successfully enters the oocyte, the egg initiates a defensive mechanism known as the __

Cortical Reaction

Triggered by calcium influx at the oocyte membrane.

exocytosis

Cortical granules release contents into the perivitelline space via __

• Zona block

• Vitelline block

Barriers to Polyspermy

Zona block

modifies the zona pellucida to prevent further penetration.

Vitelline block

makes the oocyte membrane unreceptive to other sperm. Both blocks ensure that only one sperm fertilizes the egg.

Syngamy

• The final step in fertilization

• The fusion of the male and female pronuclei

Karyotyping

Technique used to visualize chromosomes to detect genetic abnormalities.

Down Syndrome

Results from an extra copy of chromosome 21, leading to 47 total chromosomes.

Klinefelter Syndrome

Male with an extra X chromosome (XXY).

Turner Syndrome

Female possesses only one X chromosome (XO), leading to various developmental abnormalities