After fertilization and sperm cell penetration of the oocyte, the cortical reaction takes place. During the cortical reaction, a release of intracellular calcium ions triggers the exocytosis of cortical granules. Cortical granules are vesicles in the cortex of the oocyte that contain enzymes that prevent polyspermy. Exocytosis of the cortical granules releases their contents into the extracellular matrix—the zona pellucida in mammals—creating changes to prevent further sperm penetration.

The blastocoel is a fluid-fill cavity region of the blastocyst. The blastocoel is formed through cell polarization, when trophoblasts and embryoblasts differentiate. The trophoblasts are the outer layer of cells that compact to become watertight. Embryoblasts polarize to one end of the cell and form gap junctions for cell-cell communication and developmental coordination. The trophoblasts then secrete fluid into the cavity, which forms the blastocoel.

The term “zygote” is sued to describe a fertilized egg. The zygote is diploid and formed by the fusion of the sperm and egg gametes. The developing organism is called the zygote until it is composed of 16 cells during cleavage, when it is called the “morula.”

During the formation of the neural tube, the neural plate—a thick layer of differentiated columnar cells—change shape and undergo certain cell movements. The formation of the neural tube is called primary neurulation. In a complex process, the cells of the neural plate change shape, invaginating the cell layer to form the neural groove. Convergence moves the cells of the neural folds towards the developing neural groove. Eventually, the two edges of the neural plate touch and join together to form the neural tube.

The release of the secondary oocyte from the follicle is called ovulation. During this process, a hole called the “stigma” is formed and it allows the secondary oocyte to leave the follicle surrounded by a layer of cells called the cumulus oophorus. After its release, the secondary oocyte enters the fallopian tube.

Human pregnancy can be divided into three trimesters, each categorized by different symptoms and stages of fetal development. During the second trimester of pregnancy, which occurs between 13 and 28 weeks, fetal movement can be felt. This is often called “quickening,” which is the stirring of the fetus.

The menstrual cycle is the process of preparing the human female body for potential pregnancy. The cycle can be divided into two stages—the ovarian cycle and the uterine cycle. The uterine cycle has three phases that are called menstruation, the proliferative phase, and the secretory phase.

“Menarche” is the term that refers to the onset of menstrual bleeding in female humans. The timing of menarche is influenced by variety of factors including genetics and environmental factors. Age of menarche is typically between 12 to 15 years old.

After fertilization and sperm cell penetration of the oocyte, the cortical reaction takes place. During the cortical reaction, a release of intracellular calcium ions triggers the exocytosis of cortical granules. Cortical granules are vesicles in the cortex of the oocyte that contain enzymes that prevent polyspermy. Exocytosis of the cortical granules releases their contents into the extracellular matrix—the zona pellucida in mammals—creating changes to prevent further sperm penetration.

After ejaculation into the female vagina, capacitation of sperm cells takes place. During this process, sperm undergo molecular and biochemical changes that allow them to fertilize the oocyte. In this final stage of maturation, sperm cells lose many membrane proteins (including glycoproteins and steroids to ease binding to the oocyte), undergo an influx of intracellular calcium, and change their tail movement pattern. The changes that occur during sperm activation put the sperm cells into a state of hyperactivity, or heightened motility that aids fertilization.