oocyte

Examples of oocyte in the following topics:

• Oogenesis

  • The menstrual cycle begins with the maturation of oocytes through the process of oogenesis, as well as the concurrent follicle development that stimulates ovulation.
  • Oogenesis starts with the process of developing oogonia, which occurs via the transformation of primordial follicles into primary oocytes, a process called oocytogenesis.
  • Oocytogenesis is complete either before or shortly after birth in humans, and thus during the menstrual cycle primary oocytes complete maturation through further meiotic divisions.
  • An important event in the development of the tertiary follicle occurs when the primary oocyte completes the first meiotic division, resulting in the formation of a polar body and a secondary oocyte.
  • Immediately after meiosis I, the haploid secondary oocyte initiates meiosis II.

• Ovaries

  • The ovaries are the site of gamete (egg cell, oocyte) production. 
  • The developing egg cell (or oocyte) grows within the environment provided by ovarian follicles.
  • When oocyte maturation is completed, an LH surge secreted by the pituitary gland stimulates follicle rupture and oocyte release.
  • This oocyte development and release process is referred to as ovulation.

• Gametogenesis (Spermatogenesis and Oogenesis)

  • The cell starting meiosis is called a primary oocyte.
  • This results in the primary oocyte finishing the first meiotic division.
  • At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct.
  • A primary oocyte begins the first meiotic division, but then arrests until later in life when it will finish this division in a developing follicle.
  • This results in a secondary oocyte, which will complete meiosis if it is fertilized.

• Fertilization

  • Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte.

• Sperm

  • During fertilization, the sperm provides the following three essential parts to the oocyte:
  • A signalling or activating factor that causes the metabolically dormant oocyte to activate

• Microarrays and the Transciptome

  • Analysis of the transcriptomes of human oocytes and embryos is used to understand the molecular mechanisms and signaling pathways controlling early embryonic development, and could theoretically be a powerful tool in making proper embryo selection during in vitro fertilization.
  • Analysis of the transcriptomes of human oocytes and embryos is used to understand the molecular mechanisms and signaling pathways controlling early embryonic development, and could theoretically be a powerful tool in making proper embryo selection during in vitro fertilization.

• Physiological Processes in Sponges

  • Sponges may also become sequentially hermaphroditic, producing oocytes first and spermatozoa later.
  • Oocytes arise by the differentiation of amoebocytes and are retained within the spongocoel, whereas spermatozoa result from the differentiation of choanocytes and are ejected via the osculum.
  • Spermatozoa carried along by water currents can fertilize the oocytes borne in the mesohyl of other sponges.

• Female Reproductive Anatomy

  • Oocytes develop in (a) follicles, located in the ovary.
  • The (b) follicle in this light micrograph has an oocyte at its center.

• Fertilization

  • If pregnancy is considered to begin at the point of implantation, the process leading to pregnancy occurs earlier as the result of the female gamete, or oocyte, merging with the male gamete, or spermatozoon.

• Human Gestation

  • Twenty-four hours before fertilization, the egg has finished meiosis and become a mature oocyte.
  • In humans, fertilization occurs soon after the oocyte leaves the ovary.