L4.5: Concept of Pregnancy

• Egg Transport

  ○ Begins at ovulation and ends once the egg reaches the uterus.

  ○ Following ovulation, the FIMBRIAE of the fallopian tube sweeps over the ovary.

  ○ Adhesive sites on the cilia of the fimbriae are responsible for egg pickup and movement into the tube.

  ○ Transport through the tube takes about 30 hours.
• Sperm Transport

  ○ Sperm with the greatest motility travel through the layers of cervical mucus.

  ○ Once it enters the uterus, contractions propel the sperm upward into the fallopian tubes.

  ○ Motile sperm can survive in the female reproductive tract for up to five days.
• CONCEPTION

  ● Meeting up of the sperm and the egg cell containing individual haploid chromosomal characteristics inside the tract towards the fallopian tube.
• FERTILIZATION

  ● Union of the haploid gametes (sperm and egg) to form a diploid cell called a zygote.

  ● Fallopian Tube: Site of fertilization

  ● Diploid Cell: Product of fertilization

  ● Mitosis: Cellular division
• FERTILIZATION

  ● How does it happen?

  ○ The sperm binds to ZONA PELUCIDA to

  [1] Trigger the reaction of the acrosome to free its enzymes that digest the zona pelucida.

  [2] Allow the sperm to tunnel the egg’s plasma membrane which results in the

  [a] fusion of the two sex cells, and

  [b] release of the sperm’s genetic material to the egg.
• FERTILIZATION

  ● Upon successful implantation of the sperm

  ○ Cortical granules in the oocyte cause the surface of the zona pellucida to harden and become impenetrable.

  ● 3 - 5 Days

  ○ Time it takes for the zygote to travel from the fallopian tube to the uterus after fertilization while simultaneously dividing.
• IMPLANTATION

  ● Occurs when the single-celled zygote divides into a solid ball of cells

  ● Blastocyst

  ○ Hollow ball of cells that attaches to the endometrium, lining of the mother’s uterus and becomes an embryo.

  ● Uterus: Site of Implantation, specifically endometrium.

  ● Mitosis: Cellular division

  ● 7 days after fertilization: The ideal time it takes place.
• Development of Zygote-Embryo

  [1] Zygote becomes a solid ball of cells with very rapid cell division — MORULA STAGE

  [2] The solid ball of cells becomes a hollow ball of cells called a blastocyst — BLASTULATION

  [3] Blastocyst implants in the wall of the uterus where it develops into an embryo attached to a placenta and surrounded by fluid-filled membranes.

  [4] CELL DIFFERENTIATION:

  ● The inner group of cells within the blastocyst will become the embryo.

  ● The outer layer of the blastocyst will give rise to part of the placenta to nourish the baby throughout the pregnancy.
• Inner = embryo

  outer = placenta
• HUMAN CHORIONIC GONADOTROPHIN (HCG)

  ● Pregnancy hormone present in a woman’s blood from the time of conception.

  ● Produced by the cells that form the placenta.

  ● Confirms possible pregnancy as it is seen in blood or urine tests.

  ○ Fun Fact: All pregnancy tests detect the hormone human chorionic gonadotrophin (hCG), which starts to be produced around 6 days after fertilization.
• Developmental Milestones During Pregnancy

  ● First Trimester

  ○ All vital parts of the embryo are formed.

  ● Second Trimester

  ○ All parts of the body start to function

  ● Third Trimester

  ○ Growth of the fetus and preparation for delivery until term takes place.