Fertilization and Early Embryo Development

What is superfecundation?

What characterizes the morula stage?

During which stage does the blastocyst begin to form?

What is the function of the trophoblast in the blastocyst?

What occurs during the cleavage or segmentation process?

What is the site of fertilization in human reproduction?

What is the purpose of capacitation in sperm?

Which enzyme helps sperm penetrate the corona radiata during fertilization?

What reaction occurs to prevent polyspermy after fertilization?

What event follows the fusion of oocyte and sperm plasma membranes?

What type of anomaly involves being pregnant without fertilization?

What determines the sex of the embryo?

What is the chromosomal configuration of a zygote?

Fertilization

Definition: The union of male and female gametes
Location: Ampulla of the uterine tube
Steps:
- Sperm deposited in the posterior fornix of the vagina (200-600 million)
- Capacitation: Removal of proteins from sperm's head, making it more active. Happens in the female reproductive tract (5-7 hrs)
- Acrosomal reaction: Enzymes released from the acrosome of the sperm to penetrate the corona radiata and zona pellucida.
- Fusion of sperm and egg membranes
- Zona cortical reaction: Prevents polyspermy (multiple sperm fertilizing an egg)
- Second oocyte resumes meiosis, forming a female pronucleus
- Male pronucleus formation (tail lost, nucleus enlarges)
- Union of pronuclei: Formation of zygote (46 chromosomes)

First Week Results

Sex determination: Y chromosome → male; X chromosome → female
Health assessment of the embryo
Resumption of meiosis II
Restoration of normal diploid chromosomes (46)
Initiation of zygote cell division

Anomalies

Parthenogenesis: Embryo development without fertilization (all offspring female)
Dispermy (triploidy): Two sperm fertilize one ovum (zygote with 3 sets of chromosomes)
Superfecundation: Two ova are released and fertilized by sperm in the same menstrual cycle

Cleavage (Segmentation)

Definition: Repeated mitosis of blastomeres (cells) to increase cell number within the fallopian tube
Steps:
- 2-cell stage, 4-cell stage, 8-cell stage...etc.
- Morula stage: (16-32) cells; formed 3 days after fertilization; enters uterine cavity
- Blastocyst/Blastula stage: (4th day)
  - Blastocele: Fluid-filled cavity
  - Trophoblast: Outer layer of cells, forms part of placenta
  - Inner cell mass (embryoblast): Mass of cells that form the embryo

This quiz covers the complex process of fertilization, including the steps from gamete union to the formation of a zygote. It also addresses key developments during the first week after fertilization, such as sex determination and chromosome restoration. Test your understanding of these fundamental concepts in human reproduction.