Final Exam (Lecture 59) - Gamete Transport and Fertilization

Question 1

Name the major barrier for sperm in the female reproductive tract and describe the privileged pathway through this barrier.

Answer 1

Cervix

Sperm travel through the cervix via basal channels that contain less abundant and thinner mucous

Question 2

Describe three mechanisms by which sperm are inactivated or lost.

Answer 2

1) Retrograde Transport:
- Gravity that expels sperm away from the uterus

2) Phagocytosis:
- By leukocytes (especially neutrophils)

3) Microbes:
- Particularly bacteria that adhere to sperm and decrease motility
- Introduced during copulation

Question 3

What is bidirectional myometrial contractility?

Answer 3

Contractility that:
- Is toward the ovary during insemination
- Is toward the vagina during menstruation and parturition
- The direction is determined by the actin:myosin ratio and the type of myosin present

Question 4

What is sperm capacitation?

Answer 4

The facilitation of motility and viability of sperm

Question 5

Describe the fertilization process (zygotogenesis) from attachment to syngamy (fusion of the two cells).

Answer 5

• The released ovum encounters the sperm in the ampulla of the oviduct
• Sperm are randomly hyper motile in the ampulla, and one penetrates the ovum
• The penetration leads to a calcium influx into the ovum, causing a release of granules
• These granules alter the biochemistry of the surface of the ovum such that no more sperm can attach (polyspermy inhibition)
• The attachment process is driven by:
  - acrosomal receptors that recognize chemotactic chemicals released from the ovum
  - acrosomal enzymes (proteases) that break apart proteins on the corona radiata
• Binding of acrosome to receptors on zona pellucida
  - the acrosome surface contains molecules (ZBR and ARPR) that physically bind to a molecule (ZP3) on the ZP
• Acrosome reaction:
  - this reaction is inhibited by the ZBR-ZP3 binding event
  - the OAM and IAM fuse, thus causing an exocytosis of the acrosomal contents
  - hyaluronidase and acrosin are two enzymes released from the acrosome, and these enzymes promote the
  penetration of the ZP
• Fusion:
  - Sperm traverses the ZP and settles in the perivitelline space
  - the IAM fuses with the oocyte (vitelline) membrane
  - The fusion causes the release of calcium from cortical granules, initiating the zona reaction
  - The excess calcium in the perivitelline space leaks into the ZP, preventing any further penetration

Question 6

Describe the blastogenesis process.

Answer 6

• The outer blastomeres (trophoblasts) of the morula adhere because of tight junctions between the cells
• The inner blastomeres of the morula adhere together because of gap junctions between the cells
• Trophoblasts release Na+ that osmotically attracts water, thus pushing the central blastomeres
  eccentrically into the intracellular mass (ICM)
• The blastocoele pressure forces the blastocyst out of the zona pellucida
• The exocytosis process is termed hatching
• The hatched blastocyst contains the ICM, the bastocoele, and the trophoblasts
• The blastocyst is the entity that is implanted into the uterus
• Implantation occurs at the ICM locus of the blastocyst