Fertilisation and the Luteal Phase

Question 1

How does seminal fluid act to reduce sperm loss?

What happens as the ejaculate passes through the cervix?

When does the cervical mucous become less viscous? What does this allow?

Answer 1

• It coagulates and later liquefies
• Cervical mucous removes Seminal fluid, Cellular debris, and Abnormal sperm, which go into the Cervical Crypts (act as a reservoir)
• In the absence of Progesterone to allow Sperm to pass

Question 2

Sperm Capacitation:
What is it?

Why does it occur?

What promotes it?

Acrosomal Reaction:
What does it come into contact with to occur?

What occurs? How?

Answer 2

• Biological arrangement of surface glycoproteins and changes in membrane
  composition to initiate whiplashing of Sperm tail
• Increases motility and prepares it for an Acrosomal reaction
• Removal of seminal fluid, and factors in Uterine and Tubal fluid

• Zona-Cumulus complex
• Acrosomal membrane of sperm head fuses and releases enzymes to cut through the complex
  o ACROSIN on inner acrosomal membrane digests the Zona Pellucida to allow for sperm to enter

Question 3

OVULATION:
Luteal Phase:
What does the CL produce?

What does this production do to the endometrium, uterine tubes, and cervix?

What does the little Oestrogen produced do?

Death of the CL:
What occurs? What does it become

Why is it necessary if no fertilisation occurs?

How is the CL rescued in pregnancy?

Answer 3

• Mostly Progesterone
• • Prepares Endometrium for implantation
  • Suppresses cilia in Uterine tubes once Oocyte has passed
  • Makes cervical mucous viscous again to prevent further sperm penetration
• Maintains Endometrium in the Luteal phase

• Apoptosis, Vasculature breakdown, Shrinkage = CORPUS ALBICANS
• Its death = Fall in Progesterone = Inter-cycle rise in FSH
• hCG binds to LH receptors for more Progesterone production until the placenta can take over

Question 4

FERTILISATION:
What happens first?

How does the sperm then reach the oocyte?

What happens after the sperm head is taken in by phagocytosis?

What is the result of the previous step? What is the reason for this reaction occurring?

Answer 4

• Sperm penetrates Cumulus and binds to Zona Pellucida (ZP), triggering the Acrosomal reaction
• Enzymes (Acrosin) cut through ZP, allowing sperm to fuse with the Oocyte plasma membrane
• PLZ activated by basal Ca2+ inside the egg, producing DAG and IP3 = HUGE release of Intracellular Ca2+
• ↑↑Ca2+ = Release of Cortical granules in Oocyte, leading to Cortical reaction
  o It HARDENS the Oocyte coat to prevent Polyspermy

Question 5

Syngamy:
What is it?

What happens after the sperm enters the egg?

Pronuclei Formation and Breakdown:
When does it occur?

What happens first?

What happens after this? What is it egg now classified as?

Answer 5

• Fusion of 2 gametes
• Oocyte Ca2+ Influx, which causes:
  o Cortical reaction, preventing Polyspermy
  o OOCYTE COMPLETES MEIOSIS II, FORMING A 2ND POLAR BODY
  o Breakdown of Sperm nuclear membrane, Chromatin decondenses, and Chromosomes separate

• 4-7 hours after fusion
• Formation of distinct membranes around 2 sets of haploid chromosomes, forming 2 PRONUCLEI - They then replicate in preparation for 1st Mitotic division
• Pronuclei membranes breakdown and Mitosis occurs
  o One cell Zygote → Two cell Embryo