Lecture 48: Fertilisation to implantation

Question 1

What is fertilisation?

where does fertilisation occur?

What are the three phases of fertilisation?

Answer 1

Is when a male and female gamete fuse to form diploid cell
- site of fertilisation = ampulla of uterine tube usually
Three phases
- penetration of corona radiata
- penetration of zone pellucida
- penetration of the oocyte cell membrane

Question 2

How does the oocyte change upon sperm entering the oocyte?

Answer 2

• Zona pellucida becomes impenetrable
• Meiosis II completes ——> ovum produced
• Female pronucleus forms
• Spermatozoon nucleus moves close to female pronucleus
• Spermatozoon tail degenerates

Question 3

What is capacitation?

Answer 3

• is when the sperm undergoes changes in female tract
  Capacitation = increases motility & acrosome membrane becomes fragile
• undergoes a change which gives it the capacity to fertilise the egg
• 6-8 hours

Question 4

Describe the process of implantation?

Answer 4

• mitotic cell division –> blastomere
• days 3 - 14 morula
• days 4 -5 fluid filled blastocyte
• days 6 -7 blastocyte breaks out of zone pellucid and moves to endometrium; implantation begins
• day 10 blastocyst completely implanted
• trophoblast forms two layers
  = inner layer differentiates into cytotrophoblast
  = outer layer differentiates into syncytiotrophoblast
• trophoblast secretes human chorionic gonadotropin

Question 5

What happens at week 2?

- development at week 2

Answer 5

• 2 layers of trophoblast form
• 2 layers of embryo blast or inner cell mass = epiblast and hypoblast
• 2 cavities form = amniotic cavity and yolk sac
  Amniotic cavity = surrounds and protects developing embryo
  Yolk cavity = primordial germ cells

Question 6

Describe the function of the placenta?

Answer 6

• anchors developing foetus to uterus
• separate maternal and metal blood
• secretes hormones
• exchange occurs across the chorionic villi
• embryo connected to placenta via umbilical cord = blood vessels carry oxygenated blood to the foetus, deoxygenated blood away

Question 7

What is cleavage?

Answer 7

zygote —> blastomere —> morula —-> blastocyte

Question 8

What is parturition?

How does the placenta detach?

Answer 8

= Childbirth
- 1st stage: cervix dilates to allow metal head through —> contractions —> rupture of fetal membrane
- 2nd stage: contractions (short) —-> birth of baby
= placenta detaches at 3rd stage
- contractions close the maternal arteries that supplied the placenta