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Repro > Fertilisation and the Luteal Phase > Flashcards

Fertilisation and the Luteal Phase Flashcards

1
Q

Why is ejaculated semen coagulated?

A

It is coagulated to prevent loss, later liquefies.

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2
Q

What happens when sperm moves through the cervical mucus?

A

It removes seminal fluid, abnormally morphological sperm and cellular debris.

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3
Q

Why is sperm able to pass through the cervix more easily?

A

It is less viscous in the absence of progesterone allowing sperm to pass.

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4
Q

Where can sperm inhabit?

A

They can inhabit cervical crypts which may form a reservoir.

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5
Q

When does fertilisation occur?

A

Typically within 24-48 hours but sperm have been recovered alive after 5 days.

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6
Q

What may have a role in the journey of the egg through the uterus?

A

Uterine or tubal cilia

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7
Q

What attracts the sperm to the egg?

A

Chemoattractants released from the oocyte cumulus complex.

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8
Q

What happens to sperm on the journey to the egg?

A

It becomes hyperactivated, forceful tail beats with increased frequency and amplitude mediated by Ca2+ influx via CatSper channels.

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9
Q

How does sperm capacitation occur?

A

It is partly achieved by removing the sperm from the seminal fluid, also uterine or tubal fluid may contain factors which promote capcitation.

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10
Q

What is sperm capacitation?

A

The biochemical rearrangment of the surface glycoprotein and changes in membrane composition that needs to occur before the acrosome reaction

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11
Q

What is the acrosome reaction?

A

The acrosomal membrane on the sperm head fusing with zona-cumulus complex to release enzymes through the complex.

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12
Q

What happens during the acrosome reaction?

A

Acrosin binds to the inner acrosomal membrane digests the zona pellucida so that the sperm can enter.

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13
Q

What does the LH spike do?

A

It causes resumption of meiosis and ovulation. It converts the priamry oocyte to secondary oocyte plus the 1st polar body.

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14
Q

What catches the oocyte cumulus complex?

A

The fimbrae of the uterine tube

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15
Q

What is the corpus luteum?

A

Theca and granulosa cells mixed and the empty follicle.

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16
Q

What does the corpus luteum produce in the luteal phase?

A

Progesterone

17
Q

What is progesterone needed for in the luteal phase?

A
  • Makes the endometrium secretory and receptive to implantation
  • Suppresses cilia in uterine tubes once oocyte has already passed
  • Makes cervical mucus viscous again to prevent further sperm penetration
18
Q

What does oestrogen do in the luteal phase?

A
  • Helps to maintain endometrium in luteal phase
19
Q

Describe the demise of the CL

A
  • If there is no fertilisation, CL has an inbuilt finite lifespan of 14 days.
  • Regression is needed to initiate a new cycle.
  • Fall in Cl-derived steroids causes inter-cycle rise in FSH.
  • The CL shrinks and over time becomes a corpus albicans.
  • CL is rescued in pregnancy by hCG from embryo binding to its LH receptors.
  • CL continues to produce progesterone and maintain endometrium
20
Q

What is the purpose of the menstrual cycle?

A
  1. Selection of a single follicle and oocyte
  2. Regular spontaneous ovulation
  3. Correct haploid number of chromosomes in the oocyte
  4. Cyclical changes in the cervix and uterine tubes, to enable egg transport and sperm access.
  5. Preparation of the endometrium of the uterus to receive the fertilised egg
  6. Support of the implanting embryo and endometrium by corpus luteum progesterone.
  7. Initiating a new cycle if fertilisation does not occur.
21
Q

What is the cumulus oophorus?

A

It protects the egg, dervied from granulosa cells.

22
Q

What is the corona radiata?

A

Innermost layer of cumulus cells in contact with the zona pellucida. Formed by granulosa cells adhering to the oocyte before it leaves the ovarian follicle.

23
Q

What is the zona pellucida?

A

It is secreted by the egg. It becomes impenetrable after the cortical reaction.

24
Q

What is the 1st polar body?

A

Collection of chromosomes released from the primary oocyte after the first meiotic division.

25
Q

Describe the sperm binding and penetration mechanism

A
  1. The acrosome reaction occurs in contact with the zona-cumulus complex. Sperm penetrate the cumulus and bind to the ZP.
  2. Sperm enzymes cut through ZP and sperm fuses with the plasma membrane.
  3. Sperm is taken in by phagocytosis. Phospholipase Zeta activated by basal Ca2+ inside egg. PIP2 -> DAG + IP3. It causes the release of intracellular Ca2+ leading to large Ca2+ spike.
  4. Cortical reaction as wave of Ca2+ sweeps around egg. The release of proteases, peroxides and hyaline prevents polyspermy.
26
Q

What happens when sperm enters the egg?

A

It causes an increase in calcium via phospholipase zeta from sperm. Calcium causes the completion of meiosis II expelling the second polar body and cortical reaction.

27
Q

What happens when the sperm nuclear membrane breaks down?

A

The chromatin decondesnses and chromosomes separate

28
Q

When does the pronuclei form?

A

4-7 hours after sperm penetration the two sets of haploid chromosomes become surrounded by distinct membranes forming two pronuclei.

29
Q

What do the haploid structures during syngamy do?

A

They synthesise DNA in preparation for the first mitotic division.

30
Q

How does the zygote become a two cell embryo?

A

The pronuclei fuse and the mitotic metaphase spindle forms with the chromosomes assuming their position at its equator. Mitosis is completed and the one cell zygote becomes a two cell embryo.

31
Q

Summarise fertilisation

A
  • Cortical granules fuse with zona pellucida to block polyspermy.
  • Sperm enters oocyte causing Ca2+ waves
    at the same times as the completion of MII by explusion of 2nd polar body in females.
  • Nucleus of sperm transformation to male pronucleus at the same time as the female pronucleus forms.
  • The pronucleii come together, membranes break down alignment of chromosomes on spindle and mitosis occurs.
32
Q

What is the first sign of fertilisation?

A

The fertilised egg having 2 pronuclei.

33
Q

What happens 3 days after fertilisation?

A

The developing embryo contains 6-8 cells

34
Q

When does a blasocyst form?

A

Five days after fertilisation, there is a blastocyst and differentiates into an inner cell mass - blastocoel and trophoblast.

Repro (11 decks)

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