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Reproductive Sciences > Fertilisation > Flashcards

Fertilisation Flashcards

1
Q

Describe the types of ovulation.

A

About equal numbers of ovulation occur from each ovary.
Ipsilaterally: Ovary on a particular side will ovulate again on a succeeding cycle
Contralaterally: The other ovary will ovulate on the next cycle.

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2
Q

What are short follicular length cycles associated with? Ipsilateral or contralateral ovulation?

A

Short follicular length cycles (14 days) do not show any association and is random

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3
Q

What are short follulary length cycles associated with?

A

Short follicular length cycles (14 days) do not show any association and is random

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4
Q

Which type of ovulation usually leads to healthier follicles and why?

A

Dominant follicles in contralateral ovulation are usually healthier then ipsilateral ones (Fukuda et al, 1996)

This is due to intraovarian factors from the corpus luteum are thought to negatively affect the health of the dominant follicles and the enclosed oocyte.

Therefore, contralateral selection of the dominant follicle in the succeeding cycle may favour embryo development.

The chance of conceiving during a natural cycle may be affected by the side of ovulation in the preceding cycle.

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5
Q

In ovulation, what do FSH and LH do?

A

FSH: Stimulates follicle growth
LH: Stimulates follicles to secrete oestrogen

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6
Q

Describe the endocrinological overview of the menstrual cycle

A

Hypothalamus released GnRH.
This stimulates pituitary gland to secrete FSH and LH (gonadotrophic factors)
Cells of growing follicles (theca) start to produce oestrogen - when this begins to rise steeply, FSH and LH rise as well.
The high concentration of oestrogen stimulate the hypothalamus to produce more GnRH.
The maturing follicle, in response of the LH surge releases a secondary oocyte and this process is referred to as ovulation.
LH also stimulate the follicular tissue left behind to transform into the corpus luteum
Under continuous stimulation by LH, the corpus luteum secretes oestrogen and progesterone.
As oestrogen and progesterone levels rise, the combination of these hormones inhibit the secretion of GnRH and thus reduce the secretion of FSH and LH.
These low levels of FSH and LH cause the corpus luteum to disintegrate thus a sharp decline in oestrogen and progesterone levels too.
The decreasing levels of oestrogen and progesterone therefore stop the inhibition of hypothalamus to secrete GnRH and the pituitary can begin to secrete enough FSH to initiate the next ovarian cycle.

If fertilisation happens, HCG (produced by blastocyst) will take over the role of LH to maintain the corpus luteum.

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7
Q

Estrous vs menstrual cycle

A

Mestrual: Humans and some primates

  • Cycle consists of menstrual phase, proliferative phase, and secretory phase
  • Blood flows in the last few days of this cycle
  • Broken endometrium passed out during menstruation
  • Sex urge not increased during menstruation
  • Female does not permit copulation during menstrual phase of the cycle

Oestrous: Non-primates

  • Short period of oestrous (or heat) followed by passive period
  • Broken endometrium is reabsorbed
  • Sex urge increased during oestrous period
  • Female permits copulation only during oestrous period
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8
Q

Estrous vs menstrual cycle

A

Mestrual: Humans and some primates

  • Cycle consists of menstrual phase, proliferative phase, and secretory phase
  • Blood flows in the last few days of this cycle
  • Broken endometrium passed out during menstruation
  • Sex urge not increased during menstruation
  • Female does not permit copulation during menstrual phase of the cycle

Oestrous: Non-primates

  • Short period of oestrous (or heat) followed by passive period
  • Broken endometrium is reabsorbed
  • Sex urge increased during oestrous period
  • Female permits copulation only during oestrous period
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9
Q

Why would menopause have evolved in humans?

A

Menopause is unique to humans and may have evolved for a mother to provide better care for her children and grandchildren

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10
Q

Where is the sperm produced?

A

In the coiled seminiferous tubules of testes

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11
Q

Why are testes external to body?

A

To keep sperm at a lower temperature

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12
Q

Name accessory glands of male and their functions

A

Seminal vesicle: Contribute ~60% of total volume of semen
Prostate gland: Secrete slightly alkaline fluid that forms part of seminal fluid and also enzymes that contribute to liquefaction ~20 volumes of seminal fluid
Bulboureothral glands: Secrete mucoproteins that make up ~5% of seminal fluid

Both prostate and bulboureothral glands add substances needed for movement of sperm e.g. fructose

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13
Q

Describe the rolls of LH and FSH in the male reproductive system

A

LH: Stimulates the leydig cells to make testosterone
Testosterone stimulates sperm production and also the development of primary and secondary sex characteristics

FSH: Stimulates sertoli cells of seminiferous tubules promoting spermatogenesis

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14
Q

Name the stages of spermatogenesis

A

1) Spermatogonia
2) Primary spermatocytes
3) Secondary spermatocytes
4) Spermatids
5) Spermatozoa

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15
Q

What is the final stage of spermatogenesis

A

Spermiogenesis: Transforms spermatids into spermatozoa

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16
Q

What is spermiation?

A

The process by which mature spermatids are released from Sertoli cells in the seminiferous tubule lumen prior to their passage to the epididymous

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17
Q

What does the head of the sperm consist of?

A

Haploid nucleus, acrosome tip, centriole

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18
Q

What does the middle piece of sperm consist of?

A

Spiral-shaped mitochondria

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19
Q

Normal 5th edition WHO parameters of sperm analysis (volume)

A

Volume: 1.5ml

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20
Q

Normal 5th edition WHO parameters of sperm analysis (pH)

A

pH >7.2

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21
Q

Normal 5th edition WHO parameters of sperm analysis (Concentration)

A

Concentration: >15 x 10^6 per ml

22
Q

Normal 5th edition WHO parameters of sperm analysis (motility)

A

Motility: >40%

23
Q

Normal 5th edition WHO parameters of sperm analysis (morphology - Keurger strict criteria)

A

Morphology: >4%

24
Q

Normal 5th edition WHO parameters of sperm analysis (morphology - Keurger strict criteria)

A

Morphology: >4%

25
Q

Gives some examples of fates of ejaculated sperm

A 
Leakage
Destroyed by acidic environment
Fail to make it through cervix
Destroyed by phagocytic leukocytes
Reach the uterine tubes
26
Q

How does the sperm reduce rates of leakage from vagina?

A

Coagulating enzymes in semen (derived from prostate gland) interacts with fibrinogen-like substrate (derived from seminal vesicle) to form a coagulant. This acts to retain sperm in vagina and also for pH buffering against acidic vagina

27
Q

What must happen to sperm before they can penetrate the oocyte?

A

Capacitation: Destabilisation of acrosomal sperm head membrane to allow greater binding between sperm and oocyte
It is the process of sperm becoming fertile
Process takes between 4 - 5 hours in uterus

28
Q

How can capacitation be carried out in vitro?

A

By washing the sperm to remove them from seminal fluid

29
Q

Describe the steps a sperm takes to fertilise an egg

A
  1. Sperm goes through cumulus cells surrounding the egg
  2. Acrosome reaction: Acrosomal head content released including surface antigens and enzymes
  3. Membranes of sperm and egg fuse
  4. Penetration through zona pelucida
  5. The sperm deposits a single nucleus into the egg cytoplasm
  6. Following calcium oscillations, cortical granules in the oocyte fuse to the outer membrane and release chemicals that does not allow any more sperm to penetrate the egg
30
Q

How long are the ovulated oocye and ejaculated sperm viable for?

A

Oocyte: 6 - 24 hours
Sperm: 24 - 72 hours

31
Q

When should coitus occur for fertilisation to occur?

A

Three days before ovulation - 24 hours after ovulation

32
Q

Where in the fallopian tube does fertilisation occur?

A

In the apullary-isthmic region

33
Q

How can you determine ferlitisation has occured in vitro?

A

Presence of two pronuclei, 2 polar bodies (sometimes first one gets degenerated)

34
Q

What events occur during the first cell cycle?

A
  • Calcium oscillations (precede CG release but also continue into 1st cell cycle)
  • Formation of pronuclei and membranes around both paternal and maternal nuclei
  • Gene remodeling and reprogramming (e.g. replacing protamines with histones in the sperm nucleus)
  • DNA
35
Q

What events occur during the first cell cycle?

A
  • Calcium oscillations (precede CG release but also continue into 1st cell cycle)
  • Formation of pronuclei and membranes around both paternal and maternal nuclei
  • Gene remodeling and reprogramming (e.g. replacing protamines with histones in the sperm nucleus)
  • DNA needs to be replicated
  • Zygote genome activation: This takes over the maternal dependence (NOT IN FIRST>)
  • Syngamy: Fusion of both parental pronuclei. This allows the first division to take place and the appearance of two pronuclei
36
Q

What is histone replacement?

A

The pronuclear development in fertilised eggs must go through a series of transformations to restore the transcriptional competence of the inactive gamete chromatin.

A crucial part of this is the replacement of the sperm-specific basic proteins (e.g. protamines) with histones.

This allows for correct DNA synthesis and embryo development.

37
Q

What events occur during the first cell cycle?

A
  • Calcium oscillations (precede CG release but also continue into 1st cell cycle)
  • Formation of pronuclei and membranes around both paternal and maternal nuclei
  • Gene remodeling and reprogramming (e.g. replacing protamines with histones in the sperm nucleus)
  • DNA needs to be replicated
  • Syngamy: Fusion of both parental pronuclei. This allows the first division to take place and the appearance of two pronuclei
38
Q

What is histone replacement?

A

The pronuclear development in fertilised eggs must go through a series of transformations to restore the transcriptional competence of the inactive gamete chromatin.

A crucial part of this is the replacement of the sperm-specific basic proteins (e.g. protamines) with histones.

This allows for correct DNA synthesis and embryo development.

39
Q

How long does the 1st cell cycle take?

A

24 hrs

40
Q

How long do the cycles following the 1st cell cycle take?

A

16 - 18 hrs

41
Q

Describe the move in potency of the early embryo

A

Early embryo cells are totipotent but they later become pluripotent

42
Q

Cleavage stage embryo

A
  • Zygote genome activation: This takes over the maternal dependence
    Once the zygote has all of its genes active, there is a change in the metabolic requirements of the cells. The major ZGA happens between the 8th and 16 cell stage.

After the ZGA, there is a compaction of cells at the morula stage. This is calcium dependent and involves molecules such as e-cadherin. This compaction takes place by the formation of tight junctions or desmosomes between the cells and makes them hard to separate.

Cavitation: The highly polarised morula cells with the outer cells (microvilli) and inner cells with different properties start actively pumping glucose, salts, and water into the intracellular space.
This is known as the early blastocyst because a cavity can be seen at that stage.

The blastocyst expansion is dependent on a number of genes

43
Q

Cleavage stage embryo

A
  1. ZGA
  2. Compaction of cells
  3. Cavitation
  4. Blastocoele expansion
  5. Blastocyst formation
  6. Blastocyst expansion and hatching
44
Q

Describe ZGA

A

This occurs in the cleavage stage of the embryo.

Zygote genome activation: This takes over the maternal dependence
Once the zygote has all of its genes active, there is a change in the metabolic requirements of the cells. The major ZGA happens between the 8th and 16 cell stage.

45
Q

Describe the compaction of cells

A

After the ZGA, there is a compaction of cells at the morula stage. This is calcium dependent and involves molecules such as e-cadherin. This compaction takes place by the formation of tight junctions or desmosomes between the cells and makes them hard to separate.

46
Q

Describe cavitation

A

Approximately 24 hours after compaction, the cells start forming a fluid-filled cavity called a blastocoel.
The highly polarised morula cells start actively pumping glucose, salts, and water into the intracellular space.
This is known as the early blastocyst because a cavity can be seen at that stage.

47
Q

Describe blastocoele expansion

A

The blastocoele expansion is dependent on a number of genes such as the epidermal growth factor (EGF) and tumour growth factor-alpha (TGF-a).
This expansion plays an important role in differenciation between the TE and ICM.

48
Q

Describe blastocyst formation

A

The blastocyst formation is distinguishable by the formation of the two population of cells within the embryo:

  1. Inner cell mass (ICM)
  2. Trophectoderm (TE)
49
Q

How does a blastocyst implant?

A

Requires apposition of the blastocyst on the uterine lining with the ICM facing the uterine endometrial epithelium.

Shortly before the blastocyst comes in contact with the endometrium, the trophoblast cells start differentiating into two different cell masses:

  1. Outer syncytiotrophoblast
  2. Inner cytotrophoblast

The CTB cells consist of an inner irregular layer of ovoid, single-nucleus cells.
In the periphery, the STB cells form the syncytium (a multi-nucleated layer without cell boundary that arise from the fusion of the CTB cells)

The STB produces lytic enzymes and secrete factors that cause apoptosis of the endometrial epithelial cells.
The STB also crosses the basal lmina and penetrates into the stroma that lies below, eroding the wall of capillaries. With the implantation of the blastocyst in the endometrium, the STB develops quickly and will entirely surround the embryo as soon as it has completely embedded inselt in the endometrium

50
Q

How does a blastocyst implant with regard to syncytiotrophoblast and the cytotrophoblast.

A

Requires apposition of the blastocyst on the uterine lining with the ICM facing the uterine endometrial epithelium.

Shortly before the blastocyst comes in contact with the endometrium, the trophoblast cells start differentiating into two different cell masses:

  1. Outer syncytiotrophoblast
  2. Inner cytotrophoblast

The CTB cells consist of an inner irregular layer of ovoid, single-nucleus cells.
In the periphery, the STB cells form the syncytium (a multi-nucleated layer without cell boundary that arise from the fusion of the CTB cells)

The STB produces lytic enzymes and secrete factors that cause apoptosis of the endometrial epithelial cells.
The STB also crosses the basal lmina and penetrates into the stroma that lies below, eroding the wall of capillaries. With the implantation of the blastocyst in the endometrium, the STB develops quickly and will entirely surround the embryo as soon as it has completely embedded inselt in the endometrium

51
Q

Describe placentation

A

As the placenta forms, HCG levels decline and the placenta starts secreting its own progesterone.

The placental barrier is composed of structures that separate maternal and fetal blood. The makeup of this barrier changes over the course of pregnancy but the role of the barrier is to provide nutrients and remove waste.

Reproductive Sciences (4 decks)

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