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ESA 4 - Reproductive System > Fertilisation > Flashcards

Fertilisation Flashcards

1
Q

What is the normal volume of semen?

A

2-4ml

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2
Q

What is the normal sperm count in semen?

A

20-200 x 106 per ml, or >40 x 106 per ejaculate

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3
Q

What % of sperm is swimming forward vigorously in normal semen?

A

60%

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4
Q

What % of sperm has abnormal morphology in normal semen?

A

<30%

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5
Q

How long does liquefaction take to occur in normal sperm?

A

Within 1 hour

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6
Q

What is classified as oligozoospermia?

A

<20 x 106 sperm/ml

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7
Q

Draw sperm with abnormal morphology

A
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9
Q

Where do the glandular components of semen come from?

A
  • Bulbourethral glands (Cowper’s glands)
  • Seminal vesicles
  • Prostate
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10
Q

What % of semen volume comes from Cowper’s glands?

A

5%

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11
Q

What do Cowper’s gland secrete?

A

Alkaline fluid

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12
Q

What is the function of Cowper’s glands secretions?

A

Mucous lubricates the tip of the penis and urethral lining

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13
Q

What % of semen volume comes from seminal vesicles?

A

60%

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14
Q

What does secretions from seminal vesicles consist of?

A
  • Alkaline fluid
  • Fructose
  • Prostaglandins
  • Clotting factors
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15
Q

What is the function of the alkaline fluid secreted by seminal vesicles?

A

Neutralises the acid in the male urethra and female reproductive tract

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16
Q

What is the function of fructose from seminal vesicles?

A

ATP production

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17
Q

What is the function of prostaglandins from the seminal vesicles?

A
  • Increase sperm motility
  • Increase female genital smooth muscle contraction
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18
Q

What clotting factor in particular is produced by seminal vesicles?

A

Semenogelin

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19
Q

What % of semen volume is from the prostate?

A

25%

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20
Q

Describe prostate secretion

A

Milky, slightly acidic fluid

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21
Q

What do prostatic secretions consist of?

A
  • Proteolytic enzymes
  • Citric acid
  • Acid phosphatase
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22
Q

What proteolytic enzymes are found in prostate secretions?

A
  • PSA
  • Pepsinogen
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23
Q

What does pepsinogen in semen do?

A

Breaks down clotting factors from seminal vesicles

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24
Q

How long does pepsinogen take to re-liqeufy semen?

A

10-20minutes

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25
Q

What is the purpose of citric acid in prostate secretions?

A

For ATP production

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26
Q

When does endometrial proliferation typically occur in the ovarian cycle?

A

Days 7-14

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27
Q

What does endometrial proliferation occur under the influence of?

A

Oestrogen

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28
Q

What effect does oestrogen alone have on cervical mucus?

A

It makes an abundant, clear, and non-viscous

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29
Q

What is the result of the clear, non-viscous cervical mucus during endometrial proliferation?

A

Easy for sperm to get in

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30
Q

When in the ovarian cycle does ovulation occur?

A

Day 14

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31
Q

What happens on days 14-28 of the ovarian cycle?

A

Uterine secretory phase

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32
Q

What happens during the uterine secretory phase?

A

Oestrogen and progesterone from the corpus luteum produce hospitable environment for fertilisation and implantation

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33
Q

What is produced in the uterine secretory phase by oestrogen and progesterone?

A

Thick, sticky, mucus plug

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34
Q

What does oxytocin do?

A

Stimulates uterine contraction, which helps the sperm get to the ovum

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35
Q

What are the components of oocyte maturation?

A
  • Nuclear maturation
  • Cytoplasmic maturation
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36
Q

What happens in the nuclear maturation stage of oocyte maturation?

A
  • Oocyte undergoes meiosis I
  • Nuclear membrane of oocyte disappears
  • First polar body seperates and enters perivitelline space
  • Second meiotic division takes place and stops in metaphase II
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37
Q

What happens in cytoplasmic maturation stage of nuclear maturation?

A
  • Mitochondria are dispersed through the cytoplasm
  • Endoplasmic reticulum undergoes changes
  • Lipid droplet provide energy
  • Cytoskeleton is formed by microfilaments migrating towards the oocyte cortex
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38
Q

What happens to the endoplasmic reticulum during cytoplasmic maturation stage of oocyte maturation?

A
  • Accumulates in the oocyte cortex
  • Protein and lipid synthesis produce cortical granules
  • Become cortical during maturation
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39
Q

What happens to cortical granules in the immature oocyte?

A

They are displaced throughout the cytoplasm

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40
Q

What is the energy produced from lipid droplets in the cytoplasmic maturation stage of oocyte maturation needed for?

A
  • Meiosis
  • Maturation
  • Fertilisation
  • Early embryo development
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41
Q

What is the average number of sperm per ejaculation?

A

200-300 million

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42
Q

How many sperm reach the fertilisation site?

A

300

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43
Q

How many sperm are needed for fertilisation?

A

1

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44
Q

What happens to the first 299+ sperm that reach the fertilisation site?

A

They are sacrified to disperse the zona pellucida

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45
Q

How long can sperm survive in the female genital tract?

A

Up to 5 days

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46
Q

How long can an oocyte survive

A

Up to 5 days, then gets phagocytosed

47
Q

What is the fertile period for sperm deposition?

A

Up to 3 days prior to ovulation, or on day of ovulation

48
Q

How long does it take for the oocyte to travel from the ovary to the body of the uterus?

A

3-4 days

49
Q

How is the oocyte transported from the ovary to the body of the uterus?

A

By cilia and Fallopian tube peristalsis

50
Q

What does sperm need to penetrate?

A

The corona radiata (follicular cells) and zona pellucida (glycoprotein membrane)

51
Q

What allows the sperm to penetrate the corona radiata and zona pellucida?

A

It undergoes further maturation in the female reproductive tract, called capacitation

52
Q

What happens in capacitation?

A

Sperm cell membrane changes to allow fusion with oocyte cell surface

53
Q

What changes to the sperm cell membrane allows fusion with oocyte cell surface?

A

Removal of protein coat of sperm

54
Q

What happens when the protein coat of sperm is removed?

A

Acrosomal enzymes are exposed

55
Q

What is true of the acrosome when sperm contacts the corona radiate?

A

It has in intact acrosome

56
Q

What happens when sperm contacts the corona radiata?

A

It pushes through the granulosa cells of the corona radiata

57
Q

What happens once sperm has pushed through the granulosa cells on the corona radiata?

A

Proteins on sperm head bind to ZP3 proteins on zona pellucida

58
Q

What does the binding of proteins on the sperm head to ZP3 proteins on zona pellucida trigger?

A

Acrosome reaction

59
Q

What happens in the acrosome reaction?

A
  1. Key signalling mechanisms involves intracellular Ca2+
  2. Acrosomal enzymes digest path through ZP
  3. One sperm penetrates, and there is fusion of the plasma membranes
60
Q

What is the oocyte plasma membrane divided into?

A

Two major regions;

  • The part of the mmebrane that directly overlies the metaphase chromosomes
  • The remainder of the oocyte, whcih is rich in microvillar protrusions
61
Q

Describe the surface of the part of the oocyte plasma membrane that directly overlies the metaphase chromosomes

A

Has smooth surface, devoid of microvilli

62
Q

What is the region of the oocyte where the sperm and egg fuse?

A

The portion of oocyte that is rich in microvillar protrusions

63
Q

What happens once the sperm and oocyte plasma membranes have fused?

A

The sperm moves into the cytoplasm, and the oocyte and sperm form a zygote

64
Q

How is polyspermy blocked?

A

By the cortical reaction

65
Q

What are the components of the cortical reaction?

A
  • Fast block
  • Slow block
66
Q

What happens in the fast block cortical reaction?

A
  • Electrical change in oocyte membrane
  • Sodium channels open
67
Q

What is the resting potential of the oocyte?

A

-75mV

68
Q

What is the fertilisation potential of the oocyte?

A

+20mV

69
Q

How does the wave of depolarisation spread in the fast block cortical reaction?

A

Starts at the site of entry of sperm, and then propagates across the cytoplasm

70
Q

What happens in the slow block cortical reaction?

A
  • Ca2+ is released from ER, which induces local exocytosis of cortical granules.
  • Granules release enzymes to stimulate adjacent cortical granules to undergo exocytosis.
  • A wave of exocytosis occurs around oocyte in 3 dimensions from original site of sperm entry
71
Q

What happens to the tail movement of the sperm in the female genital tract?

A

Changes from a beat to a whip-like action

72
Q

How fast do sperm move in the female genital tract?

A

3mm/hour

73
Q

What is responsible for most of the movement of sperm in the female genital tract?

A

Contraction of the female genital organ

74
Q

What happens in syngamy?

A
  • The oocyte completes meiosis 1, and expels the polar body
  • Male and female pronuclei migrate towards each other, and the union of male and female pronuclei forms a diploid zygote
75
Q

What is a polyploid embryo?

A

One containing three or more pronuclei

76
Q

What can polyploid embryos occur due to?

A
  • Entry of more than one sperm
  • Failure of extrusion of the second polar body
77
Q

What happens in embryonic cleavage?

A

A series of rapid mitotic divisons and metabolic changes for upcoming cell division and embryogenesis takes place.

There is an increased number of cells (16-32 blastomeres) of decreasing size, without increase in size of fertilised ovum

78
Q

What is true of cells produced by cleavage?

A

They are totipotent

79
Q

What is meant by cells being totipotent?

A

Each cell has the capacity to develop into entire individual

80
Q

When do monozygotic twins occur?

A

When, in cleavage, totipotent cells become divided into 2 independant cell masses

81
Q

What % of twins follow seperation after the first cleavage?

A

25-35%

82
Q

When does dizygotic/non-identical twins occur?

A

When 2 eggs ovulate, and 2 eggs are fertalised

83
Q

Why is cleavage important?

A

Because it generates a large number of cells that can undergo differentiation and gastrulation to form organs

84
Q

What does cleavage result in?

A

An increase in the nuclear/cytoplasmic ratio

85
Q

Why is it important that there is an increase in nuclear/cytoplasmic ratio in the embryo?

A

Because one nucleus cannot transcribe sufficient RNA to support the enormous cytoplasm of the zygote

86
Q

Why does cleavage result in an increase in the nuclear/cytoplasm ratio?

A

No G1 (duplication of organelles and cytosol) or G2 (synthesis or enzymes and proteins) stages in cell cycle during cleavage, so ratio increases with each division

87
Q

is cleavage synchronous?

A

No, not all blastomeres divide at the same time

88
Q

When does compaction occur?

A

At the 8 cell stage

89
Q

What happens in compaction?

A

Blastomeres undergo polarisation and form tight junctions to create ‘inner embryo environment’

90
Q

When does the morula form?

A

At the 16 blastomere stage

91
Q

How long after fertilisation does morula formation occur?

A

3-4 days

92
Q

What happens once the morula has formed?

A

The embryo passes from oviduct into uterus

93
Q

What happens if there is a failure of transport of morula into uterus?

A

Ectopic pregnancy occurs

94
Q

Where does the morula implant in an ectopic pregnancy?

A

Fallopian tube, ovary, or peritoneal cavity

95
Q

What is the problem with an ectopic pregnancy?

A
  • Risk of materal haemorrhage
  • Embryo is non-viable
96
Q

Why is the embryo non-viable in ectopic pregnancy?

A

It has been implanted into a hostile environment

97
Q

When does the blastocyst stage occur?

A

5 days after fertilisation

98
Q

What is the blastocyst?

A

A fluid filled cavity that develops into the morula

99
Q

What happens to the cells in the blastocyst stage?

A

Loss of totipotency

100
Q

What is the inner cell mass of the blastocyst called?

A

The embryoblast

101
Q

What is the outer cell mass of the embryo called?

A

The trophoblast

102
Q

What is the function of the trophoblast?

A
  • Contributes to the formation of the placenta
  • Produces hCG
103
Q

What happens in hatching?

A

Local digestion of the zona pellucida by enzyme produced by trophoblast cells

104
Q

Where does hatching occur?

A

Opposite the inner cell mass

105
Q

Why does hatching occur opposite the inner cell mass?

A

Minimises risk of enzymatic damage to embryo

106
Q

What happens after the embryo has escaped from the ZP?

A

It begins the process of implantation

107
Q

When does the zygote to blastocyst transformation occur?

A

Between days 14 and 21 of the uterine cycle

108
Q

What primes the endometrium for implantation?

A

Progesterone

109
Q

How does the conceptus recieve its nutrition for the first 2-3 days?

A

Nourished in intrauterine fluid, so is floating in the uterus

110
Q

How does implantation take place?

A

The trophoblast overlying inner cell mass is ‘sticky’, so adheres to epithelium, and implantation commences

111
Q

When does implantation occur?

A

6 days after ovulation

ESA 4 - Reproductive System (31 decks)

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