Fertilisation Flashcards Preview

ESA 4 - Reproductive System > Fertilisation > Flashcards

Flashcards in Fertilisation Deck (110):
1

What is the normal volume of semen? 

2-4ml

2

What is the normal sperm count in semen? 

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

3

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

60%

4

What % of sperm has abnormal morphology in normal semen? 

<30%

5

How long does liquefaction take to occur in normal sperm? 

Within 1 hour

6

What is classified as oligozoospermia?

<20 x 106 sperm/ml

7

Draw sperm with abnormal morphology

9

Where do the glandular components of semen come from? 

  • Bulbourethral glands (Cowper's glands)
  • Seminal vesicles
  • Prostate

 

10

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

5%

11

What do Cowper's gland secrete? 

Alkaline fluid

12

What is the function of Cowper's glands secretions? 

Mucous lubricates the tip of the penis and urethral lining

13

What % of semen volume comes from seminal vesicles? 

60%

14

What does secretions from seminal vesicles consist of? 

  • Alkaline fluid
  • Fructose
  • Prostaglandins
  • Clotting factors

 

15

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

Neutralises the acid in the male urethra and female reproductive tract

16

What is the function of fructose from seminal vesicles? 

ATP production 

17

What is the function of prostaglandins from the seminal vesicles? 

  • Increase sperm motility
  • Increase female genital smooth muscle contraction

 

18

What clotting factor in particular is produced by seminal vesicles? 

Semenogelin 

19

What % of semen volume is from the prostate? 

25%

20

Describe prostate secretion

Milky, slightly acidic fluid

21

What do prostatic secretions consist of? 

  • Proteolytic enzymes
  • Citric acid
  • Acid phosphatase

 

22

What proteolytic enzymes are found in prostate secretions? 

  • PSA
  • Pepsinogen

 

23

What does pepsinogen in semen do? 

Breaks down clotting factors from seminal vesicles 

24

How long does pepsinogen take to re-liqeufy semen? 

10-20minutes

25

What is the purpose of citric acid in prostate secretions? 

For ATP production 

26

When does endometrial proliferation typically occur in the ovarian cycle? 

Days 7-14

27

What does endometrial proliferation occur under the influence of?

Oestrogen

28

What effect does oestrogen alone have on cervical mucus? 

It makes an abundant, clear, and non-viscous

29

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

Easy for sperm to get in 

30

When in the ovarian cycle does ovulation occur? 

Day 14

31

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

Uterine secretory phase

32

What happens during the uterine secretory phase? 

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

33

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

Thick, sticky, mucus plug

34

What does oxytocin do? 

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

35

What are the components of oocyte maturation? 

  • Nuclear maturation
  • Cytoplasmic maturation 

 

36

What happens in the nuclear maturation stage of oocyte maturation? 

  •  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 

 

37

What happens in cytoplasmic maturation stage of nuclear maturation? 

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

 

38

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

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

 

39

What happens to cortical granules in the immature oocyte? 

They are displaced throughout the cytoplasm

40

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

  • Meiosis
  • Maturation
  • Fertilisation
  • Early embryo development

 

41

What is the average number of sperm per ejaculation? 

200-300 million 

42

How many sperm reach the fertilisation site? 

300

43

How many sperm are needed for fertilisation? 

1

44

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

They are sacrified to disperse the zona pellucida

45

How long can sperm survive in the female genital tract? 

Up to 5 days

46

How long can an oocyte survive 

Up to 5 days, then gets phagocytosed

47

What is the fertile period for sperm deposition?

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

48

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

3-4 days

49

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

By cilia and Fallopian tube peristalsis

50

What does sperm need to penetrate? 

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

51

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

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

52

What happens in capacitation? 

Sperm cell membrane changes to allow fusion with oocyte cell surface

53

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

Removal of protein coat of sperm

54

What happens when the protein coat of sperm is removed? 

Acrosomal enzymes are exposed

55

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

It has in intact acrosome

56

What happens when sperm contacts the corona radiata? 

It pushes through the granulosa cells of the corona radiata

57

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

Proteins on sperm head bind to ZP3 proteins on zona pellucida

58

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

Acrosome reaction

59

What happens in the acrosome reaction? 

  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

What is the oocyte plasma membrane divided into? 

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

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

Has smooth surface, devoid of microvilli 

62

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

The portion of oocyte that is rich in microvillar protrusions

63

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

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

64

How is polyspermy blocked?

By the cortical reaction

65

What are the components of the cortical reaction? 

  • Fast block
  • Slow block

 

66

What happens in the fast block cortical reaction? 

  • Electrical change in oocyte membrane
  • Sodium channels open

 

67

What is the resting potential of the oocyte? 

-75mV

68

What is the fertilisation potential of the oocyte? 

+20mV

69

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

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

70

What happens in the slow block cortical reaction? 

  • 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

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

Changes from a beat to a whip-like action 

72

How fast do sperm move in the female genital tract? 

3mm/hour

73

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

Contraction of the female genital organ

74

What happens in syngamy? 

  • 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

What is a polyploid embryo? 

One containing three or more pronuclei 

76

What can polyploid embryos occur due to? 

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

77

What happens in embryonic cleavage? 

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

What is true of cells produced by cleavage? 

They are totipotent

 

 

79

What is meant by cells being totipotent? 

Each cell has the capacity to develop into entire individual

80

When do monozygotic twins occur? 

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

81

What % of twins follow seperation after the first cleavage? 

25-35%

82

When does dizygotic/non-identical twins occur? 

When 2 eggs ovulate, and 2 eggs are fertalised

83

Why is cleavage important? 

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

84

What does cleavage result in? 

An increase in the nuclear/cytoplasmic ratio

85

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

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

86

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

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

is cleavage synchronous? 

No, not all blastomeres divide at the same time

88

When does compaction occur? 

At the 8 cell stage

89

What happens in compaction? 

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

90

When does the morula form? 

At the 16 blastomere stage

91

How long after fertilisation does morula formation occur? 

3-4 days 

92

What happens once the morula has formed? 

The embryo passes from oviduct into uterus

93

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

Ectopic pregnancy occurs

94

Where does the morula implant in an ectopic pregnancy?

Fallopian tube, ovary, or peritoneal cavity

95

What is the problem with an ectopic pregnancy? 

  • Risk of materal haemorrhage
  • Embryo is non-viable

 

96

Why is the embryo non-viable in ectopic pregnancy? 

It has been implanted into a hostile environment

97

When does the blastocyst stage occur? 

5 days after fertilisation 

98

What is the blastocyst? 

A fluid filled cavity that develops into the morula

99

What happens to the cells in the blastocyst stage? 

Loss of totipotency

100

What is the inner cell mass of the blastocyst called? 

The embryoblast

101

What is the outer cell mass of the embryo called? 

The trophoblast

102

What is the function of the trophoblast? 

  • Contributes to the formation of the placenta
  • Produces hCG

 

103

What happens in hatching? 

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

104

Where does hatching occur? 

Opposite the inner cell mass

105

Why does hatching occur opposite the inner cell mass? 

Minimises risk of enzymatic damage to embryo 

106

What happens after the embryo has escaped from the ZP? 

It begins the process of implantation

 

107

When does the zygote to blastocyst transformation occur? 

Between days 14 and 21 of the uterine cycle

108

What primes the endometrium for implantation? 

Progesterone

109

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

Nourished in intrauterine fluid, so is floating in the uterus

110

How does implantation take place? 

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

111

When does implantation occur? 

6 days after ovulation