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Initiation of pregnancy Flashcards

1
Q

What is the name of the fertilised egg?

A

Zygote surrounded by a zona pellucida

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2
Q

What is the precursor to the ovum?

A

Oocyte surrounded by a cumulus

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3
Q

What is pronuclei?

A

Nuclei in the egg ovum

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4
Q

Stages of embryonic development?

A

1) Zygote
2) Blastomere (totipotent)
3) Morula, which is a 16-32 cell structure (pluripotent)

Morula can give rise to a blastocyt, containing the epiblast and hypoblast.

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5
Q

How does the blastocyst form?

A

Morula absorbs fluid between cells of the ICM and tight junctions develop, allowing it to differentiate into a blastocyst. This has an inner cell mass that becomes the embryo and outer cells called the trophoblast.

The blastocyst stage is when the fertilised structure can leave the fallopian tubes and enter the uterus for implantation.

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6
Q

What is the epiblast?

A

Gives rise to the 3 germ layers- ectoderm, mesoderm and endoderm.

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7
Q

What is the hypoblast?

A

Gives rise to the yolk sac and chorion.

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8
Q

What embryonic structure signifies the first cell differentiation?

A

Trophectoderm which is the first epithelium that forms in Third week after fertilisation.

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9
Q

When does the early embryo implant into the uterus?

A

6 days after fertilisation as a blastocyst, using the synctiotrophoblast.

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10
Q

How does the zygote prepare for implantation?

A

Day 6: the blastocyst hatches from the zona pellucida. The trophoblast allows it to bind to the endometrium of the uterus and invade it for implantation.

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11
Q

What is the first epithelium?

A

Trophoectoderm

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12
Q

Which part of the embryo implants into the uterine wall?

A

Trophoectoderm

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13
Q

How long is a ‘normal’ human pregnancy?

A

37-42 weeks from the first day of the last menstrual period.

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14
Q

What is the process of implantation?

A

Day 6: morula migrate down the fallopian tube and binds to the epithelial cells of the uterine endometrium of the uterus lining via microvilli glycoproteins .

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15
Q

What is the endometrium?

A

Mucuous membrane of the uterus

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16
Q

What happens to the uterus following implantation?

A

Blastocyst burrows by digesting into the endometrium, leaving a hole which is filled with a blood clot that eventually degenerates.

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17
Q

What does implantation trigger?

A

Triggers the trophoblast to differentiate into an inner layer, called the cytotrophoblast and an outer layer called the syncytiotrophoblast.

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18
Q

How does the synctiotrophoblast form?

A

Trophoblast that is in contact with the uterine endometrium causes these cells to lose their cell membrane and form a syncytium called the synctiotrophoblast. It surrounds the embryo.

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19
Q

What is the cytotrophoblast?

A

Inner layer of the trophoblast which gives rise to the synctiotrophoblast. It also forms the primary chorionic villi, the membrane full of blood vessels which allows exchange of nutrients with mother.

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20
Q

What is the role of the synctiotrophoblast?

A

Aids the embryo in attaching to the endometrium (mucous membrane of the uterus) due to finger-like projections, which allows access to maternal blood supply and remodelling of the spiral arteries of the endometrium.

It produces proteolytic enzymes for endometrium digestion.

The synctiotrophoblast prevents degredation of the corpus luteum by producing HCG.

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21
Q

Where is progesterone produced in the early phase post-fertilisation?

A

By the synctiotrophoblast, which occurs by conversion from cholesterol.

The synctiotrophoblast also produces hCG after 2 weeks post-fertilisation to act on the corpus luteum and increase progesterone produciton.

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22
Q

What happens following implantation?

A

Decidual reaction where the endometrial stroma differentiates into metabolically active secretory cells called decidual cells. Along with this, the endometrial glands enlarge, and the uterine wall is more vascularised.

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23
Q

What is the amniotic cavity?

A

A layer between the epiblast and the inner cytotrophoblast. It is surrounded by two layers
1) amnion
2) chorion

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24
Q

What is the amnion?

A

Tough membrane surrounding the developing embryo, which contains fluid.

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25
What is the chorion?
Outermost membrane which is responsible for eliminating foetal waste and becomes the future placenta for the exchange of blood and gases between the mother and the foetus.
26
Where does fertilisation occur in the uterus?
Ampullar-isthmic junction of the uterine tube. This is in the most superior aspect posteriorly in the uterus, where the fundus lies. Sperm motility and the contraction of the cilia in the oviduct aids this.
27
What is capacitation?
Sperm requires adaptations via the process of capacitation to induce fertilisation due to the inhibitory factors present in seminal fluid. It is driven by calcium. .
28
What are the types of capacitation?
Removal of inhibiting factors present in the seminal fluid 1) Removal of cholesterol and seminal glycoproteins from plasma membrane which increases permeability to Ca2+ ions for acrosome reaction. Acrosome reaction: Change in sperm shape via increase intracellular Ca2+. Hyperactivation allows whiplash movement of sperm and later acrosome degeneration which contains two enzymes. Hyaluronidase allows digestion of the cumulus.
29
How does capacitation occur?
1)Increased activity of adenylyl cyclase to increase cAMP. 2)This activates the second messenger for tyrosine phosphorylation. 3)Causes activation of Ca2+ channels which increases intracellular Ca2+ levels for the acrosome reaction
30
What are the features of capacitation?
Inhibition of capitation inhibiting factors such as cholesterol and seminal glycoproteins: ->Removal of seminal glycoproteins and glycoprotein coat added in epididymis maturation which prevent zona pellucida binding. -> Removal of cholesterol from plasma membrane ->Conversion of sperm from linear swimming to whiplash movement for movement progression in the oviduct.
31
What is the acrosome reaction?
Exocytotic event of hydrolytic enzymes to be released from sperm acrosome to digest the cumulus, initiated when the egg makes contact with the zona pellucida and requires an increase in intracellular calcium.
32
What is contained in the acrosome?
Acidic vacuole containing hydrolytic enzymes which breaks down hyaluronic acid for penetrating the zona pellucida of the oocyte.
33
What happens in fertilisation?
Sperm burrow through the corona radiata and bind to receptors in the zona pellucida. This triggers release of enzymes from the sperm acrosome to allow nuclear DNA to be released and combine with egg nucleus.
34
Which receptors do sperm bind to on the zona pellucida?
Glycoprotein ZP2 and ZP3
35
What is the role of the Glycoprotein ZP2 receptor?
Important in fertilisation for the attachment of the sperm to the zona pellucida.
36
What is the role of the Glycoprotein ZP3 receptor?
When bound to, induces the acrosome reaction
37
What happens once sperm reaches the zona pellucida?
Entry of the sperm into the oocyte allows cell membrane interaction and calcium increase. This triggers the cortical reaction where the cortical granules below oocyte cell membrane are released in the perivitelline space. This causes a conformational change to ZP2 and ZP3 which prevents any additional spermatozoa penetrating the oocyte and causing polyspermy.
38
What is the perivitelline space?
The perivitelline space is the space between the oocyte and zona pellucida.
39
What is an important component in the sperm cell for syngamy?
Syngamy is the fusion of two pro nuclei. Once oocyte engulfs head and tail of sperm, the phospholipase C in sperm called Factor PLZ-zeta is important for the upregulation of calcium to break down the maturation promoting factor that arrests the oocyte in metaphase II.
40
What happens following fertilisation?
Zygote travels down the fallopian tube
41
Which stage of cell division is the oocyte arrested in pre-fertilisation?
Meiosis II prophase. This is caused by the cytostatic factor which maintains a high level of the CDK-maturation activating factor.
42
What is the role of maturation promoting factor?
CDK in G2 checkpoint which arrests the sperm in cell cycle from G2 to metaphase II. This molecule is broken down in the sperm following increase in calcium due to acrosome reaction during fertilisation.
43
What is maturation activating factor formed of?
Cytostatic factor and cyclin B.
44
What causes progression of oocyte cell cycle development?
Rise in intracellular calcium via phospholipase C due to acrosome activation. This degrades cytostatic factor and maturation activating factor.
45
What is a polar body?
Haploid cell formed during oogenesis which has very little cyptoplasm that normally undergoes apoptosis.
46
What is a 2pn embryo?
Standard embryo with 2 pronuclei containing genetic material from 2 parents
47
What is a 3pn embryo?
3pn Embryo with 3 pronuclei due to fertilisation of a single ovum with two sperm
48
What is polyspermic zygote?
Fertilisation of egg by more than one sperm
49
What is a digynic zygote?
3pn embryo caused by meiotic error with 2 female pronuclei and 1 male pronuclei.
50
What is a dispermic zygote?
3pn zygote formed by meiotic error with 2 maternal pronuclei and 1 male pronuclei.
51
What is a parthonogenetic zygote?
1pn- Development of oocyte without fertilisation from a sperm
52
How long do sperm survive in the reproduction tract?
5 days
53
How long do eggs survive after ovulation?
24 hours
54
What is the role of hyaluronidase?
Digest the hyaluronic acid
55
How do hormones change in pregnancy?
Decrease in levels of LH;increase in oestrogen and progesterone
56
Which hormone is essential for pregnancy maintenance?
Progesterone and pregnenelone (precursor to oestrogen)
57
Where is pregnenelone produced?
Synthesised in the adrenal gland which can give rise to oestrogen, progesterone and testosterone.
58
What is conceptus?
Embryo in the uterus
59
Which hormone is important in the first trimester?
Chorionic gonadotrophin produced by the synctiotrophoblast. It rises after fertilisation and acts on the corpus luteum to produce progesterone. This prevents menstruation and thicken the uterine lining. It falls after the first trimester.
60
Where is progesterone produced?
Precursor is cholesterol and produced from the synctiotrophoblast and corpus luteum
61
How is oestrogen produced during development?
Androgens are produced in the foetal adrenal gland. They are aromatised in the placenta to form oestrogen.
62
How do identical twins form?
Development of two babies from a single origin zygote. Majority form via early embryo splitting.
63
What is incomplete splitting?
Complication of monozygotic twins where embryo does not split and results in conjoined twins.
64
What is the consequence of the inner cell mass splitting?
Twins which share the same placenta but different amniotic sacs. Monochorionic but diaminotic.
65
What is the consequence of the embryonic disc splitting?
Embryonic disc is the future ectoderm and endoderm. Splitting of this causes Monochorionic twins-both foetuses are in the same placenta and will also share the same amniotic sac.
66
What are alternative methods of identical twins occurring?
Splitting of the inner cell mass Fused dichorionic: fusion of placenta of two twins Embryonic disc splits Incomplete split
67
What are dizygotic twins?
Fertilisation of two separate eggs with two separate sperm in the same pregnancy
68
What is the process of IVF?
Ovary is super-ovulated and eggs are removed from the follicles. It is co-incubated with spermatozoa for 24 hrs and reimplanted into the uterus at blastocyst stage.
69
What happens prior to IVF?
Downregulation followed by superovulation.
70
What is downregulation?
Prevents the release of FSH and LH to prevent premature ovulation and make sure all eggs progress to the pre-antral stage, using GnRH agonists.
71
How does upregulation occur in IVF?
Injection with very high levels of FSH which acts on granulosa cells to cause high levels of oestrogen which maintain the pre-antral follicles and increase the number available. HCG is also injected because it is a form of LH and is used to further stimulate egg maturation before retrieval.
72
How does IVF occur?
Co-incubation of oocytes and sperm for 24 hours for fertilisation to occur. For infertile men, Intracyptoplasmic sperm injection: injecting live sperm into a harvested egg Embryo culture: immature embryo matures and grows on a dish
73
What is azoospermia?
No sperm in the ejaculate caused by ejaculatory failure or spermatic cord injury
74
What is the UK fertility regulation?
Human Fertilisation and Embryology Authority
75
What are the types of intracyptoplasmic sperm injections?
Testicular sperm extraction: removal of part of the testes for biopsy Testicular sperm aspiration: Sample of semen directly from testes Percutaneous sperm aspiration: sample of seminal fluid from epididymis Microepididymal sperm aspiration: sample of seminal fluid from epididymis
76
What is the most common cause of infertility in couples?
1) Male infertility 2) Idiopathic 3)Ovulatory disorder 4) Tubal disease 5) Endometriosis
77
What is TFR?
Total fertility rate- total number of children a woman can have if she survived to the end of her reproductive cycle.
78
Which factors affect the success rate of IVF?
Younger age, healthy diet, frozen fertilised eggs, donor eggs, previous pregnancy
79
What are the risks of IVF?
Multiple births due to previous policy of multiple embryo insertion to increase success rate. It can occur with single embryo insertion due to splitting of the inner cell mass,
80
What is the role of folic acid in pregnancy?
Prevents birth defects such as the spina bifida where there is a gap in the spinal cord, especially in the first 12 weeks of pregnancy.
81
What is the role of iron in pregnancy?
Important in immune defence and preventing oxidant damage.
82
What is the role of Vitamin D in pregnancy?
Essential for bone growth to prevent fractures or rickets in newborns.
83
What is the role of calcium in pregnancy?
Prevent osteoporosis as it is important for foetal teeth and bone development
84
How is the majority of IVF treatment funded?
Privately- higher birth rates in the North England than South
85
What happens prior to implantation?
Prior to fertilisation, development occurs in the oviducts where the blastocyst passes through the uterotubule to implant into the uterus.
86
How is the development of the egg triggered during fertilisation?
Sperm contains a phospholipase C protein called Factor PLZ-zeta that activates ryanodine receptors for increase in intracellular calcium
86
Which embryonic structure becomes the future placenta?
Chorion.
87
What is the regulatory component of polyspermy?
Cumulus layer of the egg.

Year 2 (247 decks)

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