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Mammalian Reproduction > Fertilisation, Implantation & Gestation > Flashcards

Fertilisation, Implantation & Gestation Flashcards

1
Q

How long does the ovum survive in humans and other mammals?

A

~24 hrs

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2
Q

How long does sperm usually survive in humans and other mammals?

A

About 48 hours but can survive up to 7 days in female reproductive tract

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3
Q

What is capacitation?

A
  • The process of sperm maturation (or activation) that occurs once the sperm leaves the vagina and enters the uterus
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4
Q

What happens during capacitation?

A

Mechanical:
- Sperm brushes on ciliates mucosal cells lining uterus + isthmus of fallopian tube
- Rubs away glycoprotein coat that covers sperm head, exposing receptors + making membrane more permeable to calcium (Ca)

Biochemical:
- Destabilisation of acrosomal sperm head membrane allowing greater binding between sperms + oocyte
- Influx of Ca+ that increases sperm mobility (hyperactivation)

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5
Q

How long does capacitation take roughly?

A

9 hours

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6
Q

What is capacitation aided by?

A

Secretion of lipoproteins, proteolytic & glcosaminoglycans (enzymes) from uterus

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7
Q

For IVF + IUI, when must sperm capacitation take place?

A
  • In vitro
  • Sperm cells collected through ejaculation or from epididymus
  • It is induced by adding media similar to composition of electrolytic composition of fallopian tubes of species involved
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8
Q

Media is used to induce capacitation. What does the media contain?

A
  • Energy substrates (e.g. lactate + pyruvate)
  • Bovine serum albumin or human serum albumin; used as a cholesterol acceptor to remove cholesterol from sperm cell membrane
  • Other chemicals (e.g. calcium + bicarbonate) to induce hyperactivation of sperm motility
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9
Q

What are the several stages to fertilisation?

A
  • Acrosomal membrane of sperm must fuse with egg plasma membrane
  • Sperm must penetrate the zona pellucida (ZP) to gain access to perivitelline space
  • Sperm must recognise + fuse to egg membrane to create single cell
  • Fertilised egg must prevent additional sperm fusing to avoid creating non viable polyploid embryo
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10
Q

How is the acrosomal reaction activated?

A
  • Sperm binds with sperm receptor, zona pellucida glycoprotein 3 (ZP3), on the zona pellucida
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11
Q

In species where fertilisation is external, what occurs to prevent different species from fertilising the egg?

A
  • A protein receptor on the egg, named Bouncer
  • Selects sperm from same species
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12
Q

What is SPACA4?

A
  • Sperm Acrosome Associated 4 Receptor
  • Required for efficient fertilisation
  • Similar to ‘Bouncer’, however not required for interaction of sperm/egg membrane
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13
Q

What happens once the sperm has penetrated the zona pellucida?

A
  • Head of sperm fuses with oocyte vitelline membrane
  • Allows sperm nucleus to enter oocyte
  • Sperm pronucleus formed once in oocyte
  • Ovum undergoes Meiosis II - forms egg pronucleus
  • Sperm nucleus fuses with ovum, enabling fusion of genetic material -> zygote
  • Fertilisation causes increase in Ca2+ levels in cytoplasm, triggering cortical reaction
  • This reaction inactivates ZP3 + hardens vitelline membrane, blocking further sperm from entering + preventing polyspermy.
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14
Q

How does the block to polyspermy occur?

A
  • Second meiotic division of egg
  • Fertilisation-induced Ca2+ release occurs
  • Triggers exocytosis of enzyme-filled ‘cortical’ granules in oocyte
  • Enzymes released into zona pellucida, where they inactivate ZP3
  • Prevents further sperm binding + entry
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15
Q

After fertilisation, what does the ova differentiate into?

A

A morula - a solid ball of cells

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16
Q

Where does the morula remain initially?

A

In ampulla (upper part of fallopian tube), due to constriction between ampulla + lower part of oviduct

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17
Q

What hormone prepares uterus for implantation?

A

Progesterone secretion from corpus luteum

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18
Q

What does the morula develop into?

A

A blastocyst

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19
Q

What is a blastocyst?

A

A single layer, hollow ball of ~50 cells with a fluid-filled cavity + dense mass of cells to one side (inner cell mass)

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20
Q

What does the inner cell mass become?

A

The embryo

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21
Q

What does the outer layer of cells become?

A

The trophoblast - will become the foetal portion of placenta

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22
Q

What 3 stags are involved in implantation?

A
  • Apposition
  • Adhesion
  • Embedding (invasion)
23
Q

What happens during apposition?

A
  • Can only take place during ‘implantation window’, when endometrium is at a particular stage of maturity
24
Q

What happens during the implantation window?

A
  • Changes take place in endometrial cells that bring blastocyst nearer to endometrium + immobilise it
  • Secretion of cytokines that attract blastocyst to a specific region of uterus
  • Inner cell mass of blastocyst aligns closest to decidua
  • Growth factors increase endometrial vascularisation through angiogenesis at site3 of blastocyst apposition
  • Uterine glands grow + produce secretions
25
Q

What are cytokines?

A

Signalling proteins

26
Q

What is the decidua?

A

The mucosal lining of uterus

27
Q

What happens during the adhesion stage?

A
  • A stronger attachment of blastocyst takes place
  • Trophoblastic cels release protein-digesting enzymes, allowing finger-like cords of trophoblastic cells to penetrate into endometrium
  • As these cells penetrate decidua, they differentiate to become a new type of cells - syncytiotrophoblasts
  • Cell adhesion proteins (integrins) ensure adhesive nests between embryo + endometrium
  • During this stage, blastocyst can still be eliminated + pregnancy aborted by flushing it out of uterus
28
Q

What happens during the embedding (invasion) stage?

A
  • Embedding continues with synctiotrophoblasts, reaching basal membrane beneath decidual cells, penetrating it + further invading uterine tissue
  • Endometrial tissue at contact site undergoes dramatic changes due to chemical messengers released from blastocyst
  • Endometria cells secrete prostaglandins that increase local vascularisation + nutrient storage
  • Blastocyst embeds in nutrient rich decidua + a layer of endometrial cells then covers surface
  • Syncytiotrophoblasts come into contact with maternal blood + form chorionic villi

This is the beginning of formation of placenta

29
Q

What is placentation?

A

Formation of placenta
Formed from endometrium layer of uterus + embryonic membranes

30
Q

What is the function of the placenta?

A
  • Transfer of nutrients from maternal blood to foetus
  • Removal of waste products
31
Q

Name the 3 extra-embryonic membranes

A
  • Chorion (outside, attaches to uterus)
  • Amnion (inside, nearest embryo)
  • Allantois (middle, fluid-filled bag)
32
Q

What is collected in the allantois?

A

Foetal urine produced during pregnancy

33
Q

What is amniocentesis?

A
  • A procedure that involves removing + testing a small sample of cells from amniotic fluid
  • Used primarily in prenatal diagnosis of chromosomal abnormalities (if suspected) as well as form sex determination
  • Carries risks of miscarriage + infection
34
Q

Name a newer technique used in replacement to amniocentesis

A
  • Cell-free DNA (cfDNA)
  • Non-invasive prenatal diagnosis for assessing potential problems
  • Cell-free foetal DNA is foetal DNA that enters maternal blood via placenta + circulates freely in maternal blood
35
Q

How can cell-free foetal DNA be sampled?

A

Simple venipuncture

36
Q

When does the chorion form?

A

By day 12 when the trophoblastic layer is 2 cells layers thick
Trophoblast expands + forms network of cavities in decidua
Maternal blood leaks into these cavities
Finger-like projections (chorionic villi) extend into pools of maternal blood + receive nutrients

37
Q

When does the placenta become functional (not fully developed)?

A

By 5 weeks

38
Q

What is a diffuse placenta?

A

Almost the entire surface of foetal membranes involved in formation of placenta

39
Q

What is a cotyledonary placenta?

A

Multiple, discrete areas of attachment called cotyledons are formed by interaction of patches of allanto-chorion with endometrium

40
Q

What is a zonary placenta?

A

Placenta forms a complete or incomplete band of tissue surrounding foetus

41
Q

What is a discoidal placenta?

A

A single placenta formed is discoid in shape

42
Q

How are the different types of placenta classified?

A

By how many of the potential layers of maternal tissue separate maternal blood from foetal blood

43
Q

What does epitheliochorial mean?

A

All maternal tissue layers are present
E.g. pig, horse

44
Q

What does endotheliochorial mean?

A

Two maternal tissue layers present
E.g. dog, cat

45
Q

What does haemochorial mean?

A

No maternal tissues separate the two
Nutrients + O2 simply diffuse into foetal cells from maternal blood

46
Q

What hormone breaks down progesterone?

A

Prostaglandin

47
Q

Why must progesterone levels be maintained at sufficiently high levels?

A
  • Implantation of developing embryo in endometrium of uterus can take place
  • Endometrium is maintained in state of conducive to embryonic survival
48
Q

What does maternal recognition rely on?

A

Signal from embryo that prevents literal regression, allowing corpus luteum to persist + continue to secrete progesterone

49
Q

What happens if a signal is not delivered to the mother?

A

Progesterone conc will decline + pregnancy terminated

50
Q

What does hCG stand for?

A

Human Chorionic Gonadotrophin
- Hormone

51
Q

What does hCG do?

A
  • Stimulates continued secretion of progesterone by the corpus luteum + may also block signals in corpus luteum that causes it to regress
  • This maintains endometrium + survival of blastocyst whilst placenta develops
52
Q

How long does the corpus luteum continue to produce progesterone + oestrogen before its function declines?

A

~8 weeks

53
Q

What hormone do dogs depend on during pregnancy?

A

Progesterone

54
Q

What is gestation?

A

The period between fertilisation and parturition

Mammalian Reproduction (16 decks)

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