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Module 5 Week 3 > Early Embryo Development And Maternal Recognition Of Pregnancy > Flashcards

Early Embryo Development And Maternal Recognition Of Pregnancy Flashcards

1
Q

at fertilisation, 2 haploid gametes fuse to form…

A

New diploid zygotes: spermatozoa perspective

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2
Q

Describe the steps of fertilisation from the spermatozoa perceptive
(Formation of male proncleus)

A

-Capacitated sperm reach ampulla (need to be motile enough to penetrate)
-interact with Zona Pellicuda via ZP3 protein—> leads to sperm-egg fusion (many sperms will fuse to egg but only one form the final zygote)
-spermatozoa undergo acrosome reaction; outer sperm head membrane dissolves
-dissolving causes release of proteolytic enzymes & uncovering of ZP2 receptors
-these enzymes help with penetration of the ZP
-after penetration, sperm-egg membrane fusion occurs with help of specific proteins on sperm head
-nucleus enters oocyte and decondenses
-this forms the male pronucleus

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3
Q

Capacitated cell meaning

A

Undergone maturation

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4
Q

Describe the steps of fertilisation from the secondary oocyte (the egg) perspective
(Formation of female pronuleus)

A
  1. 1st spermatozoon enters egg; calcium waves are released across the cytoplasm
  2. Calcium waves lead to;
    -cortical granule reaction-> the hardening of the ZP
    -polyspermy block-> no more spermatozoa can fuse and make connection with plasma membrane
  3. Egg in metaphase 2 resumes in meiosis II leads to formation of female pronucleus
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5
Q

What happens after both male and female pronucleus have formed?

A

Genetically new zygote has formed; containing 2 separate pronuclei and separate maternal & paternal chromosomes
-there is an immediate entry into the first cleavage division

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6
Q

In a zygote, can you tell which. Pronucleus is male (paternal) and which is female (maternal)

A

No, you cannot

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7
Q

Name the structures of the fertilised egg

A

On anki

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8
Q

Name the steps involved in early embryo development, after fertilisation, which lead to maternal recognition

A
  1. Cleavage
  2. Blastocyst formation
  3. ‘Pregnancy’ signal
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9
Q

1st step of embryo development:
1. Embryo cleavage

A

Development of the single fertilized cell (zygote) into a multicellular complex within the Zona Pellucida (Z.P.)

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10
Q

Describe the steps of Embryo cleavage; 1st step of embryo development

A

-Zygote forms into morula- propelled downwards within uterine tubes
-morula is made up of 16 blastomeres- these are totipotent
-cell becomes progressively smaller
-morula enters uterine horn
-morula divides until its reached 64 divisions; at this stage it has formed the blastocyst- this is the beginning of cell differentiation

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11
Q

2nd step of embryo development;
2. Blastocyst development

A

Blastomeres in the morula become very compacted and begin to form tight junctions with adjacent cells, & blastocyst development begins

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12
Q

Describe the steps of blastocyst development

A

-Cell divisions continue in morula—> compression of blastomeres & compaction
-cell differentiation begins= loss of totipotency
-fluid absorption occurs—> central fluid filled cavity is formed, forming the blastocyst

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13
Q

What are the 3 types of blastocyst?

A

Trophectoderm/trophoblast
Blastocoele (fluid filled cavity)
Inner cell mass (ICM) cells

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14
Q

Which of the 3 types of blastocysts remain pluripotent?

A

ICM cells

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15
Q

What do the trophoblasts become in embryo
What do the ICM cells become?

A

-these become outermost layer of placenta
-these become the proper embryo

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16
Q

3rd step of embryo development
3. Hatching & expansion of the blastocyst

-what must the blastocyst do to continue growing?

A

Needs to break free from the Z.P to continue growing

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17
Q

Describe the steps of hatching step of embryo development

A

-Blastocyst grows
-zona pellicuda breaks and this is called hatching of the blastocyst
-blastocyst begins to elongate and grow and expand due to trophoblast cells multiplying rapidly
-this leads to elongation of the embryo

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18
Q

What happens after hatching

A

Either implantation or attachment to maternal endometrium in the uterus
Implantation; invasively implants itself or just attaches itself non invasively

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19
Q

What do the trophectoderm/trophoblast cells provide after hatching?

A

Provide signals for maternal recognition of pregnancy eg ruminant, humans

20
Q

Which blastocyst cells form the embryonic shield on surface of expanding embryo

A

ICM cells

21
Q

How many days after fertilisation does hatching occur in the bovine?

A

8-10 days

22
Q

Degree of embryo expansion reflects…

A

Different strategies for signalling ‘pregnancy’ to dams

23
Q

Which embryo expansion image edicts which animal?

A

On anki

24
Q

Which animal is the exception to expansion of blastocyst and why

A

The horse- develops a capsule round the embryo, in addition it doesn’t elongate, but remains spherical- called embryonic vesicle

25
Q

What do the ‘pregnancy’ signals coming from the trophoblast cells prevent?

A

Prevent luteolysis in species with a cyclic CL lifespan that is shorter than gestation (pretty short lifespan)- this is to preserve the pregnancy and continue its growth, also means no other ovulation can occur at the same time

26
Q

What is the importance of maintained function in the corpus luteum

A

For maintenance of progesterone secretion from the CL

27
Q

What are the effects of progesterone on the reproductive tract?

A
  1. Stimulates endometrial gland secretions essential to support embryo development
  2. Reduces contractility of the reproductive tract thus leads to embryo quiescence
  3. Increases uterine growth
  4. Exerts negative feedback on hypothalamic GnRH secretion: no surges, no pre-ovulatory follicle development or mating
28
Q

What is maternal recognition of pregnancy?

A

The prevention of luteolysis initiated by signals from the embryo

29
Q

In which species are signals needed to prevent luteolysis?

A

Species with a Short CL lifespan

30
Q

Which species have a short CL lifespan and require pregnancy signals to prevent luteolysis?

A

Cow
Ewe
Sow
Mare

31
Q

Which mechanism is used to stop luteolysis in the:
-cow
-ewe
-sow
-mare

A
  1. Suppresses Oxytocin Receptors
    2.Suppresses Oxytocin Receptors
    3.Redirects PGF2a into uterine lumen
    4.Suppresses localised PGF2a synthesis
32
Q

Name the maternal recognition hormone responsible for preventing luteolysis in each of these animals:
-cow
-ewe
-sow
-mare

A

-Bovine Trophoblast protein
-Ovine Trophoblast protein
-Oestradiol
-Vets not sure about the mare

33
Q

The more functional the CL, the more likely…

A

Is the maternal recognition Of pregnancy

34
Q

What is the early embryo nourished by?

A

Endometrial secretions

35
Q

When equine embryo Hatches it develops into…

A

free-moving embryonic
vesicle travelling up and down uterine horns until day 16
(Diagram on anki)

36
Q

What does the movemnt of embryonic vesicle in horse do?

A

signals maternal recognition of pregnancy = prevents CL regression i.e regulates luteolysis

37
Q

which species have active luteolysis and which have passive luteolysis?

A

Active;
Cow
Ewe
Sow
Mare

Passive;
Human
Rodent

38
Q

Name the maternal recognition hormones found in humans and rodents

A

Humans- Human Chorionic Gonadotrophin
Rodents- prolactin pulses, Chorionic Gonadotrophin,
PGE2, placental lactogens, prolactin-like pepide

39
Q

What do species with passive luteolysis need extra of to prevent luteolysis?

A

extra luteotrophic stimuli from the embryo(s) must prevent CL regression until the placenta can take over progesterone production

40
Q

In early pregnant human females, enhancement of luteotrophic stimuli is via… what does it do?

A

hCG which stimulates LH receptors and progesterone synthesis continues

41
Q

True or false: In species with a long CL lifespan such as the bitch no embryonic signals are needed to prolong CL function

A

TRUE

42
Q

During fertilisation, which process do spermatozoa have to undergo specifically ybefore they can penetrate the zona pellucida of the egg

A

Acrosome and capacitation

43
Q

What stage of meiosis are oocytes in at the time of fertilization?

A

Metaphase II

44
Q

What is a fertilised oocyte called?

A

Zygote

45
Q

How quickly does first cell division occur after fertilization?

A

22-24 hours

Module 5 Week 3 (7 decks)

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