More embryology Flashcards

1
Q

Define pre-embryonic

A

A fertilized ovum up to 14 days old, before it becomes implanted in the uterus

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2
Q

Embryonic

A
  • The fertilized egg of a vertebrate animal following cleavage before definite form arises. 3-8 weeks.
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3
Q

Fetal

A

In humans the fetal period extends from the first day of the ninth week of intrauterine life until birth. 9-38 weeks.

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4
Q

Discuss the changes taking place as the fertilised human ovum (zygote) travels down the Fallopian (uterine) tube to the uterus

A
  • Oocyte is released from the ovary - Travels along the Fallopian (uterine) tube - Is fertilized by sperm in the ampulla - Fertilised oocyte is called the zygote - Ideal site for implantation is the posterior uterine wall
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5
Q

Zygote

A

A fertilised ovum/oocyte

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6
Q

Cleavage

A

The dividing of cells into two masses known as blastomeres. First cleavage happens ~30 hours after fertilisation (resting period)

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7
Q

Zona Pellucida

A

The glycoprotein ‘shell’ to prevent polyspermy

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8
Q

Morula

A

The result of cleavage of the fertilised oocyte, each cell is Totipotent

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9
Q

Ovary

A

The female reproductive organ producing oocytes/eggs for fertilisation

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10
Q

Fallopian tube

A

A tube the oocyte travels along to reach the uterus. The egg is fertilised at the ampulla of the fallopian tube.

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11
Q

Uterus

A

Female reproductive organ where implantation of the zygote and growth of the embryo occurs

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12
Q

Blastocyst

A

Formed from the compaction of cells that make up the morula

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13
Q

Trophoblast

A

(Outer cell mass) will later form support structures for the embryo (placenta)

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14
Q

Embryoblast

A

(Inner cell mass) will later become the bilaminar disk

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15
Q

Implantation

A

The attachment of the Blastocyst to the wall of the uterus at day 6 – 7

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16
Q

Cytotrophoblast

A

(Derivative of Trophoblast) Placental membrane around the yolk sac

17
Q

Syncytiotrophoblast

A

(Derivative of Trophoblast) Cells that invade maternal sinusoids (irregular blood vessels) resulting in uteroplacental circulation.

18
Q

What happens in week 1, within 30 hours of oocyte fertilisation?

A

Cleavagebegins 30 hours after fertilisation Results in two blastomeres of equal size This forms a morula, made up of totipotent cells. Zona pellucida forms, which prevents polyspermy.

19
Q

What happens at week 1, day 4?

A

Compaction At eight cell stage, blastomeres making up morula compact to form the Blastocyst Formation of first blastocyst cavity Embryoblast (Inner cell mass) Trophoblast (Outer cell mass)

20
Q

What changes occur in cells before and after compaction?

A

Before compaction, all cells totipotent. Afterwards, simply have multilineage potential.

21
Q

Outline an assisted reproduction technique `

A

Oocytes are fertilised in vitro and allowed to divide to the 4-8 cell stage. Morula is then transferred into the uterus.

22
Q

What is PGD?

A

Pre-implantation genetic diagnosis a single cell can be safely removed from the morula and tested for serious heritable condition prior to transfer of the embryo to the mother.

23
Q

What happens at day 5?

A

Hatching - Blastocyst hatches from the zona pellucida - No longer constrained and free to enlarge - Can now interact with the uterine surface to implant

24
Q

What happens at days 6-7?

A

Implantation Begins (Day 6–7) - The conceptus now has 107 cells. - 8 will make the embryo - 99 will begin the development of the foetal membrane

25
Q

Why is second week called the week of twos?

A

Differentiation Embryoblast–> Epiblast, Hypoblast Trophoblast–> Syncytiotrophoblast, Cytotrophoblast The bilaminar disk and amniotic cavity are formed.

26
Q

Describe theprocess of implantation

A

Implantation is interstitial (invasive, surrounded and embedded). The uterine epithelium is breached and the conceptus implants within the uterine stroma.

27
Q

What problems can occur as a results of an implantation defect? (Implantation at inappropriate site)

A

Ectopic Pregnancy – Implantation at site other than uterine body (most commonly fallopian tube). Can quickly become a life-threatening emergency. Placenta Praevia – Implantation in lower uterine segment. Placenta grows across cervical opening. Requires C-section delivery.

28
Q

Describe Week 2, Day 9 – 10

A

Embryonic pole (top bit) Rapid development of Syncytiotrophoblast Abembryonic pole (bottom bit) Primitive yolk sac formed by Heuser’s membrane spreading across the Blastocyst cavity. Yolk sac membrane is in contact with the cytotrophoblast layer.

29
Q

Week 2, Day 11

A

Primitive yolk sac membrane is pushed away from the cytotrophoblast layer by an acellular extraembryonic reticulum. Reticulum is later converted to extraembryonic mesoderm by cell migration

30
Q

Week 2, Day 12

A

Maternal sinusoids invaded by syncytiotrophoblast. Lacunae (blood lakes) in trophoplast become continuous with sinusoids. Uteroplacental circulation begins. Uterine stroma prepares for support of the embryo.

31
Q

Week 2, Day 13

A

Formation of secondary yolk sac Pinches off from the primary yolk sac A.k.a. Definitive yolk sac

32
Q

Week 2, Day 14

A

Spaces within the extraembryonic mesoderm merge to form the chorionic cavity The Connecting Stalk suspends the embryo and its cavities in the chorionic cavity. The connecting stalk is a column of mesoderm, and is the future umbilical cord. Bleeding around now can be confused with menstrual bleeding.

33
Q

What has happened at the the end of the second week?

A
  • The conceptus has implanted - The embryo and its two cavities (Amniotic cavity and Yolk sac) are - Suspended by a connecting stalk in a - Supporting Sac (Chorionic Cavity)
34
Q

Give some early pregnancy loss statistics

A

Åpproximately 50% of all zygotes are lost in the first 2-3 weeks 15% of all diagnosed pregnancies will miscarry 1% women suffer from recurrent miscarriage (miscarriage in 3 consecutive pregnancies)