Embryology: First Week of Development Quiz

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Questions and Answers

What is the function of the syncytiotrophoblast during blastocyst development?

  • It gives rise to the embryonic part of the placenta
  • It actively invades the epithelium and underlying stroma of the endometrium (correct)
  • It forms the roof of the exocoelomic cavity
  • It produces cells that fuse with the cytotrophoblast

When does uteroplacental circulation start?

  • Day 3
  • Day 5
  • Day 6
  • Day 12 (correct)

What is the role of the primary chorionic villi?

  • To establish uteroplacental circulation (correct)
  • To provide a site for implantation
  • To support the developing embryo
  • To form the primary umbilical vesicle

What characterizes the decidua basalis?

<p>It underlies the implantation site (C)</p> Signup and view all the answers

Which structure provides a site for selective transfer of nutritive materials to the embryonic disc?

<p>Primary umbilical vesicle (B)</p> Signup and view all the answers

What happens to the decidua at parturition?

<p>It is shed during childbirth (A)</p> Signup and view all the answers

What are the main events during fertilization?

<p>Capacitation, acrosomal reaction, penetration of corona radiata and zona pellucida, binding and fusion of the oocyte and sperm cell membranes (D)</p> Signup and view all the answers

What is the effect of capacitation on spermatozoa?

<p>Ability to bind to the zona pellucida, ability to undergo the acrosome reaction, acquisition of hypermotility (C)</p> Signup and view all the answers

What are the phases of implantation?

<p>Apposition, adhesion, penetration (C)</p> Signup and view all the answers

What defines important results of fertilization?

<p>Binding and fusion of the oocyte and sperm cell membranes, metabolic activation of the egg (A)</p> Signup and view all the answers

What are the main events during pre-implantation embryonic development?

<p>$8C$, $4C$, $2C$ (A)</p> Signup and view all the answers

What is meiotic arrest characteristic of?

<p>$MII$ (Secondary oocyte) (A)</p> Signup and view all the answers

What is the role of adenylyl cyclase activity in sperm capacitation?

<p>Increasing cAMP levels, tyrosine phosphorylation, and Ca2+ channel activation (C)</p> Signup and view all the answers

What is the function of ZP3's oligosaccharides in the zona pellucida?

<p>Mediating initial sperm binding (A)</p> Signup and view all the answers

What occurs during the acrosome reaction?

<p>Sperm binds to ZP3 on the zona pellucida, leading to Ca2+ influx and release of enzymes (D)</p> Signup and view all the answers

What aids in the dispersal of corona radiata cells to allow sperm penetration?

<p>Enzymes from the sperm and tubal mucosa (B)</p> Signup and view all the answers

What prevents polyspermy after fertilization?

<p>ZP3 acting as a sperm receptor and preventing polyspermy after fertilization (A)</p> Signup and view all the answers

What triggers the second meiotic division in the oocyte following fertilization?

<p>Ca2+ influx from the acrosome reaction (B)</p> Signup and view all the answers

What is genetically unique about the zygote?

<p>Its chromosomes coming from both parents leading to biparental inheritance (B)</p> Signup and view all the answers

What occurs after pronuclei formation and their fusion in the zygote?

<p>Cleavage into blastomeres followed by compaction before inner cell mass and trophoblast formation (A)</p> Signup and view all the answers

What happens during cortical and zona reactions in a fertilized egg?

<p>The release of trypsin-like proteases and a loss of sperm binding due to ZP2-3 alterations. (A)</p> Signup and view all the answers

Flashcards

Syncytiotrophoblast

The outer layer of the blastocyst that actively invades the endometrium and contributes to the placenta.

Uteroplacental Circulation

The point at which blood circulation between the mother and fetus is established.

Primary Chorionic Villi

The initial finger-like projections that develop from the trophoblast and play a crucial role in establishing the uteroplacental circulation.

Decidua Basalis

The specialized part of the endometrium that underlies the implantation site and provides crucial support to the developing embryo.

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Primary Umbilical Vesicle

A sac connected to the embryo that acts as a temporary site for nutrient and gas exchange before the placenta forms.

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Decidua Shedding

The shedding of the lining of the uterus, including the decidua basalis.

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Fertilization Events

A series of steps that a sperm must undergo to fertilize an egg.

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Capacitation

Changes in the sperm that enable it to penetrate the egg.

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Acrosomal Reaction

The release of enzymes from the sperm's acrosome that break down the zona pellucida, allowing penetration.

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Binding and Fusion

The first physical contact between the sperm and the egg.

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Cleavage

The process of the zygote dividing into smaller cells, eventually forming a blastocyst.

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2C, 4C, 8C

The stage of cell division where the zygote goes from a single cell to two cells, two cells to four, and so on.

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Meiotic Arrest (MII)

The arrest of the egg's cell division at metaphase II.

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Implantation

The process of implantation where the blastocyst attaches to the uterine lining.

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Apposition

The first stage of implantation where the blastocyst comes into contact with the endometrium.

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Adhesion

The second stage of implantation where the blastocyst adheres to the endometrium.

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Penetration

The third stage of implantation where the blastocyst burrows into the endometrium.

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ZP3

The protein on the zona pellucida that binds to the sperm.

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Ca2+ Influx

The influx of calcium ions into the sperm that triggers the acrosome reaction.

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Polyspermy Prevention

The process of the egg preventing multiple sperm from entering.

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Biparental Inheritance

The process of combining genetic material from both parents to create a unique offspring.

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Pronuclei Formation and Fusion

The process of the fertilized egg forming two pronuclei that fuse to form the zygote.

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Study Notes

  • Chu's study (PlosOne, 2018) discussed the role of adenylyl cyclase activity in increasing cAMP levels, tyrosine phosphorylation, and Ca2+ channel activation in sperm capacitation.
  • Capacitation is a necessary process for sperm hyperactivity, which helps in breaking through physical barriers and facilitating the acrosome reaction.
  • During the acrosome reaction, the sperm binds to ZP3 on the zona pellucida, leading to Ca2+ influx and subsequent release of enzymes like acrosin, neuraminidase, and esterase.
  • Enzymes from the sperm and tubal mucosa aid in the dispersal of the corona radiata cells, allowing the sperm to penetrate.
  • The zona pellucida, a glycoprotein layer surrounding the oocyte, is 13 µm thick in humans and consists of four glycoproteins (ZP1-4), with ZP2 and ZP3 forming the basic binding unit.
  • ZP3's oligosaccharides mediate initial sperm binding, while its polypeptide initiates the acrosome reaction.
  • The zona pellucida acts as a sperm receptor and prevents polyspermy after fertilization, with nearly 20,000 cumulus cells being released with the oocyte at ovulation.
  • After penetrating the zona pellucida, sperm undergo cortical and zona reactions, which include the release of trypsin-like proteases and a loss of sperm binding due to ZP2-3 alterations.
  • The second meiotic division is triggered in the oocyte following fertilization, resulting in the formation of the zygote with a diploid number of chromosomes.
  • The zygote is genetically unique, with half of its chromosomes coming from the mother and half from the father, leading to biparental inheritance and variation in the human species.
  • Following the formation of pronuclei and their fusion, the zygote undergoes cleavage and develops into blastomeres, which change shape and align against each other for compaction before inner cell mass and trophoblast formation.
  • The blastocyst hatches from the zona pellucida and implants into the uterus during the implantation window.

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