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613: Human Development and the Life Cycle > 2nd Week Of Development > Flashcards

2nd Week Of Development Flashcards

0
Q

On day 9 what begins to appear?

A

Lacunae start appearing in the syncytiotrophoblast

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1
Q

What are lacunae?

A

Vacuoles that represent the first signs of a uteroplacental exchange of nutrients

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2
Q

When does the blastocyst become completely implanted?

A

Around day 11 or 12

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4
Q

What is implantation characterized by?

A

Communication of the blood-filled lacunar networks

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5
Q

What membrane lines the inner surface of the cytotrophoblast?

A

Exocoelomic Membrane

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6
Q

The exocoelomic membrane along with the hypoblast form the lining of what cavity?

A

Exocoelomic Cavity = Primitive Yolk Sac = Primary Umbilical Vesicle

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7
Q

What are the syncytiotrophoblast’s 2 main activities initially?

A

1) Invade into the endometrium
2) Produce human chorionic Gonadotropin (hCG), which enters the maternal blood via the lacunae in the syncytiotrophoblast

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8
Q

What is the importance of hCG?

A

It maintains the hormonal activity of the corpus luteum in the ovary during pregnancy. This is important because the corpus luteum secretes estrogen and progesterone to maintain pregnancy

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9
Q

What causes a (+) pregnancy test?

A

hCG levels are high enough by the end of the 2nd week to produce this result

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10
Q

What do the lacunae fill with?

A

A mixture of maternal blood from ruptured endometrial capillaries and cellular debris from eroded uterine glans

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11
Q

What are sinusoids?

A

Endometrial capillaries around the implanted embryo that become congested and dilated because cells of the syncytiotrophoblast penetrate deeper into the stroma and erode the endothelial lining of the capillaries

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12
Q

Describe Primordial Uteroplacental Circulation

A

This is the communication of the eroded endometrial capillaries with the lacunae in the syncytiotrophoblast. The syncytial lacunae become continuous with the sinusoids

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13
Q

How does fluid from the lacunar spaces pass to the embryonic disc?

A

by way of diffusion

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14
Q

What cells appear between the inner surface of the cytotrophoblast and the outer surface of the exocoelomic cavity?

A

Extraembryonic Mesoderm

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15
Q

What is extraembryonic mesoderm derived from?

A

Yolk Sac Cells

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16
Q

What is the extraembryonic Cavity?

A

These are large cavities that develop in the extraembryonic mesoderm
*Also called the Chorionic Cavity

17
Q

The extraembryonic mesoderm lining the cytotrophoblsat and amnion is called what?

A

Extramembryonic Somatic Mesoderm

18
Q

The extraembryonic mesoderm lining the yolk sac is called what?

A

Extramembryonic Splanchnic Mesoderm

19
Q

Somatic Mesoderm will eventually do what?

A

Form the body wall

20
Q

Splanchnic Mesoderm will eventually do what?

A

Surround the gut tube

21
Q

When does the decidual reaction occur?

A

When the cells of the endometrium become polyhedral and loaded with glycogen and lipids

22
Q

After the cells swell because of the accumulation of glycogen and lipid in their cytoplasm they are known as ______ cells.

A

Decidual

23
Q

What is the primary function of the decidual reaction?

A

To provide nutrients for the early embryo and an immunological privileged site for the conceptus

24
Q

Around what day is the surface defect in the endometrium healed?

A

13th day

25
Q

How can there be inaccuracy in determining the expected delivery date>

A

Occasionally bleeding occurs at the implantation site as a result of increased blood flow into the lacunar spaces. Because this bleeding occurs near the 28th day of the menstrual cycle (13th day of pregnancy) it may be confused with normal menstrual bleeding

26
Q

Cells of the cytotrophoblast proliferate and penetrate into the syncytiotrophoblast forming what?

A

Primary Villi

27
Q

Describe the primary villi layers

A

There is extramembryonic mesoderm in the center, that is surrounded by cytotrophoblast, which itself is covered by synsytiotrophoblast

28
Q

How is the secondary (definitive) yolk sac formed?

A

Hypoblast produces additional cells that migrate along the inside of the exocoelomic membrane. These cells proliferate and gradually form this new cavity within the exocoelomic cavity

29
Q

What is the important function of the secondary (definitive) yolk sac?

A

It is the site of origin of primordial germ cells

30
Q

What is the extraembryonic coelom?

A

= Chorionic Cavity = Exocoelomic Cavity
It is a large, isolated, fluid-filled cavity that surrounds the amnion and umbilical vesicle except where they are attached to the chorion by the connecting stalk

31
Q

What 2 things form the chorion?

A
  • Extraembryonic Mesoderm

- The 2 Layers of the Trophoblast (Cytotrophoblast and Syncytiotrophoblast)

32
Q

What does the chorion form?

A

The wall of the chorionic cavity sac, within which the embryo, amniotic sac, and umbilical vesicle (yolk sac) are suspended by the connecting stalk

33
Q

What do the extraembryonic cavities expand to form>

A

The chorionic cavity

34
Q

What is the connecting stalk?

A

The only place where extraembryonic mesoderm traverses the chorionic cavity
*Becomes the umbilical cord

35
Q

What is the prechordal plate?

A

The thickened circular area on a 14 day old embryo between the oropharyngeal membrane (future mouth) and the tip of the notochord

36
Q

How do we know when uteroplacental circulation has begun?

A

Trophoblastic lacunae are now present at the embryonic pole as well as the abembryonic pole (this occurs by the end of the 2nd week)

37
Q

At the end of week 2 what do we have?

A
  • 2 Layers of the Trophoblast (cytotrophoblast and syncytiotrophoblast)
  • 2 Layers of the Embryoblast (epiblast and hypoblast)
  • 2 Layers of the Extraembronic Mesoderm (somatic and splanchnic)
  • 2 Cavities (amniotic and yolk sac)

**Known as the week of TWO’s

38
Q

What is an ectopic pregnancy?

A

Implantation outside of the uterus

*the #1 cause of maternal deaths during the first trimester

39
Q

What is placental previa?

A

Pregnancy in which the placenta is implanted in the lower part of the uterus and can cause life-threatening bleeding

613: Human Development and the Life Cycle (7 decks)

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