2nd Week Of Development

Question 0

On day 9 what begins to appear?

Answer 0

Lacunae start appearing in the syncytiotrophoblast

Question 1

What are lacunae?

Answer 1

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

Question 2

When does the blastocyst become completely implanted?

Answer 2

Around day 11 or 12

Question 4

What is implantation characterized by?

Answer 4

Communication of the blood-filled lacunar networks

Question 5

What membrane lines the inner surface of the cytotrophoblast?

Answer 5

Exocoelomic Membrane

Question 6

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

Answer 6

Exocoelomic Cavity = Primitive Yolk Sac = Primary Umbilical Vesicle

Question 7

What are the syncytiotrophoblast’s 2 main activities initially?

Answer 7

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

Question 8

What is the importance of hCG?

Answer 8

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

Question 9

What causes a (+) pregnancy test?

Answer 9

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

Question 10

What do the lacunae fill with?

Answer 10

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

Question 11

What are sinusoids?

Answer 11

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

Question 12

Describe Primordial Uteroplacental Circulation

Answer 12

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

Question 13

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

Answer 13

by way of diffusion

Question 14

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

Answer 14

Extraembryonic Mesoderm

Question 15

What is extraembryonic mesoderm derived from?

Answer 15

Yolk Sac Cells

Question 16

What is the extraembryonic Cavity?

Answer 16

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

Question 17

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

Answer 17

Extramembryonic Somatic Mesoderm

Question 18

The extraembryonic mesoderm lining the yolk sac is called what?

Answer 18

Extramembryonic Splanchnic Mesoderm

Question 19

Somatic Mesoderm will eventually do what?

Answer 19

Form the body wall

Question 20

Splanchnic Mesoderm will eventually do what?

Answer 20

Surround the gut tube

Question 21

When does the decidual reaction occur?

Answer 21

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

Question 22

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

Answer 22

Decidual

Question 23

What is the primary function of the decidual reaction?

Answer 23

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

Question 24

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

Answer 24

13th day

Question 25

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

Answer 25

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

Question 26

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

Answer 26

Primary Villi

Question 27

Describe the primary villi layers

Answer 27

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

Question 28

How is the secondary (definitive) yolk sac formed?

Answer 28

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

Question 29

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

Answer 29

It is the site of origin of primordial germ cells

Question 30

What is the extraembryonic coelom?

Answer 30

= 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

Question 31

What 2 things form the chorion?

Answer 31

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

Question 32

What does the chorion form?

Answer 32

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

Question 33

What do the extraembryonic cavities expand to form>

Answer 33

The chorionic cavity

Question 34

What is the connecting stalk?

Answer 34

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

Question 35

What is the prechordal plate?

Answer 35

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

Question 36

How do we know when uteroplacental circulation has begun?

Answer 36

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

Question 37

At the end of week 2 what do we have?

Answer 37

- 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

Question 38

What is an ectopic pregnancy?

Answer 38

Implantation outside of the uterus | *the #1 cause of maternal deaths during the first trimester

Question 39

What is placental previa?

Answer 39

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