201 L11

Question 1

What are some functions of the placenta?

Answer 1

Gas exchange

Nutrient exchange

Heat exchange

Antibody exchange - mother transfers antibodies to baby
Synthetic and secretory functions (endocrine and other)

Immunological

Separation of the maternal and fetal organisms (mothers blood and baby’s blood never mix, placenta separates the baby from its mother and prevents the mothers immune system from rejecting it)

Question 2

Name the trimesters and their time periods?

Answer 2

1st trimester - conception until 12 weeks

2nd trimester - 13 weeks until 24 weeks

3rd trimester -25 weeks until term (36-40 weeks)

Question 3

At what stage in the preimplantation of the embryo do cells stop being identical?

Answer 3

Morula stage - the cells get smaller when the embryo starts to compact

Question 4

How many cells are in the embryo at the blastocyst stage?

Answer 4

64 cells

Question 5

At the ——- stage of preimplantation around day 6, there are 2 different types of —– that comprise the embryo.

The —- —- —– forms the rest of the —— and contributes a bit to the ——.

The ——— are the sphere of cells surrounding the — — —. This is going to become the ——- of the placenta.

Answer 5

At the blastocyst stage of preimplantation around day 6, there are 2 different types of cells that comprise the embryo.

The inner cell mass forms the rest of the baby and contributes a bit to the placenta.

The trophectoderm are the sphere of cells surrounding the inner cell mass. This is going to become the trophoblast of the placenta.

Question 6

Implantation and the lacunar phase

Implantation happens around day —–, usually after ———.

The embryo always attaches to the ——– wall with the —- — —- facing the ——– wall.

The ——— cells at the leading edge —– together and form ——- ——- (———-).

The —- —- invades the ——-, forming gaps in the —— tissue called lacunae.

The ———– protrusions are called trabeculae.

The trabeculae stick out projections into the ——– tissue and secrete more ——— enzymes.

At the end of the lacunar phase the —– is completely embedded in the wall of the —- and the —— cells of the lumen have healed.

Answer 6

Implantation happens around day 7, usually after fertilisation.

The embryo always attaches to the uterine wall with the inner cell mass facing the uterine wall.

The trophectoderm cells at the leading edge fuse together and form primitive syncitium.

The primitive syncitium (syncytiotrophoblast) invades the decidua, forming gaps in the maternal tissue called lacunae.

The trophoblast protrusions are called trabeculae.

The trabeculae stick out projections into the uterine tissue and secrete more digestive enzymes.

At the end of the lacunar phase the embryo is completely embedded in the wall of the uterus and the epithelial cells of the lumen have healed.

Question 7

How long is the lacunar phase and between what days of implantation does it occur?

Answer 7

4 days

days 8-12

Question 8

When does the villous period begin?

Answer 8

From about day 12

Question 9

Villous period

The ———— at the back of the embryo at implantation migrate underneath the —— ——–.

The 2 layers are called —— —-.

The ————- proliferate and invade the ————.

The lucanar system is now called the ————- space.

At about day —–, cells from the —– —— —— invade the —— —- underneath the ———— forming —— —–.

Answer 9

The cytotrophoblasts at the back of the embryo at implantation migrate underneath the primitive syncitium (syncytiotrophoblast).

The 2 layers are called primary villi.

The cytotrophoblasts proliferate and invade the trabeculae.

The lucanar system is now called the intervillius space.

At about day 14, cells from the inner cell mass (extraembryonic mesenchyme) invade the primary villi underneath the cytotrophoblast forming secondary villi.

Question 10

Tertiary villi

About __-__ days post conception, ———- form in the villi, this is now a ——- villi.

These form in the ——– before they do in the —- — —.

So the ——— is developing just slightly ahead of the —–.

From this point on almost all villi are ——-.

The vessels in the villi connect to the ——— vessels carrying blood to and from the fetus

Answer 10

About 18-20 days post conception, capillaries form in the villi, this is now a tertiary villi.

These form in the placenta before they do in the inner cell mass (embryo proper).

So the placenta is developing just slightly ahead of the embryo.

From this point on almost all villi are tertiary.

The vessels in the villi connect to the umbilical vessels carrying blood to and from the fetus

Question 11

What percentage of conceptions are lost in humans?

Answer 11

70%

Question 12

Why is early placentae important?

Answer 12

Humans are a very infertile species

Question 13

What percentage of conceptions are lost early in pregnancy or prior to implantation?

Answer 13

60%

Question 14

What is the permed placenta covered by?

Answer 14

1 syncytiotrophoblast (primitive syncitium)

Question 15

The villi to the —— and —— aspect —– to form the smooth ——–.

Only the villi on the ——— front of the —— is going to remain as the definitive ———–.

Answer 15

The villi to the side and luminal aspect regress to form the smooth chorion.

Only the villi on the invading front of the placenta is going to remain as the definitive placenta (disc).

Question 16

What are anchoring villi?

Answer 16

The villi that come into contact with the uterus and stay in contact with it

Question 17

What villi is referred to as the floating villi?

Answer 17

Tertiary villi

Question 18

What trimester are floating villi present?

Answer 18

1st trimester (conception - week 12)

Question 19

Anchoring villi

In a few villi ———– break through the ————-

The ————— spread laterally around the ———— site forming a ———- shell

The ————— shell remains in contact with the maternal tissue throughout gestation

Columns of ————– continue to stream out of these anchoring villi to invade the —— and —– arteries during the —- and —– trimesters.

Rare at term pregnancy because the placenta has grown and it’s about exchange and separation which the ——– villi perform

Answer 19

In a few villi cytotrophoblasts break through the syncytiotrophoblasts

The cytotrophoblasts spread laterally around the implantation site forming a cytotrophoblast shell

The trophoblast shell remains in contact with the maternal tissue throughout gestation

Columns of cytotrophoblasts continue to stream out of these anchoring villi to invade the decidua (maternal tissue) and spiral arteries during the first and second trimesters.

Rare at term pregnancy because the placenta has grown and it’s about exchange and separation which the floating villi perform.

Question 20

What are extravillus trophoblasts?

Answer 20

Are fetal cells that migrate out of the fetal tissue of the placenta villus and into the decidua

Question 21

What is the function of the extravillus trophoblast?

Answer 21

Ingest away the endothelial cells and most importantly the muscular wall of the spiral arteries causing the vessels to open up which are tonically inactive.

Question 22

The spiral arteries are —– and lined by ——- cells and —- —- cells.

They —— open into the uterine cavity

Answer 22

The spiral arteries are coiled and lined by endothelial cells and smooth muscle cells.

They never open into the uterine cavity

Question 23

The spiral arteries are ——- inactive. This means that the mother —– control the blood flow to the ——, which allows the baby to grow ——— by whatever is happening to the mother.

Answer 23

The spiral arteries are tonically inactive. This means that the mother can’t control the blood flow to the placenta, which allows the baby to grow unimpeded by whatever is happening to the mother.

Question 24

In a good pregnancy there are no —— walls in the —– arteries.

Answer 24

In a good pregnancy there are no muscular walls in the spiral arteries.

Question 25

What happens when the extravillus trophoblasts don’t break down the smooth muscle layer of the spiral arteries?

Answer 25

Shallow trophoblast invasion - The vessels remain tonically active, so the mother can cut off blood supply to the baby.

Results in intrauterine growth restriction - skinny baby.

Question 26

What are floating villi?

Answer 26

Villi that are not in contact with the maternal tissues and are suspended in the intervillous space

Question 27

What is the function of floating villi?

Answer 27

Exchange (nutrient and gas) and barrier functions of the placenta

Question 28

The ——— cells of the decidua are swollen and store glycogen

Answer 28

Stromal

Question 29

What enhances the decidual reaction?

Answer 29

Implantation

Question 30

The decidua underlying the implantation site is called the decidua ——– (The leading edge of the placenta)

The decidua overlying the implantation site is called the decidua ———– (behind the embryo, i.e the part that is healing)

The decidua around the remainder of the uterus is call the decidua ———- (almost all of the decidua is parietal decidua).

Answer 30

The decidua underlying the implantation site is called the decidua basalis (the leading edge of the placenta).

The decidua overlying the implantation site is called the decidua capsularis (behind the embryo, i.e the part that is healing)

The decidua around the remainder of the uterus is call the decidua parietalis (almost all of the decidua is parietal decidua).

Question 31

As gestation progresses the ——— cavity enlarges filling the ——— cavity.

The ——- —— ——- then fuses with the decidua ——–.

So by term you can’t distinguish between the ——– and ——– decidua.

Answer 31

As gestation progresses the amniotic cavity enlarges filling the uterine cavity.

The decidua decidua capsularis then fuses with the decidua parietalis.

So by term you can’t distinguish between the capsular and parietal decidua

Question 32

What are the components that make up the umbilical chord?

Answer 32

Whartons jelly

Myofibroblasts

Mucopolysaccharides

Question 33

Why are mucopolysaccharides important for the umbilical chord?

Answer 33

Keeps the cord turgid (sorta solid - like a hose). Important so that the cord wont tie into a knot and prevent oxygen flow to the fetus

Question 34

What is the unbilical cord formed from?

Answer 34

Yolk sac and allantois

Question 35

What are the vessels of the umbilical chord derived from?

Answer 35

Allantois

Question 36

What are the umbilical chord blood vessels?

Answer 36

2 arteries - carries deoxygenated blood from the fetus to the placenta

1 vein - carries oxygenated blood from the placenta to the fetus