Post implantation and placenta development

Question 1

What does the zona pellucida do?

Answer 1

Prevent the early embryo from adhering to anything along its path to the uterus

Question 2

What does the embryo need to do when it reaches the uterus?

Answer 2

It needs to hatch from the zona pellucida and implant itself on the uterine wall

Question 3

At what day in the development does the embryo adhere itself onto the uterus wall? What is the epithelium lining of the uterine wall? What is the embryo called at this stage?

Answer 3

Day 7 Endometrium A blastocyst

Question 4

Does the implantation process have a high success rate? Why?

Answer 4

No as at least half of embryos are lost prior or during implantation It may be a mechanism that prevents the development of embryos with genetic abnormalities

Question 5

What part of the uterus is the embryo supposed to hatch onto? What is it called when it does not hatch onto the right part of the embryo?

Answer 5

The posterior wall If not here then it is called a ectopic pregnancy

Question 6

What are the types of ectopic pregnancies? Which is the most common

Answer 6

Tubal pregnancy, ovarian pregnancy and abdominal pregnancy

Question 7

What is the condition called when a blastocyst specifically hatches from the zona pellucida in the uterine tube? What can be the result of this?

Answer 7

Tubal pregnancies Can cause death to the mother as the uterus grows and cause the uterine tube to rupture

Question 8

Where do ovarian and abdominal pregnancy occur?

Answer 8

Ovarian = ovary (where the eggs are stored FYI) Abdominal = abdomen

Question 9

What happens during development and to the foetus if the embryo implants near the cervix of the uterus?

Answer 9

The placenta will form across the out of the cervical canal and possible lead to premature separation of the placenta late in pregnancy, can cause death of foetus

Question 10

Label the diagram

Answer 10

_

Question 11

How does syncytial trophoblasts differ from cellular trophoblasts?

Answer 11

Syncytial are a large multinucleate cell with a large shared cytoplasm, cellular are individual cells

Question 12

What happens to the syncytial trophoblasts and what does it do to the mothers tissue?

Answer 12

It grows larger and dissolves the mothers uterine tissue and endothelium tissue of the blood vessels within the uterus

Question 13

By dissolving the endothelium tissue of the mothers blood vessels, what does this create and where is it made?

Answer 13

Creates lacunae (lacuna for individual one FYI) in the syncytial tissue

Question 14

What are lacunae?

Answer 14

Pools of the mothers blood that accumulate in the syncytial tissue

Question 15

What is done with the blood in the lacunae? What does this allow?

Answer 15

The syncytial tissue sends projections into the lacunae This allows the nutrients from the mothers blood to be diffused into the embryo from a young age

Question 16

As an embryo develops are the lacunae still used for nutrient and waste transport? Why?

Answer 16

No because as the embryo gets bigger diffusion is no longer sufficient to transport the necessary material

Question 17

What is extra-exmbyonic mesoderm? Where does it come from?

Answer 17

It is any mesoderm tissue that is not inside the embryo itself Comes from the junction between epiblast and hypoblast

Question 18

What does extra-embryonic mesoderm do in early embryonic development?

Answer 18

It surrounds the entire embryo by forming extra-embryonic coelom

Question 19

Explain the layers of the embryo

Answer 19

-The outside layer/shell are the syncytial trophoblasts, cellular trophoblasts and extra-embryonic coelom -The inside is the embryo (made of the three germ layers) -Connection to the outside from the embryo by the extra-embryonic stalk

Question 20

Explain how the extra-embryonic coelom develop?

Answer 20

From the junction point the extra-embryonic mesoderm migration out form the junction between epiblast and hypoblasts it then positions itself under the cellular trophoblasts and begins surrounding the embryo as it forms it undergoes cavitation (creates cavities) which fill with fluid, the cavities then combine and grow forming a large continuous extra-embryonic coelom surrounding the entire embryo

Question 21

What is the extra-embryonic mesoderm that connects the inside and outside layers together? What does it develop into?

Answer 21

A mesodermal stalk Develops into the umbilical cord

Question 22

What is the function of the mesodermal stalk?

Answer 22

Attaches onto the embryo on the inside connecting it to the outside

Question 23

By the end of gastrulation, what is the three layered embryo surrounded by?

Answer 23

The amniotic cavity, the yolk sac and extra-embryonic coelom

Question 24

What separates the inner and outer balls of the embryo?

Answer 24

The extra-embryonic coelom

Question 25

What layers of the uterus are digested away to allow the blastocyst to imbed itself in the uterus?

Answer 25

The epithelium then the extra-cellular matrix

Question 26

Once the embryo is implanted in the uterus, what is the endometrium (epithelial layer of the uterus) called?

Answer 26

Decidua

Question 27

What is secreted by the embryo in order to prevent menstruations? What does this allow by doing what? What kind of cells are secreting this?

Answer 27

Human chorionic ganadotrohpin (hCG) Allows pregnancy to continue by preventing menstruations Trophoblasts

Question 28

How does the early embryo extract nutrients from the mother? How was the embryo getting nutrients before depending on the mother?

Answer 28

Digests the epithelium of the blood vessels which then pool in the lacunae, here the nutrients in the mothers blood are diffused into the embryo Before extracting nutrients from the mother the embryo was dependent on the yolk sac

Question 29

The embryo imbeds what part of itself into the mothers uterus? What surrounds the entire embryo?

Answer 29

It become entirely imbedded in the uterus (known at this point as decidua FYI) It is surrounded by syncytial trophoblasts

Question 30

What are the three layers that make the outer wall of the embryo? What is the origin of these tissues? What is the collective name for them?

Answer 30

Syncytial trophoblasts, cellular trophoblasts and extra-embryonic mesoderm Embryonic origin Chorion

Question 31

What does the chorion combine with to form what important structure involved in nutrient and waste exchange for the embryo?

Answer 31

Decidua basalis The placenta

Question 32

Label the following diagram What is being developed in this series of diagrams?

Answer 32

A chorionic villus (from primary chorionic villus in diagram 2 up to tertiary chorionic villus in diagram 4)

Question 33

At secondary chorionic villus, why do blood vessels need to be developed?

Answer 33

The chorionic villus is too large to sufficiently gather nutrients from the lacuna just by passive diffusion, requires blood vessels

Question 34

What changes occur between the secondary and tertiary chorionic villus?

Answer 34

The extra-embryonic mesoderm gives rise to fatal capillaries The cellular trophoblasts become reduced

Question 35

Why does the cellular trophoblasts undergo its particular changes between secondary and tertiary villus structures?

Answer 35

Reduces the number of layers which the nutrients and waste need to diffuse through to go from blood capillaries to lacuna

Question 36

Explain the structure and position of the fetal capillaries. What makes this advantageous for its function?

Answer 36

It is a single layer of squamous endothelium cells, located on the wall of the syncytial trophoblasts Makes diffusion very easy as it is very close to the lacuna

Question 37

What do the tributary and branch of umbilical vein and artery connect to?

Answer 37

The embryonic heart via the umbilical cord

Question 38

Why do the chrorionic villi form?

Answer 38

To increase the surface area that is exposed to the maternal blood in the lacunae

Question 39

What is the function of the amniotic sac? What is it filled with?

Answer 39

Protects the embryo, allows it to move around and prevents it from dehydrating Amniotic fluid

Question 40

The yolk sac in avian/reptiles is large and nutritious. In mammals it is neither, why is this? What is its function in mammals?

Answer 40

In mammals the embryo establishes a circulation with the mother early on to extract nutrients so doesn’t need to store it itself It does however provide nutrition for the very early stages of embryonic development before a circulation is established, also contains precursors for blood cells and produces cell stoa form the embryos primordial cells for the reproductive systems

Question 41

What is the allantois in avians/reptiles and mammals?

Answer 41

Avians/reptiles = membranous sac which is used to store nitrogenous wastes and to transport O2 and CO2 in/out of the egg Mammals = forms part of the stalk of the extra-embryonic mesoderm and contributes the formation of the umbilical cord

Question 42

What happens to the left umbilical artery as the embryo develops? Why?

Answer 42

It loses its connection to the heart and instead carrier blood to the developing liver Allows for the embryo to metabolise the rich nutrients that are taken up in the placenta

Question 43

Why does the lacunae form the chorionic villi?

Answer 43

In order to increase the surface area exposed to the mothers blood

Question 44

Label the diagram and indicate what the quality of blood going through each blood vessel is

Answer 44