Embryology 3 - Placenta/ Vascular development

Question 1

What are the outflow tracts of the foetal heart?

Answer 1

• Conus cordis + Truncus arteriosus

Question 2

What does the dorsal aortae supply?

Answer 2

• Head + Body wall
  > Also gives off vitelline (yolk) sac arteries and umbilical arteries.

Question 3

What are the 3 sets of embryological veins?

Answer 3

1- Cardinal veins (anterior and posterior) drain the head and body wall
2- Vitelline veins drain the yolk sac
3- Umbilical vein brings blood from the placenta to foetus

> All three sets of veins on each side flow into the right and left horns of the sinus venosus

Question 4

Name + Describe the 2 ways vessels are formed?

Answer 4

1- Vasculogenesis – vessels form in situ by coalescence and differentiation of mesoderm cells into endothelial tubes
e.g. Heart/ major vessels

2- Angiogenesis - smaller vessels
New vessels sprout from existing ones
Many of the vessels formed by angiogenesis develop as new organ systems differentiate and need to be supplied

Question 5

Which molecular signal is necessary for vessel formation?

Answer 5

• Vascular endothelial growth factors (VEGFs) and their receptors

Question 6

What is capillary haemangioma?

Answer 6

• Unregulated growth of developing blood vessels

Question 7

1- How many aortic arches and pharyngeal arches do we have?

2- How are they numbered?

3- What do the aortic arches supply?

Answer 7

1- 5, each pharyngeal arch contains an aortic arch.

2- I > VI (5th never forms or is rudimentary)

3- The aortic arches differentiate into vessels supplying the head and neck and upper limbs

Question 8

How do the aortic arches develop?

Answer 8

• The arches are never all present simultaneously
• The most cranial one’s form and then differentiate as more caudal ones are forming

Question 9

What is double aortic arch?

Answer 9

• Some of the arches that should have disappeared are still present at birth in addition to the normal arch.
• Babies have an aorta that is made up of two vessels instead of one.
• The two parts to the aorta have smaller arteries branching off of them.

> As a result, the two branches go around and press down on the windpipe and the tube (esophagus) that carries food from the mouth to the stomach.

Question 10

What are coarctations of the aorta?
> What are the 2 types?

Answer 10

• Birth defect in which a part of the aorta is narrower than usual

1- In preductal coarctations, the blood could pass through the patent ductus arteriosus to combat reduction of blood flow going through the descending aorta.

2- In postductal coarctation, the blood goes down the internal thoracic artery. The intercostal vessels becomes engorged.

Question 11

Describe the early formation of the placenta in the embryonic period.

Answer 11

1- Embryonic disk becomes intercalated into the endometrium > Syncytiotrophoblast forms the invasive layer for implantation and will erode uterine tissue, including blood vessels.

2- D9 > Lucunae

3- D12 > Trophoblastic lacunae are filling up with maternal blood from enlarged blood vessels = Maternal sinusoids
- New layer forms… Extraembryonic mesoderm. It has 2 layers (visceral, around the yolk sac) and parietal (next to the cytotrophoblasts). Parietal layer gives rise to the chorionic plate, fetal contribution to placenta.
- Connecting stalk = extraembryonic mesoderm.

4- D13> Cytotrophoblast begins to form primary chorionic villi ( which penetrate and expand into the surrounding syncytiotrophoblast.

5- D13 > Extra-embryonic mesoderm grows into these villi, forming a core of loose connective tissue, at which point these structures are called secondary chorionic villi.

6- End of week 3 > Embryonic vessels begin to form in the embryonic mesoderm of the secondary chorionic villi, making them tertiary chorionic villi.

6b- The cytotrophoblast cells from the tertiary villi grow towards the decidua basalis of the maternal uterus and spread across it to form a cytotrophoblastic shell. The villi that are connected to the decidua basalis through the cytotrophoblastic shell are known as anchoring villi.

6c- Villi growing outward within the intervillous space from the stem (anchoring) villi are called branching villi and provide surface area for exchange of metabolites between mother and fetus.

> Villi contain numerous blood vessels – umbilical vessels have started to form in the connecting stalk
This is the stage when the heart begins beating and circulation is established in the embryo
Well-developed villi are restricted to the embryonic pole

Question 12

What layers form primary, secondary an tertiary villi of the placenta?

Answer 12

Primary = cytotrophoblast core surrounded by syncytiotrophoblasts
Secondary = Extraembryonic mesodermal core
Tertiary = blood vessel core

Question 13

What is the foetal and maternal component of the placenta?

Answer 13

Foetal component of placenta = trophoblasts and extraembryonic mesoderm

Maternal component = uterine endometrium

Question 14

How does maternal blood reach the placenta?

Answer 14

• Spiral arteries that penetrate the cytotrophoblast shell and empty into intervillous spaces.
• Maternal veins drain these spaces

Question 15

1 month gestation what makes the barrier between the maternal and foetal blood?

Answer 15

1. Syncytium
2. Cytotrophoblast
3. Connective tissue
4. Endothelium

Question 16

By four months, the barrier separating the maternal and foetal blood is going to thin quite a bit. What forms the barrier now?

Answer 16

1. Syncytium
2. Endothelium

Question 17

Label.
- Describe the differences between the 2 images.

Answer 17

1. End of month 2, the embryo is becoming large, the yolk sack is however, withering.
2. By the end of month 3, there is no chorionic cavity.
3. The placenta is anchored to the decidua basalis which is the endometrial part- the maternal component. The chorion frondosum is the foetal component.
4. The decidua basalis is on the embryonic side. This is where nutrient exchange occurs. Opposite to this is the abembryonic side. This has more of a structural role. It is covered by the decidua capsularis.
5. As the amniotic cavity expands, the decidua capsularis comes into contact with the parietal layer of the decidua.

Question 18

What are cotyledons?

Answer 18

• Found on maternal side
  >15-25 separations of the decidua basalis of the placenta, separated by placental septa.
  > Contain foetal blood vessels

Question 19

Label.

Answer 19

Question 20

DEFINE:
1- Chorion
2- Chorion frondosum
3- Chorion laeve

4- Decidua basalis
5- Decidua parietalis

Answer 20

1- Chorion – Fetal portion of placenta consisting of extraembryonic mesoderm and trophoblastic cells. Includes villi and villus lakes
2- Chorion frondosum – villi projecting from embryonic side
3- Chorion laeve – ‘abembryonic’ side (smooth)

4- Decidua basalis – endometrium anchoring the placenta
5- Decidua parietalis – covering rest of the uterine cavity (think parietal)

Question 21

What makes up an umbilical cord?

Answer 21

2 arteries – from foetus to placenta = O2 deficient
1 vein – from placenta to foetal heart = O2 concentrated
Wharton’s jelly (core)

Question 22

Which image A/B represents maternal/foetal side of placenta?

Answer 22

A= Maternal side
B= This is the foetal surface contains the chorionic vessels and umbilical vessels (originating from the chorionic vessels) and the amnion covering it.

Question 23

What is delayed cord clamping?

Answer 23

• It is the practice (on request by parents) of leaving the baby attached to the placenta for a short while after birth to ensure the baby gets all nutrients from it.

Question 24

Describe what these issues are concerning the placenta:

• Placenta previa-
  Accreta-
  Increta-
  Percreta-

Answer 24

Placenta previa- low lying placenta (towards the cervix). This can block the birth canal.

Accreta- placenta invades deeply within the uterine wall

Increta- Placenta goes into myometrium

Percreta- Placenta into myometrium into serosa (i.e, including the perimetrium)

> Increta and Percreta presents problems when the placenta is removed following labour.