Anatomy of the Placenta

Question 1

Give an overview of what the placenta is?

Answer 1

A complex temprary structure that supports both the foetus and the mother during preganancy then is expelled during third stage of labour (location)
Is derived from both mother and foetus
Provides a connection to the foetus through the umbilical cord
Role is hormonal exchange, mainly oestrogen and progesterone.

Question 2

Where does the maternal and foetal blood mix?

Answer 2

Maternal and Foetal blood does NOT mox

Question 3

What parts of the placenta develop from the foetus v the mother?

Answer 3

Foetus - chorion fondosum
Maternal side - decidua basalis

Question 4

What is the gross anatomy of the placenta?

Answer 4

Is a flattened discoid shape organ
Roughly 20cm wide and 2.5cm thick
Thins out towards the circumference where it is continous with the chorion
Weights about 450-500g.

Question 5

What is the foetal surface of the placenta like?

Answer 5

Covered with the amnion (inner membrame)
Surface of umbilical cord insertion
More shiny and greyish in appearance

Question 6

What is the maternal surface of the placenta like?

Answer 6

Attached to the decidua.
Formed by 15-20 cotyledons (bumps), seperated by sulci.
Is dark reddish in appearance

Question 7

What is the gross anatomy of the placenta membranes?

Answer 7

The outer chorion membrane and the inner amnion membrane meet at the edges to form the chorioamnion membranes (contains amniotic fus)
Chorion is derived from the trophoblasts
Amnion is transulecnt, connective tissue based, non-cilitated epithelial cells.

Question 8

What is another term for the umbilical cord?

Answer 8

The funis

Question 9

What is the gross anatomy of the umbilical cord?

Answer 9

Contains two umbilical arteries
Contains one umbilical vein
These spiral around each other inside Whartons Jelly.
originates from the duct between the amniotic sac and the yolk sac.

Question 10

What is whartons Jelly?

Answer 10

A mucoid connective tissue that supports the umbilical vessels in the umbilical cord.

Question 11

What is the function of the umbilical vessels?

Answer 11

Vessels that originate from the foetus
Artiers carry doexygenated blood to the placenta
Blood is then oxygenated
Veins carry oxygenated blood back to the foetus from the placenta.

Question 12

What does the umbilical cord look like in histological cross section?

Answer 12

Three vessels - two arteries and one vein
Has an epithelial surface layer
Whartons Jelly is made from loose connective tisse, looks quiet white and patchy.

Question 13

What makes up the chorion?

Answer 13

The extra embryonic mesoderm and the trophoblast cells.
Has branches of umbilical vessels
Gives rise to chorionic villous tree by stem villi

Question 14

Explain the early stages of placenta development.

Answer 14

The blastopore implants in the endometrial lining
Trophoblast cells develop into two layers the mononuclear cytotrophoblast layer and the multinuclear poor cell definition syncytiotrophoblast layer.
The cytrotrophoblast layer contributes cells to the synctiotrophoblast layer
The trophoblast layer grows into chorionic villi, these are considered tertiary villi when fetal vasculature grows within them.
During this process the mothers uterine vessels have grown and developed, the blood from these vessels fills lacunae (space between the chorionic villi). This region of exchange in known as the transitional zone.
Stem villi connect the chorionic plate to the villi tree.
It is seperated from the enometrium by the formation of a cytotrophoblastic plate

Question 15

Explain the process by which the villi of the placenta develop?

Answer 15

The chorionic plate forms chorionic villi from the cytotrophoblast layer and the syncytiotrophoblast layer.
Extraembryonic mesenchymal cells enter the centre of the villi forming secondary villi
These villia are vascularised by capillaries from the embryo and are known as teriary villi.
A cytotrophoblastic plate forms enclosing the villi.
The villi attached to the plate are called anchoring villi
Free branches into the transitional zone are called branching villi.

Question 16

Give an overview of the different layers of the placenta.

Answer 16

The maternal layer consists of the basal plate containing uterine vessels and is a growth of the endometrium
Next is the transitional zone which is where exchange of nutrients occurs.
Next is the chorion layer which forms the foetal layering, containing umbilical vessels, from this layer villi form projecting into the transitional zone, this acts as a barrier between mother and feotal blood cells but allows the exchange of nutrients and waste.

Question 17

Where does the exchange of nutrients occur in the placenta?

Answer 17

In the transitional zone, also called the intervillous space
Tertiary (chorionic) villi containing foetal umbilical vessels)
Exchange with nutrients from the mothers blood that is free in the lacunae between the villi.

Question 18

When does placenta development start?

Answer 18

When implantation occurs.
Day 20 to 32 gestation period

Question 19

How does the umbilical cord form?

Answer 19

A fibrous umbilical ring forms on the embryo abdomen
From this ring structures mainly from the yolk sac (vitelline duct - attached to the midgut, allantois -drains foetal bladder) and the body stalk from extraembryonic mesoderm.
Umbilical vessels appear.
These are all pushed together by the folding of the embryonic sac around the embryo.
Eventually only the vessels remain in the cord

Question 20

How do extraembryonic mesoderm cells form?

Answer 20

Form during week 2 of development
The epiblast (still part of bilaminar disk) gives rise to extraembryonic mesoderm cells, these form an inner layer below the trophoblast cells.

Question 21

What is the purpose of trophoblast villi in early implanations.

Answer 21

Are highly invasive
Extend into the endometrium and inner third of the myometrium.
envelop uterine blood vessels in lacunae, prerequiste for the tranistional zone in the placenta.

Question 22

What are the three different parts of the trophoblastic wall that give rise to the placenta?
What is the function of each section?

Answer 22

Syncytiotrophoblast - epithelial covering of villi and main endocrine componenets of the placenta
Cytrotrophoblast layer - forms villi that protrude into the syncytiotrophoblast layer, proliferate through out pregnancy.
The extravillous trophoblast layer - non prolferative and invade the endometrium. (is derived from cytotrophoblasts)

Question 23

What is the difference between the polar and the mural cytotrophoblasts?

Answer 23

Mural - is opposite and farthest away from the inner cell mass
Polar - closest to the inner cell mass is often the first to implant on the endometrial wall
Both contribute to the formation of the chorion layer of the placenta.

Question 24

Give an overview of the basal plate.

Answer 24

Part of the endometrial lining (the decidua junction)
Is a reservoir of maternal blood
Consists of the cytotrophoblast shell
Degenerations of the cytotrophoblast shell and the endometrium
The syncytiotrophoblast.

Question 25

How does maternal blood pass through the basal plate to enter the intervillous space?

Answer 25

80 to 100 Spiral branches of the uterine arteries perforate through the basal plate.

Question 26

What forms the cotyledons?

Answer 26

Sections of the maternal placenta including the basal plate.
seperated by septa consisting of decidual elements and trophoblastic cells.

Question 27

What does decidua mean?

Answer 27

Maternal uterine tissue.

Question 28

What limits the size of the intervillous space?

Answer 28

The fusion of the chronic and basal plate towards the periphery of the placenta
Internall lining on all sides by syncytiotrophoblasts
Numerous branching villi make up the majority of the content
Slow moving maternal blood.

Question 29

What are some of the different umbilical cord clinical complications?

Answer 29

Short cord - premature seperation of the placenta and baby during labour, insufficient absorption.
Long cord - can wrap around baby neck, derpive of oxygen or can prolapse
Hypo and hyper coiled
Anamolous insertions
Vasa previa

Question 30

What are some of the consequences of a hypo coiled or hyper coiled umbilical cord?

Answer 30

Intraterine growth restriction
Fetal demise / still birth
Associated with hypertensive disorders,
Placental abruption - seperates from innter wall before birth)
Maternal diabetes
Polyhdramnios - too much amniotic fluid

Question 31

What is anomalous insertion of the umbilical cord?
What are some of its complications?

Answer 31

When the umbilical cors inserts in the marginal area of the placenta rather than the middle. Or may attach by a velamentous bifurcate - two small attachments rather than one whole
This is a less stable attachment.
More likley for the placenta to remain inside after birth leading to maternal bleeding
Foetal blood loss and anemia
Slower exchange of nutrients.

Question 32

What is vesa previa and what are some of its complications?

Answer 32

When umbilical or foetal blood vessels, often connecting the the placenta pass very close and unprotected over the cervix
Blood vessels can lead
Cause severe blood loss to the mother and foetus during deliverly
Can cause a still birth.

Question 33

What can go wrong in the development of the placenta?
What are some of the complications of this?

Answer 33

Implantation does not occur - early miscarriage
Abnormal trophoblast invasion - placenta accreta, pre eclampsia, infarction of placenta, abruption.
Location of placenta is low lying and placenta pervia (covers the cervix) - lower segment caesarean section is required.
Bilobed or succenturiate lobe (smaller seperate accessory lobe) - vasa previa, post partum hemorrhage and infection

Question 34

What is placenta accreta?

Answer 34

When the placenta develops too deeply inside the uterine wall, on delivery can cause severe blood loss from the mother