Placenta

Question 1

define the placenta

Answer 1

temporary organ that connects the mother and the fetus

Question 2

What are the functions of the placenta?

Answer 2

Endocrine
Nutrition
Excretion
Immunity

Question 3

what are the 2 parts of the placenta?

Answer 3

Fetal placenta: chorion frondosum (chorionic plate)

Maternal placenta: decidua basalis (basal plate)

Question 4

where does the umbilical cord run form?

Answer 4

Form baby’s belly button to slightly off centre on the chorion plate (fetal side of placenta)

Question 5

what is the chorionic plate of the placenta covered by and what vessels are found on its surface?

Answer 5

Avascular glossy amnion (a protestive membrane)

Vessels on the surface are called chorionic vessels

Question 6

what is the umbilical cord made up of and what do they do?

Answer 6

2 umbilical arteries: carry deoxygenated blood from the fetus to the chorionic villi in the placenta
1 umbilical vein: carries oxygenated blood from the placenta to the fetus
Coated in Wharton’s jelly

Question 7

Describe the structure of the maternal (basal) side of the placenta

Answer 7

It is arranged into lobes (cotyledons)

Top layer is the Decidua basalis

Question 8

What 2 layers does the trophoblast layer of the blastocyst form? Describe them

Answer 8

Syncytiotrophoblast: outer, non-dividing, multinucleated layer
Cytotrophoblast: inner, proliferative layer

Question 9

What are lacunae and where do they form?

Answer 9

Lacunae are fluid filled spaces that form in the syncytiotrophoblast mass. They are precursors of intervillous space

Question 10

What happens in intervillous space?

Answer 10

site of nutrient exchange between the maternal and fetal circulations

Question 11

Describe the development of the villi in placenta

Answer 11

Lacunae fill with maternal blood

Small projections of cytotrophoblasts extend into the Syncytiotrophoblast = primary chorionic villi

Extra embryonic mesoderm burrows into villi forming a core of connective tissue = secondary chorionic villi

Embryonic blood vessels have begun to form in the extrembryonic mesoderm = tertiary chorionic villi

Question 12

Describe the structure of tertiary villi in placenta

Answer 12

Structure:
outer monolayer of syncytiotrophoblast cells
inner layer of cytotrophoblast cells
Vascularised with fetal capillaries

Question 13

what are anchoring villi?

Answer 13

villi that have become attached to the basal plate

Question 14

What are extra villous cytotrophoblast cells and what do they do?

Answer 14

Subset of trophoblast cells that have differentiated.
Role: invade the endometrium, myometrium and then spiral arteries. They remodel the highly coiled spiral arteries from low flow, High resistance vessels, to become wider, high flow, low resistance vessels.

Question 15

What dos the remodelling of spiral arteries allow?

Answer 15

A higher, sufficient blood flow to the fetus

Question 16

In the first 12 weeks, why is blood flow to the fetus obstructed?

Answer 16

Because trophoblastic plug obstructs maternal blood flow into the intervillous space

Question 17

Describe the maternal circulations in placenta

Answer 17

Maternal: oxygenated blood flows from the uterine arteries into sinuses surrounding the villi, then back into the uterine veins.

Question 18

Describe the fetal circulations in placenta

Answer 18

Fetal blood flows through umbilical arteries into the capillaries of villi and returns via umbilical vein to the fetus

Question 19

what nutrients are transported from the placenta

Answer 19

Amino acids
glucose
Fatty acids