Placenta and Fetal Membranes

Question 1

The Placenta

Answer 1

• The placenta a fetomaternal organ which begins developing at implantation of the blastocyst
• it provides nutrition, gas exchange, waste removal, a source of hematopoietic stem cells, endocrine and immune support for the developing fetus

Question 2

Fetal membranes

Answer 2

• Chorion: forms most of the placenta
• Yolk sac: non-functional
• Allantois: non-functional
• Amnion: for portection

Question 3

Fetal Placenta

Answer 3

• the fetal part of the placenta is made up of the chorionic plate with its placental villi, the cytotrophoblast layer and the intervillous spaces
• the chorionic plate consists of the amnion, the extra-embryonic, mesenchymam the cytotrophoblast, and the syncytiotrophoblast

Question 4

Maternal Placenta

Answer 4

• the basal plate, the peripheral region of the placenta on the maternal side that is in contact with the uterine wall, is made up of two tissues: embryonic tissue and maternal tissue

Question 5

Hatching to Implantation

Answer 5

When the blastocyst emergers from the pellucid zone on the 5th day it comes into contact with the maternal uterine mucosa in that it embeds itself in the endometrium with its embryonic pole
- the zona pellucida posses no HLA antigen and thus acts as an immunological barrier in relation to the mother

Question 6

Endometrial Preparation

Answer 6

• At the time of implantation, the mucosa of the uterus is in the secretory phase
• During this time the uterine glands and arteries become coiled and the tissue becomes succulent
• Three distinct layers can be recognized in the endometrium: a superficial compact layer, intermediate spongy layer , thin basal layer

Question 7

Adhension

Answer 7

-the adhension of the blastocyst on the endometrium arises through cell surface glyciproteins, the specific mechanis,s of which are not well understood

Question 8

trophoblastic differentiation

Answer 8

Trophoblast differentiates into two different cell masses shortly after adhension:

• the outer syncytiotrophoblast
• the inner cytotrophoblast

Question 9

trophoblastic cell remodelling

Answer 9

The multinucleated syncytiotrophoblast forms the outer epithelial layer of the chorionic villi
- it is at the terminal branches of the chorionic villi that the majority of fetal/ maternal exchange occurs

Question 10

Placental Circulation

Answer 10

Two circulation systems:

a) Fetal circulation system
b) maternal circulation system

Question 11

The Placental Barrier

Answer 11

• composed of stuctures that separate the maternal and fetal blood
• the makeup of the placental barrier changes over the course of pregnancy

Question 12

1st Trimester Barrier

Answer 12

• In the first trimester the barrier conssits of syncytiotrophoblast, cytotrophoblast, the villus mesenchyma, and the fetal capillary walls

Question 13

2nd Trimester Barrier

Answer 13

During the 4th month the cytotrophoblast disappear from the villus wall and the thickness of the barrier decrease while the surface area increases
- in the 5th month the fetal vessels have multiplied their branches and gotten closer to the villus surface

Question 14

3rd Trimester Barrier

Answer 14

During the 6th month the nuceli of the syncytiotrophoblast group together in the so-called proliferation knots

Question 15

Respiratory Function

Answer 15

No active exchange of gases take place and there is intake of oxygen and output of carbon dioxide take place by simple diffusion across the fetal membrane

Question 16

Excretory function

Answer 16

Waste products from the fetus such as urea, uric acid, cretinine are excreted to maternal blood by simple diffusion

Question 17

Nutritive Function

Answer 17

Fetus obtains its nutrients from the maternal blood

• glucose- transferred to the fetus by facilitated diffusion
• lipids for fetal growth and development has dual origin and they are transferred across the fetal membrane or synthesized in the fetus

Question 18

placenta increta

Answer 18

occurs when the placenta attaches deep into the uterine wall and penetrates into the uterine muscle but does not penetrate the uterine serosa

Question 19

placental percreta

Answer 19

placenta villi penetrate myometrium and through the uterine serosa

Question 20

placenta previa

Answer 20

the placental overlies internal cervical os of uterus essentially covering the birth canal

Question 21

abruptio placenta

Answer 21

an interruption of the placenta by partial or complete separation, retroplacental blood clot formation and abnormal hemorrhage prior to delivery