Placenta

Question 1

What are the parts of the placenta?

Answer 1

Fetal part
Maternal part

Question 2

What type of an organ is the placenta?

Answer 2

Fetomaternal organ

Question 3

What are the parts of the placenta derived from?

Answer 3

• Fetal part: from the chorionic sac (the outermost fetal membrane)
• Maternal part: from the endometrium (innermost layer of the uterine wall)

Question 4

Outline implantation

Answer 4

• begins at day 6 of pregnancy
• trophoblast cells interact with endometrial lining of uterus after losing the Zona pellucida
• blastocyst embeds into the endometrium where it interacts with the increased vasculature + secretory glands in the endometrium

Question 5

When does implantation begin?

Answer 5

Day 6 of pregnancy

Question 6

What is decidualisation?

Answer 6

Process by which stromal cells differentiate into highly specialised secretory epitheleoid cells called decidual cells

Question 7

Function of decidual cells

Answer 7

• Control depth of invasion of trophoblast
• protect conceptus from maternal immune rejection

Question 8

When does decidualisation occur?

Answer 8

During the secretory phase

Question 9

What happens if implantation occurs where there are no decidual cells?

Answer 9

No control over the extent of invasion or rejection from maternal immune system

Question 10

What happens when implantation occurs in the correct place but the decidual reaction is suboptimal?

Answer 10

Complications in the pregnancy:
- not maintained (miscarriage or infertility)
- placental insufficiency e.g. pre eclampsia

Question 11

Normal location of implantation

Answer 11

Upper posterior uterine wall

Question 12

Normal invasion location

Answer 12

Within the stratum/decidual functionalis

Question 13

Outline the attachment of the blastocyst

Answer 13

• trophoblastic cells have microvilli which attach to pinopodes on endometrium
• stronger connection made between integrins + receptors on endometrium
• blastocyst is attached to endometrium of uterus

Question 14

What does the trophoblast differentiate into?

Answer 14

Cytotrophoblast
Syncytiotrophoblast

Question 15

What produces hCG?

Answer 15

Syncytiotrophoblast

Question 16

When does placenta formation start?

Answer 16

Second week of pregnancy

Question 17

What happens in the case of a disease placenta or failed implantation of placenta?

Answer 17

Miscarriage
(Embryo isn’t provided nutrients and oxygen)

Question 18

What part of the embryo becomes the placenta?

Answer 18

Trophoblast

Question 19

Describe the layers of chorionic villia

Answer 19

• syncytiotrophoblast (outer layer)
• cytotrophoblast
• core of extra embryonic mesoderm with fetal vessels

Question 20

Formation of the primary villus

Answer 20

• cytotrophoblast send projections through the syncytiotrophoblast
• intervillus space between the projections
• forms a cytotrophoblastic shell

Question 21

Formation of secondary villus

Answer 21

• extra embryonic mesoderm invades into the primary villli
• this forms the 3 layered secondary villus

Question 22

What happens at the same time as secondary villus formation?

Answer 22

The connecting stalk differentiates to form umbilical vessels
2 arteries + a vein

Question 23

Formation of the tertiary villus

Answer 23

Chorionic vessels grow up into villus

Question 24

What is a cotyledon?

Answer 24

Decidual cells of endometrium invaginate into placenta causing septae which separate tertiary villi into groups

Question 25

How does the placenta change throughout pregnancy?

Answer 25

- initially, barrier between fetal and maternal blood is thick which a full layer of cytotrophoblast + syncytiotrophoblast - as pregnancy progress, the barrier thins by reducing the cytotrophoblast cells to optimise transport

Question 26

Changes in the embryonic spaces during pregnancy

Answer 26

- yolk sac disappear - amniotic sac enlarges - chorionic sac is occupied by expanding amniotic sac

Question 27

Outline the umbilical vessels

Answer 27

- **two umbilical arteries**: deoxygenated blood + waste products from fetus to placenta - **one umbilical vein**: oxygenated blood + nutrients from placenta to fetus

Question 28

What conditions can occur due to implantation at incorrect site?

Answer 28

Ectopic pregnancy Placenta praevia

Question 29

What conditions occur if implantation is too shallow?

Answer 29

Placental insufficiency Pre-eclampsia

Question 30

What conditions occur if implantation is too deep?

Answer 30

Placenta accreta Placenta increta Placenta precreta Increasing depth (alphabetic order)

Question 31

Three functions of the placenta

Answer 31

Endocrine function Metabolic changes Transport function

Question 32

Describe the endocrine function of the placenta

Answer 32

- syntiotrophoblasts produces **human chorionic gonadotropin hCG** - **hCG sustains the corpus luteum** in the 1st trimester . - placenta also produces **steroid hormones** at the start of the 2nd trimester - placenta takes over the role of the corpus luteum - produces enough **oestrogen + progesterone** to keep the HPG axis in the ‘pregnancy state’

Question 33

What hormones are produced by the placenta?

Answer 33

Human chorionic gonadotropin hCG Oestrogen Progesterone

Question 34

Describe the metabolic function of the placenta

Answer 34

- **progesterone increases maternal appetite** > increased fat deposition to support the fetus + breastfeeding - **human placental lactose hPL creates diabetogenic state** to cause **insulin resistance in mother** > increases glucose availability to fetus

Question 35

What hormone is related to gestational diabetes?

Answer 35

Human placental lactogen hPL

Question 36

What are the three ways transport occurs in the placenta? Examples of substances for each

Answer 36

- **Simple diffusion**: *e.g. water, gases, electrolytes* - **Facilitated diffusion**: *e.g. glucose* - **Active transport**: *e.g. amino acids*

Question 37

How is the rate of exchange in gas exchange limited between mother and baby? What is needed?

Answer 37

**Flow limited** Adequate uteroplacental circulation is needed

Question 38

What specific immunoglobulin crosses the placenta?

Answer 38

IgG

Question 39

What are teratogens?

Answer 39

Substances that cause congenital disorders in developing fetus *e.g. alcohol, drugs, medications*

Question 40

When do teratogens have the greatest effect?

Answer 40

- Early pregnancy - Especially embryonic stage (3-8 weeks) as organs systems are most at risk of damage

Question 41

Why is hCG pregnancy specific?

Answer 41

It is produced by the syncytiotrophoblast

Question 42

What system is at a continual risk of damage by teratogens during development?

Answer 42

Central nervous system Long development

Question 43

Function of human placental lactogen

Answer 43

- Puts mother in diabetogenic state - causes insulin resistance in mother - increases glucose availability to fetus

Question 44

What are TORCH infections?

Answer 44

**Infections that can pass across the placenta** Toxoplasmosis Other- syphilis, HIV Rubella Cytomegalovirus Herpes simplex

Question 45

What antibody can pass from the mother to the fetus? By what process does this happen?

Answer 45

**IgG** Receptor mediated endocytosis

Question 46

How soon after fertilisation can hCG be detected reliably in maternal urine?

Answer 46

14 days