Placentation and implantation

Question 1

What are the 3 phases of linking between the foetus and mother?

Answer 1

• Invasion - of conceptus to endometrium
• Decidualisation - endometrial remodeling including secretory transformation of the uterine glands, influx of specialised uterine natural killer cells
• Placentation - i.e placenta formation

Question 2

What is the embryonic portion of the placenta supplied by?

Answer 2

Outermost layers of trophoblast cells (ie the chorion)

Question 3

What is the chorion?

Answer 3

The outermost membrane surrounding the embryo

Question 4

What is each villi surrounded by?

Answer 4

Pool/sinus of maternal blood (due to endometrium being changed by enzymes and paracrine agents)

Question 5

What happens to the blastocyst around day 6/7?

Answer 5

Leaves the zona pelucida and bathed by uterine secretions for 2 days:

• Progesterone prepares supportive uterine environment increasing glandular tissue
• Oestrodiol is required to release the glandular secretions

Question 6

How does attachment and implantation work?

Answer 6

• Very limited time window
• Synciotrophoblast cells ‘flow’ into the endometrium
• Causes oedema, glycogen synthesis and increased vascularisation (decidualisation). The pregnant endometrium is now termed the decidua

Question 7

What do syncytiotrophoblast cells do around day 13?

Answer 7

They erde through the walls of large maternal capillaries which then bleed into the spaces - primitive placental circulation

Question 8

What is the 1st trimester embryo largely dependant on for nutrients and O2?

Answer 8

Uterine tissues

Question 9

What seperates maternal and foetal blood?

Answer 9

Placental membrane

Question 10

What is thought to account for a large amount of 1st trimester pregnancy losses?

Answer 10

Lack of hormonal support (luteal phase defect)

Question 11

How thick should the endometrium ne for successful implantation?

Answer 11

8mm

Question 12

What do maternal blood vessels near the syncytiotrophoblast expand to become?

Answer 12

MAternal sinusoids

Question 13

What are trophoblastic lacunae?

Answer 13

Interconnected cords from the syncytiotrophoblast which invade the endometrium and erode maternal capillaries

Question 14

For how long does LH support the steroid secretion of the corpus luteum?

Answer 14

10 - 12 days

Question 15

What day is attachment usually in the menstraul cycle?

Answer 15

22

Question 16

How does hCG influence progesterone?

Answer 16

hCG maintains progesterone secretion from the corpus luteum until the placenta can synthesise its own progesterone

Question 17

When do syncytiotrophoblasrs secrete hCG?

Answer 17

Soon after implantation (peaks 8-10 weeks of gestation)

Question 18

When does hCG become measurable?

Answer 18

7 - 8 days postconception

Question 19

When does the CL fail in a non-fertile cycle?

Answer 19

10 days after menstruation

Question 20

How does an implanted embryo prevent menstruation?

Answer 20

• The syncytiotrophoblasts secrete hCG
• hCG mimics the action of LH and supports the steroid synthesis of the corpus luteum terefore preventing menstruation and any further follicular development

Question 21

When can hCG be detected in the blood by immunoassay?

Answer 21

From day 6-7

Question 22

When can Commercial kits detect hCG in the urine?

Answer 22

After 14 days

Question 23

What does hCG stimulate in male fetuses?

Answer 23

Stimulates Leydig cells to produce testosterone - important for development of the male duct system

Question 24

When is the CL not required / when can the placenta secrete all steroid hormones required for pregnancy?

Answer 24

After 4 - 5 weeks

Question 25

What does progesterone do in pregnancy?

Answer 25

Increases throughout - Suppression of follicular growth and ovulation - Suppression of immune response - Maintenance of endometrium

Question 26

What is the substrate for progesterone production?

Answer 26

Cholesterol from the maternal circulation

Question 27

What are the functions of oestrogen/oestrodiol in pregnancy?

Answer 27

- Stimulate continuous growth of uterine myometrium - Stimulates growth (with progesterone) of ductal tissue of breasts - Along with relaxin, relaxes and softens maternal pelvic ligaments and symphysis pubis of pelvic bones - allows expansion of uterus - Stimulate LDL cholesterol uptake and activity of P450 enzymes - contribute to progesterone synthesis - Foetal well being and placental function can be measured by monitoring oestrogen levels

Question 28

What does the foetus and placenta make up?

Answer 28

Feto-placental unit

Question 29

What are the functions of the placenta?

Answer 29

- Essential complex endocrine organ - synthesises steroids and proteins that affect both maternal and foetal metabolism - 1st month - villus formation - 2nd month -increasing surface area and circulation - 3rd month - growing, becoming increasingly efficient - Adopts functions of the GI, respiratory and renal systems - Supplies nutrients, exchanges O2 and CO2, regulates fluid volumes and disposes of waste and metabolites

Question 30

After 20 weeks what happens to the placental membrane?

Answer 30

thins even more due to loss of cytotrophoblasts (most molecules can move through)

Question 31

What can happen to 3rd trimester syncytiotrophoblastic cells?

Answer 31

Can be lost into maternal blood

Question 32

WHat do lipids cross the placenta as?

Answer 32

Free fatty acids

Question 33

How are amino acids transported across the placenta?

Answer 33

Actively

Question 34

How does nutrient exchange vary throughout pregnancy?

Answer 34

Rapid and increases as pregnancy does, decreases slightly near term

Question 35

How does glucose pass through the placenta?

Answer 35

Via facillitated diffusion, some glycogen stored in liver for postnatal requirments (foetus has little capacity for gluconeogenesis)

Question 36

Why are babies of diabetic mothers usually heavier than average?

Answer 36

They are exposed more glucose

Question 37

What happens to gas exchange towards the end of pregnancy?

Answer 37

Exchange capacity decreases and placenta is less able to meet demands of foetus

Question 38

What has a greter affinity for oxygen foetal or adult haemoglobin?

Answer 38

Foetal (contains 2 gamma subunits insted of 2 beta) (both contain 2 alpha)