Implantation, placentation and hormone changes in pregnancy

Question 1

What is a trophoblast?

Answer 1

• cells of the blastocyst that invade the endometrium and myometrium

Question 2

When is the endometrium and myometrium invaded by the blastocyst?

Answer 2

• 5-6 days post fertilisation

Question 3

What do trophoblasts become?

Answer 3

syncitioblasts

Question 4

What do syncitioblasts do?

Answer 4

secrete beta hCG

Question 5

What is the chorion?

Answer 5

layer of blastocyst that becomes the placenta

Question 6

What is the amnion?

Answer 6

layer of the blastocyst that becomes the amniotic sac which contains the amniotic fluid

Question 7

What does a fertilized embryo become?

Answer 7

• moves down fallopian tube
• develops into ball of cells
• called morula
• by day 4

Question 8

What does the morula develop into?

Answer 8

• develops into an inner cell mass
• this develops into the baby
• it has blastocoel cavity and layer cells

Question 9

What does trophectoderm develop into?

Answer 9

placenta

Question 10

What processes need to happen in order for the placenta to develop?

Answer 10

• differentiation of the trophoblast
• trophoblast needs to invade the decidua of myometrium
• remodeling of the maternal vasculature

Question 11

What is the decidua?

Answer 11

thick layer of modified mucous membrane which lines the uterus during pregnancy

Question 12

Why is there remodelling of the maternal vasculature for the placenta to develop?

Answer 12

• uterus has tight small spiral arteries to reduce blood volume lost during menses
• tiny vessels not good enough for baby
• transform to bigger vessels to accomodate the baby

Question 13

What is the window of implantation?

Answer 13

• narrow time point where implantation can occur

- if embryo implant too early or too later= risky

Question 14

If a woman has a longer window of implantation, what happens?

Answer 14

• recurrent pregnancy losses
• bc low quality embryos are accepted to be implanted
• embryos might have aneuploidy

Question 15

What is the role of bhCG?

Answer 15

• signals to the corpus luteum that there is a pregnancy

- corpus luteum is maintained

Question 16

What does the corpus luteum do?

Answer 16

• secrete progesterone

- decidualizes endometrium

Question 17

When does the corpus luteum stop playing a role in pregnancy?

Answer 17

• after 12 weeks

- placenta itself establishes steroidogenesis and takes over from the corpus luteum

Question 18

What is bhCG?

Answer 18

• hormone

- basis of urinary pregnancy test

Question 19

When is the amount of bhCG in the body maximum?

Answer 19

9-11 weeks

Question 20

Why is serum bhCG checked?

Answer 20

• useful to monitor early pregnancy complications
• falling bhCG= ectopic/miscarriage= failing preggo
• doubling bhCG= SUCCESSFUL uterine preggo

Question 21

What does the placenta act like?

Answer 21

• an endocrine organ
• remove CO2, urea, ammonia minerals, other waste
• barrier

Question 22

What does the placenta secrete?

Answer 22

• steroid hormones like oestrogen and progesterone

- HPL

Question 23

Why is placenta useful in baby lungs and kidneys?

Answer 23

transfer oxygen, carbohydrates, fats, amino acids, vitamins, minerals and antibodies (passive immunity)
that are required to develop the ball of cells into a baby

Question 24

How is the placenta adapted?

Answer 24

• huge maternal uterine blood supply (by end of pregnancy, motherm feeding 750mls blood/minute to baby)
• blood delivered at low pressure (gentle over villi)
• huge function reserve
• high surface area contact with maternal blood
• transport system in placenta= adapted and efficient

Question 25

What differentiates into the syncitiotrophoblast?

Answer 25

cytotrophoblast (mononuclear cell layer in central systems of the villi)

Question 26

What does the placenta look like day 14-15?

Answer 26

• trophectoderm (another word for the trophoblast)
• syncytiotrophoblast is the layer of cells = grows ouwards= incades into maternal endometrium decidua
• cytotrophoblast is a mononuclear stem cell layer that is in the central stems of the villi which will differentiate into syncytiotrophoblast
• middle= lacuna filled with maternal blood