Embryology first 2 weeks

Question 1

When does the placenta start to develop?

Answer 1

The process of placentation start on day 9 when throphoblastic lacunae form and maternal capillaries form materna sinoids that anastomose with the throphoblastic lacunae.
The placenta is important because simple diffusion for nutrient, gas and waste exchange is not enough anymore.

Question 2

Why is the yolk sac important?

Answer 2

The yolk sac is important because it is a major site of hemotopoiesis, the process of formation of blood cell components.

Question 3

What is placentation?

Answer 3

Placentation is the process of formation of the placenta, the organ responsible for nutrient, gas and waste exchange between the mother and the child.

1. Maternal sinusoids form within trophoblastic lacunae.
2. Cytotrophoblasts extend to form primary chorionic stem villi, which will eventually become the baby blood vessels.
3. The chorionic villi become secondary chorionic stem villi.
4. Then become tertiary chorionic stem villi, which contain differentiated blood vessels.

The placenta is the fusion between the embryonic chorion and the maternal uterine tissue. The umbilical chord connect the embryo to the placenta.

The placenta, other that being the site for exchange, it also secrete hormones that maintain pregnancy:

1. Human chorionic gonadotropin (hCG): signals the corpus luteum to enlarge and produce progesterone
2. Placental lactogen: prepare mammary gland, milk production and growth
3. Relaxin: increase the flexibility of the pelvis during delivery and suppresses oxytocin to delay onset of labor
4. Progesterone and estrogen

Question 4

What is ectopic implantation?

Answer 4

Ectopic implantation is an abnormal implantation, where the oocyte is implanted in the tubal, ovaries or abdomen instead of the uterus.
The most common risk factors are:
- Infections
- Surgeries
- Smoking
- IVF
- Congenital abnormalities
- Endometriosis

An ectopic implantation can lead to Placenta Previa. It is mainly caused by:
- scars, cesarian deliveries, miscarriages
- low nutrients
And it causes vaginal bleeding and the detachment of the placenta before the uterus is born.