Hello and welcome to the Zero to Finals podcast.

My name is Tom and in this episode I'm going to be talking to you about the development of the placenta.

You can find written notes on this topic at zero tofinals.com slash placenta

or in the reproductive system section of the Zero to Fin, obstetrics and gynecology book.

So let's get straight into it.

During the follicular phase of the menstrual cycle, the endometrium thickens and gets ready for a fertilized egg to arrive.

The myometrium, which is the muscle layer of the uterus, sends off artery branches into the endometrium.

Initially, these arteries grow straight outwards like plant shoots. As they continue to grow, they coil

into a spiral. These are thick-walled and coiled arteries that are bunched together making the endometrial

tissue highly vascular. And these are known as the spiral arteries which describe the coil shape.

Let's talk about placental and umbilical cord development.

When the blastocyst implants onto the endometrium, the outer layer of the blastocyst, which is called

the syncytrophoblast, grows into the endometrium. It forms finger-like projections which are

called corionic vilai. are called Corionic villi.

And these corionic villi contain fetal blood vessels.

The corionic villi nearest to the connecting stalk of the developing embryo are the most vascular and they contain mesoderm.

This area is called the Corian frondosum. The cells in the Corian

frondosum proliferate and become the placenta. The connecting stalk becomes the umbilical

cord. Placental development is usually complete by 10 weeks gestation.

Next we'll talk about the development of the lacunae.

When the triphablast invades the endometrium in a specific area, it sends signals to the spiral arteries in that area, reducing their vascular resistance and making them more

fragile. The blood flow in these arteries increases and eventually the arteries break down

...