The Placenta: Its Development and Function

Summary

This video explores the early stages of placental development, beginning with implantation and the differentiation of trophoblast cells. It describes the formation of lacunae filled with maternal blood, the growth of chorionic villi, and the establishment of uteroplacental circulation. The process progresses through the formation of secondary and tertiary chorionic villi, the development of fetal blood vessels, and nutrient exchange between mother and fetus. By the fourth week, fetal circulation is established, ensuring the transfer of oxygen and nutrients to the developing fetus, and waste products are removed. The placenta plays a vital role in supporting fetal development throughout pregnancy.

Takeaways

• 😀 The development of the placenta begins during implantation when the blastocyst adheres to the endometrial epithelium.
• 😀 Trophoblast cells differentiate into two layers: an inner cytotrophoblast layer and an outer syncytiotrophoblast layer.
• 😀 The syncytiotrophoblast secretes proteolytic enzymes and sends out finger-like projections to help the blastocyst embed into the endometrium.
• 😀 Lacunae, or spaces, form within the syncytiotrophoblast as it erodes the endometrial blood vessels, eventually becoming filled with maternal blood and glandular secretions.
• 😀 As the lacunae fuse, they form a network that establishes early uteroplacental circulation.
• 😀 By the end of the second week, the cytotrophoblast begins to form primary chorionic villi.
• 😀 In the third week, extraembryonic mesoderm grows into the villi, forming a core of loose connective tissue.
• 😀 By the end of the third week, embryonic blood vessels form in the extraembryonic mesoderm, transforming the villi into tertiary chorionic villi.
• 😀 Anchoring villi, connected to the decidua basalis, anchor the placenta to the uterine wall, while branch villi serve as the sites of nutrient exchange between mother and fetus.
• 😀 By the fourth week, fetal blood flow is established through paired umbilical arteries, with waste products and carbon dioxide being exchanged for oxygen and nutrients through the placenta.

Q & A

What is the first step in the development of the placenta?

The development of the placenta begins during implantation when the blastocyst adheres to the endometrial epithelium.

How do trophoblast cells differentiate during implantation?

Trophoblast cells differentiate into two layers: the inner cytotrophoblast layer and the outer syncytiotrophoblast layer.

What is the role of the syncytiotrophoblast in implantation?

The syncytiotrophoblast secretes proteolytic enzymes and forms finger-like projections that allow the blastocyst to embed into the endometrium.

What happens after the syncytiotrophoblast erodes the endometrial blood vessels?

Lacunae, or spaces, form within the syncytiotrophoblast and become filled with maternal blood and glandular secretions, establishing early uteroplacental circulation.

What are primary chorionic villi, and when do they begin to form?

Primary chorionic villi begin to form toward the end of the second week, as small projections of the cytotrophoblast expand into the syncytiotrophoblast.

How do secondary chorionic villi develop?

Early in the third week, extraembryonic mesoderm grows into the primary chorionic villi, forming a core of loose connective tissue, turning them into secondary chorionic villi.

What are tertiary chorionic villi, and how are they formed?

By the end of the third week, embryonic blood vessels form in the extraembryonic mesoderm of the secondary chorionic villi, transforming them into tertiary chorionic villi.

What is the function of the anchoring villi?

Anchoring villi, which connect the decidua basalis to the placenta, help anchor the placenta in place and allow for nutrient exchange.

How does fetal blood flow through the placenta?

Fetal blood is transported to the placenta through the paired umbilical arteries, which branch into capillary networks in the villi, allowing for exchange of gases and nutrients.

What is the pathway for oxygenated blood to return to the fetus?

Oxygenated fetal blood travels through veins, which converge to form a single umbilical vein that carries the blood back to the fetus.