The Placenta: Its Development and Function

Summary

The transcript details the early stages of placental development, beginning with the blastocyst's implantation in the endometrium. Trophoblast cells differentiate and form structures like the syncytiotrophoblast, which helps embed the blastocyst. Maternal blood enters lacunae, and by the third week, chorionic villi form to facilitate maternal-fetal exchange. By the fourth week, fetal blood flow is established, transporting oxygen and nutrients through the placenta while removing waste. This vital process ensures fetal nourishment throughout pregnancy, with the placenta being delivered after childbirth.

Takeaways

• 😀 Development of the placenta begins during implantation when the blastocyst adheres to the endometrial epithelium.
• 😀 Trophoblast cells differentiate into an inner spiral trophoblast layer and an outer syncytiotrophoblast layer.
• 😀 Syncytiotrophoblast secretes proteolytic enzymes that help the blastocyst embed into the endometrium.
• 😀 Lacunae form within the syncytiotrophoblast, filled with maternal blood and glandular secretions, establishing early uteroplacental circulation.
• 😀 Primary chorionic villi form by the end of the second week, expanding into the syncytiotrophoblast.
• 😀 Extraembryonic mesoderm grows into the chorionic villi in the third week, forming secondary chorionic villi.
• 😀 By the end of the third week, embryonic blood vessels begin to form in the secondary chorionic villi, transforming them into tertiary chorionic villi.
• 😀 Tertiary villi grow toward the decidua basalis, forming a syncytiotrophoblastic shell that anchors the placenta.
• 😀 Branch villi, surrounded by intervillous space, serve as the main sites for exchange between mother and fetus.
• 😀 By the fourth week, fetal blood flow is established, with oxygen and nutrients transported across the placental membrane to the fetus and waste products removed.
• 😀 The placenta nourishes the fetus throughout development and is delivered shortly after parturition.

Q & A

At which stage does the development of the placenta begin?

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

What is the role of the trophoblast cells during implantation?

During implantation, trophoblast cells differentiate into an inner spiral trophoblast layer and an outer syncytiotrophoblast layer, facilitating the attachment of the blastocyst to the endometrium.

What happens to the cytotrophoblast cells as they proliferate?

As the cytotrophoblast cells proliferate, newly formed cells migrate into the syncytium, where they lose their cell membranes and form a multinucleated mass, aiding in the placenta's growth.

What is the significance of the finger-like projections formed by the syncytiotrophoblast?

The finger-like projections formed by the syncytiotrophoblast, known as trophoblastic projections, allow the blastocyst to embed into the endometrium more deeply, securing its position.

How do lacunae contribute to the development of the placenta?

Lacunae, or spaces, begin to form within the syncytiotrophoblast as it erodes endometrial blood vessels and glands. These lacunae 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 are small projections formed by the cytotrophoblast around the end of the second week. These projections later grow into secondary and tertiary villi as development progresses.

How do secondary chorionic villi differ from primary villi?

Secondary chorionic villi are formed when extraembryonic mesoderm grows into the primary villi, creating a core of loose connective tissue within them.

What role do tertiary chorionic villi play in placental development?

Tertiary chorionic villi are formed by the development of embryonic blood vessels in the extraembryonic mesoderm of the secondary villi, which enables fetal blood circulation within the placenta.

What is the function of the anchoring villi in the placenta?

Anchoring villi, which are attached to the decidua basalis through the syncytiotrophoblastic shell, anchor the placenta to the uterine wall, securing its position for nutrient and waste exchange.

How is the fetal circulation established in the placenta?

Fetal circulation is established by the formation of capillary networks in the tertiary chorionic villi. Poorly oxygenated blood is transported from the fetus to the placenta, where gas exchange occurs with maternal blood.