Lecture Notes on Placenta Development and Functions

Summary

In this lecture, we delved into the detailed development of the placenta, its structure, differentiation, and hormonal functions alongside clinical correlations. The lecture began with the stages of early embryonic development including cleavage, implantation, and development of the blastocyst. It further explored how the placenta forms and its critical role in supporting pregnancy through nutrient transfer, waste removal, and hormone production.

Development of the Placenta

Early Embryonic Development

• Zygote to Morula

  • Fertilization occurs in the fallopian tube where the zygote forms, surrounded by the zona pellucida.
  • Zygote divides through cleavage stages: 2-cell stage, 4-cell stage, 8-cell stage reaching the 16-cell stage called morula.

• Blastocyst Formation

  • Continuing division leads to formation of blastocyst, consisting of an inner cell mass (embryoblast) and an outer cell mass (trophoblast).
  • Water enters the morula, forming a fluid-filled cavity called the blastocoel.

Implantation and Differentiation

• Implantation

  • Blastocyst implants into the endometrium. The trophoblast (outer cell mass) facilitates attachment and invasion into the uterine lining.
  • Differentiates into cytotrophoblast and syncytiotrophoblast.

• Formation of Extraembryonic Structures

  • Formation of the chorionic cavity (extraembryonic coelom) and the chorionic plate.

Formation of Chorionic Villi

• Trophoblast proliferates and begins forming finger-like projections called primary villi, which mature into secondary and then tertiary villi containing embryonic blood vessels.

Hormonal Functions and Clinical Implications

• Hormonal Role
  • The syncytiotrophoblast produces human chorionic gonadotropin (hCG) to maintain the corpus luteum and progesterone production.
• Clinical Correlations
  • Conditions like placenta accreta, increta, or percreta can occur if the blastocyst invades too deeply, leading to complications requiring surgical intervention post-delivery.

Functional Anatomy of the Developed Placenta

Layers and Membranes

• Decidua Basalis and Chorionic Frondosum

  • Interface forming the functional placenta; maternal and fetal tissue interaction site for nutrient and waste exchange.

• Chorionic Villi System

  • Maturation of villi enhances nutrient and oxygen exchange between mother and fetus. Composed of tertiary villi with core capillaries surrounded by trophoblastic layers.

• Amniotic and Chorionic Membranes

  • Separate the fetus from the uterine wall, involved in protecting and containing the amniotic fluid around the fetus.

Functions

• Metabolic Functions

  • Gas exchange (O2 in, CO2 out), nutrient delivery (glucose, amino acids, fatty acids), waste removal (urea, uric acid), and transport of water-soluble vitamins and minerals.

• Hormonal Functions

  • Production of estrogen and progesterone to maintain endometrial lining and facilitate fetal growth.
  • Secretion of other hormones like placental lactogen, affecting maternal insulin sensitivity and metabolic adjustments during pregnancy.

Clinical Significance

• Incorrect placental attachment can lead to conditions such as placenta accreta, potentially requiring the removal of the uterus postpartum to resolve severe complications.
• Hormones produced by the placenta are crucial for maintaining pregnancy and preparing the fetal environment for development and growth.

This lecture underscores the complexity and critical nature of placental function throughout gestation, illustrating essential processes that support fetal development and maternal health.